Exhibit 10.15

PROPRIETARY INFORMATION, INVENTIONS, AND COMPETITION AGREEMENT

AGREEMENT, dated this 30th day of November 2006, by and between ImmunoGen, Inc.,
a Massachusetts corporation having its principal place of business at 128 Sidney
Street, Cambridge, Massachusetts 02139 (the “Company”), and Mitchel Sayare, an
individual residing at 2 Avery Street, Suite 27c, Boston, MA 02111 (“Employee”).

WITNESSETH:

WHEREAS, the Employee has been hired by the Company to perform certain services;
and

WHEREAS, the Employee may be exposed, have access to, create or make
contributions to the Proprietary Information as defined below and/or inventions
of the Company;

NOW, THEREFORE, in consideration for the Company’s employment of the Employee,
and for other good and valuable consideration the receipt and sufficiency of
which is hereby acknowledged, the parties covenant and agree as follows:

1.             Acknowledgements. The Employee understands and acknowledges that:

(a)           As part of his/her services as an employee of the Company, he/she
may be exposed or have access to, or make new contributions and inventions of
value to, the past, present and future business, products, operations and
policies of the Company.

(b)           His/Her position as an employee creates a relationship of
confidence and trust between the Employee and the Company with respect to (i)
information which is related or applicable to the Company’s Field of Interest
(as defined in 1(c) below) and the manner in which the Company engages in
business in such Field of Interest, and (ii) information which is related or
applicable to the business of the Company or any client, customer, joint venture
or other person with which the Company has a business relationship, (a ”Business
Associate”), any of which information has been or may be made known to the
Employee by the Company (including, without limitation, any member of the
Company’s Scientific Advisory Board) or by any Business Associate of the
Company, or any of which has been otherwise learned by the Employee as a result
of or in connection with his/her service as an employee of the Company.

(c)           The Company possesses and will continue to possess information
that has been created by, discovered by, developed by or otherwise become known
to the Company (including, without limitation, information created, discovered,
developed or made known by the Employee related to or arising out of his/her
service as an employee of the Company) and/or in which property rights have been
assigned or otherwise conveyed to the Company, which information has commercial
value to its business interests and/or in the Field of Interest in which the
Company is presently engaged or will be engaged.  The term “Field of Interest”
shall mean the development of products based on monoclonal antibodies or other
biological molecules capable of binding to specific tissue, or the conjugation
of monoclonal antibodies or other biological molecules capable of binding to
specific tissue with other substances, for use in the treatment, diagnosis or
prevention of cancer and/or other diseases.  During an individual’s employment,
the term “Field of Interest” may be expanded from time to time to include such
other areas of therapy,

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diagnosis or prevention as may be designated by the Company. All of the
aforementioned information is hereinafter called “Proprietary Information.” By
way of illustration, but not limitation, formulas, data, know-how, improvements,
inventions, techniques, marketing plans, strategies, forecasts, and customer
lists are Proprietary Information.

2.             Proprietary Information.

(a)           All Proprietary Information shall be the sole property of the
Company and its successors and assigns, and the Company and its successors and
assigns shall be the sole owner of all patents and other rights in connection
therewith. The Employee hereby assigns to the Company any rights he/she may have
or acquire in such Proprietary Information, and agrees to take such action and
sign such documents from time to time as the Company reasonably requires to
effect or confirm such assignment.

(b)           At all times, both during the term of this Agreement and
thereafter until such information becomes known to the public, the Employee
will, subject to the provisions of Section 3 hereof regarding publication, keep
in confidence and trust all Proprietary Information and any other confidential
information of the Company, and he/she will not use or disclose any Proprietary
Information or anything relating to it without the prior written consent of the
Company, except as may be necessary in the ordinary course of performing his/her
duties as an employee of the Company or as required by law; provided that if
disclosure is required by law, the Employee agrees to provide the Company with
written notice of such disclosure obligation prior to making such disclosure and
no more than two (2) days after the Employee learns of such disclosure
requirement.

(c)           All documents, records, apparatus, equipment and other physical
property, whether or not pertaining to Proprietary Information, furnished to the
Employee by the Company or produced by the Employee or others in connection with
the Employee’s services hereunder shall be and remain the sole property of the
Company. The Employee will return and deliver such property to the Company as
and when requested by the Company. Should the Company not so request at an
earlier time, the Employee shall return and deliver all such property upon
termination of his/her service as an employee to the Company for any reason, and
the Employee will not take with him/her any such property or any reproduction of
such property upon such termination.

