Exhibit 10.1

EXECUTION COPY

SECURITIES PURCHASE AGREEMENT

This Securities Purchase Agreement (this “Agreement”) is dated as of June 20, 2008, between ImmunoGen, Inc., a Massachusetts corporation (the “Company”), and Ziff Asset Management, L.P., a Delaware limited partnership (the “Purchaser”).

WHEREAS, subject to the terms and conditions set forth in this Agreement and pursuant to an effective registration statement under the Securities Act (as defined below), the Company desires to issue and sell to the Purchaser, and the Purchaser desires to purchase from the Company, securities of the Company as more fully described in this Agreement; and

WHEREAS, the parties hereto are concurrently entering into a registration rights agreement in the form of Exhibit A hereto (the “Registration Rights Agreement”) pursuant to which the Company shall register the Shares (as defined below) for resale by the Purchaser upon the terms and subject to the conditions set forth therein.

NOW, THEREFORE, IN CONSIDERATION of the mutual covenants contained in this Agreement, and for other good and valuable consideration the receipt and adequacy of which are hereby acknowledged, the Company and the Purchaser agree as follows:

ARTICLE I.

DEFINITIONS

1.1           Definitions.  In addition to the terms defined elsewhere in this Agreement, for all purposes of this Agreement, the following terms have the meanings set forth in this Section 1.1:

“Action” shall have the meaning ascribed to such term in Section 3.1(j).

“Affiliate” means any Person that, directly or indirectly through one or more intermediaries, controls or is controlled by or is under common control with a Person as such terms are used in and construed under Rule 405 under the Securities Act.

“Board of Directors” means the board of directors of the Company.

“Business Day” means any day except any Saturday, any Sunday, any day which is a federal legal holiday in the United States or any day on which banking institutions in the State of New York are authorized or required by law or other governmental action to close.

“Closing” means the closing of the purchase and sale of the Shares pursuant to Section 2.1.

“Closing Date” means the date hereof.

“Commission” means the United States Securities and Exchange Commission or any other federal agency at the time administering the Securities Act.

“Common Stock” means the common stock of the Company, par value $0.01 per

share, any class of common stock of the Company hereafter created, and any other class of securities into which such Common Stock may hereafter be reclassified or changed into.

“Common Stock Equivalents” means any securities of the Company or the Subsidiaries which would entitle the holder thereof to acquire at any time Common Stock, including, without limitation, any debt, preferred stock, rights, options, warrants or other instrument that is at any time convertible into or exercisable or exchangeable for, or otherwise entitles the holder thereof to receive, Common Stock.

“Company Counsel” means Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., with offices located at One Financial Center, Boston, MA 02111.

“Disclosure Schedules” means the Disclosure Schedules of the Company delivered concurrently herewith.

“Evaluation Date” shall have the meaning ascribed to such term in Section 3.1(r).

“Exchange Act” means the Securities Exchange Act of 1934, as amended, and the rules and regulations promulgated thereunder.

“FDA” shall have the meaning ascribed to such term in Section 3.1(gg).

“FDCA” shall have the meaning ascribed to such term in Section 3.1(gg).

“GAAP” shall have the meaning ascribed to such term in Section 3.1(h).

“Indebtedness” means (a) any liabilities for borrowed money or amounts owed in excess of $50,000 (other than trade accounts payable incurred in the ordinary course of business), (b) all guaranties, endorsements and other contingent obligations in respect of indebtedness of others, whether or not the same are or should be reflected in the Company’s balance sheet (or the notes thereto), except guaranties by endorsement of negotiable instruments for deposit or collection or similar transactions in the ordinary course of business; and (c) the present value of any lease payments in excess of $50,000 due under leases required to be capitalized in accordance with GAAP.

“Intellectual Property Rights” shall have the meaning ascribed to such term in Section 3.1(o).

“Lien” means any lien, claim, pledge, charge, security interest, encumbrance, right of first refusal, preemptive right or other restriction.

“Lock-up Agreements” shall have the meaning ascribed to such term in Section 2.2(a)(iii).

“Losses” shall have the meaning ascribed to such term in Section 4.7.

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“Material Adverse Effect” shall have the meaning ascribed to such term in Section 3.1(b).

