OPTION AND LICENSE AGREEMENT

This Option and License Agreement ("Agreement") is made effective as of

September 5, 2000 (the "Effective Date") by and between IMMUNOGEN, INC., a

Massachusetts corporation with a principal place of business at 128 Sidney

Street, Cambridge, Massachusetts 02139 ("IMMUNOGEN"), and ABGENIX, INC., a

Delaware corporation with a place of business at 7601 Dumbarton Circle, Fremont,

California 94555 ("ABX"). IMMUNOGEN and ABX are each hereafter referred to

individually as a "Party" and together as the "Parties".

WHEREAS, ABX is the owner of or otherwise controls certain patents and

technology relating to antibodies; and

WHEREAS, IMMUNOGEN is the owner of or otherwise controls certain

proprietary patents and technology relating to or otherwise useful in the

conjugation of certain cytotoxic compounds such as DM1 (as hereinafter defined)

to antibodies; and

WHEREAS, ABX desires to have access to certain IMMUNOGEN Background

Technology (as hereinafter defined) in order to use such IMMUNOGEN Background

Technology to research, discover and develop one or more conjugates of certain

cytotoxic compounds and antibodies owned or controlled by ABX; and

WHEREAS, in connection therewith, ABX desires to receive, and IMMUNOGEN

desires to grant, Options to obtain one or more licenses having the terms set

forth herein and in one or more License Agreements to be executed by the

Parties.

NOW, THEREFORE, in consideration of the mutual covenants contained herein,

and for other good and valuable consideration, the receipt and adequacy of which

are hereby acknowledged, the Parties hereby agree as follows:

1. DEFINITIONS

Whenever used in the Agreement with an initial capital letter, the terms

defined in this Section 1 shall have the meanings specified below.

1.1 "ABX ANTIBODY" shall mean any antibody or fragment thereof directed to

a Proposed Licensed Target or a Licensed Target.

1.2 "AFFILIATE" shall mean any corporation, firm, limited liability

company, partnership or other entity which directly or indirectly controls or is

controlled by or is under common control with a Party to this Agreement.

"Control" means, for purposes of this Section 1.2, ownership, directly or

through one or more Affiliates, of more than fifty percent (50%) of the shares

of stock entitled to vote for the election of directors, in the case of a

corporation, or more than fifty percent (50%) of the equity interests in the

case of any other type of

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

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legal entity, status as a general partner in any partnership, or any other

arrangement whereby a Party controls or has the right to control the Board of

Directors or equivalent governing body of a corporation or other entity.

1.3 "BLA" shall mean a biologics license application (as defined in Title

21 of the United States Code of Federal Regulations, as amended from time to

time) filed with the FDA seeking Regulatory Approval to market and sell any

Licensed Product in the United States for a particular indication within the

Field.

1.4 "CLINICAL MATERIALS" shall mean (a) supplies of ansamitocin P-3, DM1,

and/or any other May Compound as manufactured in accordance with all applicable

GMPs and other legal requirements and all applicable Specifications for such May

Compound for use in human clinical testing, and (b) supplies of any Licensed

Product as manufactured in accordance with all applicable GMPs and other legal

requirements and all applicable Specifications for such Licensed Product for use

in human clinical testing of any Licensed Product.

1.5 "COMBINATION PRODUCT" shall mean any Licensed Product that contains, in

addition to any conjugate of any ABX Antibody with any May Compound, one or more

other ingredients that has biologic activity.

1.6 "CONTROL" OR "CONTROLLED" shall mean (a) with respect to patents,

know-how or other intangible rights, the possession by Party of the ability to

grant a license or sublicense of such patent rights, know-how or other

intangible rights as provided for herein without violating the terms of any

arrangement or agreements between such Party and any Third Party and (b) with

respect to any material, the possession by a Party of the ability to use such

material as provided herein without violating the terms of any agreement between

such Party and any Third Party.

1.7 [________________] shall mean any and all [________________], whether

[________________________________________________________], and shall include,

without limitation, [____________________________________________], in each case

[___________ ________________________________]. [_______________] shall include,

without limitation, [_____________].

1.8 "DM1" shall mean that certain maytansine derivative having the specific

chemical name N2'deacetyl - N2'- (3-mercapto-1-oxopropyl) - maytansine.

1.9 "EXCLUSIVE OPTION" shall have the meaning set forth in Section 2.1.1.

1.10 "EXCLUSIVE OPTION PERIOD" shall have the meaning set forth in Section

2.1.3.

1.11 "EXCLUSIVE OPTION REQUEST" shall have the meaning set forth in

Sections 2.1.2.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

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1.12 "EXCLUSIVE OPTION RESPONSE" shall have the meaning set forth in

Sections 2.1.2.

1.13 "FDA" shall mean the United States Food and Drug Administration and

any successor agency or authority thereto.

1.14 "FIELD" shall mean any human medical use.

1.15 "FOREIGN REGULATORY AUTHORITIES" shall mean any applicable

supranational, national, federal, state or local regulatory agency, department,

bureau or other governmental entity of any country or jurisdiction in the

Territory (other than the FDA in the United States), having responsibility in

such country or jurisdiction for any Regulatory Approvals of any kind in such

country or jurisdiction, and any successor agency or authority thereto.

1.16 "FULLY BURDENED MANUFACTURING COST" shall mean, with respect to any

Preclinical Materials or Clinical Materials produced by IMMUNOGEN for ABX under

this Agreement, the sum of the following components, as determined by IMMUNOGEN

in accordance with generally accepted accounting principles in the United

States, consistently applied, and consistent with the application given to other

goods produced by IMMUNOGEN: (a) the costs of goods produced, including, without

limitation, direct labor, material and product testing costs of such Preclinical

Materials or Clinical Materials; (b) any Third Party royalty costs that are

actually paid by IMMUNOGEN and are based solely and directly on the manufacture

and sale to ABX of such Preclinical Materials or Clinical Materials; (c) all

overhead costs incurred by IMMUNOGEN directly and solely attributable to the

cost of goods under clause (a) above, including, without limitation, supervisory

services, occupancy costs, payroll, information systems, human relations,

purchasing, accounts receivable or accounts payable functions, and other general

and administrative functions; and (d) any other costs borne by IMMUNOGEN

directly and solely for the transport, customs clearance, duty and/or insurance

for such Preclinical Materials or Clinical Materials to ABX hereunder.

1.17 "GMPS" shall mean all good manufacturing practices under Title 21 of

the United States Code of Federal Regulations, as amended from time to time.

1.18 "IMMUNOGEN BACKGROUND TECHNOLOGY" shall mean all inventions,

discoveries, patent rights, trade secrets and know-how, including without

limitation, laboratory scientific information and procedural techniques,

Controlled by IMMUNOGEN during the Term of this Agreement or any License

Agreement that are necessary or useful for ABX to research, develop, make, have

made, use, have used, sell, offer for sale, have sold, import or have imported

Licensed Products (or any component thereof, including any linker) for use in

the Field, together with all patent rights covering the foregoing; provided,

however, that IMMUNOGEN Background Technology shall expressly exclude any Target

Specific Rights. IMMUNOGEN Background Technology covered by issued patents

and/or filed patent applications as of the Effective Date is listed on Schedule

I attached hereto.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

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1.19 "JOINT INVENTION" shall have the meaning set forth in Article 6.

1.20 "LICENSE AGREEMENT" shall mean a license agreement executed by the

Parties upon exercise of any Option pursuant to Section 2.1 or 2.2 in

substantially the form set forth in Appendix A or B attached hereto.

1.21 "LICENSED PRODUCT" shall mean any product containing any conjugate of

any ABX Antibody with any May Compound, and shall include, without limitation,

any formulation thereof (including, without limitation, any lyophilized, liquid,

sustained release or aerosolized formulation). "Licensed Product" shall also

include any and all Combination Products (if any).

1.22 "LICENSED TARGET" shall mean a Proposed Licensed Target selected by

ABX and approved by IMMUNOGEN as set forth in Section 2.1.2 or 2.2.2, which is

the subject of a License Agreement between the Parties.

1.23 "MAY COMPOUND" shall mean any and all maytansinoid compounds

(including, without limitation, maytansine, ansamitocin P-3 and DM1), whether

produced by a botanical source, natural fermentation or chemical synthesis, and

shall include, without limitation, all variants, fragments or derivatives of any

of the foregoing, in each case owned or otherwise Controlled by IMMUNOGEN. May

Compounds shall include, without limitation, DM1.

1.24 "NDA" shall mean a new drug application (as defined in Title 21 of the

United States Code of Federal Regulations, as amended from time to time) filed

with the FDA seeking Regulatory Approval to market and sell any Licensed Product

in the United States for a particular indication within the Field.

1.25 "NONEXCLUSIVE OPTION" shall have the meaning set forth in Section

2.2.1.

1.26 "NONEXCLUSIVE OPTION PERIOD" shall have the meaning set forth in

Section 2.2.3.

1.27 "NONEXCLUSIVE OPTION REQUEST" shall have the meaning set forth in

Sections 2.2.2.

1.28 "NONEXCLUSIVE OPTION RESPONSE" shall have the meaning set forth in

Sections 2.2.2.

1.29 "OPTION" shall mean, an Exclusive Option or a Nonexclusive Option.

1.30 "OPTION GRANT FEE" shall have the meaning set forth in Section 4.1

hereof.

1.31 "OPTION PERIOD" shall have the meaning set forth in Sections 2.1.3 and

2.2.3.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

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1.32 "PHASE II CLINICAL STUDY" shall mean, as to a particular Licensed

Product for a particular indication, a controlled and lawful study in humans of

the safety, dose ranging and efficacy of such Licensed Product for such

indication, which is prospectively designed to generate sufficient data (if

successful) to commence a Phase III Clinical Trial of such Licensed Product for

such indication.

1.33 "PHASE III CLINICAL TRIAL" shall mean, as to a particular Licensed

Product for a particular indication, a controlled and lawful study in humans of

the safety and efficacy of such Licensed Product for such indication, which is

prospectively designed to demonstrate statistically whether such Licensed

Product is safe and effective for use in such indication in a manner sufficient

to file a BLA or NDA to obtain Regulatory Approval to market and sell that

Licensed Product in the United States for the indication under investigation in

such study.

1.34 "PRECLINICAL MATERIALS" shall mean (a) supplies of ansamitocin P-3,

DM1 and/or any other May Compound as manufactured in accordance with all

applicable legal requirements and all applicable Specifications for such May

Compound for use in preclinical testing, and (b) supplies of any Licensed

Product as manufactured in accordance with all applicable legal requirements and

all applicable Specifications for such Licensed Product for use in preclinical

testing of any Licensed Product.

1.35 "REGULATORY APPROVAL" shall mean any and all approvals (including

pricing and reimbursement approvals), product and establishment licenses,

registrations or authorizations of any kind of the FDA or its foreign equivalent

necessary for the development, pre-clinical and/or human clinical testing,

manufacture, quality testing, supply, use, storage, importation, export,

transport, marketing and sale of a Licensed Product (or any component thereof)

for use in the Field in any country or other jurisdiction in the Territory.

1.36 "RESEARCH ACTIVITIES" shall mean research conducted by, on behalf of

or with ABX using the IMMUNOGEN Background Technology for the purpose of

developing information necessary or useful to determine whether to exercise an

Option with respect to a Proposed Licensed Target.

1.37 "RESEARCH DATA" shall mean any data generated by or on behalf of ABX

(including by IMMUNOGEN at the request and on behalf of ABX) resulting from its

direct and material use of the IMMUNOGEN Background Technology during the

Research Term. ABX shall solely own all Research Data and all patent rights and

other intellectual property rights therein.

1.38 "RESEARCH INVENTION" shall mean any discovery, invention, know-how or

trade secret (other than Research Data and Research Materials) conceived or made

by or on behalf of ABX (including by IMMUNOGEN at the request and on behalf of

ABX) through the direct and material use of IMMUNOGEN Background Technology,

Research Data or Research Materials during the Research Term. ABX shall solely

own all Research Inventions and all patent rights and other intellectual

property rights therein.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

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1.39 "RESEARCH MATERIALS" shall mean any materials, including but not

limited to, antibodies or drug candidates, identified or developed by or on

behalf of ABX (including by IMMUNOGEN at the request and on behalf of ABX)

through the direct and material use of IMMUNOGEN Background Technology during

the Research Term. ABX shall solely own all Research Materials and all patent

rights and other intellectual property rights therein.

1.40 "RESEARCH PATENT RIGHTS" shall mean the rights and interests in and to

issued patents and pending patent applications in any country, including, but

not limited to, all provisional applications, substitutions, continuations,

continuations-in-part, divisions, and renewals, all letters patent granted

thereon, and all reissues, reexaminations and extensions thereof, wherein at

least one claim of such Research Patent Right is directed to any Research Data,

Research Inventions or Research Materials. ABX shall solely own all Research

Patent Rights.

1.41 "RESEARCH TERM" shall have the meaning set forth in Section 2.4.4.

1.42 "SPECIFICATIONS" shall mean any specifications specified by ABX and

reasonably acceptable to IMMUNOGEN relating to the manufacturing and supply of

any May Compound and/or Licensed Product hereunder.

1.43 "TARGET" shall mean (a) any particular antigen, and (b) any and all

epitopes of that antigen.

1.44 "TARGET SPECIFIC RIGHTS" shall mean all inventions, discoveries,

patent rights, trade secrets and know-how, including without limitation,

laboratory scientific information and procedural techniques Controlled by

IMMUNOGEN during the Term of this Agreement or the term of any License Agreement

constituting (a) the composition of matter or use of a Target, (b) the

composition of matter or use of an antibody binding to a Target, or (c) the

composition of matter or use of a conjugate of an antibody binding to a Target

with a May Compound.

1.45 "TECHNOLOGY" shall mean and include any and all unpatented proprietary

ideas, inventions, discoveries, Confidential Information, materials, data,

results, formulae, designs, specifications, methods, processes, formulations,

techniques, ideas, know-how, technical information (including, without

limitation, structural and functional information), process information,

pre-clinical information, clinical information, and any and all proprietary

biological, chemical, pharmacological, toxicological, pre-clinical, clinical,

assay, control and manufacturing data and materials.

1.46 "TERM" shall have the meaning set forth in Section 8.1.

1.47 "TERRITORY" shall mean the world.

1.48 "THIRD PARTY" shall mean any person or entity other than IMMUNOGEN,

ABX and their respective Affiliates.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

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1.49 "THIRD PARTY LICENSEE" shall mean a Third Party to which IMMUNOGEN has

granted rights to use IMMUNOGEN Background Technology or rights with respect to

any Target.

1.50 "UNEXERCISED EXCLUSIVE OPTION" shall have the meaning set forth in

Section 2.1.3.

1.51 "UNEXERCISED NONEXCLUSIVE OPTION" shall have the meaning set forth in

Sections 2.2.3.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

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<PAGE> 8

2. GRANT OF RIGHTS

2.1 OPTIONS FOR EXCLUSIVE LICENSES.

2.1.1 EXCLUSIVE OPTION RIGHTS. Subject to the limitations set forth in

Sections 2.1.2, 2.1.3 and 2.1.4 of this Agreement, IMMUNOGEN hereby grants to

ABX the right, prior to the [________] anniversary of the Effective Date, to

obtain an exclusive option (the "Exclusive Option") to obtain an exclusive

license in the Territory under the IMMUNOGEN Background Technology, under Target

Specific Rights with respect to any Target specified in ABX's notice of election

of Option (the "Proposed Licensed Target"), for the sole purpose of researching,

developing, making, having made, using, having used, selling, offering for sale,

having sold, importing and having imported Licensed Products directed to such

Proposed Licensed Target, for any and all uses within the Field, under the

relevant terms and subject to the conditions set forth in the applicable License

Agreement.

2.1.2 EXCLUSIVE OPTION GRANT. ABX may from time to time during the

term of this Agreement request any Exclusive Option pursuant to Section 2.1.1

[_____________ _______________________________________], which [______] shall

specify in detail the [_________________] to be

[_____________________________________________________ __________]. IMMUNOGEN

shall [____________________________________] of any [___

_____________________________________________________________________________];

provided, however, that [__________________________________

________________________________________] if: (a)

[_______________________________ ______________] with

[_________________________________________________________ _____]; or (b)

[_______________________________] with [____________________________

____________________________________________________________] and has [_________

________________________________________________________________________] for a,

[_________________] whose [_____________________________________] to

[___________ _____________________], or (c)

[_________________________________________________ ___] to [__________] for a

[______________________________________________________ ________]; or (d)

[____________________________________] with [__________] that is [___ _____] as

of [__________________________] that [___________________________________

______] a [______] for such [_________________] on the terms and conditions of

this Agreement. Upon the grant of an Exclusive Option to ABX as provided in this

Section 2.1.2, [___________________________________________________________]

concerning the [________] regarding, or otherwise [_______________], or

otherwise [_______________] any [______ ] concerning, any [______] regarding a

[__________________________] to the [__________________________________]. If in

an [_______________________, ________________] that the [______________________]

is [_______________] for a [______ __________], IMMUNOGEN shall [_____________]

in such [__________________________ _______________________________] is [_____]

for [______________________]. If, within [________] of

[_______________________________] that [_________________] is [______] for

[__________________________________________________________________________

________________________] for [_______________________], then [_____________]

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

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<PAGE> 9

_____________________________] for [_______________________] without the

[______] for any [_________________________].

2.1.3 OPTION PERIOD; UNEXERCISED OPTIONS. The rights set forth in this

Section 2.1 shall be exercisable with respect to any Proposed Licensed Target at

any time during the period commencing on the date of the Exclusive Option

Response granting an Exclusive Option to such Proposed Licensed Target and

continuing until the earlier of (a) [____________ ______] following the date of

such Exclusive Option Response (subject to extension as provided below), and (b)

[________________________________________________________________ ____________]

(such period being referred to herein as the "Exclusive Option Period"). ABX

shall have the right to extend the Exclusive Option Period for any Exclusive

Option regarding a Proposed Licensed Target [___________________________] by

giving to IMMUNOGEN written notice thereof prior to the expiration of

[_____________] following the date of the applicable Exclusive Option Response,

and paying the applicable extension fee as set forth in Section 4.3. In the

event that ABX fails to exercise or otherwise abandons any Exclusive Option

during the applicable Exclusive Option Period (such Exclusive Option in either

case being referred to herein as an "Unexercised Exclusive Option"), (a) all

rights under the IMMUNOGEN Background Technology regarding Licensed Products

directed to the Proposed Licensed Target, and under Target Specific Rights with

respect to the Proposed Licensed Target, that is the subject of the Unexercised

Exclusive Option [_____________________________], and (b)

[_______________________________________________________________] with [_____

_______] concerning [_________], or otherwise [_______________________], or

otherwise [__________] any [_______] concerning,

[___________________________________________ _______] to the

[__________________] by [__________________].

2.1.4 LIMITATIONS ON EXCLUSIVE OPTION EXERCISE. Notwithstanding anything to

the contrary set forth in this Agreement, the Parties hereby agree that ABX

shall have the right to select and maintain no more than [_____] active

Exclusive Options at any one time during the Term of this Agreement; provided,

that, Unexercised Exclusive Options shall not count as Exclusive Options for

purposes of this limitation.

2.1.5 EXERCISE OF EXCLUSIVE OPTIONS. Upon exercise of an Exclusive Option

by ABX in accordance with Section 2.1.3, (a) the Parties shall execute a License

Agreement in the form of Appendix A attached hereto and, upon payment of the

license fee specified in the License Agreement, such Proposed Licensed Target

shall become a Licensed Target and shall be licensed to ABX as specified in the

relevant License Agreement and (b) IMMUNOGEN shall thereafter not grant any

license or other rights to any Third Party or pursue any internal development

program regarding a May Compound conjugate product to the Licensed Target.

2.1.6 OPTION TO OBTAIN NONEXCLUSIVE LICENSES. Upon the written request of

ABX given at the time of ABX's exercise of an Exclusive Option, ABX shall have

the right to obtain a nonexclusive license under the IMMUNOGEN Background

Technology and Target Specific Rights pursuant to Section 2.2.5 as if such

Exclusive Option were a Nonexclusive Option.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

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<PAGE> 10

2.2 OPTIONS FOR NONEXCLUSIVE LICENSES.

2.2.1 NONEXCLUSIVE OPTION RIGHTS. Subject to the limitations set forth

in Sections 2.2.2, 2.2.3 and 2.2.4 of this Agreement, IMMUNOGEN hereby grants to

ABX the right, prior to the [________] anniversary of the Effective Date, to

obtain a nonexclusive option (the "Nonexclusive Option") to obtain a

nonexclusive license in the Territory under the IMMUNOGEN Background Technology,

under Target Specific Rights with respect to any Proposed Licensed Target, for

the sole purpose of researching, developing, making, having made, using, having

used, selling, offering for sale, having sold, importing and having imported

Licensed Products directed to such Proposed Licensed Target, for any and all

uses within the Field, under the relevant terms and subject to the conditions

set forth in the applicable License Agreement.

2.2.2 NONEXCLUSIVE OPTION GRANT. ABX may from time to time during the

term of this Agreement request any Nonexclusive Option pursuant to Section 2.2.1

[_______ _____________________________________________], which [_______] shall

specify in detail the [___________________] to be

[________________________________________________ _____________]. IMMUNOGEN

shall [_______________________________________] of any

[_____________________________________________] the [______________________

_________________________________________]; provided, however, that the

[______________________________________________________________________] if: (a)

[______________] is [________________________] with a [________________________

_____] to [________________________]; or (b) [____________] is

[____________________ _________] for a [______] for a

[_________________________________________________ ______] and has

[________________________________________], or [_________________ __________]

for a [_______] with [_________], whose [_______________________________ ___] to

[_______________________], or (c) [_______________________________________

______________] to a [__________] for a [___________________________] to

[___________ ____________]; or (d) [_________________________________________]

with a [________] that is [______] as of [________________________________]that

[______________________ _________________________] for

[________________________] on the terms and conditions of this Agreement. Upon

the grant of a Nonexclusive Option to ABX as provided in this Section 2.2.2,

[_________________________________________________________________] concerning

the [______________] regarding, or otherwise [______________], or otherwise

[__________] any [______] concerning, [_________] regarding

[_________________________ __________] to the

[________________________________________________].

2.2.3 OPTION PERIOD; UNEXERCISED OPTIONS. The rights set forth in this

Section 2.2 shall be exercisable with respect to any Proposed Licensed Target at

any time during the period commencing on the date of the Nonexclusive Option

Response granting a Nonexclusive Option to such Proposed Licensed Target and

continuing until the earlier of (a) [_____ _______] following the date of such

Nonexclusive Option Response (subject to extension as provided below), and (b)

[_____________________________________________ ________________________________]

(such period being referred to herein as the "Nonexclusive Option Period"). ABX

shall have the right to extend the Nonexclusive Option

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

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<PAGE> 11

Period for any Nonexclusive Option for any Proposed Licensed Target

[____________________ ____________] by giving to IMMUNOGEN written notice

thereof prior to the expiration of [_____________] following the date of the

applicable Nonexclusive Option Response, and paying the applicable extension fee

as set forth in Section 4.3. In the event that ABX fails to exercise or

otherwise abandons any Nonexclusive Option during the applicable Nonexclusive

Option Period (such Nonexclusive Option in either case being referred to herein

as an "Unexercised Nonexclusive Option"), (a) [_____________] under the

[_______________ _____________] regarding [__________________] to the

[____________________], and under [_______________] with respect to the

[__________________], that is the [____________ ___________________________]

shall [____________________________], and (b) IMMUNOGEN shall

[______________________________________] with [___________] concerning the

[__________] regarding, or otherwise [__________________] any [__________

____________] regarding [__________________________] to the

[______________________ ______________________________].

2.2.4 LIMITATIONS ON NONEXCLUSIVE OPTION EXERCISE. Notwithstanding anything

to the contrary set forth in this Agreement, the Parties hereby agree that ABX

shall have the right to select and maintain no more than [_______] active

Nonexclusive Options at any one time during the Term of this Agreement;

provided, that, Unexercised Nonexclusive Options shall not count as Nonexclusive

Options for purposes of this limitation.

2.2.5 EXERCISE OF NONEXCLUSIVE OPTIONS. Upon exercise of a Nonexclusive

Option by ABX in accordance with Section 2.2.3(a), the Parties shall execute a

License Agreement in the form of Appendix B attached hereto and, upon payment of

the license fee specified in the License Agreement, such Proposed Licensed

Target shall become a Licensed Target and shall be licensed to ABX as specified

in the relevant License Agreement and (b) IMMUNOGEN shall not grant any

exclusive license or other rights to any Third Party regarding a May Compound

conjugate antibody product to the Licensed Target.

2.2.6 OPTION TO CONVERT TO EXCLUSIVE OPTIONS. Upon the written request of

ABX given at any time during the Nonexclusive Option Period applicable to a

Nonexclusive Option for a Proposed Licensed Target, ABX shall have the right to

convert such Nonexclusive Option into an Exclusive Option, provided that

[________] of [_________], an [____________] for [_____________________] is

[__________] in accordance with Section 2.1.2. [__________ _________________] of

any [________________________________] shall give [___________

___________________] an [___________] for the [________________________] is

[________ _______] in accordance with Section 2.1.2. If [_____________________],

then such Nonexclusive Option shall be converted to an Exclusive Option

effective as of the date of such request, and ABX shall pay to IMMUNOGEN a

conversion fee as set forth in clause (c) of Section 4.2.

2.2.7 OPTION TO OBTAIN EXCLUSIVE LICENSES. Upon the written request of ABX

given at the time of ABX's exercise of a Nonexclusive Option, ABX shall have the

right to obtain an exclusive license under the IMMUNOGEN Background Technology

and Target Specific Rights pursuant to Section 2.1.5 as if such Nonexclusive

Option were an Exclusive

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

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Option, provided that [_______] of [___________], an [___________] for the

[_____________ ____________________] is [__________] in accordance with Section

2.1.2. [______________ _____________] of any [______________________] shall give

[_______________________ ______ ]an [________________________________________]

is [___________] in accordance with Section 2.1.2.

2.3 NON-EXCLUSIVE LICENSE. On and after the expiration of a Nonexclusive

Option Period or Exclusive Option Period, as the case may be, with respect to a

Proposed Licensed Target, ABX shall thereafter be granted a non-exclusive

license in the Territory under the IMMUNOGEN Background Technology, but not

under any Target Specific Rights with respect to such Proposed Licensed Target,

solely during the Research Term for the sole purpose of conducting preclinical

research with respect to Licensed Products directed to such Proposed Licensed

Target, for any and all uses in the Field. Such License shall continue during

the Research Term until such time as IMMUNOGEN gives express written notice to

ABX of IMMUNOGEN's grant to a Third Party of a bona fide exclusive license

regarding a May Compound conjugate product to such Proposed Licensed Target, in

which case such license shall immediately terminate.

2.4 NON-EXCLUSIVE RESEARCH LICENSES TO ABX.

2.4.1 RESEARCH LICENSE. IMMUNOGEN hereby grants to ABX a non-exclusive,

royalty-free license under IMMUNOGEN Background Technology, solely during the

Research Term and as further described below (i) to conjugate a May Compound to

one (1) or more additional ABX Antibodies that are not part of a Licensed

Product for use as a control for any Licensed Product licensed to it under a

License Agreement, (ii) to conduct toxicity studies (i.e., in vivo animal

studies designed to identify and measure the toxicity of a Licensed Product) on

any Licensed Product licensed to it hereunder and (iii) to conduct Research

Activities. The foregoing licenses may be sublicensed only in connection with a

sublicense of the IMMUNOGEN Background Technology hereunder or under a License

Agreement.