3.             Inventions.

(a)           The Employee will promptly disclose to the Company, or any persons
designated by it, all improvements, inventions, formulas, processes, techniques,
know-how and data, whether or not patentable, made or conceived or reduced to
practice or learned by him/her, either alone or jointly with others, related to
or arising out of his/her position as an employee or which are related to or
useful in the business of the Company, or result from tasks which have been or
may be assigned to the Employee by the Company or result from use of premises
owned, leased or contracted for by the Company (all said improvements,
inventions, formulas, processes, techniques, know-how and data being hereinafter
collectively called “Inventions”).

(b)           The Employee agrees that all Inventions shall be the sole property
of the Company and its assigns, and the Company and its assigns shall be the
sole owner of all patents and other rights in connection therewith. The Employee
hereby assigns to the Company any rights he/she may have or acquire in such
Inventions. The Employee further agrees as to

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all such Inventions to assist the Company in every reasonable manner (but at the
Company’s expense) to obtain, and from time to time enforce, patents on said
Inventions in any and all countries, and to that end the Employee will execute
all documents for use in applying for and obtaining such patents thereon and
enforcing the same, as the Company may desire, together with any assignments
thereof to the Company or persons designated by it. The Employee’s obligation to
assist the Company in obtaining and enforcing patents for such Inventions in any
and all countries shall continue beyond the termination of his/her employment by
the Company, but the Company shall compensate the Employee at a reasonable rate
after such termination for time actually spent by him/her at the Company’s
request on such assistance. In the event that the Company is unable for any
reason whatsoever to secure the Employee’s signature to any lawful and necessary
documents required to apply for or execute any patent application with respect
to such an Invention (including renewals, extensions, continuations, divisions
or continuations in part thereof), the Employee hereby irrevocably designates
and appoints the Company and its duly authorized officers and agents, as his/her
agents and attorneys-in-fact to act for and on his/her behalf and instead of
him/her, to execute and file any such application and to do all other lawfully
permitted acts to further the prosecution and issuance of patents thereon with
the same legal force and effect as if executed by the Employee, and such power
of attorney created hereby is coupled with an interest.

4.             Competition.  While the Employee is employed by the Company and
for a period of twelve (12) months following the termination of the Employee’s
employment (the “Noncompetition Period”), regardless of the reason for such
termination, the Employee shall not, for himself/herself or on behalf of any
other person or entity, directly or indirectly, whether as principal, partner,
agent, independent contractor, stockholder, employee, consultant, representative
or in any other capacity, own, manage, operate or control, be concerned or
connected with, or employed by, or otherwise associate in any manner with,
engage in or have a financial interest in any business that is engaged in the
Field of Interest, anywhere in the world, except that nothing in this Agreement
shall preclude the Employee from (a) purchasing or owning securities of any such
business if such securities are publicly traded, and provided that the
Employee’s holdings do not exceed three (3%) percent of the issued and
outstanding securities of any class of securities of such business; or (b)
working for any academic or government institutions.  For the purposes of this
paragraph only, following termination of the Executive’s employment, the term
“Field of Interest” shall be limited to mean the development of products based
on the conjugation of monoclonal antibodies or other biological molecules
capable of binding to specific tissue with other substances, for use in the
treatment, diagnosis or prevention of cancer and/or other diseases.

5.             Solicitation of Employees.  During the Noncompetition Period the
Employee shall not, either individually or on behalf of or through any third
party, directly or indirectly (a) entice, solicit or encourage any director,
employee or consultant to leave the Company, or (b) be involved for any entity
other than the Company in the recruitment, engagement, or hiring of any Company
director or employee.  This section shall prohibit the aforesaid activities by
the Employee with respect to any person both while such person is a director,
employee or consultant of the Company and for thirty (30) days thereafter.

6.             Publications.  The Employee agrees to consult with the Company
prior to publishing (in writing or by seminar, lecture or other oral
presentation) any material relating to his/her activities that relate to the
Company’s Field of Interest, and to furnish copies of any such publication
(written or oral) to the Company for prior clearance at least sixty (60) days
prior to the proposed publication. The Company agrees to review such submissions
and to apply for patents as promptly as practicable so as to avoid or keep to a
minimum any delay in publishing material of scientific importance.

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7.             Prior Work and Legal Obligations

(a)           By signing this Agreement, the Employee represents that she/he has
no agreement with or other legal obligation to any prior employer or any other
person or entity that restricts his/her ability to engage in employment
discussions, to accept employment with, or to perform any function for the
Company.