“Material Permits” shall have the meaning ascribed to such term in Section 3.1(m).

“Person” means an individual or corporation, partnership, trust, incorporated or unincorporated association, joint venture, limited liability company, joint stock company, government (or an agency or subdivision thereof) or other entity of any kind.

“Pharmaceutical Product” shall have the meaning ascribed to such term in Section 3.1(gg).

“Prospectus” means the final prospectus filed as a part of the Registration Statement.

“Prospectus Supplement” means the supplement to the Prospectus complying with Rule 424(b) of the Securities Act that is filed with the Commission with respect to the transactions contemplated hereby.

“Purchase Price” means $25,000,000.

“Purchaser Party” shall have the meaning ascribed to such term in Section 4.7.

“Registration Rights Agreement” shall have the meaning set forth in the recitals of this Agreement.

“Registration Statement” means the effective registration statement with Commission file No. 333-144488 which registers the sale of the Shares to the Purchaser.

“Required Approvals” shall have the meaning ascribed to such term in Section 3.1(e).

“Rule 144” means Rule 144 promulgated by the Commission pursuant to the Securities Act, as such Rule may be amended from time to time, or any similar rule or regulation hereafter adopted by the Commission having substantially the same effect as such Rule.

“SEC Reports” shall have the meaning ascribed to such term in Section 3.1(h).

“Securities Act” means the Securities Act of 1933, as amended, and the rules and regulations promulgated thereunder.

“Shares” means 7,812,500 shares of Common Stock to be issued to the Purchaser pursuant to this Agreement.

“Short Sales” means all “short sales” as defined in Rule 200 of Regulation SHO under the Exchange Act and all types of direct and indirect stock pledges, forward sale

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contracts, options, puts, calls, short sales, swaps and similar arrangements (including on a total return basis), and sales and other transactions through non-U.S. broker-dealers or foreign regulated brokers.

“Subsidiary” means any subsidiary of the Company as set forth on Schedule 3.1(a) , which shall include any direct or indirect subsidiary of the Company formed or acquired after the date hereof.

“Trading Day” means a day on which the Nasdaq Global Market is open for trading.

“Trading Market” means any of the following markets or exchanges on which the Common Stock is then listed or quoted for trading on the date in question: the American Stock Exchange, the Nasdaq Capital Market, the Nasdaq Global Market, the Nasdaq Global Select Market, the New York Stock Exchange or the OTC Bulletin Board.

“Transaction Documents” means this Agreement, the Registration Rights Agreement, the Lock-up Agreements and any other documents or agreements executed in connection with the transactions contemplated hereunder.

“Transfer Agent” means Mellon Investor Service LLC, the current transfer agent of the Company, with a mailing address of 111 Founders Plaza, Suite 1100, East Hartford, CT 06108 and a facsimile number of ###-###-#### and any successor transfer agent of the Company.

ARTICLE II.
PURCHASE AND SALE

2.1           Closing.  On the Closing Date, upon the terms and subject to the conditions set forth herein, substantially concurrent with the execution and delivery of this Agreement by the parties hereto, the Company agrees to sell, and the Purchaser agrees to purchase the Shares.  The Purchaser shall deliver to the Company, via wire transfer, immediately available funds equal to the Purchase Price and the Company shall deliver to the Purchaser the Shares, and the Company and the Purchaser shall deliver the other items set forth in Section 2.2 deliverable at the Closing.  Upon satisfaction of the covenants and conditions set forth in Sections 2.2 and 2.3, the Closing shall occur at the offices of Fried, Frank, Harris, Shriver & Jacobson LLP, One New York Plaza, New York, NY 10004 or such other location as the parties shall mutually agree.