2.4.2 RESEARCH RECORDS. ABX shall maintain records of access to and

use of the IMMUNOGEN Background Technology.

2.4.3 EXPIRATION OF RESEARCH TERM. Unless otherwise provided in a

License Agreement or otherwise set forth in this Agreement, upon termination or

expiration of the Research Term, ABX shall discontinue use of the IMMUNOGEN

Background Technology and destroy all portions and copies of the IMMUNOGEN

Background Technology; provided, however, that ABX shall have the right to

retain one (1) copy for its legal files.

2.4.4 RESEARCH TERM. The term of the Research shall expire upon the

last to expire of the Option Periods, unless this Agreement is earlier

terminated by either Party pursuant to the provisions of Section 8 (the

"Research Term").

2.5 [_____________________] hereby [__________________] a

[__________________________________________________] of [_____________] under

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

12

<PAGE> 13

[____________], if any, in [____________] within the

[_____________________________ ________] to the extent [__________________] or

[_________] of the [_________] that are [____________________________________]

to the [___________] to [_______________] and [___________________] and

[__________] to [_________________________________ __________] to

[_______________________________________] (other than [____________] to a

[____________________] or a [____________]). [_______________________________

_____________] of the [________] of [_____________] of which it [____________].

[_______ ______] to [__________] includes [___________________________] to

[_________] from whom [________________________________________] to the

[________] they [___________ __________] or

[_____________________________________] to [____________] with the [______] to

[______________] hereunder, and [_________________________ ]to

[________________________________], but [__________________] with respect to

[_______________]. Notwithstanding the foregoing, the [________________________]

pursuant to this Section 2.5 [________________________________] of [______] to

any [_______________].

2.6 TECHNOLOGY TRANSFER. As soon as practicable after, and in any event on

or before [_____________] from, the Effective Date, (a) ABX and IMMUNOGEN will

agree upon a schedule to permit two (2) representatives designated by ABX to

visit IMMUNOGEN's facilities for a period of no more than

[______________________________________________ ________________] to

[_______________________________________________] to an [__________] and to

[______] the [______________] and [____________] used [____________

____________], and (b) [______] shall [_______________] with [______________] of

such [__ ____________] to

[_____________________________________________________________ ___________].

During such visit, IMMUNOGEN shall deliver to ABX all IMMUNOGEN Background

Technology existing as of the Effective Date. [______________________], the

[________________] shall [______] to [__________] and

[______________________________

____________________________________________________________________]. As soon

as practicable thereafter, but in any event on or before [______________] from

[_____________ ________] of [_________________________________], the Parties

shall, in order to [________

___________________________________________________________________] attached

hereto and [____________________________________], and the

[______________________ _________________] between the [________], if any. The

initial technology transfer under this Section 2.6 shall be complete for

purposes of Section 4.1 at such time as [__________________

_______________________________________________________]. Promptly, but not less

than quarterly thereafter, IMMUNOGEN shall deliver to ABX all IMMUNOGEN

Background Technology not previously delivered to ABX. From time to time during

the Research Term, IMMUNOGEN shall provide ABX with such technical assistance as

reasonably requested by ABX regarding the use of the IMMUNOGEN Background

Technology. Such technical assistance and expertise shall include, but not be

limited to, visits by IMMUNOGEN personnel to ABX and visits by ABX personnel to

IMMUNOGEN, at ABX's expense, at such times and for such periods of time as may

be reasonably acceptable to the Parties. Additionally, at the reasonable request

of ABX, IMMUNOGEN shall transfer all applicable IMMUNOGEN Background Technology,

and provide such technical assistance, to such Third Party collaborator,

sublicensee or contract manufacturer as ABX designates.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

13

<PAGE> 14

2.7 NO OTHER RIGHTS. ABX shall receive no rights to utilize IMMUNOGEN

Background Technology, or rights with respect to use of IMMUNOGEN Background

Technology, except as expressly set forth herein or in a License Agreement.

IMMUNOGEN shall receive no rights to Research Data, Research Materials, Research

Technology or Research Patent Rights thereon except as expressly set forth

herein. ABX's rights in Research Patent Rights are subject to

[___________________________________].

2.8 IN LICENSES. IMMUNOGEN represents and warrants to ABX that it has

provided ABX true and correct copies of all agreements pursuant to which

IMMUNOGEN Background Technology existing as of the Effective Date, is licensed

to or otherwise acquired by IMMUNOGEN from a third party. IMMUNOGEN promptly

shall provide ABX with true and correct copies of all agreements pursuant to

which IMMUNOGEN Background Technology licensed or acquired after the Effective

Date, is licensed to or otherwise acquired by IMMUNOGEN from a Third Party;

provided, however, that IMMUNOGEN shall have the right to redact confidential

financial information and any provisions that shall not bind ABX. To the extent

the IMMUNOGEN Background Technology is licensed to or acquired by IMMUNOGEN from

a Third Party and is reasonably necessary to permit ABX to exercise its rights

granted hereunder, IMMUNOGEN shall use reasonable commercial efforts to maintain

in full force and effect such license. In the event of the termination of any

such license with a Third Party, IMMUNOGEN shall cause such Third Party to grant

a direct license to ABX to the extent necessary to permit ABX to exercise its

rights granted hereunder, and all sums owing by ABX to such Third Party shall be

fully deducted from any amounts owing to IMMUNOGEN under the License Agreements.

3. JOINT PROCESS DEVELOPMENT COMMITTEE

3.1 ESTABLISHMENT OF COMMITTEE. Promptly after the Effective Date, the

Parties shall form a Joint Process Development Committee ("JPDC") whose mandate

shall be to serve as a forum for coordination and communication between the

Parties with respect to development (to the extent ABX requests the assistance

or services of IMMUNOGEN) of manufacturing processes applicable to any May

Compound or Licensed Product covered by this Agreement (including, without

limitation, all process science and process development work, formulation work,

and quality control/assurance work hereunder) to assist ABX in its exercise of

its rights to make or have made Licensed Products under this Agreement. Within

thirty (30) days following the Effective Date, the Parties shall each nominate

an equal number of representatives (which shall be no less than two (2)) for

membership on the JPDC. Each Party may change its representatives as it may deem

necessary by notice to the other Party. The input of the IMMUNOGEN

representatives on the JPDC shall be reasonably considered by the JPDC;

provided, however, that, all decisions of the JPDC shall be subject to the final

approval of ABX.

3.2 CHAIR OF COMMITTEE; MEETINGS. The chair of the JPDC shall be one of the

ABX representatives on the JPDC, as designated by ABX. All decisions of the JPDC

shall be subject to the approval of the ABX chair. The JPDC shall meet on a

semi-annual basis or other schedule agreed upon by the Parties, unless at least

thirty (30) days in advance of any meeting there is a determination by the Chair

of the JPDC that no new business or other activity

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

14

<PAGE> 15

has transpired since the previous meeting, and that there is no need for a

meeting. In such instance, the next JPDC meeting shall also be scheduled as

agreed upon by the Parties. The location of such meetings shall alternate

between IMMUNOGEN's offices in the Cambridge, Massachusetts metropolitan area

and ABX's offices in the Fremont, California metropolitan area unless otherwise

agreed upon between the Parties. As agreed upon by the Parties, JPDC meetings

may be face-to-face meetings or may be conducted through teleconferences and/or

videoconferences. In addition to its JPDC representatives, each Party shall be

entitled to have such additional number (as the Parties mutually agree) of other

employees attend such meetings to present and participate, though not in a

decision-making capacity. Each Party shall bear all costs and expenses,

including travel and lodging expense, that may be incurred by its JPDC

representatives or other of its attendees at JPDC meetings. Minutes of each JPDC

meeting will be transcribed and issued to the members of the JPDC by the Chair

within thirty (30) days after each meeting and shall be reviewed and modified as

mutually required to obtain approval promptly thereafter.

3.3 SUPPLY OF PRECLINICAL MATERIALS. In the event that, during the Term of

this Agreement, ABX desires IMMUNOGEN to supply ABX with sufficient quantities

of Preclinical Materials to enable it to conduct pre-clinical development

activities relating to Licensed Products, ABX shall provide IMMUNOGEN with

written notice of same and the Parties shall negotiate in good faith and execute

a supply agreement providing for such supply. IMMUNOGEN shall deliver all

ordered amounts of Preclinical Materials in accordance with advance ordering

timeframes and delivery timeframes to be agreed upon by the Parties through such

mutually acceptable written supply agreement for such purpose. In connection

with any ordering of Preclinical Materials by ABX, IMMUNOGEN shall provide ABX

promptly with IMMUNOGEN's good faith estimate of the Fully Burdened

Manufacturing Cost for manufacture and supply of such Preclinical Materials.

IMMUNOGEN's price to supply Preclinical Materials to ABX shall equal [______] of

IMMUNOGEN's Fully Burdened Manufacturing Cost for such Preclinical Materials as

approved by ABX. Nothing herein shall preclude ABX from making its own

arrangements for manufacture and supply of Preclinical Materials on its own or

with Third Parties. ABX hereby agrees that (a) it shall not use the Preclinical

Materials in any human subject, and (b) it shall use the Preclinical Materials

in compliance with all applicable federal, state and local laws and regulations.

3.4 SUPPLY OF CLINICAL MATERIALS. In the event that, during the Term of

this Agreement, ABX desires IMMUNOGEN to supply to ABX with sufficient

quantities of Clinical Materials to enable it to conduct human clinical trials

of Licensed Products through the conclusion of Phase II Clinical Studies, ABX

shall provide IMMUNOGEN with written notice of same and the Parties shall

negotiate in good faith and execute a supply agreement providing for such

supply. IMMUNOGEN shall deliver all ordered amounts of Clinical Materials in

accordance with forecasting parameters, advance ordering timeframes and delivery

timeframes to be agreed upon by the Parties through such mutually acceptable

written supply agreement for such purpose. In connection with any ordering of

Clinical Materials by ABX, IMMUNOGEN shall provide ABX promptly with IMMUNOGEN's

good faith estimate of the Fully Burdened Manufacturing Cost for manufacture and

supply of such Clinical Materials. IMMUNOGEN's price to supply Clinical

Materials to ABX shall equal [___] of IMMUNOGEN's Fully Burdened

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

15

<PAGE> 16

Manufacturing Cost for such Clinical Materials as approved by ABX. Nothing

herein shall preclude ABX from making its own arrangements for manufacture and

supply of Clinical Materials on its own or with Third Parties. ABX hereby agrees

that it shall use the Clinical Materials in compliance with all applicable

federal, state and local laws. IMMUNOGEN shall provide ABX with all information,

filings and assistance regarding manufacturing as reasonably requested by ABX in

connection with applications for Regulatory Approvals.

4. FINANCIAL TERMS

4.1 INITIAL FEES. ABX shall to pay to IMMUNOGEN a non-refundable fee in the

amount of [________] within [__________] after the Effective Date. Additionally,

ABX shall to pay to IMMUNOGEN a non-refundable fee in the amount of [________]

within [_____ _______]after [________________________________________________].

4.2 OPTION FEES. ABX agrees to pay to IMMUNOGEN an option fee (a) in the

amount of [______] for each Exclusive Option granted hereunder, (b) in the

amount of [_______] for each Nonexclusive Option granted hereunder and (c) in

the amount of [_____] for each conversion of a Nonexclusive Option into an

Exclusive Option in accordance with Section 2.2.6 hereof. Such fees shall be

paid on or before [_______] from the date of grant of such Exclusive Option or

Nonexclusive Option, or conversion of such Nonexclusive Option, as the case may

be.

4.3 OPTION EXTENSION FEES. ABX agrees to pay to IMMUNOGEN option extension

fees (a) in the amount of [______] for the extension of each option under

Section 2.1.3 hereof and (b) in the amount of [______] for the extension of each

option extension under Section 2.2.3 hereof. Such fees shall be paid on or

before [__________] after the date of each such extension.

5. TREATMENT OF CONFIDENTIAL INFORMATION

5.1 CONFIDENTIAL INFORMATION. During the Term of this Agreement, each Party

may disclose to the other Party confidential information, including but not

limited to IMMUNOGEN Background Technology, Research Inventions, Research Data

and Research Materials. Such information of the disclosing Party hereunder, if

so identified in writing by the disclosing Party to the receiving Party either

pursuant to this Section 5.1 or otherwise upon disclosure to the receiving

Party, shall be "Confidential Information" of the disclosing Party. During the

Term of this Agreement and during the term of any License Agreement, and for a

period of five (5) years thereafter, except as expressly permitted hereunder,

the receiving Party shall keep confidential all such Confidential Information of

the other Party and will not disclose such Confidential Information of the other

Party to Third Parties by publication or otherwise. Each Party further agrees

not to use Confidential Information of the other Party for any purpose other

than conducting research hereunder or exercising any rights granted to it or

reserved by it hereunder. Upon any termination or expiration of this Agreement,

upon request, a Party shall return to a requesting Party all copies of any of

such requesting Party's Confidential Information which is not the subject of a

License Agreement or the grant of a license hereunder, provided that

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

16

<PAGE> 17

it may retain one copy for its legal files. Notwithstanding the foregoing, it is

understood and agreed that the receiving Party's obligations of confidentiality

and nonuse herein shall not apply to any information which:

(a) is, at the time of disclosure by the disclosing Party

hereunder, or thereafter becomes, a part of the public domain or publicly known

or available through no fault or negligence of the receiving Party or any of its

Affiliates; or

(b) was otherwise in the receiving Party's lawful possession

prior to disclosure by the disclosing Party, other than under an obligation of

confidentiality; or

(c) was independently discovered or developed by the receiving

Party or any of its Affiliates, without use of the other Party's Confidential

Information, as can be demonstrated by competent proof; or

(d) is lawfully disclosed to the receiving Party or any of its

Affiliates on a non-confidential basis by a third party who is not in violation

of an obligation of confidentiality to the disclosing Party relative to such

information.

Each Party may disclose information to the extent such disclosure is

reasonably necessary in (i) filing and prosecuting patent applications and

maintaining patents, or (ii) filing, prosecuting or defending litigation or

(iii) complying with applicable laws, regulations or court orders; provided,

however, that if a Party is required to make any such disclosure of the other

Party's Confidential Information or the terms of this Agreement, it will give

reasonable advance notice to the other Party of such disclosure requirement and

will use reasonable efforts to assist such other Party in efforts to secure

confidential treatment of such information required to be disclosed.

5.2 PUBLICITY. A Party may not use the name of the other Party in any

publicity or advertising and, except as provided in Section 5.1, may not issue a

press release or otherwise publicize or disclose any information related to this

Agreement or the terms or conditions hereof, without the prior written consent

of the other Party. The Parties shall mutually agree on a press release

announcing the execution of this Agreement. The Parties shall also be permitted

hereunder to disclose the general nature of this Agreement to the extent

reasonably necessary to obtain financing from Third Parties or potential

collaborators, and to make such other disclosures as mutually agreed by the

Parties. Once any written statement is approved for disclosure by both Parties,

either Party may make subsequent public disclosures of the contents of such

statement without the further approval of the other Party. Nothing in the

foregoing, however, shall prohibit a Party from making such disclosures to the

extent deemed necessary under applicable federal or state securities laws or any

rule or regulation of any nationally recognized securities exchange; provided,

that, in such event, the disclosing Party shall use good faith efforts to

consult with the other Party prior to such disclosure and, where applicable,

shall request confidential treatment to the extent available.

6. INTELLECTUAL PROPERTY RIGHTS

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

17

<PAGE> 18

Except as otherwise expressly provided herein, all inventions and

discoveries governed by this Agreement shall be owned based on inventorship, as

inventorship is determined in accordance with United States patent law.

Notwithstanding anything to the contrary in this Agreement, Research Inventions,

Research Data, Research Materials and Research Patent Rights shall be solely

owned by ABX. Any inventions jointly invented by the Parties ("Joint

Inventions") shall be jointly owned, and any patent rights obtained thereon

shall be jointly owned by the Parties. The rights and interests of IMMUNOGEN and

ABX in Joint Inventions, and any patent rights obtained thereon, shall be

subject to the provisions of this Section 6. Each Party shall have the right,

subject to the terms of this Agreement and any License Agreement, to freely

exploit, transfer, license or encumber its rights and interests in Joint

Inventions, and any patent rights obtained thereon.

7. PROVISIONS CONCERNING THE FILING, PROSECUTION

AND MAINTENANCE OF PATENT RIGHTS

7.1 APPLICABILITY. The provisions of this Section 7 shall be applicable to

all patents covering IMMUNOGEN Background Technology and all Research Patent

Rights thereon unless and until they become subject to a License Agreement,

whereupon the License Agreement will govern the rights of the Parties with

respect to the subject matter thereof.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

18

<PAGE> 19

7.2 PATENT FILING.

7.2.1 Subject to the License Agreements, IMMUNOGEN shall have the

obligation to prepare, file, prosecute, obtain and maintain patent applications

and patents covering IMMUNOGEN Background Technology, with the expenses for any

such preparation, filing, prosecution and maintenance to be borne by IMMUNOGEN.

7.2.2 ABX shall have the right (but not the obligation) to prepare,

file, prosecute, obtain and maintain patent applications and patents

constituting Research Patent Rights, with the expenses for any such preparation,

filing, prosecution and maintenance to be borne by ABX.

7.2.3 Subject to the License Agreements, as regards any joint

invention hereunder (other than Research Inventions, Research Data and Research

Materials), the Party from whom the majority of the data underlying any such

joint invention arose (the "controlling Party") will have the first right, but

not the obligation, to undertake filing(s), prosecution and maintenance of

inventorship certificate(s) and patent(s) thereon. In connection with any such

filing(s), the controlling Party will use patent counsel mutually acceptable to

each Party (in its reasonable determination) and the Parties will, prior to

filing of the patent application, agree on mutually acceptable sharing of the

costs and expenses of such filing(s), prosecution and maintenance. In any case

the controlling Party (i) will provide the non-controlling Party with a copy of

any such proposed patent application for review and comment reasonably in

advance of filing, and (ii) will keep the non-controlling Party reasonably

informed of the status of such filing, prosecution and maintenance, including,

without limitation, (A) by providing the non-controlling Party with copies of

all communications received from or filed in patent office(s) with respect to

such filing, and (B) by providing the non-controlling Party, a reasonable time

prior to taking or failing to take any action that would affect the scope or

validity of any such filing (including the substantially narrowing, cancellation

or abandonment of any claim(s) without retaining the right to pursue such

subject matter in a separate application, or the failure to file or perfect the

filing of any claim(s) in any country), with prior written notice of such

proposed action or inaction so that the non-controlling Party has a reasonable

opportunity to review and comment. If the controlling Party fails to undertake

the filing(s) of any such patent application with respect to any such invention

within ninety (90) days after receipt of written notice from the other Party

that the other Party believes filing(s) of such an application by such Party is

appropriate, the other Party may undertake such filing(s) at its own expense, in

which case the controlling Party will assign all of its rights to such joint

invention to the other Party and any subsequently issued patent thereon will be

owned solely by the other Party. Either Party, in its discretion, may assign its

rights hereunder to any jointly owned invention, inventorship certificate,

patent application or patent to the other Party, who will then have the right,

in its discretion, to assume the filing, prosecution and/or maintenance thereof

as the sole owner thereof and at its sole cost and expense.

7.2.4 Each Party agrees to cooperate reasonably with the other party

in the preparation, filing, and prosecution of any patent applications pursuant

to this Section 7.2. Such cooperation includes, but is not limited to, executing

all papers and instruments, or

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

19

<PAGE> 20

requiring its employees or agents to execute such papers and instruments, so as

to effectuate the ownership of such patent applications and any patents thereon

and to enable the filing and prosecution of applications in any country.

7.3 INFRINGEMENT.

7.3.1 ABX shall have all rights, at its own expense, to bring suit (or

other appropriate legal action) against any actual or suspected infringement of

Research Patent Rights.

7.3.2 Subject to the License Agreements, IMMUNOGEN shall have all

rights, at its own expense, to bring suit (or other appropriate legal action)

against any actual or suspected infringement of patents covering IMMUNOGEN

Background Technology.

7.3.3 Subject to the License Agreements, in the event of the

infringement of any patent claiming any Joint Invention hereunder (other than

Research Inventions, Research Data and Research Materials), the parties shall

meet and in good faith discuss the appropriate course of action to enforce such

patent(s) and which Party shall control such action.

7.4 COOPERATION. Each Party shall give notice to the other party of any

potential infringement or actual infringement by a third party of any Research

Patent Right or patents covering IMMUNOGEN Background Technology and shall

execute all papers and perform such other acts (other than monetary) as may be

reasonably required to maintain any infringement suit brought in accordance with

Section 7.3 above (including giving legal consent for bringing such suit, and

agreeing to be named as a plaintiff or otherwise joined in such suit), and at

its option and expense, may be represented in such suit by counsel of its

choice. In addition, the Parties shall reasonably cooperate with each other in

obtaining patent term restoration or supplemental protection certificates or

their equivalents in any country in the Territory where applicable to Research

Patent Rights and IMMUNOGEN Background Technology.

7.5 NO OBLIGATION. No Party shall have any obligation to the other Party

under this Agreement to pay any fees or costs: (i) for that Party's bringing a

lawsuit or other action to enforce any of the Research Patent Rights, any

patents covering IMMUNOGEN Background Technology, or any other patent owned by a

Party against an actual or suspected infringement or (ii) for any other Party to

obtain for its own benefit independent business or legal advice concerning any

of the patent rights set forth in clause (i) hereof.

8. TERM AND TERMINATION

8.1 TERM. Unless earlier terminated as provided in this Section 8, the term

of this Agreement shall expire upon the expiration of the last to expire Option

(the "Term").

8.2 TERMINATION. This Agreement and the rights and options granted

herein may be terminated by either Party upon any material breach by the other

Party of any material

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

20

<PAGE> 21

obligation or condition, effective [____________] after giving written notice to

the breaching Party of such termination in the case of a payment breach and

[____________] after giving written notice to the breaching Party of such

termination in the case of any other breach, which notice shall describe such

breach in reasonable detail. The foregoing notwithstanding, if such default or

breach is cured or shown to be non-existent within the aforesaid [______] or

[______ ____] period, the notice shall be automatically withdrawn and of no

effect. However, prior to giving any notice for breach, the Parties shall first

attempt to resolve any disputes as to the existence of any breach as set forth

in Section 9.14.

8.3 REMEDIES. If either Party shall fail to perform or observe or otherwise

breaches any of its material obligations under this Agreement, in addition to

any right to terminate this Agreement, the non-defaulting Party may elect to

obtain other relief and remedies available under law.

8.4 SURVIVING PROVISIONS. Notwithstanding any provision herein to the

contrary, the rights and obligations set forth in Sections 5, 6, 7, 8.3, 9.3,

9.4, 9.7, 9.14, 9.16, 9.17, 9.18 and 9.19 hereof shall survive the expiration or

termination of the Term of this Agreement.

9. MISCELLANEOUS

9.1 IMMUNOGEN REPRESENTATIONS. IMMUNOGEN represents and warrants to ABX

that: (a) the execution and delivery of this Agreement and the performance of

the transactions contemplated hereby have been duly authorized by all

appropriate IMMUNOGEN corporate action; (b) this Agreement is a legal and valid

obligation binding upon IMMUNOGEN and enforceable in accordance with its terms,

and the execution, delivery and performance of this Agreement by the Parties

does not conflict with any agreement, instrument or understanding to which

IMMUNOGEN is a party or by which it is bound; (c) IMMUNOGEN has the full right

and legal capacity to grant the rights to ABX pursuant to Section 2 above

without violating the rights of any third party; (d) IMMUNOGEN is the sole owner

or exclusive licensee of the IMMUNOGEN Background Technology; (e) IMMUNOGEN is

not aware of any Third Party patent, patent application or other intellectual

property rights that would be infringed (i) by practicing any process or method

or by making, using or selling any composition which is claimed or disclosed in,

or which constitutes, IMMUNOGEN Background Technology, or (ii) by making, using,

offering for sale, selling or importing Licensed Products; and (f) IMMUNOGEN is

not aware of any infringement or misappropriation by a Third Party of the

IMMUNOGEN Background Technology.

9.2 ABX REPRESENTATIONS. ABX represents and warrants to IMMUNOGEN that: (a)

the execution and delivery of this Agreement and the performance of the

transactions contemplated hereby have been duly authorized by all appropriate

ABX corporate action; (b) this Agreement is a legal and valid obligation binding

upon ABX and enforceable in accordance with its terms, and the execution,

delivery and performance of this Agreement by the Parties does not conflict with

any agreement, instrument or understanding to which ABX is a party of or by

which it is bound; and (c) ABX has the full right and legal capacity to grant

the rights to IMMUNOGEN pursuant to Section 2 above without violating the rights

of any Third Party.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

21

<PAGE> 22

9.3 NO WARRANTIES.

9.3.1 Nothing in this Agreement is or shall be construed as:

(a) a warranty or representation by either Party as to the

validity or scope of any patent application or patent licensed hereunder;

(b) a warranty or representation that anything made, used, sold

or otherwise disposed of under any license granted pursuant to this Agreement is

or will be free from infringement of patents, copyrights, and other rights of

third parties.

9.3.2 Except as expressly set forth in this Agreement, NEITHER PARTY

MAKES ANY REPRESENTATION OR EXTENDS ANY WARRANTIES OF ANY KIND, EITHER EXPRESS

OR IMPLIED. THERE ARE NO EXPRESS OR IMPLIED WARRANTIES OF MERCHANTABILITY OR

FITNESS FOR A PARTICULAR PURPOSE, OR OF NON-INFRINGEMENT OF ANY PATENT,

COPYRIGHT, TRADEMARK, OR OTHER RIGHTS OF THIRD PARTIES, OR ANY OTHER EXPRESS OR

IMPLIED WARRANTIES.

9.4 [________]. NOTWITHSTANDING ANYTHING ELSE IN THIS AGREEMENT OR

OTHERWISE, [_______________] WILL BE [___________________] TO [________________]

OF THIS AGREEMENT [_________________________________

_______________________________] OR [____________] OR [__________________] FOR

(I) [____________________________________________________________________] OR

[_____________] OR (II) [___________________________________________________

_____________________________].

9.5 NOTICES. Any notices, requests, deliveries, approvals or consents

required or permitted to be given under this Agreement to ABX or IMMUNOGEN shall

be in writing and shall be effective on receipt when delivered to the applicable

address specified below (or to such other address as may be specified in writing

to the other Party hereto):

If to IMMUNOGEN: IMMUNOGEN, Inc.

128 Sidney Street

Cambridge, MA 02139

Attn: Chief Executive Officer

With a copy to: Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.

One Financial Center

Boston, MA 02111

Attn: Jeffrey M. Wiesen, Esq

Telecopy: 617-542-2241

If to ABX: Abgenix, Inc.

7601 Dumbarton Circle

Fremont, California 94555

Attn: President

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

22

<PAGE> 23

With a copy to: Gray Cary Ware & Freidenrich LLP

4365 Executive Drive, Suite 1600

San Diego, California 92121-2189

Attn: Mark R. Wicker

9.6 GOVERNING LAW. This Agreement will be construed, interpreted and

applied in accordance with the laws of the Commonwealth of Massachusetts

(excluding its body of law controlling conflicts of law).

9.7 LIMITATIONS. Except as set forth elsewhere in this Agreement, neither

Party grants to the other Party any right or license to any of its intellectual

property.

9.8 ENTIRE AGREEMENT. This is the entire Agreement between the Parties with

respect to the subject matter hereof and supersedes all prior representations,

understandings and agreements between the Parties with respect to the subject

matter hereof. No modification shall be effective unless in writing with

specific reference to this Agreement and signed by the Parties.