(b)           The Employee also acknowledges that the Company has advised the
Employee that at no time, either during any pre-employment discussions or at any
time thereafter, should the Employee divulge to or use for the benefit of the
Company any trade secret or confidential or proprietary information of any
previous employer.  By signing this Agreement, the Employee affirms that she/he
has not divulged or used any such information for the benefit of the Company,
and that she/he has not and will not misappropriate any proprietary information
of a former employer that the Employee played any part in creating while working
for such former employer.

8.             Provisions Necessary and Reasonable/Injunctive Relief The
Employee specifically agrees that the provisions of Sections 1-5 of this
Agreement are necessary and reasonable to protect the Company’s Proprietary
Information, goodwill and business interests.  The Employee acknowledges that
given his/her skills and work experience, such restrictions will not prevent the
Employee from earning a living in his/her general field of occupation during the
term of such restrictions.  The Employee further agrees that a breach or
threatened breach by the Employee of Sections 1-5 of this Agreement would pose
the risk of irreparable harm to the Company, and that in the event of a breach
or threatened breach of any of such covenants, without posting any bond or
security, the Company shall be entitled to seek and obtain equitable relief, in
the form of specific performance, or temporary, preliminary or permanent
injunctive relief, or any other equitable remedy which then may be available. 
The seeking of such injunction or order shall not affect the Company’s right to
seek and obtain damages or other equitable relief on account of any such actual
or threatened breach.

9.             Disclosure to Future and Prospective Employers.  The Employee
agrees that so long as this Agreement is effective the Employee will notify
his/her employers of this Agreement and that the Company may notify any of the
Employee’s future or prospective employers or other third parties of this
Agreement and may provide a copy of this Agreement to such parties without the
Employee’s further consent.

10.           Transfer, Promotion or Reassignment.  The Employee acknowledges
and agrees that if she/he should transfer between or among any affiliates of the
Company or be promoted or reassigned to functions other than the Employee’s
present functions, all terms of this Agreement shall continue to apply with full
force.

11.           Severability.  The parties intend this Agreement to be enforced as
written.  However, if any portion or provision of this Agreement shall to any
extent be declared illegal or unenforceable by a duly authorized court having
jurisdiction, both parties desire that such portion or provision be modified by
such a court so as to make it enforceable (“blue-penciled”), and that the
remainder of this Agreement be enforced to the fullest extent permitted by law. 
In the event that such court deems any provision of this Agreement wholly
unenforceable, then all remaining provisions shall nevertheless remain in full
force and effect.

12.           Notices.  Except as otherwise specifically provided herein, any
notice required or permitted by this Agreement shall be in writing and shall be
delivered as follows with notice deemed given as indicated: (i) by personal
delivery when delivered personally; (ii) by overnight courier upon written

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verification of receipt; (iii) by telecopy or facsimile transmission upon
acknowledgment of receipt of electronic transmission; or (iv) by certified or
registered mail, return receipt requested, upon verification of receipt. 
Notices to Employee shall be sent to the last known address in the Company’s
records or such other address as Employee may specify in writing.  Notices to
the Company shall be sent to the Company’s Chairman or to such other Company
representative as the Company may specify in writing.

13.           Binding Effect.  The Agreement will be binding upon and inure to
the benefit of (a) the heirs, executors and legal representatives of the
Employee upon the Employee’s death and (b) any successor of the Company.  Any
such successor of the Company will be deemed substituted for the Company under
the terms of the Agreement for all purposes.  For this purpose, “successor”
means any person, firm, corporation or other business entity which at any time,
whether by purchase, merger or otherwise, directly or indirectly acquires all or
substantially all of the assets or business of the Company.  The Employee’s
obligations hereunder shall survive the termination of the Employee’s employment
by the Company, regardless of the reason for such termination.

14.           Waivers. No waivers, express or implied, of any breach of this
agreement shall be held or construed as a waiver of any other breach of the same
or any other covenant, agreement or duty hereunder.

15.           Governing Law.  This agreement shall be construed and enforced in
accordance with the law of the Commonwealth of Massachusetts, without giving
effect to conflict of law principles.  This agreement represents the entire
agreement of the parties with respect to the subject matter hereof, and may only
be amended or modified by a written instrument signed by the parties.

16.           Meaning of Headings.  The headings in this Agreement are for
convenience only, and both parties agree that they shall not be construed or
interpreted to modify or affect the construction or interpretation of any
provision of this Agreement.

 

IN WITNESS WHEREOF, the parties have executed this Agreement as of the date
first above written.

 

IMMUNOGEN, INC.

 

 

 

 

 

 

 

 

Daniel M. Junius

 

 

Chief Financial Officer and

 

 

Executive Vice President, Finance

 

 

 

 

 

 

 

 

 

 

 

Employee Signature

 

 

 

 

 

Date:

 

 

 

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