2.2           Closing Deliveries.

(a)           On or prior to the Closing Date, the Company shall deliver or cause to be delivered to the Purchaser the following:

(i)            this Agreement duly executed by the Company;

(ii)           the Registration Rights Agreement duly executed by the Company;

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(iii)          lock-up agreements in substantially the form attached hereto as Exhibit B duly executed by the Company and each of the Persons listed in Exhibit C (collectively, the “Lock-up Agreements”)

(iv)          a legal opinion of Company Counsel, substantially in the form of Exhibit D attached hereto;

(v)           a legal opinion of the Company’s General Counsel, substantially in the form of Exhibit E attached hereto;

(vi)          a copy of the irrevocable instructions to the Company’s transfer agent instructing the transfer agent to deliver, via the Depository Trust Company Deposit Withdrawal Agent Commission System, the Shares to the Purchaser’s accounts, as directed by the Purchaser; and

(vii)         evidence of the approval for listing of the Shares on the Nasdaq Global Market.

(b)           On or prior to the Closing Date, the Purchaser shall deliver or cause to be delivered to the Company the following:

(i)            this Agreement duly executed by the Purchaser;

(ii)           the Registration Rights Agreement duly executed by the Purchaser; and

(iii)          the Purchase Price by wire transfer to the account specified in writing by the Company to the Purchaser at least three Business days prior to the Closing Date.

2.3           Closing Conditions.

(a)           The obligations of the Company hereunder in connection with the Closing are subject to the following conditions being met:

(i)            the accuracy in all material respects on the Closing Date of the representations and warranties of the Purchaser contained herein;

(ii)           all obligations, covenants and agreements of the Purchaser required to be performed at or prior to the Closing Date shall have been performed; and

(iii)          the delivery by the Purchaser of the items set forth in Section 2.2(b) of this Agreement.

(b)           The obligations of the Purchaser hereunder in connection with the Closing are subject to the following conditions being met:

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(i)            the accuracy in all material respects on the Closing Date of the representations and warranties of the Company contained herein;

(ii)           all obligations, covenants and agreements of the Company required to be performed at or prior to the Closing Date shall have been performed; and

(iii)          the delivery by the Company of the items set forth in Section 2.2(a) of this Agreement.

ARTICLE III.
REPRESENTATIONS AND WARRANTIES

3.1           Representations and Warranties of the Company.  Except as set forth in the Disclosure Schedules, which Disclosure Schedules shall be deemed a part hereof and shall qualify any representation or otherwise made herein to the extent of the disclosure contained in the corresponding section of the Disclosure Schedules, the Company hereby makes the following representations and warranties to the Purchaser as of the date of this Agreement, except for any representations and warranties made as of other dates set forth in such representations and warranties:

(a)           Subsidiaries.  All of the direct and indirect Subsidiaries of the Company are set forth on Schedule 3.1(a).  The Company owns, directly or indirectly, all of the capital stock or other equity interests of each Subsidiary free and clear of any Liens, and all of the issued and outstanding shares of capital stock of each Subsidiary are validly issued and are fully paid, non-assessable and free of preemptive and similar rights to subscribe for or purchase securities created by the certificate of incorporation, bylaws or other organizational or charter documents of such Subsidiaries or any agreement to which the Company or any Subsidiary is a party.

(b)           Organization and Qualification.  The Company and each of the Subsidiaries is an entity duly incorporated or otherwise organized, validly existing and in good standing under the laws of the jurisdiction of its incorporation or organization (as applicable), with the requisite power and authority to own and use its properties and assets and to carry on its business as currently conducted.  Neither the Company nor any Subsidiary is in violation or default of any of the provisions of its respective certificate or articles of incorporation, bylaws or other organizational or charter documents.  The Company and each of the Subsidiaries is duly qualified to conduct business and is in good standing as a foreign corporation or other entity in each jurisdiction in which the nature of the business conducted or property owned by it makes such qualification necessary, except where the failure to be so qualified or in good standing, as the case may be, could not, individually or in the aggregate, have or reasonably be expected to result in (i) a material adverse effect on the legality, validity or enforceability of any Transaction Document, (ii) a material adverse effect on the results of operations, assets, business, prospects or condition (financial or otherwise) of the Company and the Subsidiaries, taken as a whole, or (iii) a material adverse effect on the Company’s ability to perform in any material respect on a timely basis its obligations under any Transaction Document

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(any of (i), (ii) or (iii), a “Material Adverse Effect”) and no Action has been instituted in any such jurisdiction revoking, limiting or curtailing or seeking to revoke, limit or curtail such power and authority or qualification.  The Company has made available to the Purchaser, prior to the date of this Agreement, true and complete copies of the Amended and Restated Articles of Organization of the Company and the Amended and Restated Bylaws of the Company, in each case as in effect on the date of this Agreement.