9.9 WAIVER. The terms or conditions of this Agreement may be waived only by

a written instrument executed by the Party waiving compliance. The failure of

either Party at any time or times to require performance of any provision hereof

shall in no manner affect its rights at a later time to enforce the same. No

waiver by either Party of any condition or term shall be deemed as a continuing

waiver of such condition or term or of another condition or term.

9.10 HEADINGS. Section and subsection headings are inserted for convenience

of reference only and do not form part of this Agreement.

9.11 ASSIGNMENT. Neither this Agreement nor any right or obligation

hereunder may be assigned, delegated or otherwise transferred , in whole or

part, by either party without the prior express written consent of the other;

provided, however, that either party may, without the written consent of the

other, assign this Agreement and its rights and delegate its obligations

hereunder to its Affiliates, or in connection with the transfer or sale of all

or substantially all of such party's assets or business related to this

Agreement, or in the event of its merger, consolidation, change in control or

similar transaction. Any permitted assignee shall assume all obligations of its

assignor under this Agreement. Any purported assignment in violation of this

Section 9.11 shall be void. The terms and conditions of this Agreement shall be

binding upon and inure to the benefit of the permitted successors and assigns of

the parties.

9.12 FORCE MAJEURE. Neither Party shall be liable for failure of or delay

in performing obligations set forth in this Agreement, and neither shall be

deemed in breach of its obligations, if such failure or delay is due to natural

disasters or any causes beyond the reasonable control of such Party. In event of

such force majeure, the Party affected thereby shall use reasonable efforts to

cure or overcome the same and resume performance of its obligations hereunder.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

23

<PAGE> 24

9.13 CONSTRUCTION. The Parties hereto acknowledge and agree that: (i) each

Party and its counsel reviewed and negotiated the terms and provisions of this

Agreement and have contributed to its revision; (ii) the rule of construction to

the effect that any ambiguities are resolved against the drafting Party shall

not be employed in the interpretation of this Agreement; and (iii) the terms and

provisions of this Agreement shall be construed fairly as to all Parties hereto

and not in favor of or against any Party, regardless of which Party was

generally responsible for the preparation of this Agreement.

9.14 DISPUTES.

9.14.1 The Parties recognize that a bona fide dispute as to certain

matters may from time to time arise during the term of this Agreement which

relates to either Party's rights and/or obligations hereunder. In the event of

the occurrence of such a dispute, either Party may, by written notice to the

other Party, have such dispute referred to their respective senior officials

designated below or their successors, for attempted resolution by good faith

negotiations within thirty (30) days after such notice is received. Said

designated senior officials are as follows:

For ABX: Chief Executive Officer

For IMMUNOGEN: Chief Executive Officer

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

24

<PAGE> 25

In the event the designated senior officials are not able to resolve such

dispute within the thirty (30) day period, either Party may invoke the

provisions of Section 9.14.2.

9.14.2 Any dispute, controversy or claim initiated by either Party

arising out of, resulting from or relating to this Agreement, or the performance

by either Party of its obligations under this Agreement (other than bona fide

third party actions or proceedings filed or instituted in an action or

proceeding by a Third Party against a Party), whether before or after

termination of this Agreement, shall be finally resolved by binding arbitration.

Whenever a Party shall decide to institute arbitration proceedings, it shall

give written notice to that effect to the other Party. Any such arbitration

shall be conducted under the Commercial Arbitration Rules of the American

Arbitration Association by a panel of three arbitrators appointed in accordance

with such rules. Any such arbitration shall be held in Boston, Massachusetts if

initiated by ABX, and in San Francisco, California if initiated by IMMUNOGEN.

The method and manner of discovery in any such arbitration proceeding shall be

governed by California Code of Civil Procedure ss.1282 ET SEQ. (including

without limitation California Code of Civil Procedure ss.1283.05). The

arbitrators shall have the authority to grant specific performance and to

allocate between the parties the costs of arbitration in such equitable manner

as they determine. Judgment upon the award so rendered may be entered in any

court having jurisdiction or application may be made to such court for judicial

acceptance of any award and an order of enforcement, as the case may be. In no

event shall a demand for arbitration be made after the date when institution of

a legal or equitable proceeding based upon such claim, dispute or other matter

in question would be barred by the applicable statute of limitations.

Notwithstanding the foregoing, either Party shall have the right, without

waiving any right or remedy available to such Party under this Agreement or

otherwise, to seek and obtain from any court of competent jurisdiction any

interim or provisional relief that is necessary or desirable to protect the

rights or property of such Party, pending the selection of the arbitrators

hereunder or pending the arbitrators' determination of any dispute, controversy

or claim hereunder.

9.15 SEVERABILITY. If any provision(s) of this Agreement are or become

invalid, are ruled illegal by any court of competent jurisdiction or are deemed

unenforceable under then current applicable law from time to time in effect

during the Term hereof, it is the intention of

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

25

<PAGE> 26

the Parties that the remainder of this Agreement shall not be affected thereby

provided that a Party's rights under this Agreement are not materially affected.

The Parties hereto covenant and agree to renegotiate any such term, covenant or

application thereof in good faith in order to provide a reasonably acceptable

alternative to the term, covenant or condition of this Agreement or the

application thereof that is invalid, illegal or unenforceable, it being the

intent of the Parties that the basic purposes of this Agreement are to be

effectuated.

9.16 STATUS. Nothing in this Agreement is intended or shall be deemed to

constitute a partner, agency, employer-employee, or joint venture relationship

between the Parties.

9.17 INDEMNIFICATION.

9.17.1 ABX INDEMNITY. ABX shall [________] and [_____________

_____________________] and [__________________________________], and [______]

and [______________________________](the "Indemnitees")

[____________________________ ____________________] (including

[______________________] and [_______________]) [_________] or

[_______________________], or [________], in connection with [_________

______________________________________], including, without limitation,

[____________ ________________] matters (but

[_________________________________________________ ______], which are

[______________________]), to the extent arising out of (i) [_________

______________] in the [______________________________________________________

__________________________________] of any [_________________________________

______________________________________] under this Agreement, (ii)

[_______________] of this Agreement [_____], or (iii)

[_____________________________] of the [__________], in any [_______] under this

Section 9.17.1 except to [_______________________________] therefor under

Section 9.17.2 below.

9.17.2 IMMUNOGEN INDEMNITY. Subject to Section 9.17.1 above,

IMMUNOGEN shall indemnify, defend and hold harmless ABX, its Affiliates and

their respective directors, officers, employees, and agents, and their

respective successors, heirs and assigns (also the "Indemnitees"), from and

against any liability, damage, loss or expense (including reasonable attorneys'

fees and expenses of litigation) incurred by or imposed upon such Indemnitees,

or any of them, in connection with any Third Party claims, suits, actions,

demands or judgments, including, without limitation, personal injury and product

liability matters (but excluding any patent, trademark or tradename infringement

matters, which are governed by Section 7 above), to the extent arising out of

(i) any actions or omissions of IMMUNOGEN or subcontractor of IMMUNOGEN in the

development, testing, production, manufacture or supply of any Licensed Product

(or any component thereof) manufactured and supplied by IMMUNOGEN or any

subcontractor of IMMUNOGEN under this Agreement, (ii) any material breach of

this Agreement by IMMUNOGEN, or (iii) gross negligence or willful misconduct on

the part of IMMUNOGEN.

9.18 INDEMNIFICATION PROCEDURES. In the event that any Indemnitee is

seeking indemnification under Section 9.17 above from a Party (the "Indemnifying

Party"), the other

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

26

<PAGE> 27

Party shall notify the Indemnifying Party of such claim with respect to such

Indemnitee as soon as reasonably practicable after the Indemnitee receives

notice of the claim, and the Party (on behalf of itself and such Indemnitee)

shall permit the Indemnifying Party to assume direction and control of the

defense of the claim (including the right to settle the claim solely for

monetary consideration) and shall cooperate as requested (at the expense of the

Indemnifying Party) in the defense of the claim. The indemnification obligations

under Section 9.17 shall not apply to amounts paid in settlement of any claim,

demand, action or other proceeding if such settlement is effected without the

consent of the Indemnifying Party, which consent shall not be withheld or

delayed unreasonably. The Indemnitee, its employees and agents, shall reasonably

cooperate with the Indemnifying Party and its legal representatives in the

investigation of any claim, demand, action or other proceeding covered by

Section 9.17.

9.19 SECTION 365(n). All licenses granted under this Agreement are deemed

to be, for purposes of Section 365(n) of the U.S. Bankruptcy Code, licenses of

right to "intellectual property" as defined in Section 101 of such Code. The

Parties agree that the licensee may fully exercise all of its rights and

elections under the U.S. Bankruptcy Code, regardless of whether either Party

files for bankruptcy in the United States or other jurisdiction. The Parties

further agree that, in the event a licensee elects to retain its rights as a

licensee under such Code, the licensee shall be entitled to complete access to

any technology licensed to it hereunder and all embodiments of such technology.

Such embodiments of the technology shall be delivered to the licensee not later

than:

9.19.1 the commencement of bankruptcy proceedings against the

licensor, upon written request, unless the licensor elects to perform its

obligations under the Agreement, or

9.19.2 if not delivered under Section 9.19.1 above, upon the

rejection of this Agreement by or on behalf of the licensor, upon written

request.

9.20 FURTHER ASSURANCES. Each Party agrees to execute, acknowledge and

deliver such further instructions, and to do all such other acts, as may be

necessary or appropriate in order to carry out the purposes and intent of this

Agreement.

9.21 COUNTERPARTS. This Agreement may be executed simultaneously in one or

more counterparts, each of which shall be deemed an original, but all of which

together shall constitute one and the same instrument.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

27

<PAGE> 28

IN WITNESS WHEREOF, the Parties have caused this Agreement to be executed

by their duly authorized representative in two (2) originals.

ABGENIX, INC. IMMUNOGEN, INC.

By: By:

---------------------------- -----------------------------

Title: Title:

-------------------------- --------------------------

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

28

<PAGE> 29

SCHEDULE I

IMMUNOGEN BACKGROUND TECHNOLOGY

[____________________________]

<TABLE>

<CAPTION>

_________________________________________________________________________________________________________________________________

Attorney Country Appl. No. Filing Date Priority Date Patent No. Issue Date Exp. Date

Reference No.

_________________________________________________________________________________________________________________________________

<S> <C> <C> <C> <C> <C> <C> <C>

[________] [________] [________] [________] [________]

_________________________________________________________________________________________________________________________________

[________] [________]

[________] [________] [________] [________] [_______] [______]

_________________________________________________________________________________________________________________________________

[________] [________] [________] [________] [________] [______]

[________] [_______]

_________________________________________________________________________________________________________________________________

[________] [________] [________] [________] [________] [________] [______] [______]

_________________________________________________________________________________________________________________________________

[________]

_________________________________________________________________________________________________________________________________

[________] [________] [________] [________] [________] [________]

_________________________________________________________________________________________________________________________________

[________] [________] [________] [________] [________] [________]

_________________________________________________________________________________________________________________________________

</TABLE>

<TABLE>

<CAPTION>

[___________________________________________________________]

_________________________________________________________________________________________________________________________________

Attorney Country Appl. No. Filing Date Priority Date Patent No. Issue Date Exp. Date

Reference No.

_________________________________________________________________________________________________________________________________

<S> <C> <C> <C> <C> <C> <C> <C>

[________] [________] [________] [________] [________]

_________________________________________________________________________________________________________________________________

[_____________________________]

_________________________________________________________________________________________________________________________________

Attorney Country Appl. No. Filing Date Priority Date Patent No. Issue Date Exp. Date

Reference No.

_________________________________________________________________________________________________________________________________

[________] [________] [________] [________] [________]

_________________________________________________________________________________________________________________________________

</TABLE>

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

29

<PAGE> 30

SCHEDULE II

[___________________________]

[____________________________________________________________________________

________________________________________________________].

[___________________________________________________].

<TABLE>

<CAPTION>

___________________________________________________________________________________________________________________

[________] [________] [________]

___________________________________________________________________________________________________________________

<S> <C> <C>

___________________________________________________________________________________________________________________

[________________] [________] [________]

(a)________________________________________________________________________________________________________________

[________] [________] [________]

___________________________________________________________________________________________________________________

[________]

___________________________________________________________________________________________________________________

[________]

___________________________________________________________________________________________________________________

[________] [________] [________] (b)

___________________________________________________________________________________________________________________

[________] [________] [________](b)

___________________________________________________________________________________________________________________

[________] [________] [________](b)

___________________________________________________________________________________________________________________

[________] [________] [________]

___________________________________________________________________________________________________________________

[________] [________] [________]

___________________________________________________________________________________________________________________

[________] [________] [________]

___________________________________________________________________________________________________________________

[________]:

[________] (c) [________] [________]

and/or

___________________________________________________________________________________

___________________________________________________________________________________

[________] (c) [________]

[________] (d)

___________________________________________________________________________________________________________________

</TABLE>

(a) [________]

(b) [________].

(c) [________].

(d) [________].

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

30

<PAGE> 31

FORM OF EXCLUSIVE LICENSE AGREEMENT

This Exclusive License Agreement ("Agreement") is made effective as of as

of _________, 20__ (the "Effective Date") by and between IMMUNOGEN, INC., a

Massachusetts corporation with a principal place of business at 128 Sidney

Street, Cambridge, Massachusetts 02139 ("IMMUNOGEN"), and ABGENIX, INC., a

Delaware corporation with a place of business at 7601 Dumbarton Circle, Fremont,

California 94555 ("ABX"). IMMUNOGEN and ABX are each hereafter referred to

individually as a "Party" and together as the "Parties".

WHEREAS, ABX is the owner of or otherwise controls certain patents and

technology relating to antibodies; and

WHEREAS, IMMUNOGEN is the owner of or otherwise controls certain

proprietary patents and technology relating to or otherwise useful in the

conjugation of certain cytotoxic compounds such as DM1 (as hereinafter defined)

to antibodies; and

WHEREAS, ABX desires to obtain certain rights from IMMUNOGEN to develop and

commercialize one or more conjugates of certain cytotoxic compounds and

antibodies and IMMUNOGEN is willing to grant to ABX such rights on the terms

provided herein; and

WHEREAS, the Parties have heretofore executed an Option and License

Agreement (as hereinafter defined) pursuant to which IMMUNOGEN has granted ABX

certain options related to IMMUNOGEN's proprietary technology and know-how; and

WHEREAS, ABX has exercised an Option (as hereinafter defined) to obtain

such rights and, in connection therewith, desires to enter into this Agreement

in accordance with the terms of the Option and License Agreement.

NOW, THEREFORE, in consideration of the mutual covenants contained herein,

and for other good and valuable consideration, the receipt and adequacy of which

are hereby acknowledged, the Parties hereby agree as follows:

1. DEFINITIONS

Whenever used in the Agreement with an initial capital letter, the terms

defined in this Section 1 shall have the meanings specified.

1.1 "ABX ANTIBODY" shall mean any antibody or fragment thereof directed to

the Target.

1.2 "ADVERSE EVENT" shall mean any serious adverse event or medical

occurrence in a patient or subject who is administered a Licensed Product,

whether or not

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

1

<PAGE> 32

considered related to the Licensed Product, including, without limitation, any

undesirable sign (including abnormal laboratory findings of clinical concern),

symptom or disease temporally associated with the use of such Licensed Product.

1.3 "AFFILIATE" shall mean any corporation, firm, limited liability

company, partnership or other entity which directly controls or is controlled by

or is under common control with a Party to this Agreement. "Control" for

purposes of this Section 1.3 means ownership, directly or indirectly through one

or more Affiliates, of fifty percent (50%) or more of the shares of stock

entitled to vote for the election of directors, in the case of a corporation, or

fifty percent (50%) or more of the equity interests in the case of any other

type of legal entity, status as a general partner in any partnership, or any

other arrangement whereby a Party controls or has the right to control the Board

of Directors or equivalent governing body of a corporation or other entity.

1.4 "BLA" shall mean a biologics license application (as defined in Title

21 of the United States Code of Federal Regulations, as amended from time to

time) filed with the FDA seeking Regulatory Approval to market and sell any

Licensed Product in the United States for a particular indication within the

Field.

1.5 "CLINICAL MATERIALS" shall mean (a) supplies of ansamitocin P-3, DM1,

and/or any other May Compound as manufactured in accordance with all applicable

GMPs and other legal requirements and all applicable Specifications for such May

Compound for use in human clinical testing, and (b) supplies of any Licensed

Product as manufactured in accordance with all applicable GMPs and other legal

requirements and all applicable Specifications for such Licensed Product for use

in human clinical testing of any Licensed Product.

1.6 "COMBINATION PRODUCT" shall mean any Licensed Product that contains, in

addition to any conjugate of any ABX Antibody with any May Compound, one or more

other ingredients that has biologic activity.

1.7 "CONTROL" OR "CONTROLLED" shall mean (a) with respect to patents,

know-how or other intangible rights, the possession by Party of the ability to

grant a license or sublicense of such patent rights, know-how or other

intangible rights as provided for herein without violating the terms of any

arrangement or agreements between such Party and any Third Party and (b) with

respect to any material, the possession by a Party of the ability to use such

material as provided herein without violating the terms of any agreement between

such Party and any Third Party.

1.8 [________________] shall mean [_________________________], whether

[________________________________________________________], and shall include,

without limitation, [_____________________________________________], in each

case [_____________________________________]. [___________________] shall

include, without limitation, [________________].

1.9 "DEVELOPMENT" AND "DEVELOP" shall mean, with respect to any Licensed

Product, all activities with respect to such Licensed Product relating to

research, development

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

2

<PAGE> 33

and seeking, obtaining and/or maintaining any Regulatory Approval for such

Licensed Product in the Field in the Territory, including without limitation,

all pre-clinical research and development activities, all human clinical

studies, all activities relating to developing the ability to manufacture any

Licensed Product or any component thereof (including, without limitation,

process development work), and all other activities relating to seeking,

obtaining and/or maintaining any Regulatory Approvals from the FDA and/or any

Foreign Regulatory Authority.

1.10 "DM1" shall mean that certain maytansine derivative having the

specific chemical name N2'-deacetyl-N2'-(3-mercapto-1-oxopropyl)-maytansine.

1.11 "DRUG APPROVAL APPLICATION" shall mean any application for Regulatory

Approval (including pricing and reimbursement approvals) required prior to any

commercial sale or use of a Licensed Product in any country or jurisdiction in

the Territory, including, without limitation, (a) any BLA, NDA or other

regulatory application filed with the FDA required prior to any commercial sale

or use of a Licensed Product in the United States, and (b) any equivalent

application (including an MAA) filed with any Foreign Regulatory Authority for

Regulatory Approval (including pricing and reimbursement approvals) required

prior to any commercial sale or use of a Licensed Product in any country or

jurisdiction in the Territory.

1.12 "FDA" shall mean the United States Food and Drug Administration and

any successor agency or authority thereto.

1.13 "FIELD" shall mean any human medical use.

1.14 "FIRST COMMERCIAL SALE" shall mean the date of the first commercial

sale (other than for purposes of obtaining Regulatory Approval) of a Licensed

Product by or on behalf of ABX or an Affiliate or Sublicensee of ABX.

1.15 "FOREIGN REGULATORY AUTHORITIES" shall mean any applicable

supranational, national, federal, state or local regulatory agency, department,

bureau or other governmental entity of any country or jurisdiction in the

Territory (other than the FDA in the United States), having responsibility in

such country or jurisdiction for any Regulatory Approvals of any kind in such

country or jurisdiction, and any successor agency or authority thereto.

1.16 "FULLY BURDENED MANUFACTURING COST" shall mean, with respect to any

Preclinical Materials or Clinical Materials produced by IMMUNOGEN for ABX under

this Agreement, the sum of the following components as determined by IMMUNOGEN

in accordance with generally accepted accounting principles in the United

States, consistently applied, and consistent with the application given to other

goods produced by IMMUNOGEN: (a) the costs of goods produced, including, without

limitation, direct labor, material and product testing costs of such Preclinical

Materials or Clinical Materials; (b) any Third Party royalty costs that are

actually paid by IMMUNOGEN and are based solely and directly on the manufacture

and sale to ABX of such Preclinical Materials or Clinical Materials; (c) all

overhead costs incurred by IMMUNOGEN directly and solely attributable to the

cost of goods under clause (a) above, including, without limitation, supervisory

services, occupancy costs, payroll, information

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

3

<PAGE> 34

systems, human relations, purchasing, accounts receivable or accounts payable

functions, and other general and administrative functions; and (d) any other

costs borne by IMMUNOGEN directly and solely for the transport, customs

clearance, duty and/or insurance for such Preclinical Materials or Clinical

Materials to ABX hereunder.

1.17 "GMPS" shall mean all good manufacturing practices under Title 21 of

the United States Code of Federal Regulations, as amended from time to time.

1.18 "IMMUNOGEN BACKGROUND TECHNOLOGY" shall mean all inventions,

discoveries, patent rights, trade secrets and know-how, including without

limitation, laboratory scientific information and procedural techniques,

Controlled by IMMUNOGEN during the term of the Option and License Agreement or

the Term of this Agreement that are necessary or useful for ABX to research,

develop, make, have made, use, have used, sell, offer for sale, have sold,

import or have imported Licensed Products (or any component thereof, including

any linker) for use in the Field; provided, however, that IMMUNOGEN Background

Technology shall expressly exclude any Target Specific Rights.

1.19 "IND" shall mean an investigational new drug application (as defined

in Title 21 of the United States Code of Federal Regulation, as amended from

time to time) filed or to be filed with the FDA with regard to any Licensed

Product.

1.20 "IND ACCEPTANCE" shall mean the expiration of thirty (30) days

following receipt by ABX of a notice from the FDA to ABX that the FDA has

received an IND for a Licensed Product filed by ABX for the purpose of obtaining

approval or authority to commence human clinical trials in the United States

with such Licensed Product; provided, however, that if the FDA puts a clinical

hold on the IND during such thirty (30) day period, the term "IND Acceptance"

shall mean that date during the term of this Agreement when ABX receives written

confirmation from the FDA that the clinical hold has been removed and that ABX

has the approval or authority to commence human clinical trials of such Licensed

Product under such IND in the United States. Notwithstanding anything set forth

herein, "IND Acceptance" shall not have occurred in any circumstances where ABX

withdraws any IND filed with the FDA for a Licensed Product at any time prior to

the commencement of human clinical trials with such Licensed Product in the

United States.

1.21 "INDEMNITEES" AND "INDEMNIFYING PARTY" shall have the meanings set

forth in Section 9.

1.22 "JPDC" shall have the meaning set forth in Section 3.4.1.

1.23 "LICENSED PATENT RIGHTS" shall mean all Patent Rights covering

IMMUNOGEN Background Technology. All Licensed Patent Rights as of the Effective

Date are listed on Schedule I attached hereto.

1.24 "LICENSED PRODUCT" shall mean any product containing any conjugate of

any ABX Antibody with any May Compound, and shall include, without limitation,

any formulation thereof (including, without limitation, any lyophilized, liquid,

sustained release or

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

4

<PAGE> 35

aerosolized formulation). "Licensed Product" shall also include any and all

Combination Products (if any).

1.25 "MAA" shall mean an application filed with the relevant Foreign

Regulatory Authorities in Europe seeking Regulatory Approval to market and sell

any Licensed Product in Europe or any country or territory therein for a

particular indication within the Field.

1.26 "MAY COMPOUND" shall mean any and all maytansinoid compounds

(including, without limitation, maytansine, ansamitocin P-3 and DM1), whether

produced by a botanical source, natural fermentation or chemical synthesis, and

shall include, without limitation, all variants, fragments or derivatives of any

of the foregoing, in each case owned or otherwise Controlled by IMMUNOGEN. May

Compounds shall include, without limitation, DM1.

1.27 "NDA" shall mean a new drug application (as defined in Title 21 of the

United States Code of Federal Regulations, as amended from time to time) filed

with the FDA seeking Regulatory Approval to market and sell any Licensed Product

in the United States for a particular indication within the Field.

1.28 "NET SALES" shall mean, as to each calendar quarter during the Term,

the gross invoiced sales prices charged for all Licensed Products sold by ABX,

its Affiliates or its Sublicensees to Third Parties throughout the Territory

during such calendar quarter, less the following amounts incurred or paid by ABX

or its Affiliates or Sublicensees during such calendar quarter with respect to

sales of Licensed Products regardless of the calendar quarter in which such

sales were made:

1.28.1 trade, cash and quantity discounts or rebates actually allowed

or taken, including discounts or rebates to governmental or managed care

organizations;

1.28.2 credits or allowances actually given or made for rejection of

or return of, and for uncollectible amounts on, previously sold Licensed

Products or for retroactive price reductions (including Medicare and similar

types of rebates);

1.28.3 any charges for insurance, freight, and other transportation

costs directly related to the delivery of Licensed Product to the extent

included in the gross invoiced sales price;

1.28.4 any tax, tariff, duty or governmental charge levied on the

sales, transfer, transportation or delivery of a Licensed Product (including any

tax such as a value added or similar tax or government charge) borne by the

seller thereof, other than franchise or income tax of any kind whatsoever; and

1.28.5 any import or export duties or their equivalent borne by the

seller. "Net Sales" shall not include sales or transfers between ABX and its

Affiliates or Sublicensees, unless the Licensed Product is consumed by the

Affiliate or Sublicensee.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

5

<PAGE> 36

1.29 "OPTION" shall have the meaning set forth in the Option and License

Agreement.

1.30 "OPTION AND LICENSE AGREEMENT" shall mean that certain Option and

License Agreement dated as of September 5, 2000, by and between IMMUNOGEN and

ABX.

1.31 "PATENT RIGHTS" shall mean the rights and interests in and to any and

all issued patents and pending patent applications (including inventor's

certificates and utility models) in any country or jurisdiction in the

Territory, including any and all provisionals, non-provisionals, substitutions,

continuations, continuations-in-part, divisionals and other continuing

applications, supplementary protection certificates, renewals, all letters

patent on any of the foregoing, and any and all reissues, reexaminations,

extensions, confirmations, registrations and patents of addition on any of the

foregoing.

1.32 "PHASE II CLINICAL STUDY" shall mean, as to a particular Licensed

Product for a particular indication, a controlled and lawful study in humans of

the safety, dose ranging and efficacy of such Licensed Product for such

indication, which is prospectively designed to generate sufficient data (if

successful) to commence a Phase III Clinical Trial of such Licensed Product for

such indication.

1.33 "PHASE III CLINICAL TRIAL" shall mean, as to a particular Licensed

Product for a particular indication, a controlled and lawful study in humans of

the safety and efficacy of such Licensed Product for such indication, which is

prospectively designed to demonstrate statistically whether such Licensed

Product is safe and effective for use in such indication in a manner sufficient

to file a BLA or NDA to obtain Regulatory Approval to market and sell that

Licensed Product in the United States for the indication under investigation in

such study.

1.34 "PRECLINICAL MATERIALS" shall mean (a) supplies of ansamitocin P-3,

DM1 and/or any other May Compound as manufactured in accordance with all

applicable legal requirements and all applicable Specifications for such May

Compound for use in preclinical testing, and (b) supplies of any Licensed

Product as manufactured in accordance with all applicable legal requirements and

all applicable Specifications for such Licensed Product for use in preclinical

testing of any Licensed Product.

1.35 "REGULATORY APPROVAL" shall mean any and all approvals (including

pricing and reimbursement approvals), product and establishment licenses,

registrations or authorizations of any kind of the FDA or its foreign equivalent

necessary for the development, pre-clinical and/or human clinical testing,

manufacture, quality testing, supply, use, storage, importation, export,

transport, marketing and sale of a Licensed Product (or any component thereof)

for use in the Field in any country or other jurisdiction in the Territory.

1.36 "SPECIFICATIONS" shall mean any specifications specified by ABX and

reasonably acceptable to IMMUNOGEN relating to the manufacturing and supply of

any May Compound and/or Licensed Product hereunder.

1.37 "SUBLICENSEE" shall have the meaning set forth in Section 2.1.1(b).

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

6

<PAGE> 37

1.38 "TARGET" shall mean _________________________.

1.39 "TARGET SPECIFIC RIGHTS" shall mean all inventions, discoveries,

patent rights, trade secrets and know-how, including without limitation,

laboratory scientific information and procedural techniques, Controlled by

IMMUNOGEN during the term of the Option and License Agreement or the Term of

this Agreement constituting (a) the composition of matter or use of the Target,

(b) the composition of matter or use of an antibody binding to the Target, or

(c) the composition of matter or use of a conjugate of an antibody binding to

the Target with a May Compound.

1.40 "TECHNOLOGY" shall mean and include any and all unpatented proprietary

ideas, inventions, discoveries, Confidential Information, materials, data,

results, formulae, designs, specifications, methods, processes, formulations,

techniques, ideas, know-how, technical information (including, without

limitation, structural and functional information), process information,

pre-clinical information, clinical information, and any and all proprietary

biological, chemical, pharmacological, toxicological, pre-clinical, clinical,

assay, control and manufacturing data and materials.

1.41 "TERM" shall mean the period commencing on the Effective Date and

continuing until the expiration or termination of this Agreement in accordance

with the terms hereof (including Section 7).

1.42 "TERRITORY" shall mean all countries and jurisdictions of the world.

1.43 "THIRD PARTY" shall mean any person or entity other than ABX,

IMMUNOGEN and their respective Affiliates.

1.44 "THIRD PARTY PAYMENTS" shall have the meaning set forth in Section

4.3.2.

1.45 "VALID CLAIM" shall mean a claim in an issued, unexpired patent within

the Licensed Patent Rights that (i) has not been finally cancelled, withdrawn,

abandoned or rejected by any administrative agency or other body of competent

jurisdiction, and (ii) has not been revoked, held invalid, or declared

unpatentable or unenforceable in a decision of a court or other body of

competent jurisdiction that is unappealable or unappealed within the time

allowed for appeal, and (iii) has not been rendered unenforceable through

disclaimer or otherwise, and (iv) is not lost through an interference

proceeding.

2. GRANT OF RIGHTS

2.1 LICENSE GRANT.

2.1.1 LICENSE TO ABX.

(a) IMMUNOGEN hereby grants to ABX an exclusive (even

as to IMMUNOGEN) license within the Territory, including the right to grant

sublicenses as described in Section 2.2 below, under the Licensed Patent Rights

and IMMUNOGEN

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

7

<PAGE> 38

Background Technology to research, develop, make, have made, use, have used,

sell, offer for sale, have sold, import and have imported Licensed Products, for

any and all uses within the Field, subject to the other terms and conditions of

this Agreement. Promptly, but not less than quarterly, IMMUNOGEN shall deliver

to ABX all IMMUNOGEN Background Technology not previously delivered to ABX.

(b) ABX shall have the right freely to grant

sublicenses to all or any portion of its rights under the license granted

pursuant to Section 2.1.1 hereof to any Affiliate or Third Party (in any case, a

"Sublicensee"); provided, however, that ABX shall remain obligated for payment

of royalty and milestone obligations as set forth in Section 4.

(c) [_____________________________] or [_______] to

[________________], or otherwise [______________________] concerning, a

[_____________ __________] to the [__________].

2.1.2 LICENSE TO IMMUNOGEN.

(a) To the extent legally possible, [______] hereby

[_________ __________] a [____________________________________________________

_______________________], if any, in any [_____________________________________]

to the [_____________________] to or [____________] of the [____________] that

are [______ ________________] of this Agreement, [__________] to the

[__________] to [______________ ______________________] and [____________] to

[__________________________________ __________] to [________] and/or

[_________________] and/or [__________(____________] to a [________________] or

a [____________], each as defined in the Option and License Agreement).

(b) Such [______] to [_________] includes the

[__________ ________] to [___________] from [_____________________________

_____________________________] to the [________] they [_____________] or

[___________] of the [____________ _____] to [______________] with the

[_________] to [_______________] hereunder, and [_____________________________]

to [________________________]. Notwithstanding the foregoing, the

[______________________________] pursuant to this Section 2.1.2 [_________

_________________] of [__________] to [__________________] (as defined in the

Option and License Agreement).

2.2 IMMUNOGEN RETAINED RIGHTS; ABX TECHNOLOGY OR PATENT RIGHTS.

2.2.1 RETAINED RIGHTS. Subject to the other terms of this

Agreement and the Option and License Agreement, IMMUNOGEN retains the right to

use the IMMUNOGEN Background Technology and practice the Licensed Patent Rights

(i) to perform its work under Sections 3.3, 3.4, 3.5 and 3.6 hereof relating to

the JPDC and to manufacture and supply of Preclinical Materials and Clinical

Materials for ABX (and its Sublicensees), and (ii) to research, develop, make,

have made, use, have used, sell, offer for sale, have sold, import and have

imported any product that is not a Licensed Product.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

8

<PAGE> 39

2.2.2 NO RIGHTS TO ABX TECHNOLOGY OR PATENT RIGHTS. Except

as otherwise expressly set forth in Section 2.1.2, nothing in this Agreement

shall be construed as a grant to IMMUNOGEN of any license or other rights with

respect to any Technology (including, without limitation, any Confidential

Information) or Patent Rights owned or Controlled (in whole or in part) by ABX.

2.3 IN LICENSES. IMMUNOGEN represents and warrants to ABX that it

has provided ABX true and correct copies of all agreements pursuant to which

Licensed Patent Rights or IMMUNOGEN Background Technology, existing as of the

Effective Date, is licensed to or otherwise acquired by IMMUNOGEN from a Third

Party. IMMUNOGEN promptly shall provide ABX with true and correct copies of all

agreements pursuant to which Licensed Patent Rights or IMMUNOGEN Background

Technology, licensed or acquired after the Effective Date, is licensed to or

otherwise acquired by IMMUNOGEN from a Third Party; provided, however, that

IMMUNOGEN shall have the right to redact confidential financial information and

any provisions that shall not bind ABX. To the extent the Licensed Patent Rights

or IMMUNOGEN Background Technology are licensed to or acquired by IMMUNOGEN from

a Third Party and are reasonably necessary to permit ABX to exercise its rights

granted hereunder, IMMUNOGEN shall use reasonable commercial efforts to maintain

in full force and effect such license. In the event of the termination of any

such license with a Third Party, IMMUNOGEN shall cause such Third Party to grant

a direct license to ABX to the extent necessary to permit ABX to exercise its

rights granted hereunder, and all sums owing by ABX to such Third Party shall be

fully deducted from any amounts owing to IMMUNOGEN hereunder.

3. DEVELOPMENT AND COMMERCIALIZATION OF LICENSED PRODUCTS.

3.1 DEVELOPMENT AND COMMERCIALIZATION.

3.1.1 RESPONSIBILITY. On and after the Effective Date, ABX shall have

full control and authority over all Development and commercialization of

Licensed Products in the Field in the Territory, including, without limitation,

(i) all pre-clinical Development activities (including any pharmaceutical

development work on formulations or process development relating to any Licensed

Product), (ii) all activities related to human clinical trials (including any

phase I studies, any Phase II Clinical Studies or any Phase III Clinical

Trials), (iii) all activities relating to manufacture and supply of all ABX

Antibodies, all May Compounds (including ansamitocin P-3 and DM1) and all

Licensed Products, solely to the extent such activities relate to the

Development and commercialization of Licensed Products (including all required

process development and scale up work with respect thereto), (iv) all marketing,

promotion, sales, distribution, import and export activities relating to any

Licensed Product (including any post-marketing trials or databases and

post-marketing safety surveillance), and (v) all activities relating to any

regulatory filings, registrations, applications and Regulatory Approvals

relating to any of the foregoing (including any INDs or foreign equivalents, any

manufacturing facility validation and/or licensure, any Drug Approval

Applications and any other Regulatory Approvals). Except as described in the

next sentence, ABX shall own all data, results and all other information arising

from any such activities under this Agreement, including, without limitation,

all regulatory filings, registrations, applications and Regulatory Approvals

relating to

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

9

<PAGE> 40

Licensed Products (including any INDs or foreign equivalents, any Drug Approval

Applications and any other Regulatory Approvals), and all of the foregoing

information, documentation and materials shall be considered Confidential

Information and Technology solely owned by ABX. IMMUNOGEN shall own all data,

results and all other information arising from IMMUNOGEN's activities directly

regarding the manufacture and supply of May Compounds to ABX (other than

activities undertaken at the request of ABX), and all of the foregoing

information, documentation and materials shall be considered Confidential

Information and Technology solely owned by IMMUNOGEN. All activities relating to

Development and commercialization by or on behalf of ABX under this Agreement

shall be undertaken at ABX's sole cost and expense, except as otherwise

expressly provided in this Agreement.

3.1.2 DILIGENCE. ABX will exercise its commercially reasonable efforts

and diligence in Developing and commercializing Licensed Products in accordance

with its business, legal, medical and scientific judgment, and in undertaking

investigations and actions required to obtain appropriate Regulatory Approvals

necessary to market Licensed Products in the Field in the Territory, such

reasonable efforts and diligence to be in accordance with the efforts and

resources ABX would use for a compound owned by it or to which it has rights,

which is of similar market potential at a similar stage in development as the

applicable Licensed Product, taking into account the competitiveness of the

marketplace, the proprietary position of the Licensed Product, the relative

potential safety and efficacy of the Licensed Product, the regulatory

requirements involved in its Development, commercialization and Regulatory

Approval, the cost of goods and availability of capacity to manufacture and

supply the Licensed Product at commercial scale, the profitability of the

applicable Licensed Product, and other relevant factors including, without

limitation, technical, legal, scientific or medical factors. In the event that

[_______________] its [___________] to [___________________________], then on a

Licensed Product-by-Licensed Product basis as to the Licensed Product [_________

___________________________________________________________________________,

___________________________] shall be, in its [___________], (i) to

[__________________ _________________] of this Agreement [____________________

___________] (including the [________] and [______] therein) or (ii) to

[_______________________________] of this Agreement from [____________________

________], in either case [____] as [__________] apply to [_____________], which

[_________] or [__________], as the case may be, shall [_______________________

___________________________________________] provided that [___ ________]

remains [___________________________].

3.2 UPDATES AND REPORTS; EXCHANGES OF ADVERSE EVENT INFORMATION.

3.2.1 UPDATES AND REPORTS. ABX (or its Sublicensee) shall provide

IMMUNOGEN with brief written reports no less frequently than on [___________] of

the [________________ (______________] with the [____________] of the

[____________]) summarizing ABX's material efforts to Develop and commercialize

all Licensed Products hereunder, identify the Drug Approval Applications with

respect to any Licensed Product that ABX and its Sublicensees have filed, sought

or obtained in the prior [______________] period, and any they reasonably expect

to make, seek or attempt to obtain in the following [__________ ____] period. In

addition, ABX (or its Sublicensee) shall provide IMMUNOGEN with prompt written

notice of the occurrence of any event giving rise to an obligation to make a

milestone

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

10

<PAGE> 41

payment to IMMUNOGEN under Section 4.2, and shall provide IMMUNOGEN with prompt

written notice of the occurrence of the First Commercial Sale of any particular

Licensed Product.

3.2.2 ADVERSE EVENTS. In addition to such reports, ABX agrees to

provide IMMUNOGEN with Adverse Event information relating to Licensed Products

(but not relating to any other products of ABX) as compiled by ABX in the normal

course of business in connection with the Development, commercialization or sale

of any Licensed Product, within time frames consistent with IMMUNOGEN's

reporting obligations under applicable laws and regulations. IMMUNOGEN agrees to

provide ABX with Adverse Event information relating to any product containing

any May Compound (but not any other products of IMMUNOGEN or such Third Party)

that is compiled by IMMUNOGEN or any Third Party in the normal course of

business in connection with the development, commercialization or sale of any

such product, within time frames consistent with ABX's reporting obligations

under applicable laws and regulations.

3.2.3 CONFIDENTIAL INFORMATION. All reports, updates, Adverse Event

and other information provided by one Party to the other Party under this

Agreement (including under this Section 3), shall be considered Confidential

Information of the disclosing Party, subject to the terms of Section 5.

3.3 TECHNICAL ASSISTANCE BY IMMUNOGEN. In connection with the exclusive

grant of rights to ABX under Section 2.1 above, and subject to the other terms

of this Agreement, IMMUNOGEN shall provide ABX such information and materials

comprising the IMMUNOGEN Background Technology and/or Licensed Patent Rights as

ABX may reasonably request. Without limiting the generality of the foregoing,

IMMUNOGEN shall provide all of such technical assistance within IMMUNOGEN's area

of expertise concerning the Development and commercialization of Licensed

Products as may be reasonably requested by ABX from time to time during the

Term, provided that such technical assistance and expertise is within the scope

of the IMMUNOGEN Background Technology and/or Licensed Patent Rights covered

under this Agreement. Such technical assistance and expertise shall include, but

not be limited to, visits by IMMUNOGEN personnel to ABX and visits by ABX

personnel to IMMUNOGEN, at ABX's expense, at such times and for such periods of

time as may be reasonably acceptable to the Parties. Additionally, at the

reasonable request of ABX, IMMUNOGEN shall transfer all applicable IMMUNOGEN

Background Technology, and provide such technical assistance, to such Third

Party collaborator, sublicensee or contract manufacturer as ABX designates.

3.4 JOINT PROCESS DEVELOPMENT COMMITTEE.

3.4.1 MANDATE AND ESTABLISHMENT OF COMMITTEE. The Joint Process

Development Committee ("JPDC") formed pursuant to the Option and License

Agreement, shall serve as a forum for coordination and communication between the

Parties with respect to Development (to the extent ABX requests the assistance

or services of IMMUNOGEN) of manufacturing processes applicable to any May

Compound or Licensed Product covered by this Agreement (including, without

limitation, all process science and process development work, formulation work,

and quality control/assurance work hereunder), to assist ABX in its exercise of

its rights to make or have made Licensed Products under this Agreement. The

input of the

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

11

<PAGE> 42

IMMUNOGEN representatives on the JPDC shall be reasonably considered by the

JPDC; provided, however, that, all decisions of the JPDC shall be subject to the

final approval of ABX.

3.4.2 CHAIR OF COMMITTEE; MEETINGS. The chair of the JPDC shall be one

of the ABX representatives on the JPDC, as designated by ABX. All decisions of

the JPDC shall be subject to the approval of ABX. The JPDC shall meet on a

semi-annual basis or other schedule agreed upon by the Parties, unless at least

thirty (30) days in advance of any meeting there is a determination by the Chair

of the JPDC that no new business or other activity has transpired since the

previous meeting, and that there is no need for a meeting. In such instance, the

next JPDC meeting shall also be scheduled as agreed upon by the Parties. The

location of such meetings shall alternate between IMMUNOGEN's offices in the

Cambridge, Massachusetts metropolitan area and ABX's offices in the Fremont,

California metropolitan area unless otherwise agreed upon between the Parties.

As agreed upon by the Parties, JPDC meetings may be face-to-face meetings or may

be conducted through teleconferences and/or videoconferences. In addition to its

JPDC representatives, each Party shall be entitled to have such additional

number (as the Parties mutually agree) of other employees attend such meetings

to present and participate, though not in a decision-making capacity. Each Party

shall bear all costs and expenses, including travel and lodging expense, that

may be incurred by its JPDC representatives or other of its attendees at JPDC

meetings. Minutes of each JPDC meeting will be transcribed and issued to the

members of the JPDC by the Chair within thirty (30) days after each meeting and

shall be reviewed and modified as mutually required to obtain approval promptly

thereafter.

3.5 SUPPLY OF PRECLINICAL MATERIALS. In the event that, during the Term of

this Agreement, ABX desires IMMUNOGEN to supply ABX with quantities of

Preclinical Materials in order to conduct all pre-clinical Development

activities relating to Licensed Products, ABX shall provide IMMUNOGEN with

written notice of same and the Parties shall negotiate in good faith and execute

a supply agreement providing for such supply. IMMUNOGEN shall deliver all

ordered amounts in accordance with advance ordering timeframes and delivery

timeframes to be agreed upon by the Parties through such mutually acceptable

written supply agreement for such purpose. In connection with any ordering of

Preclinical Materials by ABX, IMMUNOGEN shall provide ABX promptly with

IMMUNOGEN's good faith estimate of the Fully Burdened Manufacturing Cost for

manufacture and supply of such Preclinical Materials. IMMUNOGEN's price to

supply Preclinical Materials to ABX shall equal [_____] of IMMUNOGEN's Fully

Burdened Manufacturing Cost for such Preclinical Materials as approved by ABX.

Nothing herein shall preclude ABX from making its own arrangements for

manufacture and supply of Preclinical Materials on its own or with Third

Parties. ABX hereby agrees that (a) it shall not use the Preclinical Materials

in any human subject, and (b) it shall use the Preclinical Materials in

compliance with all applicable federal, state and local laws and regulations.

3.6 SUPPLY OF CLINICAL MATERIALS. In the event that, during the Term of

this Agreement, IMMUNOGEN desires to supply ABX with quantities of Clinical

Materials in order to conduct all human clinical trials of Licensed Products

through the conclusion of Phase II Clinical Studies, ABX shall provide IMMUNOGEN

with written notice of same and the Parties shall negotiate in good faith and

execute a supply agreement providing for such supply. IMMUNOGEN shall deliver

all ordered amounts in accordance with forecasting parameters,

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

12

<PAGE> 43

advance ordering timeframes and delivery timeframes to be agreed upon by the

Parties such mutually acceptable written supply agreement for such purpose. In

connection with any ordering of Clinical Materials by ABX, IMMUNOGEN shall

provide ABX promptly with IMMUNOGEN's good faith estimate of the Fully Burdened

Manufacturing Cost for manufacture and supply of such Clinical Materials.

IMMUNOGEN's price to supply Clinical Materials to ABX shall equal [_______] of

IMMUNOGEN's Fully Burdened Manufacturing Cost for such Clinical Materials as

approved by ABX. Nothing herein shall preclude ABX from making its own

arrangements for manufacture and supply of Clinical Materials on its own or with

Third Parties. ABX hereby agrees that it shall use the Clinical Materials in

compliance with all applicable federal, state and local laws. IMMUNOGEN shall

provide ABX with all information, filings and assistance regarding manufacturing

as reasonably requested by ABX in connection with applications for Regulatory

Approvals.

4. PAYMENTS AND ROYALTIES

4.1 LICENSE FEE. Within thirty (30) days after the Effective Date, ABX

shall pay to IMMUNOGEN the nonrefundable, noncreditable license fee of [________

___________].

4.2 MILESTONE PAYMENTS FOR LICENSED PRODUCTS.

4.2.1 MILESTONES. ABX will make the following nonrefundable,

noncreditable payments to IMMUNOGEN within thirty (30) days after the first

achievement of each of the milestones set forth below:

MILESTONE MILESTONE PAYMENT

--------- -----------------

(a) [__________________________] [________________]

(b) [__________________________] [________________]

(c) [__________________________] [________________]

(d) [__________________________] [________________]

(e) [__________________________] [________________]

(f) [__________________________] [________________]

(g) [__________________________] [________________]

4.2.2 If the milestone described in [__________], is [___________

__________] of the milestone described in [________________], then [__________

_______] to IMMUNOGEN hereunder of the milestone payment described in

[_______________], [_______ ____________________________________________] of the

milestone payment described in [_________________].

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

13

<PAGE> 44

4.2.3 It is hereby acknowledged and agreed that any milestone payment

shall be made only once, with respect to the first achievement of the relevant

milestone for the first Licensed Product, regardless of how many times such

milestones are achieved by Licensed Products and regardless of how many times a

particular Licensed Product achieves such milestones. ABX shall notify IMMUNOGEN

of the achievement of milestones hereunder as provided in Section 3.2.1 above.

4.3 PAYMENT OF ROYALTIES; ROYALTY RATES; ACCOUNTING FOR ROYALTIES AND

RECORDS.

4.3.1 ROYALTY PAYMENTS.

(a) In consideration of the grant of the license by IMMUNOGEN

hereunder, and subject to the other terms of this Agreement (including the

remainder of this Section 4), commencing on the first date of First Commercial

Sale of each Licensed Product in such country or jurisdiction in the Territory,

ABX shall pay to IMMUNOGEN the following royalties based on total Net Sales of

each Licensed Product sold by ABX and/or its Affiliates, on an incremental basis

in each calendar year during the Term, at the following rates:

For Net Sales of Licensed Product Royalty Rate

in any Calendar Year During the Term: (% of Net Sales)

------------------------------------ ----------------

[__________________________________________________________]

[__________________________________________________________]

(b) In consideration of the grant of the license by IMMUNOGEN

hereunder, and subject to the other terms of this Agreement (including the

remainder of this Section 4), commencing on the first date of First Commercial

Sale of each Licensed Product in such country or jurisdiction in the Territory,

ABX shall pay to IMMUNOGEN the following royalties based on total Net Sales of

each Licensed Product sold by each Sublicensee, on an incremental basis in each

calendar year during the Term, at a rate equal to [____________________________

_________________________________________________] in consideration for the

grant of the sublicense under the Licensed Patents and IMMUNOGEN Background

Technology; provided, however, that the royalty rate under this Section 4.3.1(b)

for any royalty period shall not be (i) less than [__________________________

______________________________] or (ii) more than [___________________________]

4.3.2 [______________________]. Notwithstanding anything set forth in

Section 4.3.1 above, [___________] set forth therein shall apply, [___________

__________________________________________], to [__________] of [_____________

_________________________] or [______________________] would, [_______________

___________________ _____________________________________________________]

(excluding any [_________ _________________________________________________]).

Subject to the other terms of this

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

14

<PAGE> 45

Agreement, [_______________________________________________________] where and

as of when [______________] under Section 4.3.1 [___________________] this

Section 4.3.2, [_____________________________] a [___________________________

_______] set forth in Section 4.3.1 for [______________] of [_______________].

4.3.3 [____________]. In the event that in any royalty period,

[_____], in order to [_______________________________________] of this

Agreement, [____ _______], is [_____________________________________] to

[____________ ("_________________]") (a) to [____________] to

[__________________] in the [__________] the [_________________] of a

[__________________________________________________________________] and/or (b)

to [_____________] to [_____________________________] to the [__________________

__] to [_____________________] to [________], in the [_______________] the

[_______________] to [____________________] to [______________________] as part

of a [________________________________] (as [_________], to the [______________

_______________], by [___________________ _______]), then [_________] the [____]

to [_______________________________________________________________________] for

[___________________] by [_______________________] of [______________].

Notwithstanding the foregoing, such [____________________________________] for

[_____________] in [__________________] to [________________________] of

[____________________] in [_______________].

4.3.4 [__________________]. In determining [_______] of any

[_________________] under this Agreement, [________] shall first [_______] in

accordance with the definition of "Net Sales" above, then [________] by

[___________] of the [________________________] in the [________________],

[__________________________________________________________________] of the

[______________________________________] of the [______________]. The

[_______________] of the [_________________] shall be for a [_______] to that

[_____________________________________] and [___________________________.] When

[___________________] is [___________] for the [___________________] shall

[___________] a [________________________] for the [______________________] the

[_____________________________________] as are then [___________] to all

[_______________________________________] and having an [__________________];

provided, however, that if [______________________________________________], the

Parties shall [__________ _____________] to [__________________________] and a

[______________________________________________].

4.4 ONE ROYALTY. Only one royalty, calculated at the highest applicable

royalty rate under this Section 4, shall be payable to IMMUNOGEN hereunder for

each sale of a Licensed Product.

4.5 ROYALTY TERM. ABX shall pay royalties with respect to each Licensed

Product on a country-by-country and Licensed Product-by-Licensed Product basis

until [ ______ __] (a) the [_______________________] of [_______________] of

[__________] that [_______

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

15

<PAGE> 46

________________] or (b) [________________________] of the [___________________

_____] of [_________________________]. Following such royalty term, ABX shall

have a fully paid-up, irrevocable, freely transferable and sublicensable license

in such country under the relevant Licensed Patent Rights and IMMUNOGEN

Background Technology, to research, develop, make, have made, use, have used,

sell, offer for sale, have sold, import and have imported Licensed Products for

any and all uses within the Field in such country.

4.6 PAYMENT TERMS.

4.6.1 PAYMENT OF MILESTONES; PAYMENT OF ROYALTIES; ROYALTY REPORTS.

ABX shall make any milestone payments owed to IMMUNOGEN hereunder in United

States Dollars, using the wire transfer provisions of this Section 4.6. ABX

shall make any royalty payments owed to IMMUNOGEN in United States Dollars,

[______________________ ______] the [_______________________] for which

[________________] (as provided in the next sentence), using the wire transfer

provisions of this Section 4.6. For purposes of determining when a sale of any

Licensed Product occurs under this Agreement, royalties shall accrue on the date

of the invoice to the purchaser of the Licensed Product. Each royalty payment

[_________________________________________________] in which [_____________

______________] in the [_________________________________], specifying: the

[_______] (if available) and [_____] in [_________________]; the [_____________]

under this Agreement; the[__________________________________], including an

[________________ ______________] in the [__________________]; the [__________

_______] to [_______] from [__________________] to [_______________] under this

Section 4.6; and the [_____________ _________________].

4.6.2 FOREIGN CURRENCY EXCHANGE. All royalties shall be payable in

full in the United States in United States Dollars, regardless of the countries

in which sales are made. For the purpose of computing Net Sales for Licensed

Products sold in any currency other than United States Dollars, the quarterly

royalty payment will be calculated as follows:

(A/B) x C = United States Dollars royalty payment on foreign current

sales, where

A = foreign "Net Sales" (as defined above) per quarter;

B = foreign exchange conversion rate, expressed in local currency per

United States Dollar (using as the applicable foreign exchange rate

the rate published in the western edition of THE WALL STREET JOURNAL,

under the heading "Money Rates," or any other mutually agreed upon

source, for the last business day of the calendar quarter); and

C = the royalty rate applicable to such Net Sales under this

Agreement.

4.6.3 TAX WITHHOLDING; RESTRICTIONS ON PAYMENT. All payments hereunder

shall be made free and clear of any taxes, duties, levies, fees or charges,

except for withholding taxes (to the extent applicable). ABX shall make any

applicable withholding payments due on behalf of IMMUNOGEN and shall promptly

provide IMMUNOGEN with such written documentation of any such payment as

available to ABX relating to an application by IMMUNOGEN for a foreign tax

credit for such payment with the United States Internal Revenue Service. If by

law, regulations or fiscal policy of a particular country in the Territory,

remittance of royalties in United States Dollars is restricted or forbidden,

written notice thereof shall

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

16

<PAGE> 47

promptly be given to IMMUNOGEN, and payment of the royalty shall be made by the

deposit thereof in local currency to the credit of IMMUNOGEN in a recognized

banking institution reasonably designated by IMMUNOGEN by written notice to ABX.

When in any country in the Territory the law or regulations prohibit both the

transmittal and the deposit of royalties on sales in such country, royalty

payments shall be suspended for as long as such prohibition is in effect and as

soon as such prohibition ceases to be in effect, all royalties that ABX would

have been under an obligation to transmit or deposit but for the prohibition

shall forthwith be deposited or transmitted, to the extent allowable.

4.6.4 WIRE TRANSFERS. All payments hereunder shall be made to

IMMUNOGEN by bank wire transfer in immediately available funds to the account

designated by IMMUNOGEN by written notice to ABX from time to time.

4.7 RECORDS RETENTION; REVIEW.

4.7.1 ROYALTIES. Commencing as of the date of First Commercial Sale of

the first Licensed Product, ABX and its Sublicensees shall keep for at least

[_________] from the end of the calendar year to which they pertain complete and

accurate records of sales by ABX or its Sublicensees, as the case may be, of

each Licensed Product, in sufficient detail to allow the accuracy of the

royalties to be confirmed.

4.7.2 FULLY BURDENED MANUFACTURING COSTS. Commencing as of the

Effective Date, IMMUNOGEN shall keep for at least [________] following the end

of the calendar year to which they pertain complete and accurate records of all

of IMMUNOGEN's Fully Burdened Manufacturing Costs for Preclinical Materials and

Clinical Materials supplied to ABX (or its Sublicensee) hereunder, in sufficient

detail to allow the accuracy of the Fully Burdened Manufacturing Costs to be

confirmed.

4.7.3 REVIEW. Subject to the other terms of this Section 4.7.3, at the

request of either Party, upon at least thirty (30) days' prior written notice

from the requesting Party, and at the expense of the requesting Party (except as

otherwise provided herein), the other Party shall permit an independent

certified public accountant of nationally recognized standing reasonably

selected by the requesting Party and reasonably acceptable to the other Party to

inspect (during regular business hours) the relevant records required to be

maintained by the other Party under this Section 4.7. At IMMUNOGEN's request

(which shall not be made more frequently than once per year during the Term),

the accountant shall be entitled to review the then-preceding [_______] of ABX's

records under this Section 4.7 for purposes of verifying ABX's royalty

calculations. At ABX's request (which shall not be made more frequently than

once per year during the Term), the accountant shall be entitled to review the

then-preceding [_________] of IMMUNOGEN's records under this Section 4.7 for

purposes of verifying IMMUNOGEN's Fully Burdened Manufacturing Cost

calculations. In every case the accountant must have previously entered into a

confidentiality agreement with both Parties substantially similar to the

provisions of Section 5 and limiting the disclosure and use of such information

by such accountant to authorized representatives of the Parties and the purposes

germane to this Section 4.7. Such accountant shall report to the Parties only

whether or not such calculations are correct and the amount of any discrepancy.

No other information shall be shared. Results of any

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

17

<PAGE> 48

such review shall be binding on both Parties absent manifest error. Each Party

agrees to treat the results of any such accountant's review of the other Party's

records under this Section 4.7 as Confidential Information of the other Party

subject to the terms of Section 5. If any review reveals a deficiency in the

calculation of royalties resulting from any underpayment by ABX, ABX shall

promptly pay IMMUNOGEN the amount remaining to be paid, and if such underpayment

is by [______________] or more, ABX shall pay the reasonable out-of-pocket costs

and expenses of the review. If any review reveals a deficiency in the

calculation of Fully Burdened Manufacturing Costs resulting from any overpayment

by ABX, IMMUNOGEN shall promptly refund ABX the amount of any such overpayment,

and if such overpayment is by [___ ___________] or more, IMMUNOGEN shall pay the

reasonable out-of-pocket costs and expenses of the review.

5. TREATMENT OF CONFIDENTIAL INFORMATION

5.1 CONFIDENTIAL INFORMATION. During the Term of this Agreement, each Party

may disclose to the other Party confidential information, including but not

limited to IMMUNOGEN Background Technology, Research Inventions, Research Data

and Research Materials. Such information of the disclosing Party hereunder, if

so identified in writing by the disclosing Party to the receiving Party either

pursuant to this Section 5.1 or otherwise upon disclosure to the receiving

Party, shall be "Confidential Information" of the disclosing Party. During the

Term of this Agreement and during the term of any License Agreement, and for a

period of five (5) years thereafter, except as expressly permitted hereunder,

the receiving Party shall keep confidential all such Confidential Information of

the other Party and will not disclose such Confidential Information of the other

Party to Third Parties by publication or otherwise. Each Party further agrees

not to use Confidential Information of the other Party for any purpose other

than conducting research hereunder or exercising any rights granted to it or

reserved by it hereunder. Upon any termination or expiration of this Agreement,

upon request, a Party shall return to a requesting Party all copies of any of

such requesting Party's Confidential Information which is not the subject of a

License Agreement or the grant of a license hereunder, provided that it may

retain one copy for its legal files. Notwithstanding the foregoing, it is

understood and agreed that the receiving Party's obligations of confidentiality

and nonuse herein shall not apply to any information which:

(a) is, at the time of disclosure by the disclosing Party

hereunder, or thereafter becomes, a part of the public domain or publicly known

or available through no fault or negligence of the receiving Party or any of its

Affiliates; or

(b) was otherwise in the receiving Party's lawful possession

prior to disclosure by the disclosing Party, other than under an obligation of

confidentiality; or

(c) was independently discovered or developed by the

receiving Party or any of its Affiliates, without use of the other Party's

Confidential Information, as can be demonstrated by competent proof; or

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

18

<PAGE> 49

(d) is lawfully disclosed to the receiving Party or any of

its Affiliates on a non-confidential basis by a third party who is not in

violation of an obligation of confidentiality to the disclosing Party relative

to such information.

Each Party may disclose information to the extent such disclosure is

reasonably necessary in (i) filing and prosecuting patent applications and

maintaining patents, or (ii) filing, prosecuting or defending litigation or

(iii) complying with applicable laws, regulations or court orders; provided,

however, that if a Party is required to make any such disclosure of the other

Party's Confidential Information or the terms of this Agreement, it will give

reasonable advance notice to the other Party of such disclosure requirement and

will use reasonable efforts to assist such other Party in efforts to secure

confidential treatment of such information required to be disclosed.

5.2 PUBLICITY. A Party may not use the name of the other Party in any

publicity or advertising and, except as provided in Section 5.1, may not issue a

press release or otherwise publicize or disclose any information related to the

other Party's activities under this Agreement or the terms or conditions hereof,

without the prior written consent of the other Party. Prior to execution of this

Agreement, the parties have agreed upon the substance of information that can be

used to describe the terms and conditions of this Agreement, and each party may

disclose such information, as modified by mutual written agreement the parties,

without the consent of the other party. Once any written statement is approved

for disclosure by both Parties, either Party may make subsequent public

disclosures of the contents of such statement without the further approval of

the other Party. Nothing in the foregoing, however, shall prohibit a Party from

making such disclosures to the extent deemed necessary under applicable federal

or state securities laws or any rule or regulation of any nationally recognized

securities exchange; PROVIDED, HOWEVER, that such party shall provide written

notice thereof to the other party, consult with the other party with respect to

such disclosure and provide the other party sufficient opportunity to comment on

or object to any such disclosure or to request confidential treatment thereof.

6. PROVISIONS CONCERNING THE FILING, PROSECUTION AND

MAINTENANCE OF PATENT RIGHTS

6.1 PATENT FILING, PROSECUTION AND MAINTENANCE. Subject to the other terms

of this Section 6.1, IMMUNOGEN shall have the right to prepare, file, prosecute,

obtain and maintain, at its sole cost and expense, all Licensed Patent Rights.

Any such preparation, filing, prosecution and maintenance shall be conducted

with commercially reasonable diligence by IMMUNOGEN, using patent counsel

selected by IMMUNOGEN and reasonably acceptable to ABX. IMMUNOGEN (i) will

provide ABX with a copy of any proposed patent application within Licensed

Patent Rights for review and comment reasonably in advance of filing (which

shall under no circumstances be in excess of thirty (30) days), and (ii) will

keep ABX reasonably informed of the status of such filing, prosecution and

maintenance, including, without limitation, (A) by providing ABX with copies of

all communications received from or filed in patent office(s) with respect to

such filing, and (B) by providing ABX, a reasonable time prior to taking or

failing to take any action that would affect the scope or validity of any such

of any such filing (including the substantially narrowing, cancellation or

abandonment of any claim(s) without

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

19

<PAGE> 50

retaining the right to pursue such subject matter in a separate application, or

the failure to file or perfect the filing of any claim(s) in any country), with

prior written notice of such proposed action or inaction so that ABX has a

reasonable opportunity to review and comment. [____ ____________] for

[__________] of [____________________________________________ ______] with

respect to [________________] shall be [_____________________________

_________]. If IMMUNOGEN fails to undertake the filing(s) of any patent

application or submission with respect to any invention under such Licensed

Patent Rights, then not less than ninety (90) days prior to the last date for

making the applicable filing or submission to preserve rights under such patent

application, ABX may undertake such filing(s) at its own expense, in which case

IMMUNOGEN will assign to ABX all of its rights to such patent application and

invention and any subsequently issued patent thereon, each of which thereafter

will be owned solely by ABX.

6.2 NOTICE OF INFRINGEMENT. If, during the Term of this Agreement, either

Party learns of any actual, alleged or threatened infringement by a Third Party

of any Licensed Patent Rights under this Agreement, such Party shall promptly

notify the other Party and shall provide such other Party with available

evidence of such infringement.

6.3 INFRINGEMENT OF PATENT RIGHTS. IMMUNOGEN shall have the first right

(but not the obligation), at its own expense and with legal counsel of its own

choice, to bring suit (or take other appropriate legal action) against any

actual, alleged or threatened infringement of the Licensed Patent Rights caused

by the research, development, manufacture, use, offer for sale, sale or import

of Licensed Products. ABX shall have the right, at its own expense, to be

represented in any such action by IMMUNOGEN by counsel of ABX's own choice;

provided, however, that under no circumstances shall the foregoing affect the

right of IMMUNOGEN to control the suit as described in the first sentence of

this Section 6.3. If IMMUNOGEN does not file any action or proceeding against

such infringement within one hundred twenty (120) days after the later of (i)

IMMUNOGEN's notice to ABX under Section 6.2 above, (ii) ABX's notice to

IMMUNOGEN under Section 6.2 above, or (iii) a written request from ABX to take

action with respect to such infringement, then ABX shall have the right (but not

the obligation), at its own expense, to bring suit (or take other appropriate

legal action) against such actual, alleged or threatened infringement, with

legal counsel of its own choice. Any damages, monetary awards or other amounts

recovered, whether by judgment or settlement, pursuant to any suit, proceeding

or other legal action taken under this Section 6.3, shall applied as follows:

6.3.1 First, to reimburse the Parties for their respective costs and

expenses (including reasonable attorneys' fees and costs) incurred in

prosecuting such enforcement action;

6.3.2 Second, [_________________________________] associated with

[_________________] and to [__________________________________________________]

based on [_______________];

6.3.3 Third, any amounts remaining shall be allocated as follows: (a)

if IMMUNOGEN is the Party bringing such suit or proceeding or taking such other

legal action, [_________________________], (b) if ABX is the Party bringing such

suit or proceeding or

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

20

<PAGE> 51

taking such other legal action, [________________________] and (c) if the suit

is brought jointly, [____________________].

If a Party brings any such action or proceeding hereunder, the other Party

agrees to be joined as party plaintiff if necessary to prosecute such action or

proceeding, and to give the Party bringing such action or proceeding reasonable

assistance and authority to file and prosecute the suit; provided, however, that

neither Party shall be required to transfer any right, title or interest in or

to any property to the other Party or any Third Party to confer standing on a

Party hereunder.

6.4 THIRD PARTY PATENTS. If any Third Party claims that a patent it owns or

controls claims any aspect of a Licensed Product or its manufacture, use or

sale, the Party with notice of such claim shall notify the other Party promptly,

and the Parties shall as soon as practicable thereafter discuss in good faith

regarding a response.

6.5 TRADEMARKS. All Licensed Products shall be sold under one (1) or more

trademarks and tradenames selected by ABX (or its Sublicensee) in the Territory.

IMMUNOGEN shall notify ABX promptly upon learning of any actual, alleged or

threatened infringement of a trademark or tradename applicable to a Licensed

Product in the Territory, or of any unfair trade practices, trade dress

imitation, passing off of counterfeit goods, or like offenses in the Territory.

All of the costs, expenses and legal fees in bringing, maintaining and

prosecuting any action to maintain, protect or defend any trademarks or

tradenames owned by ABX (or its Sublicensee) hereunder, and any damages or other

recovery, shall be ABX's (or its Sublicensee's) sole responsibility, and taken

in its sole discretion.

7. TERM AND TERMINATION

7.1 TERM; EXPIRATION. The term of this Agreement shall expire upon the

expiration of the final royalty payment obligation under Section 4.5 above. Upon

such expiration of the Term of this Agreement, ABX shall have a fully paid-up,

irrevocable, freely transferable and sublicensable license in such country under

the relevant Licensed Patent Rights and IMMUNOGEN Background Technology, to

research, develop, make, have made, use, have used, sell, offer for sale, have

sold, import and have imported Licensed Products, for any and all uses within

the Field in the Territory.

7.2 TERMINATION. Subject to the other terms of this Agreement:

7.2.1 BREACH. This Agreement and the rights and options granted herein

may be terminated by either Party upon any material breach by the other Party of

any material obligation or condition, effective [____________] after giving

written notice to the breaching Party of such termination in the case of a

payment breach and [_____________] after giving written notice to the breaching

Party of such termination in the case of any other breach, which notice shall

describe such breach in reasonable detail. The foregoing notwithstanding, if

such default or breach is cured or shown to be non-existent within the aforesaid

[______] or [_____ _______] period, the notice shall be automatically withdrawn

and of no effect. However, prior to giving any notice for breach, the Parties

shall first attempt to resolve any disputes as to the existence of any breach as

set forth in Section 8.14.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

21

<PAGE> 52

7.2.2 UNILATERAL TERMINATION BY ABX. ABX, in its sole discretion, at

any time may terminate this Agreement, and the rights and obligations hereunder,

or may remove any Licensed Product and the licenses related thereto from

operation of this Agreement, in any case effective [______________] after

written notice thereof to IMMUNOGEN. In the event of any termination under this

Section 7.2.2 only as to a Licensed Product, the consequences set forth in

Section 7.3 below relating to termination of the Agreement under this Section

7.2.2 shall apply only with respect to such terminated Licensed Product, and

this Agreement and the rights and obligations hereunder shall continue in full

force and effect as to any and all other Licensed Products.

7.3 EFFECTS OF TERMINATION.

7.3.1 Upon any termination of this Agreement by IMMUNOGEN under

Section 7.2.1 or by ABX under Section 7.2.2, as of the effective date of such

termination, all relevant licenses and sublicenses granted by IMMUNOGEN to ABX

hereunder shall terminate automatically. Notwithstanding the foregoing, (a) no

such termination of this Agreement shall be construed as a termination of any

valid sublicense of any Sublicensee hereunder, and thereafter each such

Sublicensee shall be considered a direct licensee of IMMUNOGEN, provided that

(i) such Sublicensee is then in full compliance with all terms and conditions of

its sublicense, (ii) all accrued payments obligations to IMMUNOGEN have been

paid, and (iii) such Sublicensee agrees in writing to assume all applicable

obligations of ABX under this Agreement, and (b) ABX and its Sublicensees shall

have the right, [_________________] or such longer time period (if any) on which

the Parties mutually agree in writing, to sell or otherwise dispose of all

Licensed Products then on hand, with royalties to be paid to IMMUNOGEN on all

Net Sales of such Licensed Products as provided for in this Agreement. Nothing

set forth in this Section 7 or any other provision of this Agreement shall

entitle IMMUNOGEN to any ownership interest in, or to any license under or other

rights with respect to (including any rights to use or request any transfer to

IMMUNOGEN or any Third Party), any Confidential Information of ABX or any

Technology or Patent Rights owned by ABX under this Agreement.

7.3.2 Upon any termination of this Agreement by ABX under Section

7.2.1, as of the effective date of such termination, ABX thereafter

automatically shall have a fully sublicensable, fully paid up (subject to the

remainder of this Section 7.3.2), exclusive license in the Territory under the

Licensed Patent Rights and IMMUNOGEN Background Technology, to research,

develop, make, have made, use, have used, sell, offer for sale, have sold,

import and have imported Licensed Products, for any and all uses within the

Field in the Territory, provided that ABX shall pay, for the remainder of the

royalty term under Section 4.5 above, in lieu of any payments including

milestones or royalties it would otherwise owe to IMMUNOGEN under this

Agreement, a royalty equal to [____________________________________________]

with respect to the Licensed Product under Section 4 of this Agreement.

7.4 REMEDIES. Except as otherwise expressly set forth in this Agreement,

the termination provisions of this Section 7 are in addition to any other relief

and remedies available to either Party at law.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

22

<PAGE> 53

7.5 SURVIVING PROVISIONS. Notwithstanding any provision herein to the

contrary, the rights and obligations of the Parties set forth in Sections 4.7,

5, 6, 7.3, 7.4, 8.3, 8.4, 8.7, 8.14, 8.16, 8.17, 8.18 and 8.19 hereof, as well

as any rights or obligations otherwise accrued hereunder (including any accrued

payment obligations), shall survive the expiration or termination of the Term of

this Agreement. Without limiting the generality of the foregoing, ABX shall have

no obligation to make any milestone or royalty payment to IMMUNOGEN that has not

accrued prior to the effective date of any termination of this Agreement, but

shall remain liable for all such payment obligations accruing prior to the

effective date of such termination.

8. MISCELLANEOUS

8.1 IMMUNOGEN REPRESENTATIONS. IMMUNOGEN represents and warrants to ABX

that: (a) the execution and delivery of this Agreement and the performance of

the transactions contemplated hereby have been duly authorized by all

appropriate IMMUNOGEN corporate action; (b) this Agreement is a legal and valid

obligation binding upon IMMUNOGEN and enforceable in accordance with its terms,

and the execution, delivery and performance of this Agreement by the Parties

does not conflict with any agreement, instrument or understanding to which

IMMUNOGEN is a party or by which it is bound; (c) IMMUNOGEN has the full right

and legal capacity to grant the rights to ABX pursuant to Section 2 above

without violating the rights of any Third Party; (d) IMMUNOGEN is the sole owner

or exclusive licensee of the IMMUNOGEN Background Technology; (e) IMMUNOGEN is

not aware of any Third Party patent, patent application or other intellectual

property rights that would be infringed (i) by practicing any process or method

or by making, using or selling any composition which is claimed or disclosed in,

or which constitutes, IMMUNOGEN Background Technology, or (ii) by making, using,

offering for sale, selling or importing Licensed Products; and (f) IMMUNOGEN is

not aware of any infringement or misappropriation by a Third Party of the

IMMUNOGEN Background Technology.

8.2 ABX REPRESENTATIONS. ABX represents and warrants to IMMUNOGEN that: (a)

the execution and delivery of this Agreement and the performance of the

transactions contemplated hereby have been duly authorized by all appropriate

ABX corporate action; (b) this Agreement is a legal and valid obligation binding

upon ABX and enforceable in accordance with its terms, and the execution,

delivery and performance of this Agreement by the Parties does not conflict with

any agreement, instrument or understanding to which ABX is a party of or by

which it is bound; and (c) ABX has the full right and legal capacity to grant

the rights to IMMUNOGEN pursuant to Section 2 above without violating the rights

of any Third Party.

8.3 NO WARRANTIES.

8.3.1 Nothing in this Agreement is or shall be construed as:

(a) a warranty or representation by either Party as to the

validity or scope of any patent application or patent licensed hereunder;

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

23

<PAGE> 54

(b) a warranty or representation that anything made, used, sold

or otherwise disposed of under any license granted pursuant to this Agreement is

or will be free from infringement of patents, copyrights, and other rights of

third parties.

8.3.2 Except as expressly set forth in this Agreement, NEITHER PARTY

MAKES ANY REPRESENTATION OR EXTENDS ANY WARRANTIES OF ANY KIND, EITHER EXPRESS

OR IMPLIED. THERE ARE NO EXPRESS OR IMPLIED WARRANTIES OF MERCHANTABILITY OR

FITNESS FOR A PARTICULAR PURPOSE, OR OF NON-INFRINGEMENT OF ANY PATENT,

COPYRIGHT, TRADEMARK, OR OTHER RIGHTS OF THIRD PARTIES, OR ANY OTHER EXPRESS OR

IMPLIED WARRANTIES.

8.4 [_____________] NOTWITHSTANDING ANYTHING ELSE IN THIS AGREEMENT, OR

OTHERWISE, [_____________________________________________] TO [_______________

__________] OF THIS AGREEMENT [_______________________________________________

_______________________________________________] FOR (I) [____________________

_____________________________________________________ _________] OR (II)

[____________________________________________________________________________].

8.5 NOTICES. Any notices, requests, deliveries, approvals or consents

required or permitted to be given under this Agreement to ABX or IMMUNOGEN shall

be in writing and shall be effective on receipt when delivered to the applicable

address specified below (or to such other address as may be specified in writing

to the other Party hereto):

<TABLE>

<S> <C>

If to IMMUNOGEN: IMMUNOGEN, Inc.

128 Sidney Street

Cambridge, MA 02139

Attn: Chief Executive Officer

With a copy to: Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.

One Financial Center

Boston, MA 02111

Attn: Jeffrey M. Wiesen, Esq

Telecopy: 617-542-2241

If to ABX: Abgenix, Inc.

7601 Dumbarton Circle

Fremont, California 94555

Attn: President

With a copy to: Gray Cary Ware & Freidenrich LLP

4365 Executive Drive, Suite 1600

San Diego, California 92121-2189

Attn: Mark R. Wicker

</TABLE>

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

24

<PAGE> 55

8.6 GOVERNING LAW. This Agreement will be construed, interpreted and

applied in accordance with the laws of the Commonwealth of Massachusetts

(excluding its body of law controlling conflicts of law).

8.7 LIMITATIONS. Except as set forth elsewhere in this Agreement, neither

Party grants to the other Party any right or license to any of its intellectual

property.

8.8 ENTIRE AGREEMENT. This is the entire Agreement between the Parties with

respect to the subject matter hereof and supersedes all prior representations,

understandings and agreements between the Parties with respect to the subject

matter hereof. No modification shall be effective unless in writing with

specific reference to this Agreement and signed by the Parties.

8.9 WAIVER. The terms or conditions of this Agreement may be waived only by

a written instrument executed by the Party waiving compliance. The failure of

either Party at any time or times to require performance of any provision hereof

shall in no manner affect its rights at a later time to enforce the same. No

waiver by either Party of any condition or term shall be deemed as a continuing

waiver of such condition or term or of another condition or term.

8.10 HEADINGS. Section and subsection headings are inserted for convenience

of reference only and do not form part of this Agreement.

8.11 ASSIGNMENT. Neither this Agreement nor any right or obligation

hereunder may be assigned, delegated or otherwise transferred , in whole or

part, by either party without the prior express written consent of the other;

provided, however, that either party may, without the written consent of the

other, assign this Agreement and its rights and delegate its obligations

hereunder to its Affiliates, or in connection with the transfer or sale of all

or substantially all of such party's assets or business related to this

Agreement, or in the event of its merger, consolidation, change in control or

similar transaction. Any permitted assignee shall assume all obligations of its

assignor under this Agreement. Any purported assignment in violation of this

Section 8.11 shall be void. The terms and conditions of this Agreement shall be

binding upon and inure to the benefit of the permitted successors and assigns of

the parties.

8.12 FORCE MAJEURE. Neither Party shall be liable for failure of or delay

in performing obligations set forth in this Agreement, and neither shall be

deemed in breach of its obligations, if such failure or delay is due to natural

disasters or any causes beyond the reasonable control of such Party. In event of

such force majeure, the Party affected thereby shall use reasonable efforts to

cure or overcome the same and resume performance of its obligations hereunder.

8.13 CONSTRUCTION. The Parties hereto acknowledge and agree that: (i) each

Party and its counsel reviewed and negotiated the terms and provisions of this

Agreement and have contributed to its revision; (ii) the rule of construction to

the effect that any ambiguities are resolved against the drafting Party shall

not be employed in the interpretation of this Agreement; and (iii) the terms and

provisions of this Agreement shall be construed fairly as to all Parties hereto

and not in favor of or against any Party, regardless of which Party was

generally responsible for the preparation of this Agreement.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

25

<PAGE> 56

8.14 DISPUTES.

8.14.1 The Parties recognize that a bona fide dispute as to certain

matters may from time to time arise during the term of this Agreement which

relates to either Party's rights and/or obligations hereunder. In the event of

the occurrence of such a dispute, either Party may, by written notice to the

other Party, have such dispute referred to their respective senior officials

designated below or their successors, for attempted resolution by good faith

negotiations within thirty (30) days after such notice is received. Said

designated senior officials are as follows:

For ABX: Chief Executive Officer

For IMMUNOGEN: Chief Executive Officer

In the event the designated senior officials are not able to resolve such

dispute within the thirty (30) day period, either Party may invoke the

provisions of Section 8.14.2.

8.14.2 Any dispute, controversy or claim initiated by either Party

arising out of, resulting from or relating to this Agreement, or the performance

by either Party of its obligations under this Agreement (other than bona fide

third party actions or proceedings filed or instituted in an action or

proceeding by a Third Party against a Party), whether before or after

termination of this Agreement, shall be finally resolved by binding arbitration.

Whenever a Party shall decide to institute arbitration proceedings, it shall

give written notice to that effect to the other Party. Any such arbitration

shall be conducted under the Commercial Arbitration Rules of the American

Arbitration Association by a panel of three arbitrators appointed in accordance

with such rules. Any such arbitration shall be held in Boston, Massachusetts if

initiated by ABX, and in San Francisco, California if initiated by IMMUNOGEN.

The method and manner of discovery in any such arbitration proceeding shall be

governed by California Code of Civil Procedure ss.1282 ET SEQ. (including

without limitation California Code of Civil Procedure ss.1283.05). The

arbitrators shall have the authority to grant specific performance and to

allocate between the parties the costs of arbitration in such equitable manner

as they determine. Judgment upon the award so rendered may be entered in any

court having jurisdiction or application may be made to such court for judicial

acceptance of any award and an order of enforcement, as the case may be. In no

event shall a demand for arbitration be made after the date when institution of

a legal or equitable proceeding based upon such claim, dispute or other matter

in question would be barred by the applicable statute of limitations.

Notwithstanding the foregoing, either Party shall have the right, without

waiving any right or remedy available to such Party under this Agreement or

otherwise, to seek and obtain from any court of competent jurisdiction any

interim or provisional relief that is necessary or desirable to protect the

rights or property of such Party, pending the selection of the arbitrators

hereunder or pending the arbitrators' determination of any dispute, controversy

or claim hereunder.

8.15 SEVERABILITY. If any provision(s) of this Agreement are or become

invalid, are ruled illegal by any court of competent jurisdiction or are deemed

unenforceable under then current applicable law from time to time in effect

during the Term hereof, it is the intention of the Parties that the remainder of

this Agreement shall not be affected thereby provided that a

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

26

<PAGE> 57

Party's rights under this Agreement are not materially affected. The Parties

hereto covenant and agree to renegotiate any such term, covenant or application

thereof in good faith in order to provide a reasonably acceptable alternative to

the term, covenant or condition of this Agreement or the application thereof

that is invalid, illegal or unenforceable, it being the intent of the Parties

that the basic purposes of this Agreement are to be effectuated.

8.16 STATUS. Nothing in this Agreement is intended or shall be deemed to

constitute a partner, agency, employer-employee, or joint venture relationship

between the Parties.

8.17 INDEMNIFICATION.

8.17.1 ABX INDEMNITY. ABX shall [______________] and [________

__________________________________________________________] and [_______] and

[___________________________________](the "Indemnitees") [_____________________

_____________________] (including [___________________] and [_______________])

[__________] or [______________________], or [___________], in connection with

[_____ _______________________________________], including, without limitation,

[_________ ______________________] (but [_____________________________________

________], [________________________]), to the extent arising out of (i)

[_______________________] in the [____________________________________________

___________________________] of any [________________(___________________)

_______________________________________] under this Agreement, (ii) [_________]

of this Agreement [_____], or (iii) [____________________________] of the

[________], in any [________] under this Section 8.17.1 except to [___________

___________________] therefor under Section 8.17.2 below.

8.17.2 IMMUNOGEN INDEMNITY. Subject to Section 8.17.1 above, IMMUNOGEN

shall indemnify, defend and hold harmless ABX, its Affiliates and their

respective directors, officers, employees, and agents, and their respective

successors, heirs and assigns (also the "Indemnitees"), from and against any

liability, damage, loss or expense (including reasonable attorneys' fees and

expenses of litigation) incurred by or imposed upon such Indemnitees, or any of

them, in connection with any Third Party claims, suits, actions, demands or

judgments, including, without limitation, personal injury and product liability

matters (but excluding any patent, trademark or tradename infringement matters,

which are governed by Section 6 above), to the extent arising out of (i) any

actions or omissions of IMMUNOGEN or subcontractor of IMMUNOGEN in the

development, testing, production, manufacture or supply of any Licensed Product

(or any component thereof) manufactured and supplied by IMMUNOGEN or any

subcontractor of IMMUNOGEN under this Agreement, (ii) any material breach of

this Agreement by IMMUNOGEN, or (iii) gross negligence or willful misconduct on

the part of IMMUNOGEN.

8.18 INDEMNIFICATION PROCEDURES. In the event that any Indemnitee is

seeking indemnification under Section 8.17 above from a Party (the "Indemnifying

Party"), the other Party shall notify the Indemnifying Party of such claim with

respect to such Indemnitee as soon as reasonably practicable after the

Indemnitee receives notice of the claim, and the Party (on

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

27

<PAGE> 58

behalf of itself and such Indemnitee) shall permit the Indemnifying Party to

assume direction and control of the defense of the claim (including the right to

settle the claim solely for monetary consideration) and shall cooperate as

requested (at the expense of the Indemnifying Party) in the defense of the

claim. The indemnification obligations under Section 8.17 shall not apply to

amounts paid in settlement of any claim, demand, action or other proceeding if

such settlement is effected without the consent of the Indemnifying Party, which

consent shall not be withheld or delayed unreasonably. The Indemnitee, its

employees and agents, shall reasonably cooperate with the Indemnifying Party and

its legal representatives in the investigation of any claim, demand, action or

other proceeding covered by Section 8.17.

8.19 SECTION 365(n). All licenses granted under this Agreement are deemed

to be, for purposes of Section 365(n) of the U.S. Bankruptcy Code, licenses of

right to "intellectual property" as defined in Section 101 of such Code. The

Parties agree that the licensee may fully exercise all of its rights and

elections under the U.S. Bankruptcy Code, regardless of whether either Party

files for bankruptcy in the United States or other jurisdiction. The Parties

further agree that, in the event a licensee elects to retain its rights as a

licensee under such Code, the licensee shall be entitled to complete access to

any technology licensed to it hereunder and all embodiments of such technology.

Such embodiments of the technology shall be delivered to the licensee not later

than:

8.19.1 the commencement of bankruptcy proceedings against the

licensor, upon written request, unless the licensor elects to perform its

obligations under the Agreement, or

8.19.2 if not delivered under Section 8.19.1 above, upon the rejection

of this Agreement by or on behalf of the licensor, upon written request.

8.20 FURTHER ASSURANCES. Each Party agrees to execute, acknowledge and

deliver such further instructions, and to do all such other acts, as may be

necessary or appropriate in order to carry out the purposes and intent of this

Agreement.

8.21 COUNTERPARTS. This Agreement may be executed simultaneously in one or

more counterparts, each of which shall be deemed an original, but all of which

together shall constitute one and the same instrument.

IN WITNESS WHEREOF, the Parties have caused this Agreement to be executed

by their duly authorized representative in two (2) originals.

ABGENIX, INC. IMMUNOGEN, INC.

By: ______________________________ By: ________________________________

Title: ___________________________ Title: _____________________________

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

28

<PAGE> 59

SCHEDULE I

LICENSED PATENT RIGHTS

[___________________________________________]

<TABLE>

<CAPTION>

- ---------------------------------------------------------------------------------------------------------------------------------

Attorney Country Appl. No. Filing Date Priority Date Patent No. Issue Date Exp. Date

Reference No.

- ---------------------------------------------------------------------------------------------------------------------------------

- ---------------------------------------------------------------------------------------------------------------------------------

<S> <C> <C> <C> <C> <C> <C> <C>

[________] [________] [________] [________] [________]

- ---------------------------------------------------------------------------------------------------------------------------------

[________] [________] [________] [________] [________] [________] [_______] [_______]

--------------------------------------------------------------------------------------------------------------------------------

[________] [________] [________] [________] [________] [________] [_______] [_______]

- ---------------------------------------------------------------------------------------------------------------------------------

[________] [________]* [________] [________] [________] [________] [_______] [_______]

- ---------------------------------------------------------------------------------------------------------------------------------

*[________]

- ---------------------------------------------------------------------------------------------------------------------------------

[________] [________] [________] [________] [________] [________]

- ---------------------------------------------------------------------------------------------------------------------------------

[________] [________] [________] [________] [________] [________]

- ---------------------------------------------------------------------------------------------------------------------------------

</TABLE>

[_____________________________________________________________________________]

<TABLE>

<CAPTION>

- ---------------------------------------------------------------------------------------------------------------------------------

Attorney Country Appl. No. Filing Date Priority Date Patent No. Issue Date Exp. Date

Reference No.

- ---------------------------------------------------------------------------------------------------------------------------------

<S> <C> <C> <C> <C> <C> <C> <C>

[________] [________] [________] [________] [________]

- ---------------------------------------------------------------------------------------------------------------------------------

</TABLE>

[___________________________________________]

<TABLE>

<CAPTION>

- ---------------------------------------------------------------------------------------------------------------------------------

Attorney Country Appl. No. Filing Date Priority Date Patent No. Issue Date Exp. Date

Reference No.

- ---------------------------------------------------------------------------------------------------------------------------------

<S> <C> <C> <C> <C> <C> <C> <C>

[________] [________] [________] [________] [________]

- ---------------------------------------------------------------------------------------------------------------------------------

</TABLE>

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

29

<PAGE> 60

FORM OF NONEXCLUSIVE LICENSE AGREEMENT

This Nonexclusive License Agreement ("Agreement") is made effective as

of as of _____________, 20__ (the "Effective Date") by and between IMMUNOGEN,

INC., a Massachusetts corporation with a principal place of business at 128

Sidney Street, Cambridge, Massachusetts 02139 ("IMMUNOGEN"), and ABGENIX, INC.,

a Delaware corporation with a place of business at 7601 Dumbarton Circle,

Fremont, California 94555 ("ABX"). IMMUNOGEN and ABX are each hereafter referred

to individually as a "Party" and together as the "Parties".

WHEREAS, ABX is the owner of or otherwise controls certain patents and

technology relating to antibodies; and

WHEREAS, IMMUNOGEN is the owner of or otherwise controls certain

proprietary patents and technology relating to or otherwise useful in the

conjugation of certain cytotoxic compounds such as DM1 (as hereinafter defined)

to antibodies; and

WHEREAS, ABX desires to obtain certain rights from IMMUNOGEN to develop

and commercialize one or more conjugates of certain cytotoxic compounds and

antibodies and IMMUNOGEN is willing to grant to ABX such rights on the terms

provided herein; and

WHEREAS, the Parties have heretofore executed an Option and License

Agreement (as hereinafter defined) pursuant to which IMMUNOGEN has granted ABX

certain options related to IMMUNOGEN's proprietary technology and know-how; and

WHEREAS, ABX has exercised an Option (as hereinafter defined) to obtain

such rights and, in connection therewith, desires to enter into this Agreement

in accordance with the terms of the Option and License Agreement.

NOW, THEREFORE, in consideration of the mutual covenants contained

herein, and for other good and valuable consideration, the receipt and adequacy

of which are hereby acknowledged, the Parties hereby agree as follows:

1. DEFINITIONS

Whenever used in the Agreement with an initial capital letter, the

terms defined in this Section 1 shall have the meanings specified.

1.1 "ABX ANTIBODY" shall mean any antibody or fragment thereof

directed to the Target.

1.2 "ADVERSE EVENT" shall mean any serious adverse event or medical

occurrence in a patient or subject who is administered a Licensed Product,

whether or not

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

1

<PAGE> 61

considered related to the Licensed Product, (including, without

limitation, any undesirable sign (including abnormal laboratory findings of

clinical concern), symptom or disease temporally associated with the use of such

Licensed Product.

1.3 "AFFILIATE" shall mean any corporation, firm, limited liability

company, partnership or other entity which directly controls or is controlled by

or is under common control with a Party to this Agreement. "Control" for

purposes of this Section 1.3 means ownership, directly or indirectly through one

or more Affiliates, of fifty percent (50%) or more of the shares of stock

entitled to vote for the election of directors, in the case of a corporation, or

fifty percent (50%) or more of the equity interests in the case of any other

type of legal entity, status as a general partner in any partnership, or any

other arrangement whereby a Party controls or has the right to control the Board

of Directors or equivalent governing body of a corporation or other entity.

1.4 "BLA" shall mean a biologics license application (as defined in

Title 21 of the United States Code of Federal Regulations, as amended from time

to time) filed with the FDA seeking Regulatory Approval to market and sell any

Licensed Product in the United States for a particular indication within the

Field.

1.5 "CLINICAL MATERIALS" shall mean (a) supplies of ansamitocin P-3,

DM1, and/or any other May Compound as manufactured in accordance with all

applicable GMPs and other legal requirements and all applicable Specifications

for such May Compound for use in human clinical testing, and (b) supplies of any

Licensed Product as manufactured in accordance with all applicable GMPs and

other legal requirements and all applicable Specifications for such Licensed

Product for use in human clinical testing of any Licensed Product

1.6 "COMBINATION PRODUCT" shall mean any Licensed Product that

contains, in addition to any conjugate of any ABX Antibody with any May

Compound, one or more other ingredients that has biologic activity.

1.7 "CONTROL" OR "CONTROLLED" shall mean (a) with respect to patents,

know-how or other intangible rights, the possession by Party of the ability to

grant a license or sublicense of such patent rights, know-how or other

intangible rights as provided for herein without violating the terms of any

arrangement or agreements between such Party and any Third Party and (b) with

respect to any material, the possession by a Party of the ability to use such

material as provided herein without violating the terms of any agreement between

such Party and any Third Party.

1.8 "DEVELOPMENT" AND "DEVELOP" shall mean, with respect to any

Licensed Product, all activities with respect to such Licensed Product relating

to research, development and seeking, obtaining and/or maintaining any

Regulatory Approval for such Licensed Product in the Field in the Territory,

including without limitation, all pre-clinical research and development

activities, all human clinical studies, all activities relating to developing

the ability to manufacture any Licensed Product or any component thereof

(including, without limitation,

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

2

<PAGE> 62

process development work), and all other activities relating to seeking,

obtaining and/or maintaining any Regulatory Approvals from the FDA and/or any

Foreign Regulatory Authority.

1.9 "DM1" shall mean that certain maytansine derivative having the

specific chemical name N2'-deacetyl-N2'-(3-mercapto-1-oxopropyl)-maytansine.

1.10 "DRUG APPROVAL APPLICATION" shall mean any application for

Regulatory Approval (including pricing and reimbursement approvals) required

prior to any commercial sale or use of a Licensed Product in any country or

jurisdiction in the Territory, including, without limitation, (a) any BLA, NDA

or other regulatory application filed with the FDA required prior to any

commercial sale or use of a Licensed Product in the United States, and (b) any

equivalent application (including an MAA) filed with any Foreign Regulatory

Authority for Regulatory Approval (including pricing and reimbursement

approvals) required prior to any commercial sale or use of a Licensed Product in

any country or jurisdiction in the Territory.

1.11 "FDA" shall mean the United States Food and Drug Administration

and any successor agency or authority thereto.

1.12 "FIELD" shall mean any human medical use.

1.13 "FIRST COMMERCIAL SALE" shall mean the date of the first

commercial sale (other than for purposes of obtaining Regulatory Approval) of a

Licensed Product by or on behalf of ABX or an Affiliate or Sublicensee of ABX.

1.14 "FOREIGN REGULATORY AUTHORITIES" shall mean any applicable

supranational, national, federal, state or local regulatory agency, department,

bureau or other governmental entity of any country or jurisdiction in the

Territory (other than the FDA in the United States), having responsibility in

such country or jurisdiction for any Regulatory Approvals of any kind in such

country or jurisdiction, and any successor agency or authority thereto.

1.15 "FULLY BURDENED MANUFACTURING COST" shall mean, with respect to

any Preclinical Materials or Clinical Materials produced by IMMUNOGEN for ABX

under this Agreement, the sum of the following components as determined by

IMMUNOGEN in accordance with generally accepted accounting principles in the

United States, consistently applied, and consistent with the application given

to other goods produced by IMMUNOGEN: (a) the costs of goods produced,

including, without limitation, direct labor, material and product testing costs

of such Preclinical Materials or Clinical Materials; (b) any Third Party royalty

costs that are actually paid by IMMUNOGEN and are based solely and directly on

the manufacture and sale to ABX of such Preclinical Materials or Clinical

Materials; (c) all overhead costs incurred by IMMUNOGEN directly and solely

attributable to the cost of goods under clause (a) above, including, without

limitation, supervisory services, occupancy costs, payroll, information systems,

human relations, purchasing, accounts receivable or accounts payable functions,

and other general and administrative functions; and (d) any other costs borne by

IMMUNOGEN

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

3

<PAGE> 63

directly and solely for the transport, customs clearance, duty and/or

insurance for such Preclinical Materials or Clinical Materials to ABX hereunder.

1.16 "GMPs" shall mean all good manufacturing practices under Title 21

of the United States Code of Federal Regulations, as amended from time to time.

1.17 "IMMUNOGEN BACKGROUND TECHNOLOGY" shall mean all inventions,

discoveries, patent rights, trade secrets and know-how, including without

limitation, laboratory scientific information and procedural techniques,

Controlled by IMMUNOGEN during the term of the Option and License Agreement or

the Term of this Agreement that are necessary or useful for ABX to research,

develop, make, have made, use, have used, sell, offer for sale, have sold,

import or have imported Licensed Products (or any component thereof, including

any linker) for use in the Field; provided, however, that IMMUNOGEN Background

Technology shall expressly exclude any Target Specific Rights.

1.18 "IND" shall mean an investigational new drug application (as

defined in Title 21 of the United States Code of Federal Regulation, as amended

from time to time) filed or to be filed with the FDA with regard to any Licensed

Product.

1.19 "IND ACCEPTANCE" shall mean the expiration of thirty (30) days

following receipt by ABX of a notice from the FDA to ABX that the FDA has

received an IND for a Licensed Product filed by ABX for the purpose of obtaining

approval or authority to commence human clinical trials in the United States

with such Licensed Product; provided, however, that if the FDA puts a clinical

hold on the IND during such thirty (30) day period, the term "IND Acceptance"

shall mean that date during the term of this Agreement when ABX receives written

confirmation from the FDA that the clinical hold has been removed and that ABX

has the approval or authority to commence human clinical trials of such Licensed

Product under such IND in the United States. Notwithstanding anything set forth

herein, "IND Acceptance" shall not have occurred in any circumstances where ABX

withdraws any IND filed with the FDA for a Licensed Product at any time prior to

the commencement of human clinical trials with such Licensed Product in the

United States.

1.20 "INDEMNITEES" AND "INDEMNIFYING PARTY" shall have the meanings

set forth in Section 9.

1.21 "JPDC" shall have the meaning set forth in Section 3.4.1.

1.22 "LICENSED PATENT RIGHTS" shall mean all Patent Rights covering

IMMUNOGEN Background Technology. All Licensed Patent Rights as of the Effective

Date are listed on Schedule I attached hereto.

1.23 "LICENSED PRODUCT" shall mean any product containing any

conjugate of any ABX Antibody with any May Compound, and shall include, without

limitation, any formulation thereof (including, without limitation, any

lyophilized, liquid, sustained release or

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

4

<PAGE> 64

aerosolized formulation). "Licensed Product" shall also include any and all

Combination Products (if any).

1.24 "MAA" shall mean an application filed with the relevant Foreign

Regulatory Authorities in Europe seeking Regulatory Approval to market and sell

any Licensed Product in Europe or any country or territory therein for a

particular indication within the Field.

1.25 "MAY COMPOUND" shall mean any and all maytansinoid compounds

(including, without limitation, maytansine, ansamitocin P-3 and DM1), whether

produced by a botanical source, natural fermentation or chemical synthesis, and

shall include, without limitation, all variants, fragments or derivatives of any

of the foregoing, in each case owned or otherwise Controlled by IMMUNOGEN. May

Compounds shall include, without limitation, DM1.

1.26 "NDA" shall mean a new drug application (as defined in Title 21

of the United States Code of Federal Regulations, as amended from time to time)

filed with the FDA seeking Regulatory Approval to market and sell any Licensed

Product in the United States for a particular indication within the Field.

1.27 "NET SALES" shall mean, as to each calendar quarter during the

Term, the gross invoiced sales prices charged for all Licensed Products sold by

ABX, its Affiliates or its Sublicensees to Third Parties throughout the

Territory during such calendar quarter, less the following amounts incurred or

paid by ABX or its Affiliates or Sublicensees during such calendar quarter with

respect to sales of Licensed Products regardless of the calendar quarter in

which such sales were made:

1.27.1 trade, cash and quantity discounts or rebates actually allowed

or taken, including discounts or rebates to governmental or managed care

organizations;

1.27.2 credits or allowances actually given or made for rejection of

or return of, and for uncollectible amounts on, previously sold Licensed

Products or for retroactive price reductions (including Medicare and similar

types of rebates);

1.27.3 any charges for insurance, freight, and other transportation

costs directly related to the delivery of Licensed Product to the extent

included in the gross invoiced sales price;

1.27.4 any tax, tariff, duty or governmental charge levied on the

sales, transfer, transportation or delivery of a Licensed Product (including any

tax such as a value added or similar tax or government charge) borne by the

seller thereof, other than franchise or income tax of any kind whatsoever; and

1.27.5 any import or export duties or their equivalent borne by the

seller. "Net Sales" shall not include sales or transfers between ABX and its

Affiliates or Sublicensees, unless the Licensed Product is consumed by the

Affiliate or Sublicensee.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

5

<PAGE> 65

1.28 "OPTION" shall have the meaning set forth in the Option and

License Agreement.

1.29 "OPTION AND LICENSE AGREEMENT" shall mean that certain

Option and License Agreement dated as of September 5, 2000, by and between

IMMUNOGEN and ABX.

1.30 "PATENT RIGHTS" shall mean the rights and interests in and

to any and all issued patents and pending patent applications (including

inventor's certificates and utility models) in any country or jurisdiction in

the Territory, including any and all provisionals, non-provisionals,

substitutions, continuations, continuations-in-part, divisionals and other

continuing applications, supplementary protection certificates, renewals, all

letters patent on any of the foregoing, and any and all reissues,

reexaminations, extensions, confirmations, registrations and patents of addition

on any of the foregoing.

1.31 "PHASE II CLINICAL STUDY" shall mean, as to a particular

Licensed Product for a particular indication, a controlled and lawful study in

humans of the safety, dose ranging and efficacy of such Licensed Product for

such indication, which is prospectively designed to generate sufficient data (if

successful) to commence a Phase III Clinical Trial of such Licensed Product for

such indication.

1.32 "PHASE III CLINICAL TRIAL" shall mean, as to a particular

Licensed Product for a particular indication, a controlled and lawful study in

humans of the safety and efficacy of such Licensed Product for such indication,

which is prospectively designed to demonstrate statistically whether such

Licensed Product is safe and effective for use in such indication in a manner

sufficient to file a BLA or NDA to obtain Regulatory Approval to market and sell

that Licensed Product in the United States for the indication under

investigation in such study.

1.33 "PRECLINICAL MATERIALS" shall mean (a) supplies of ansamitocin

P-3, DM1 and/or any other May Compound as manufactured in accordance with all

applicable legal requirements and all applicable Specifications for such May

Compound for use in preclinical testing, and (b) supplies of any Licensed

Product as manufactured in accordance with all applicable legal requirements and

all applicable Specifications for such Licensed Product for use in preclinical

testing of any Licensed Product.

1.34 "REGULATORY APPROVAL" shall mean any and all approvals (including

pricing and reimbursement approvals), product and establishment licenses,

registrations or authorizations of any kind of the FDA or its foreign equivalent

necessary for the development, pre-clinical and/or human clinical testing,

manufacture, quality testing, supply, use, storage, importation, export,

transport, marketing and sale of a Licensed Product (or any component thereof)

for use in the Field in any country or other jurisdiction in the Territory.

1.35 "SPECIFICATIONS" shall mean any specifications specified by ABX

and reasonably acceptable to IMMUNOGEN relating to the manufacturing and supply

of any May Compound and/or Licensed Product hereunder.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

6

<PAGE> 66

1.36 "SUBLICENSEE" shall have the meaning set forth in Section

2.1.1(b).

1.37 "TARGET" shall mean _________________________.

1.38 "TARGET SPECIFIC RIGHTS" shall mean all inventions, discoveries,

patent rights, trade secrets and know-how, including without limitation,

laboratory scientific information and procedural techniques, Controlled by

IMMUNOGEN during the term of the Option and License Agreement or the Term of

this Agreement constituting (a) the composition of matter or use of the Target,

(b) the composition of matter or use of an antibody binding to the Target, or

(c) the composition of matter or use of a conjugate of an antibody binding to

the Target with a May Compound.

1.39 "TECHNOLOGY" shall mean and include any and all unpatented

proprietary ideas, inventions, discoveries, Confidential Information, materials,

data, results, formulae, designs, specifications, methods, processes,

formulations, techniques, ideas, know-how, technical information (including,

without limitation, structural and functional information), process information,

pre-clinical information, clinical information, and any and all proprietary

biological, chemical, pharmacological, toxicological, pre-clinical, clinical,

assay, control and manufacturing data and materials.

1.40 "TERM" shall mean the period commencing on the Effective Date and

continuing until the expiration or termination of this Agreement in accordance

with the terms hereof (including Section 7).

1.41 "TERRITORY" shall mean all countries and jurisdictions of the

world.

1.42 "THIRD PARTY" shall mean any person or entity other than ABX,

IMMUNOGEN and their respective Affiliates.

1.43 "THIRD PARTY PAYMENTS" shall have the meaning set forth in

Section 4.3.2.

1.44 "VALID CLAIM" shall mean a claim in an issued, unexpired patent

within the Licensed Patent Rights that (i) has not been finally cancelled,

withdrawn, abandoned or rejected by any administrative agency or other body of

competent jurisdiction, and (ii) has not been revoked, held invalid, or declared

unpatentable or unenforceable in a decision of a court or other body of

competent jurisdiction that is unappealable or unappealed within the time

allowed for appeal, and (iii) has not been rendered unenforceable through

disclaimer or otherwise, and (iv) is not lost through an interference

proceeding.

2. GRANT OF RIGHTS

2.1 LICENSE GRANT.

2.1.1 LICENSE TO ABX.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

7

<PAGE> 67

(a) IMMUNOGEN hereby grants to ABX a nonexclusive license

within the Territory, including the right to grant sublicenses as described in

Section 2.2 below, under the Licensed Patent Rights and IMMUNOGEN Background

Technology to research, develop, make, have made, use, have used, sell, offer

for sale, have sold, import and have imported Licensed Products, for any and all

uses within the Field, subject to the other terms and conditions of this

Agreement. Promptly, but not less than quarterly, IMMUNOGEN shall deliver to ABX

all IMMUNOGEN Background Technology not previously delivered to ABX.

(b) ABX shall have the right freely to grant sublicenses to

all or any portion of its rights under the license granted pursuant to Section

2.1.1 hereof to any Affiliate or Third Party (in any case, a "Sublicensee");

provided, however, that ABX shall remain obligated for payment of royalty and

milestone obligations as set forth in Section 4.

2.1.2 License to IMMUNOGEN.

--------------------

(a) To the extent legally possible, [______] hereby

[______ ____________] a [______________________________________ ______________],

if any, in any [_____________________________] to the [______________________]

to or [________] of the [_____________] that are [_______ ____________] of

this Agreement, [_______] to the [____________] to [_________________

___________________] and [____________] to [_____________________________ _____]

to [_________] and/or [___________] and/or [__________(______________________]

to a [_________________] or a [________________], each as defined in the

Option and License Agreement). [_________________________] of the [______] of

[__________________] of which it [_____________].

(b) Such [_____] to [________] includes the [__________ __________] to

[____________] from [__________________________________________ __________] to

the [____] they [_______________] or [_________] of the [____________] with the

[_______________________________], and [_____________________] to

[_________________________]. Notwithstanding the foregoing, the

[_________________ _____________] pursuant to this Section 2.1.2 [____________]

the [_____________________ _________________________] (as defined in the Option

and License Agreement).

2.2 IMMUNOGEN RETAINED RIGHTS; ABX TECHNOLOGY OR PATENT RIGHTS. Except

as otherwise expressly set forth in Section 2.1.2, nothing in this Agreement

shall be construed as a grant to IMMUNOGEN of any license or other rights with

respect to any Technology (including, without limitation, any Confidential

Information) or Patent Rights owned or Controlled (in whole or in part) by ABX.

2.3 In Licenses. IMMUNOGEN represents and warrants to ABX that it has

provided ABX true and correct copies of all agreements pursuant to which

Licensed Patent Rights or IMMUNOGEN Background Technology existing as of the

Effective Date, is licensed to or otherwise acquired by IMMUNOGEN from a Third

Party. IMMUNOGEN promptly shall provide ABX with true and correct copies of all

agreements pursuant to which Licensed Patent

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

8

<PAGE> 68

Rights or IMMUNOGEN Background Technology licensed or acquired after the

Effective Date, is licensed to or otherwise acquired by IMMUNOGEN from a Third

Party; provided, however, that IMMUNOGEN shall have the right to redact

confidential financial information and any provisions that shall not bind ABX.

To the extent the Licensed Patent Rights or IMMUNOGEN Background Technology are

licensed to or acquired by IMMUNOGEN from a Third Party and are reasonably

necessary to permit ABX to exercise its rights granted hereunder, IMMUNOGEN

shall use reasonable commercial efforts to maintain in full force and effect

such license. In the event of the termination of any such license with a Third

Party, IMMUNOGEN shall cause such Third Party to grant a direct license to ABX

to the extent necessary to permit ABX to exercise its rights granted hereunder,

and all sums owing by ABX to such Third Party shall be fully deducted from any

amounts owing to IMMUNOGEN hereunder.

3. DEVELOPMENT AND COMMERCIALIZATION OF LICENSED PRODUCTS.

3.1 DEVELOPMENT AND COMMERCIALIZATION.

3.1.1 RESPONSIBILITY. On and after the Effective Date, ABX shall

have full control and authority over all Development and commercialization of

Licensed Products in the Field in the Territory, including, without limitation,

(i) all pre-clinical Development activities (including any pharmaceutical

development work on formulations or process development relating to any Licensed

Product), (ii) all activities related to human clinical trials (including any

phase I studies, any Phase II Clinical Studies or any Phase III Clinical

Trials), (iii) all activities relating to manufacture and supply of all ABX

Antibodies, all May Compounds (including ansamitocin P-3 and DM1) and all

Licensed Products, solely to the extent such activities relate to the

Development and commercialization of Licensed Products (including all required

process development and scale up work with respect thereto), (iv) all marketing,

promotion, sales, distribution, import and export activities relating to any

Licensed Product (including any post-marketing trials or databases and

post-marketing safety surveillance), and (v) all activities relating to any

regulatory filings, registrations, applications and Regulatory Approvals

relating to any of the foregoing (including any INDs or foreign equivalents, any

manufacturing facility validation and/or licensure, any Drug Approval

Applications and any other Regulatory Approvals). Except as described in the

next sentence, ABX shall own all data, results and all other information arising

from any such activities under this Agreement, including, without limitation,

all regulatory filings, registrations, applications and Regulatory Approvals

relating to Licensed Products (including any INDs or foreign equivalents, any

Drug Approval Applications and any other Regulatory Approvals), and all of the

foregoing information, documentation and materials shall be considered

Confidential Information and Technology solely owned by ABX. IMMUNOGEN shall own

all data, results and all other information arising from IMMUNOGEN's activities

directly regarding the manufacture and supply of May Compounds to ABX (other

than activities undertaken at the request of ABX), and all of the foregoing

information, documentation and materials shall be considered Confidential

Information and Technology solely owned by IMMUNOGEN. All activities relating to

Development and commercialization by or on behalf of ABX under this Agreement

shall be undertaken at ABX's sole cost and expense, except as otherwise

expressly provided in this Agreement.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

9

<PAGE> 69

3.1.2 DILIGENCE. ABX will exercise its good faith efforts in

Developing and commercializing Licensed Products in accordance with its

business, legal, medical and scientific judgment, and in undertaking

investigations and actions required to obtain appropriate Regulatory Approvals

necessary to market Licensed Products in the Field in the Territory. In the

event that ABX materially breaches its obligation to use good faith efforts as

required hereunder, then on a Licensed Product-by-Licensed Product basis as to

the Licensed Product for which ABX has materially breached its obligation to use

good faith efforts as required hereunder, IMMUNOGEN's exclusive remedy shall be,

in its sole discretion, to terminate the licenses granted under Section 2.1 of

this Agreement for breach under Section 7.2.1 below (including the notice and

cure provisions therein), only as such licenses apply to such Licensed Product,

which termination shall be effective upon expiration of the cure period

specified in Section 7.2.1 below provided that such failure remains uncured upon

such expiration.

3.2 UPDATES AND REPORTS; EXCHANGES OF ADVERSE EVENT INFORMATION.

3.2.1 UPDATES AND REPORTS. ABX (or its Sublicensee) shall provide

IMMUNOGEN with brief written reports no less frequently than on the anniversary

of the Effective Date during the Term (commencing with the first anniversary of

the Effective Date) summarizing ABX's material efforts to Develop and

commercialize all Licensed Products hereunder, identify the Drug Approval

Applications with respect to any Licensed Product that ABX and its Sublicensees

have filed, sought or obtained in the prior twelve (12)-month period, and any

they reasonably expect to make, seek or attempt to obtain in the following

twelve (12)-month period. In addition, ABX (or its Sublicensee) shall provide

IMMUNOGEN with prompt written notice of the occurrence of any event giving rise

to an obligation to make a milestone payment to IMMUNOGEN under Section 4.2, and

shall provide IMMUNOGEN with prompt written notice of the occurrence of the

First Commercial Sale of any particular Licensed Product.

3.2.2 ADVERSE EVENTS. In addition to such reports, ABX agrees to

provide IMMUNOGEN with Adverse Event information relating to Licensed Products

(but not relating to any other products of ABX) as compiled by ABX in the normal

course of business in connection with the Development, commercialization or sale

of any Licensed Product, within time frames consistent with IMMUNOGEN's

reporting obligations under applicable laws and regulations. IMMUNOGEN agrees to

provide ABX with Adverse Event information relating to any product containing

any May Compound (but not any other products of IMMUNOGEN or such Third Party)

that is compiled by IMMUNOGEN or any Third Party in the normal course of

business in connection with the development, commercialization or sale of any

such product, within time frames consistent with ABX's reporting obligations

under applicable laws and regulations.

3.2.3 CONFIDENTIAL INFORMATION. All reports, updates, Adverse

Event and other information provided by one Party to the other Party under this

Agreement (including under this Section 3), shall be considered Confidential

Information of the disclosing Party, subject to the terms of Section 5.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

10

<PAGE> 70

3.3 TECHNICAL ASSISTANCE BY IMMUNOGEN. In connection with the

nonexclusive grant of rights to ABX under Section 2.1 above, and subject to the

other terms of this Agreement, IMMUNOGEN shall provide ABX such information and

materials comprising the IMMUNOGEN Background Technology and/or Licensed Patent

Rights as ABX may reasonably request. Without limiting the generality of the

foregoing, IMMUNOGEN shall provide all of such technical assistance within

IMMUNOGEN's area of expertise concerning the Development and commercialization

of Licensed Products as may be reasonably requested by ABX from time to time

during the Term, provided that such technical assistance and expertise is within

the scope of the IMMUNOGEN Background Technology and/or Licensed Patent Rights

covered under this Agreement. Such technical assistance and expertise shall

include, but not be limited to, visits by IMMUNOGEN personnel to ABX and visits

by ABX personnel to IMMUNOGEN, at ABX's expense, at such times and for such

periods of time as may be reasonably acceptable to the Parties. Additionally, at

the reasonable request of ABX, IMMUNOGEN shall transfer all applicable IMMUNOGEN

Background Technology, and provide such technical assistance, to such Third

Party collaborator, sublicensee or contract manufacturer as ABX designates.

3.4 JOINT PROCESS DEVELOPMENT COMMITTEE.

3.4.1 MANDATE AND ESTABLISHMENT OF COMMITTEE. The Joint Process

Development Committee ("JPDC") formed pursuant to the Option and License

Agreement, shall serve as a forum for coordination and communication between the

Parties with respect to Development (to the extent ABX requests the assistance

or services of IMMUNOGEN) of manufacturing processes applicable to any May

Compound or Licensed Product covered by this Agreement (including, without

limitation, all process science and process development work, formulation work,

and quality control/assurance work hereunder), to assist ABX in its exercise of

its rights to make or have made Licensed Products under this Agreement. The

input of the IMMUNOGEN representatives on the JPDC shall be reasonably

considered by the JPDC; provided, however, that, all decisions of the JPDC shall

be subject to the final approval of ABX.

3.4.2 CHAIR OF COMMITTEE; MEETINGS. The chair of the JPDC shall

be one of the ABX representatives on the JPDC, as designated by ABX. All

decisions of the JPDC shall be subject to the approval of ABX. The JPDC shall

meet on a semi-annual basis or other schedule agreed upon by the Parties, unless

at least thirty (30) days in advance of any meeting there is a determination by

the Chair of the JPDC that no new business or other activity has transpired

since the previous meeting, and that there is no need for a meeting. In such

instance, the next JPDC meeting shall also be scheduled as agreed upon by the

Parties. The location of such meetings shall alternate between IMMUNOGEN's

offices in the Cambridge, Massachusetts metropolitan area and ABX's offices in

the Fremont, California metropolitan area unless otherwise agreed upon between

the Parties. As agreed upon by the Parties, JPDC meetings may be face-to-face

meetings or may be conducted through teleconferences and/or videoconferences. In

addition to its JPDC representatives, each Party shall be entitled to have such

additional number (as the Parties mutually agree) of other employees attend such

meetings to present and participate, though not in a decision-making capacity.

Each Party shall bear all costs and expenses, including travel and lodging

expense, that may be incurred by its JPDC representatives

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

11

<PAGE> 71

or other of its attendees at JPDC meetings. Minutes of each JPDC meeting will be

transcribed and issued to the members of the JPDC by the Chair within thirty

(30) days after each meeting and shall be reviewed and modified as mutually

required to obtain approval promptly thereafter.

3.5 SUPPLY OF PRECLINICAL MATERIALS. In the event that, during the

Term of this Agreement, ABX desires IMMUNOGEN to supply ABX with quantities of

Preclinical Materials in order to conduct all pre-clinical Development

activities relating to Licensed Products, ABX shall provide IMMUNOGEN with

written notice of same and the Parties shall negotiate in good faith and execute

a supply agreement providing for such supply. IMMUNOGEN shall deliver all

ordered amounts in accordance with advance ordering timeframes and delivery

timeframes to be agreed upon by the Parties through such mutually acceptable

written supply agreement for such purpose. In connection with any ordering of

Preclinical Materials by ABX, IMMUNOGEN shall provide ABX promptly with

IMMUNOGEN's good faith estimate of the Fully Burdened Manufacturing Cost for

manufacture and supply of such Preclinical Materials. IMMUNOGEN's price to

supply Preclinical Materials to ABX shall equal [______] of IMMUNOGEN's Fully

Burdened Manufacturing Cost for such Preclinical Materials as approved by ABX.

Nothing herein shall preclude ABX from making its own arrangements for

manufacture and supply of Preclinical Materials on its own or with Third

Parties. ABX hereby agrees that (a) it shall not use the Preclinical Materials

in any human subject, and (b) it shall use the Preclinical Materials in

compliance with all applicable federal, state and local laws and regulations.

3.6 SUPPLY OF CLINICAL MATERIALS. In the event that, during the Term

of this Agreement, IMMUNOGEN desires to supply ABX with quantities of Clinical

Materials in order to conduct all human clinical trials of Licensed Products

through the conclusion of Phase II Clinical Studies, ABX shall provide IMMUNOGEN

with written notice of same and the Parties shall negotiate in good faith and

execute a supply agreement providing for such supply. IMMUNOGEN shall deliver

all ordered amounts in accordance with forecasting parameters, advance ordering

timeframes and delivery timeframes to be agreed upon by the Parties such

mutually acceptable written supply agreement for such purpose. In connection

with any ordering of Clinical Materials by ABX, IMMUNOGEN shall provide ABX

promptly with IMMUNOGEN's good faith estimate of the Fully Burdened

Manufacturing Cost for manufacture and supply of such Clinical Materials.

IMMUNOGEN's price to supply Clinical Materials to ABX shall equal [_______] of

IMMUNOGEN's Fully Burdened Manufacturing Cost for such Clinical Materials as

approved by ABX. Nothing herein shall preclude ABX from making its own

arrangements for manufacture and supply of Clinical Materials on its own or with

Third Parties. ABX hereby agrees that it shall use the Clinical Materials in

compliance with all applicable federal, state and local laws. IMMUNOGEN shall

provide ABX with all information, filings and assistance regarding manufacturing

as reasonably requested by ABX in connection with applications for Regulatory

Approvals.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

12

<PAGE> 72

4. PAYMENTS AND ROYALTIES

4.1 LICENSE FEE. Within thirty (30) days after the Effective Date,

ABX shall pay to IMMUNOGEN the nonrefundable, noncreditable license fee of

[_________________ ____________________].

4.2 MILESTONE PAYMENTS FOR LICENSED PRODUCTS.

4.2.1 MILESTONES. ABX will make the following nonrefundable,

noncreditable payments to IMMUNOGEN within thirty (30) days after the first

achievement of each of the milestones set forth below:

Milestone Milestone Payment

(a) [__________________________] [________________]

(b) [__________________________] [________________]

(c) [__________________________] [________________]

(d) [__________________________] [________________]

(e) [__________________________] [________________]

(f) [__________________________] [________________]

(g) [__________________________] [________________]

4.2.2 If the milestone described in [________] is [___________

___________] of the milestone described [_____________], then [__________] to

IMMUNOGEN hereunder of the milestone payment described [____________], [_______

_________________________________________] of the milestone payment described in

[_______________].

4.2.3 It is hereby acknowledged and agreed that any milestone

payment shall be made only once, with respect to the first achievement of the

relevant milestone for the first Licensed Product, regardless of how many times

such milestones are achieved by Licensed Products and regardless of how many

times a particular Licensed Product achieves such milestones. ABX shall notify

IMMUNOGEN of the achievement of milestones hereunder as provided in Section

3.2.1 above.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

13

<PAGE> 73

4.3 PAYMENT OF ROYALTIES; ROYALTY RATES; ACCOUNTING FOR ROYALTIES AND

RECORDS.

4.3.1 ROYALTY PAYMENTS.

(a) In consideration of the grant of the license by

IMMUNOGEN hereunder, and subject to the other terms of this Agreement (including

the remainder of this Section 4), commencing on the first date of First

Commercial Sale of each Licensed Product in such country or jurisdiction in the

Territory, ABX shall pay to IMMUNOGEN the following royalties based on total Net

Sales of each Licensed Product sold by ABX and/or its Affiliates, on an

incremental basis in each calendar year during the Term, at the following rates:

For Net Sales of Licensed Product Royalty Rate

in any Calendar Year During the Term: (% of Net Sales)

------------------------------------ ----------------

[_________________] [_____]

[_________________] [_____]

(b) In consideration of the grant of the license by

IMMUNOGEN hereunder, and subject to the other terms of this Agreement (including

the remainder of this Section 4), commencing on the first date of First

Commercial Sale of each Licensed Product in such country or jurisdiction in the

Territory, ABX shall pay to IMMUNOGEN the following royalties based on total Net

Sales of each Licensed Product sold by each Sublicensee, on an incremental basis

in each calendar year during the Term, at a rate equal to

[__________________________________________________________________ ________] in

consideration for the grant of the sublicense under the Licensed Patents and

IMMUNOGEN Background Technology; provided, however, that the royalty rate under

this Section 4.3.1(b) for any royalty period shall not be (i) less than

[______________________ ___________________________________], or (ii) more than

[_________________________ _____________________________________].

4.3.2 [______________________]. Notwithstanding anything set

forth in Section 4.3.1 above, [_______] set forth therein shall apply,

[_________________________ ______________________________], to [_______] of

[______________________________ ____________] or

[__________________________________] would, [___________________

___________________________________________________________] (excluding any [___

______________________________________________]). Subject to the other terms of

this Agreement, [__________________________________________________________]

where and as of when [____________] under Section 4.3.1 [_____________________]

this Section 4.3.2, [_________________] a

[_______________________________________] set forth in Section 4.3.1 for

[______] of [___________________________].

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

14

<PAGE> 74

4.3.3 [________________]. In the event that in any royalty

period, [______], in order to [__________________________________] of this

Agreement [_______ _______] , is [________________________] to

[_____________________ ("_____________ ________] ") (a) to

[________________________________] in the [_____________] the [____

_____________] of a [_________________________________________________________

_________] and/or (b) to [_______________________________________] to the [_____

______________________________________] to [__________], in the [___________]

the [______________________] to [__________________] to an [___________] as part

of a [____________________________________](as evidenced, to the

[_____________________ ___________], by [___________________]), then

[____________] the [_____] to [_________

________________________________________________________________] for [________

_____________] by [_____________] of [__________________]. Notwithstanding the

foregoing, such [____________________________________] for [______________] in

[_____ __________] to [____________________________________________] of

[__________ __________] in [____________].

4.3.4 [________________]. In determining [_______]of any

[________________] under this Agreement, [________]shall first [_________] in

accordance with the definition of "Net Sales" above, then [________] by

[___________] of the [________ _______________] in the [________________],

[____________________________________

____________________________________________________________________________] of

the [__________]. The [___________________] of the [______________] shall be for

a [_______________] to that [_____________________________] and of the

[______________ _________]. When [__________________] is [_______] for the

[________________, _____ ____________________] a [___________________] for the

[_________________, _________ ____________] of [_________________] as are then

[_________] to all [_________________ __________________________] and having an

[___________________]; provided, however, that if

[____________________________________________], the Parties shall [___________

_________________________________________] and [______________________________

_______________________].

4.3.5 [______________________________________]. If IMMUNOGEN

[______________] or [_________________] a [_____] to a

____________________________________________ [_____] for a

[__________________________________________], then the [__________] set forth in

this Section 4.3 that are [________] as a

[______________________________________________ ________________________].

4.4 ONE ROYALTY. Only one royalty, calculated at the highest

applicable royalty rate under this Section 4, shall be payable to IMMUNOGEN

hereunder for each sale of a Licensed Product.

4.5 ROYALTY TERM. ABX shall pay royalties with respect to each

Licensed Product on a country-by-country and Licensed Product-by-Licensed

Product basis until [______ ___] (a) the [_________________] of [_____________]

of [_____________________________ ___________________________], or (b)

[_______________________] of the [____________

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

15

<PAGE> 75

_____] of [______________] in [_________]. Following such royalty term, ABX

shall have a fully paid-up, irrevocable, freely transferable and sublicensable

license in such country under the relevant Licensed Patent Rights and IMMUNOGEN

Background Technology, to research, develop, make, have made, use, have used,

sell, offer for sale, have sold, import and have imported Licensed Products for

any and all uses within the Field in such country.

4.6 PAYMENT TERMS.

4.6.1 PAYMENT OF MILESTONES; PAYMENT OF ROYALTIES; ROYALTY

REPORTS. ABX shall make any milestone payments owed to IMMUNOGEN hereunder in

United States Dollars, using the wire transfer provisions of this Section 4.6.

ABX shall make any royalty payments owed to IMMUNOGEN in United States Dollars,

[__________________________ __________________________________________] for

which such royalties accrue (as provided in the next sentence), using the wire

transfer provisions of this Section 4.6. For purposes of determining when a sale

of any Licensed Product occurs under this Agreement, royalties shall accrue on

the date of the invoice to the purchaser of the Licensed Product. Each royalty

payment shall be accompanied by a report for each country in the Territory in

which sales of Licensed Products occurred in the calendar quarter covered by

such statement, specifying: the gross sales (if available) and Net Sales in each

country's currency; the applicable royalty rate under this Agreement; the

royalties payable in each country's currency, including an accounting of

deductions taken in the calculation of Net Sales; the applicable exchange rate

to convert from each country's currency to United States Dollars under this

Section 4.6; and the royalties payable in United States Dollars.

4.6.2 FOREIGN CURRENCY EXCHANGE. All royalties shall be payable

in full in the United States in United States Dollars, regardless of the

countries in which sales are made. For the purpose of computing Net Sales for

Licensed Products sold in any currency other than United States Dollars, the

quarterly royalty payment will be calculated as follows:

(A/B) x C = United States Dollars royalty payment on foreign current

sales, where A = foreign "Net Sales" (as defined above) per quarter; B

= foreign exchange conversion rate, expressed in local currency per

United States Dollar (using as the applicable foreign exchange rate

the rate published in the western edition of The Wall Street Journal,

under the heading "Money Rates," or any other mutually agreed upon

source, for the last business day of the calendar quarter); and C =

the royalty rate applicable to such Net Sales under this Agreement.

4.6.3 TAX WITHHOLDING; RESTRICTIONS ON PAYMENT. All payments

hereunder shall be made free and clear of any taxes, duties, levies, fees or

charges, except for withholding taxes (to the extent applicable). ABX shall make

any applicable withholding payments due on behalf of IMMUNOGEN and shall

promptly provide IMMUNOGEN with such written documentation of any such payment

as available to ABX relating to an application by IMMUNOGEN for a foreign tax

credit for such payment with the United States Internal Revenue Service. If by

law, regulations or fiscal policy of a particular country in the Territory,

remittance of royalties in United States Dollars is restricted or forbidden,

written notice thereof shall

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

16

<PAGE> 76

promptly be given to IMMUNOGEN, and payment of the royalty shall be made by the

deposit thereof in local currency to the credit of IMMUNOGEN in a recognized

banking institution reasonably designated by IMMUNOGEN by written notice to ABX.

When in any country in the Territory the law or regulations prohibit both the

transmittal and the deposit of royalties on sales in such country, royalty

payments shall be suspended for as long as such prohibition is in effect and as

soon as such prohibition ceases to be in effect, all royalties that ABX would

have been under an obligation to transmit or deposit but for the prohibition

shall forthwith be deposited or transmitted, to the extent allowable.

4.6.4 WIRE TRANSFERS. All payments hereunder shall be made to

IMMUNOGEN by bank wire transfer in immediately available funds to the account

designated by IMMUNOGEN by written notice to ABX from time to time.

4.7 RECORDS RETENTION; REVIEW.

4.7.1 ROYALTIES. Commencing as of the date of First Commercial

Sale of the first Licensed Product, ABX and its Sublicensees shall keep for at

least [___________] from the end of the calendar year to which they pertain

complete and accurate records of sales by ABX or its Sublicensees, as the case

may be, of each Licensed Product, in sufficient detail to allow the accuracy of

the royalties to be confirmed.

4.7.2 FULLY BURDENED MANUFACTURING COSTS. Commencing as of the

Effective Date, IMMUNOGEN shall keep for at least [_________] following the end

of the calendar year to which they pertain complete and accurate records of all

of IMMUNOGEN's Fully Burdened Manufacturing Costs for Preclinical Materials and

Clinical Materials supplied to ABX (or its Sublicensee) hereunder, in sufficient

detail to allow the accuracy of the Fully Burdened Manufacturing Costs to be

confirmed.

4.7.3 REVIEW. Subject to the other terms of this Section 4.7.3,

at the request of either Party, upon at least thirty (30) days' prior written

notice from the requesting Party, and at the expense of the requesting Party

(except as otherwise provided herein), the other Party shall permit an

independent certified public accountant of nationally recognized standing

reasonably selected by the requesting Party and reasonably acceptable to the

other Party to inspect (during regular business hours) the relevant records

required to be maintained by the other Party under this Section 4.7. At

IMMUNOGEN's request (which shall not be made more frequently than once per year

during the Term), the accountant shall be entitled to review the then-preceding

[_______] of ABX's records under this Section 4.7 for purposes of verifying

ABX's royalty calculations. At ABX's request (which shall not be made more

frequently than once per year during the Term), the accountant shall be entitled

to review the then-preceding [__________] of IMMUNOGEN's records under this

Section 4.7 for purposes of verifying IMMUNOGEN's Fully Burdened Manufacturing

Cost calculations. In every case the accountant must have previously entered

into a confidentiality agreement with both Parties substantially similar to the

provisions of Section 5 and limiting the disclosure and use of such information

by such accountant to authorized representatives of the Parties and the purposes

germane to this Section 4.7. Such accountant shall report to the Parties only

whether or not such calculations are

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

17

<PAGE> 77

correct and the amount of any discrepancy. No other information shall be shared.

Results of any such review shall be binding on both Parties absent manifest

error. Each Party agrees to treat the results of any such accountant's review of

the other Party's records under this Section 4.7 as Confidential Information of

the other Party subject to the terms of Section 5. If any review reveals a

deficiency in the calculation of royalties resulting from any underpayment by

ABX, ABX shall promptly pay IMMUNOGEN the amount remaining to be paid, and if

such underpayment is by [______________] or more, ABX shall pay the reasonable

out-of-pocket costs and expenses of the review. If any review reveals a

deficiency in the calculation of Fully Burdened Manufacturing Costs resulting

from any overpayment by ABX, IMMUNOGEN shall promptly refund ABX the amount of

any such overpayment, and if such overpayment is by [___ ____________] or more,

IMMUNOGEN shall pay the reasonable out-of-pocket costs and expenses of the

review.

5. TREATMENT OF CONFIDENTIAL INFORMATION

5.1 CONFIDENTIAL INFORMATION. During the Term of this Agreement, each

Party may disclose to the other Party confidential information, including but

not limited to IMMUNOGEN Background Technology, Research Inventions, Research

Data and Research Materials. Such information of the disclosing Party hereunder,

if so identified in writing by the disclosing Party to the receiving Party

either pursuant to this Section 5.1 or otherwise upon disclosure to the

receiving Party, shall be "Confidential Information" of the disclosing Party.

During the Term of this Agreement and during the term of any License Agreement,

and for a period of five (5) years thereafter, except as expressly permitted

hereunder, the receiving Party shall keep confidential all such Confidential

Information of the other Party and will not disclose such Confidential

Information of the other Party to Third Parties by publication or otherwise.

Each Party further agrees not to use Confidential Information of the other Party

for any purpose other than conducting research hereunder or exercising any

rights granted to it or reserved by it hereunder. Upon any termination or

expiration of this Agreement, upon request, a Party shall return to a requesting

Party all copies of any of such requesting Party's Confidential Information

which is not the subject of a License Agreement or the grant of a license

hereunder, provided that it may retain one copy for its legal files.

Notwithstanding the foregoing, it is understood and agreed that the receiving

Party's obligations of confidentiality and nonuse herein shall not apply to any

information which:

(a) is, at the time of disclosure by the disclosing Party

hereunder, or thereafter becomes, a part of the public domain or publicly known

or available through no fault or negligence of the receiving Party or any of its

Affiliates; or

(b) was otherwise in the receiving Party's lawful possession

prior to disclosure by the disclosing Party, other than under an obligation of

confidentiality; or

(c) was independently discovered or developed by the receiving

Party or any of its Affiliates, without use of the other Party's Confidential

Information, as can be demonstrated by competent proof; or

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

18

<PAGE> 78

(d) is lawfully disclosed to the receiving Party or any of its

Affiliates on a non-confidential basis by a third party who is not in violation

of an obligation of confidentiality to the disclosing Party relative to such

information.

Each Party may disclose information to the extent such disclosure is

reasonably necessary in (i) filing and prosecuting patent applications and

maintaining patents, or (ii) filing, prosecuting or defending litigation or

(iii) complying with applicable laws, regulations or court orders; provided,

however, that if a Party is required to make any such disclosure of the other

Party's Confidential Information or the terms of this Agreement, it will give

reasonable advance notice to the other Party of such disclosure requirement and

will use reasonable efforts to assist such other Party in efforts to secure

confidential treatment of such information required to be disclosed.

5.2 PUBLICITY. A Party may not use the name of the other Party in any

publicity or advertising and, except as provided in Section 5.1, may not issue a

press release or otherwise publicize or disclose any information related to the

other Party's activities under this Agreement or the terms or conditions hereof,

without the prior written consent of the other Party. Prior to execution of this

Agreement, the parties have agreed upon the substance of information that can be

used to describe the terms and conditions of this Agreement, and each party may

disclose such information, as modified by mutual written agreement the parties,

without the consent of the other party. Once any written statement is approved

for disclosure by both Parties, either Party may make subsequent public

disclosures of the contents of such statement without the further approval of

the other Party. Nothing in the foregoing, however, shall prohibit a Party from

making such disclosures to the extent deemed necessary under applicable federal

or state securities laws or any rule or regulation of any nationally recognized

securities exchange; provided, however, that such party shall provide written

notice thereof to the other party, consult with the other party with respect to

such disclosure and provide the other party sufficient opportunity to comment on

or object to any such disclosure or to request confidential treatment thereof.

6. PROVISIONS CONCERNING THE FILING, PROSECUTION AND

MAINTENANCE OF PATENT RIGHTS

6.1 PATENT FILING, PROSECUTION AND MAINTENANCE. Subject to the other

terms of this Section 6.1, IMMUNOGEN shall have the right to prepare, file,

prosecute, obtain and maintain, at its sole cost and expense, all Licensed

Patent Rights. Any such preparation, filing, prosecution and maintenance shall

be conducted with commercially reasonable diligence by IMMUNOGEN, using patent

counsel selected by IMMUNOGEN and reasonably acceptable to ABX. IMMUNOGEN (i)

will provide ABX with a copy of any proposed patent application within Licensed

Patent Rights for review and comment reasonably in advance of filing (which

shall under no circumstances be in excess of thirty (30) days), and (ii) will

keep ABX reasonably informed of the status of such filing, prosecution and

maintenance, including, without limitation, (A) by providing ABX with copies of

all communications received from or filed in patent office(s) with respect to

such filing, and (B) by providing ABX, a reasonable time prior to taking or

failing to take any action that would affect the scope or validity of any such

of any such filing

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

19

<PAGE> 79

(including the substantially narrowing, cancellation or abandonment of any

claim(s) without retaining the right to pursue such subject matter in a separate

application, or the failure to file or perfect the filing of any claim(s) in any

country), with prior written notice of such proposed action or inaction so that

ABX has a reasonable opportunity to review and comment. [______ __________] for

[______] of [_________________________________________________ ______] with

respect to [________________] shall be [______________________________

________]. If IMMUNOGEN fails to undertake the filing(s) of any patent

application or submission with respect to any invention under such Licensed

Patent Rights, then not less than ninety (90) days prior to the last date for

making the applicable filing or submission to preserve rights under such patent

application, ABX may undertake such filing(s) at its own expense, in which case

IMMUNOGEN will assign to ABX all of its rights to such patent application and

invention and any subsequently issued patent thereon, each of which thereafter

will be owned solely by ABX.

6.2 NOTICE OF INFRINGEMENT. If, during the Term of this Agreement,

either Party learns of any actual, alleged or threatened infringement by a Third

Party of any Licensed Patent Rights under this Agreement, such Party shall

promptly notify the other Party and shall provide such other Party with

available evidence of such infringement.

6.3 INFRINGEMENT OF PATENT RIGHTS. IMMUNOGEN shall have the first

right (but not the obligation), at its own expense and with legal counsel of its

own choice, to bring suit (or take other appropriate legal action) against any

actual, alleged or threatened infringement of the Licensed Patent Rights caused

by the research, development, manufacture, use, offer for sale, sale or import

of Licensed Products. ABX shall have the right, at its own expense, to be

represented in any such action by IMMUNOGEN by counsel of ABX's own choice;

provided, however, that under no circumstances shall the foregoing affect the

right of IMMUNOGEN to control the suit as described in the first sentence of

this Section 6.3. If IMMUNOGEN does not file any action or proceeding against

such infringement within one hundred twenty (120) days after the later of (i)

IMMUNOGEN's notice to ABX under Section 6.2 above, (ii) ABX's notice to

IMMUNOGEN under Section 6.2 above, or (iii) a written request from ABX to take

action with respect to such infringement, then ABX shall have the right (but not

the obligation), at its own expense, to bring suit (or take other appropriate

legal action) against such actual, alleged or threatened infringement, with

legal counsel of its own choice. Any damages, monetary awards or other amounts

recovered, whether by judgment or settlement, pursuant to any suit, proceeding

or other legal action taken under this Section 6.3, shall applied as follows:

6.3.1 First, to reimburse the Parties for their respective costs

and expenses (including reasonable attorneys' fees and costs) incurred in

prosecuting such enforcement action;

6.3.2 Second, [_________________________________] associated with

[_________________] and to [_________________________________________] based on

[_______________]

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

20

<PAGE> 80

6.3.3 Third, any amounts remaining shall be allocated as follows:

(a) if IMMUNOGEN is the Party bringing such suit or proceeding or taking such

other legal action, [_________________________], (b) if ABX is the Party

bringing such suit or proceeding or taking such other legal action,

[______________________], and (c) if the suit is brought jointly,

[________________________].

If a Party brings any such action or proceeding hereunder, the other Party

agrees to be joined as party plaintiff if necessary to prosecute such action or

proceeding, and to give the Party bringing such action or proceeding reasonable

assistance and authority to file and prosecute the suit; provided, however, that

neither Party shall be required to transfer any right, title or interest in or

to any property to the other Party or any Third Party to confer standing on a

Party hereunder.

6.4 THIRD PARTY PATENTS. If any Third Party claims that a patent it

owns or controls claims any aspect of a Licensed Product or its manufacture, use

or sale, the Party with notice of such claim shall notify the other Party

promptly, and the Parties shall as soon as practicable thereafter discuss in

good faith regarding a response.

6.5 TRADEMARKS. All Licensed Products shall be sold under one (1) or

more trademarks and tradenames selected by ABX (or its Sublicensee) in the

Territory. IMMUNOGEN shall notify ABX promptly upon learning of any actual,

alleged or threatened infringement of a trademark or tradename applicable to a

Licensed Product in the Territory, or of any unfair trade practices, trade dress

imitation, passing off of counterfeit goods, or like offenses in the Territory.

All of the costs, expenses and legal fees in bringing, maintaining and

prosecuting any action to maintain, protect or defend any trademarks or

tradenames owned by ABX (or its Sublicensee) hereunder, and any damages or other

recovery, shall be ABX's (or its Sublicensee's) sole responsibility, and taken

in its sole discretion.

7. TERM AND TERMINATION

7.1 TERM; EXPIRATION. The term of this Agreement shall expire upon the

expiration of the final royalty payment obligation under Section 4.5 above. Upon

such expiration of the Term of this Agreement, ABX shall have a fully paid-up,

irrevocable, freely transferable and sublicensable license in such country under

the relevant Licensed Patent Rights and IMMUNOGEN Background Technology, to

research, develop, make, have made, use, have used, sell, offer for sale, have

sold, import and have imported Licensed Products, for any and all uses within

the Field in the Territory.

7.2 TERMINATION. Subject to the other terms of this Agreement:

7.2.1 BREACH. This Agreement and the rights and options granted

herein may be terminated by either Party upon any material breach by the other

Party of any material obligation or condition, effective [____________] after

giving written notice to the breaching Party of such termination in the case of

a payment breach and [_____________] after giving written notice to the

breaching Party of such termination in the case of any other breach, which

notice shall describe such breach in reasonable detail. The foregoing

notwithstanding, if such

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

21

<PAGE> 81

default or breach is cured or shown to be non-existent within the aforesaid

[______] or [_____ ______] period, the notice shall be automatically withdrawn

and of no effect. However, prior to giving any notice for breach, the Parties

shall first attempt to resolve any disputes as to the existence of any breach as

set forth in Section 8.14.

7.2.2 UNILATERAL TERMINATION BY ABX. ABX, in its sole discretion,

at any time may terminate this Agreement, and the rights and obligations

hereunder, or may remove any Licensed Product and the licenses related thereto

from operation of this Agreement, in any case effective [_____________] after

written notice thereof to IMMUNOGEN. In the event of any termination under this

Section 7.2.2 only as to a Licensed Product, the consequences set forth in

Section 7.3 below relating to termination of the Agreement under this Section

7.2.2 shall apply only with respect to such terminated Licensed Product, and

this Agreement and the rights and obligations hereunder shall continue in full

force and effect as to any and all other Licensed Products.

7.3 EFFECTS OF TERMINATION.

7.3.1 Upon any termination of this Agreement by IMMUNOGEN under

Section 7.2.1 or by ABX under Section 7.2.2, as of the effective date of

such termination, all relevant licenses and sublicenses granted by

IMMUNOGEN to ABX hereunder shall terminate automatically. Notwithstanding

the foregoing, (a) no such termination of this Agreement shall be construed

as a termination of any valid sublicense of any Sublicensee hereunder, and

thereafter each such Sublicensee shall be considered a direct licensee of

IMMUNOGEN, provided that (i) such Sublicensee is then in full compliance

with all terms and conditions of its sublicense, (ii) all accrued payments

obligations to IMMUNOGEN have been paid, and (iii) such Sublicensee agrees

in writing to assume all applicable obligations of ABX under this

Agreement, and (b) ABX and its Sublicensees shall have the right, for

[__________] or such longer time period (if any) on which the Parties

mutually agree in writing, to sell or otherwise dispose of all Licensed

Products then on hand, with royalties to be paid to IMMUNOGEN on all Net

Sales of such Licensed Products as provided for in this Agreement. Nothing

set forth in this Section 7 or any other provision of this Agreement shall

entitle IMMUNOGEN to any ownership interest in, or to any license under or

other rights with respect to (including any rights to use or request any

transfer to IMMUNOGEN or any Third Party), any Confidential Information of

ABX or any Technology or Patent Rights owned by ABX under this Agreement.

7.3.2 Upon any termination of this Agreement by ABX under Section

7.2.1, as of the effective date of such termination, ABX thereafter

automatically shall have a fully sublicensable, fully paid up (subject to

the remainder of this Section 7.3.2), nonexclusive license in the Territory

under the Licensed Patent Rights and IMMUNOGEN Background Technology, to

research, develop, make, have made, use, have used, sell, offer for sale,

have sold, import and have imported Licensed Products, for any and all uses

within the Field in the Territory, provided that ABX shall pay, for the

remainder of the royalty term under Section 4.5 above, in lieu of any

payments including milestones or royalties it would otherwise owe to

IMMUNOGEN under this Agreement, a royalty equal to [______________________

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

22

<PAGE> 82

________________________] with respect to the Licensed Product under Section 4

of this Agreement.

7.4 REMEDIES. Except as otherwise expressly set forth in this

Agreement, the termination provisions of this Section 7 are in addition to any

other relief and remedies available to either Party at law.

7.5 SURVIVING PROVISIONS. Notwithstanding any provision herein to the

contrary, the rights and obligations of the Parties set forth in Sections 4.7,

5, 6, 7.3, 7.4, 8.3, 8.4, 8.7, 8.14, 8.16, 8.17, 8.18 and 8.19 hereof, as well

as any rights or obligations otherwise accrued hereunder (including any accrued

payment obligations), shall survive the expiration or termination of the Term of

this Agreement. Without limiting the generality of the foregoing, ABX shall have

no obligation to make any milestone or royalty payment to IMMUNOGEN that has not

accrued prior to the effective date of any termination of this Agreement, but

shall remain liable for all such payment obligations accruing prior to the

effective date of such termination.

8. MISCELLANEOUS

8.1 IMMUNOGEN REPRESENTATIONS. IMMUNOGEN represents and warrants to

ABX that: (a) the execution and delivery of this Agreement and the performance

of the transactions contemplated hereby have been duly authorized by all

appropriate IMMUNOGEN corporate action; (b) this Agreement is a legal and valid

obligation binding upon IMMUNOGEN and enforceable in accordance with its terms,

and the execution, delivery and performance of this Agreement by the Parties

does not conflict with any agreement, instrument or understanding to which

IMMUNOGEN is a party or by which it is bound; (c) IMMUNOGEN has the full right

and legal capacity to grant the rights to ABX pursuant to Section 2 above

without violating the rights of any Third Party; (d) IMMUNOGEN is the sole owner

or exclusive licensee of the IMMUNOGEN Background Technology; (e) IMMUNOGEN is

not aware of any Third Party patent, patent application or other intellectual

property rights that would be infringed (i) by practicing any process or method

or by making, using or selling any composition which is claimed or disclosed in,

or which constitutes, IMMUNOGEN Background Technology, or (ii) by making, using,

offering for sale, selling or importing Licensed Products; and (f) IMMUNOGEN is

not aware of any infringement or misappropriation by a Third Party of the

IMMUNOGEN Background Technology.

8.2 ABX REPRESENTATIONS. ABX represents and warrants to IMMUNOGEN

that: (a) the execution and delivery of this Agreement and the performance of

the transactions contemplated hereby have been duly authorized by all

appropriate ABX corporate action; (b) this Agreement is a legal and valid

obligation binding upon ABX and enforceable in accordance with its terms, and

the execution, delivery and performance of this Agreement by the Parties does

not conflict with any agreement, instrument or understanding to which ABX is a

party of or by which it is bound; and (c) ABX has the full right and legal

capacity to grant the rights to IMMUNOGEN pursuant to Section 2 above without

violating the rights of any Third Party.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

23

<PAGE> 83

8.3 NO WARRANTIES.

8.3.1 Nothing in this Agreement is or shall be construed as:

(a) a warranty or representation by either Party as to the

validity or scope of any patent application or patent licensed hereunder;

(b) a warranty or representation that anything made, used,

sold or otherwise disposed of under any license granted pursuant to this

Agreement is or will be free from infringement of patents, copyrights, and other

rights of third parties.

8.3.2 Except as expressly set forth in this Agreement, NEITHER

PARTY MAKES ANY REPRESENTATION OR EXTENDS ANY WARRANTIES OF ANY KIND, EITHER

EXPRESS OR IMPLIED. THERE ARE NO EXPRESS OR IMPLIED WARRANTIES OF

MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, OR OF NON-INFRINGEMENT OF

ANY PATENT, COPYRIGHT, TRADEMARK, OR OTHER RIGHTS OF THIRD PARTIES, OR ANY OTHER

EXPRESS OR IMPLIED WARRANTIES.

8.4 [______]. NOTWITHSTANDING ANYTHING ELSE IN THIS AGREEMENT OR

OTHERWISE, [________________] WILL BE __________ [_________________] TO

[__________________] OF THIS AGREEMENT [___________________________

_________________________________________________] OR [_________________] FOR

(I) [___________________________________________________________________] OR

[____________________] OR (II) [____________________________________________

__________________________.

8.5 NOTICES. Any notices, requests, deliveries, approvals or consents

required or permitted to be given under this Agreement to ABX or IMMUNOGEN shall

be in writing and shall be effective on receipt when delivered to the applicable

address specified below (or to such other address as may be specified in writing

to the other Party hereto):

If to IMMUNOGEN: IMMUNOGEN, Inc.

128 Sidney Street

Cambridge, MA 02139

Attn: Chief Executive Officer

With a copy to: Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.

One Financial Center

Boston, MA 02111

Attn: Jeffrey M. Wiesen, Esq

Telecopy: 617-542-2241

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

24

<PAGE> 84

If to ABX: Abgenix, Inc.

7601 Dumbarton Circle

Fremont, California 94555

Attn: President

With a copy to: Gray Cary Ware & Freidenrich LLP

4365 Executive Drive, Suite 1600

San Diego, California 92121-2189

Attn: Mark R. Wicker

8.6 GOVERNING LAW. This Agreement will be construed, interpreted and

applied in accordance with the laws of the Commonwealth of Massachusetts

(excluding its body of law controlling conflicts of law).

8.7 LIMITATIONS. Except as set forth elsewhere in this Agreement,

neither Party grants to the other Party any right or license to any of its

intellectual property.

8.8 ENTIRE AGREEMENT. This is the entire Agreement between the Parties

with respect to the subject matter hereof and supersedes all prior

representations, understandings and agreements between the Parties with respect

to the subject matter hereof. No modification shall be effective unless in

writing with specific reference to this Agreement and signed by the Parties.

8.9 WAIVER. The terms or conditions of this Agreement may be waived

only by a written instrument executed by the Party waiving compliance. The

failure of either Party at any time or times to require performance of any

provision hereof shall in no manner affect its rights at a later time to enforce

the same. No waiver by either Party of any condition or term shall be deemed as

a continuing waiver of such condition or term or of another condition or term.

8.10 HEADINGS. Section and subsection headings are inserted for

convenience of reference only and do not form part of this Agreement.

8.11 ASSIGNMENT. Neither this Agreement nor any right or obligation

hereunder may be assigned, delegated or otherwise transferred , in whole or

part, by either party without the prior express written consent of the other;

provided, however, that either party may, without the written consent of the

other, assign this Agreement and its rights and delegate its obligations

hereunder to its Affiliates, or in connection with the transfer or sale of all

or substantially all of such party's assets or business related to this

Agreement, or in the event of its merger, consolidation, change in control or

similar transaction. Any permitted assignee shall assume all obligations of its

assignor under this Agreement. Any purported assignment in violation of this

Section 8.11 shall be void. The terms and conditions of this Agreement shall be

binding upon and inure to the benefit of the permitted successors and assigns of

the parties.

8.12 FORCE MAJEURE. Neither Party shall be liable for failure of or

delay in performing obligations set forth in this Agreement, and neither shall

be deemed in breach of its obligations, if such failure or delay is due to

natural disasters or any causes beyond the

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

25

<PAGE> 85

reasonable control of such Party. In event of such force majeure, the Party

affected thereby shall use reasonable efforts to cure or overcome the same and

resume performance of its obligations hereunder.

8.13 CONSTRUCTION. The Parties hereto acknowledge and agree that: (i)

each Party and its counsel reviewed and negotiated the terms and provisions of

this Agreement and have contributed to its revision; (ii) the rule of

construction to the effect that any ambiguities are resolved against the

drafting Party shall not be employed in the interpretation of this Agreement;

and (iii) the terms and provisions of this Agreement shall be construed fairly

as to all Parties hereto and not in favor of or against any Party, regardless of

which Party was generally responsible for the preparation of this Agreement.

8.14 DISPUTES.

8.14.1 The Parties recognize that a bona fide dispute as to

certain matters may from time to time arise during the term of this Agreement

which relates to either Party's rights and/or obligations hereunder. In the

event of the occurrence of such a dispute, either Party may, by written notice

to the other Party, have such dispute referred to their respective senior

officials designated below or their successors, for attempted resolution by good

faith negotiations within thirty (30) days after such notice is received. Said

designated senior officials are as follows:

For ABX: Chief Executive Officer

For IMMUNOGEN: Chief Executive Officer

In the event the designated senior officials are not able to resolve

such dispute within the thirty (30) day period, either Party may invoke the

provisions of Section 8.14.2.

8.14.2 Any dispute, controversy or claim initiated by either

Party arising out of, resulting from or relating to this Agreement, or the

performance by either Party of its obligations under this Agreement (other than

bona fide third party actions or proceedings filed or instituted in an action or

proceeding by a Third Party against a Party), whether before or after

termination of this Agreement, shall be finally resolved by binding arbitration.

Whenever a Party shall decide to institute arbitration proceedings, it shall

give written notice to that effect to the other Party. Any such arbitration

shall be conducted under the Commercial Arbitration Rules of the American

Arbitration Association by a panel of three arbitrators appointed in accordance

with such rules. Any such arbitration shall be held in Boston, Massachusetts if

initiated by ABX, and in San Francisco, California if initiated by IMMUNOGEN.

The method and manner of discovery in any such arbitration proceeding shall be

governed by California Code of Civil Procedure ss. 1282 ET SEQ. (including

without limitation California Code of Civil Procedure ss. 1283.05). The

arbitrators shall have the authority to grant specific performance and to

allocate between the parties the costs of arbitration in such equitable manner

as they determine. Judgment upon the award so rendered may be entered in any

court having jurisdiction or application may be made to such court for judicial

acceptance of any award and an order of

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

26

<PAGE> 86

enforcement, as the case may be. In no event shall a demand for arbitration be

made after the date when institution of a legal or equitable proceeding based

upon such claim, dispute or other matter in question would be barred by the

applicable statute of limitations. Notwithstanding the foregoing, either Party

shall have the right, without waiving any right or remedy available to such

Party under this Agreement or otherwise, to seek and obtain from any court of

competent jurisdiction any interim or provisional relief that is necessary or

desirable to protect the rights or property of such Party, pending the selection

of the arbitrators hereunder or pending the arbitrators' determination of any

dispute, controversy or claim hereunder.

8.15 SEVERABILITY. If any provision(s) of this Agreement are or become

invalid, are ruled illegal by any court of competent jurisdiction or are deemed

unenforceable under then current applicable law from time to time in effect

during the Term hereof, it is the intention of the Parties that the remainder of

this Agreement shall not be affected thereby provided that a Party's rights

under this Agreement are not materially affected. The Parties hereto covenant

and agree to renegotiate any such term, covenant or application thereof in good

faith in order to provide a reasonably acceptable alternative to the term,

covenant or condition of this Agreement or the application thereof that is

invalid, illegal or unenforceable, it being the intent of the Parties that the

basic purposes of this Agreement are to be effectuated.

8.16 STATUS. Nothing in this Agreement is intended or shall be deemed

to constitute a partner, agency, employer-employee, or joint venture

relationship between the Parties.

8.17 INDEMNIFICATION.

8.17.1 ABX Indemnity. ABX shall [______________] and [________

___________________________________________ __________________] and [_____] and

[___________________________________] (the "Indemnitees") [____________________

______________________] (including [___________________] and [______________])

[_________] or [_______________________], or [________], in connection with

[__________ ______________________________________], including, without

limitation, [____________ _______________________] (but

[__________________________________________ ________], which are

[_______________]), to the extent arising out of (i) [_____________

_______________] in the [_____________________________________________________

___________________________] of [_______________(____________________)

_______________________________________] under this Agreement, (ii)

[_____________] of this Agreement [______], or (iii)

[___________________________] of the [________], in any [______] under this

Section 8.17.1 except to [_______________________________] therefor under

Section 8.17.2 below.

8.17.2 IMMUNOGEN INDEMNITY. Subject to Section 8.17.1 above,

IMMUNOGEN shall indemnify, defend and hold harmless ABX, its Affiliates and

their respective directors, officers, employees, and agents, and their

respective successors, heirs and assigns (also the "Indemnitees"), from and

against any liability, damage, loss or expense (including reasonable attorneys'

fees and expenses of litigation) incurred by or imposed upon

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

27

<PAGE> 87

such Indemnitees, or any of them, in connection with any Third Party claims,

suits, actions, demands or judgments, including, without limitation, personal

injury and product liability matters (but excluding any patent, trademark or

tradename infringement matters, which are governed by Section 6 above), to the

extent arising out of (i) any actions or omissions of IMMUNOGEN or subcontractor

of IMMUNOGEN in the development, testing, production, manufacture or supply of

any Licensed Product (or any component thereof) manufactured and supplied by

IMMUNOGEN or any subcontractor of IMMUNOGEN under this Agreement, (ii) any

material breach of this Agreement by IMMUNOGEN, or (iii) gross negligence or

willful misconduct on the part of IMMUNOGEN.

8.18 INDEMNIFICATION PROCEDURES. In the event that any Indemnitee is

seeking indemnification under Section 8.17 above from a Party (the "Indemnifying

Party"), the other Party shall notify the Indemnifying Party of such claim with

respect to such Indemnitee as soon as reasonably practicable after the

Indemnitee receives notice of the claim, and the Party (on behalf of itself and

such Indemnitee) shall permit the Indemnifying Party to assume direction and

control of the defense of the claim (including the right to settle the claim

solely for monetary consideration) and shall cooperate as requested (at the

expense of the Indemnifying Party) in the defense of the claim. The

indemnification obligations under Section 8.17 shall not apply to amounts paid

in settlement of any claim, demand, action or other proceeding if such

settlement is effected without the consent of the Indemnifying Party, which

consent shall not be withheld or delayed unreasonably. The Indemnitee, its

employees and agents, shall reasonably cooperate with the Indemnifying Party and

its legal representatives in the investigation of any claim, demand, action or

other proceeding covered by Section 8.17.

8.19 SECTION 365(n). All licenses granted under this Agreement are

deemed to be, for purposes of Section 365(n) of the U.S. Bankruptcy Code,

licenses of right to "intellectual property" as defined in Section 101 of such

Code. The Parties agree that the licensee may fully exercise all of its rights

and elections under the U.S. Bankruptcy Code, regardless of whether either Party

files for bankruptcy in the United States or other jurisdiction. The Parties

further agree that, in the event a licensee elects to retain its rights as a

licensee under such Code, the licensee shall be entitled to complete access to

any technology licensed to it hereunder and all embodiments of such technology.

Such embodiments of the technology shall be delivered to the licensee not later

than:

8.19.1 the commencement of bankruptcy proceedings against the

licensor, upon written request, unless the licensor elects to perform its

obligations under the Agreement, or

8.19.2 if not delivered under Section 8.19.1 above, upon the

rejection of this Agreement by or on behalf of the licensor, upon written

request.

8.20 FURTHER ASSURANCES. Each Party agrees to execute, acknowledge and

deliver such further instructions, and to do all such other acts, as may be

necessary or appropriate in order to carry out the purposes and intent of this

Agreement.

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

28

<PAGE> 88

8.21 COUNTERPARTS. This Agreement may be executed simultaneously in

one or more counterparts, each of which shall be deemed an original, but all of

which together shall constitute one and the same instrument.

8.22 [__________________].

8.22.1 If [_____________________________] or [___________] to a

[_____________] a [__________] under the [_________________] or

[_________________ ____________________] to

[____________________________________________________

_______________________________________________________].

8.22.2 If the [______________________] of [___________________]

are [___________ (________)] to [___________] than the [_____________________]

hereunder are to [___________________________] in the [______________________

_____________________________________________] of [________________________

_______] after [_______] of any [__________], if [_____________________________]

of [________], the [______________________] of this Agreement shall be

[_________________] to [_____] to [____________________________]. If

[____________________] as set forth in this Section 8.22.2 [_________________],

then [_____________] in accordance with this Section 8.22 with respect to a

[______________________] shall [___________].

8.22.3 If [___________________] that the [______________________]

of [____________________] are [______________(_____________)] than the

[___________ _________________] are to [____], then

[___________________________________________ _____] an

[______________________(____________] and [_______________] to [__________] and

[_____________________________________________] as may be reasonably requested

[______________]) to have [________] and [__________________ ______] at

[____________________________________] and to [________] whether such

[_________________________________________] are [___________(_____________])

than the [_____________________________] are to [____] (without disclosing to

[___] the [__________] or [__________________________] of

[____________________]). In the event of [____________________________] as to

[______________________________________ ______ (_____________)], then

[_____________] shall be [_________________________ ______________].

IN WITNESS WHEREOF, the Parties have caused this Agreement to be executed

by their duly authorized representative in two (2) originals.

ABGENIX, INC. IMMUNOGEN, INC.

By: ______________________________ By: ______________________________

Title: ___________________________ Title: ___________________________

Portions of this Exhibit were omitted and have been filed separately with the

Secretary of the Commission pursuant to the Company's application requesting

confidential treatment under Rule 24b-2 of the Securities Exchange Act.

29

<PAGE> 89

SCHEDULE I

LICENSED PATENT RIGHTS

[_________________________________]

<TABLE>

<CAPTION>

- ---------------------------------------------------------------------------------------------------------------------------------

Attorney Country Appl. No. Filing Date Priority Date Patent No. Issue Date Exp. Date

Reference No.

- ---------------------------------------------------------------------------------------------------------------------------------

<S> <C> <C> <C> <C> <C> <C> <C>

[________] [________] [________] [________] [________]

- ---------------------------------------------------------------------------------------------------------------------------------

[________] [________] [________] [________] [________] [________] [________] [________]

- ---------------------------------------------------------------------------------------------------------------------------------

[________] [________] [________] [________] [________] [________] [________] [________]

- ---------------------------------------------------------------------------------------------------------------------------------

[________] [________]* [________] [________] [________] [________] [_______] [______]

- ---------------------------------------------------------------------------------------------------------------------------------

*[________]

- ---------------------------------------------------------------------------------------------------------------------------------

[________] [________] [________] [________] [________] [________]

- ---------------------------------------------------------------------------------------------------------------------------------

[________] [________] [________] [________] [________] [________]

- ---------------------------------------------------------------------------------------------------------------------------------

[________________________________________________________________________]

- ---------------------------------------------------------------------------------------------------------------------------------

Attorney Country Appl. No. Filing Date Priority Date Patent No. Issue Date Exp. Date

Reference No.

- ---------------------------------------------------------------------------------------------------------------------------------

[________] [________]

[________] [________] [________]

- ---------------------------------------------------------------------------------------------------------------------------------

[-------------------------]

- ---------------------------------------------------------------------------------------------------------------------------------

Attorney Country Appl. No. Filing Date Priority Date Patent No. Issue Date Exp. Date

Reference No.

- ---------------------------------------------------------------------------------------------------------------------------------

[________]

[________] [________] [________] [________]

- ---------------------------------------------------------------------------------------------------------------------------------

</TABLE>