(c)           Authorization; Enforcement.  The Company has the requisite corporate power and authority to enter into and to consummate the transactions contemplated by each of the Transaction Documents and otherwise to carry out its obligations hereunder and thereunder.  The execution and delivery of each of the Transaction Documents by the Company and the consummation by it of the transactions contemplated hereby and thereby have been duly authorized by all necessary action on the part of the Company and no further action is required by the Company, the Board of Directors or the Company’s stockholders in connection therewith other than in connection with the Required Approvals.  Each Transaction Document has been (or upon delivery will have been) duly executed by the Company and, when delivered in accordance with the terms hereof and thereof, will constitute the valid and binding obligation of the Company enforceable against the Company in accordance with its terms, except (i) as limited by general equitable principles and applicable bankruptcy, insolvency, reorganization, moratorium and other laws of general application affecting enforcement of creditors’ rights generally, (ii) as limited by laws relating to the availability of specific performance, injunctive relief or other equitable remedies and (iii) insofar as indemnification and contribution provisions may be limited by applicable law.

(d)           No Conflicts.  The execution, delivery and performance of the Transaction Documents by the Company, the issuance and sale of the Shares and the consummation by the Company of the other transactions contemplated hereby and thereby do not and will not (i) conflict with or violate any provision of the Company’s or any Subsidiary’s certificate or articles of incorporation, bylaws or other organizational or charter documents, or (ii) conflict with, or constitute a default (or an event that with notice or lapse of time or both would become a default) under, result in the creation of any Lien upon any of the properties or assets of the Company or any Subsidiary, or give to others any rights of termination, amendment, acceleration or cancellation (with or without notice, lapse of time or both) of, any note, bond, mortgage, indenture, deed of trust, license, lease, agreement, credit facility, debt (or other instrument evidencing a Company or Subsidiary debt or otherwise) or other instrument or understanding to which the Company or any Subsidiary is a party or by which any property or asset of the Company or any Subsidiary is bound or affected, or (iii) subject to obtaining the Required Approvals, conflict with or result in a violation of any law, rule, regulation, order, judgment, injunction, decree or other restriction of any court or governmental authority to which the Company or a Subsidiary is subject (including federal and state securities laws and regulations, and the regulations of any self-regulatory organization to which the Company or its Subsidiaries are subject), or by which any property or asset of the Company or a Subsidiary is bound or affected; except in the case of each of clauses (ii) and (iii), such as could not, individually or in the aggregate, have or reasonably be

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expected to result in a Material Adverse Effect.

(e)           Filings, Consents and Approvals.  The Company is not required to obtain any consent, waiver, authorization or order of, give any notice to, or make any filing or registration with, any court or other federal, state, local or other governmental authority or any other Person in connection with the execution, delivery and performance by the Company of the Transaction Documents, other than prior notification to NASDAQ of the issuance of the Shares, which the Company has given in a timely manner, and (i) the filing with the Commission of the Prospectus Supplement and (ii) such filings as are required to be made under applicable state securities laws (the filings required in clauses (i) and (ii), collectively, the “Required Approvals”).  Except for the Required Approvals, all consents, authorizations, orders, filings and registrations which the Company is required to obtain, and all notices, filings and registrations it is required to make, in connection with the transactions contemplated by each of the Transaction Documents have been obtained or effected or been timely made, on or prior to the Closing Date.

(f)            Issuance of the Shares; Registration.  The Shares are duly authorized and, when issued and paid for in accordance with the applicable Transaction Documents, will be duly and validly issued, fully paid and nonassessable, free and clear of all Liens (other than Liens created by the Purchaser).  The Company has prepared and filed the Registration Statement in conformity in all material respects with the requirements of the Securities Act, which became effective on August 13, 2007 (the “Effective Date”), including the Prospectus, and such amendments and supplements thereto as may have been required to the date of this Agreement.  The Registration Statement is effective under the Securities Act and no stop order preventing or suspending the effectiveness of the Registration Statement or suspending or preventing the use of the Prospectus has been issued by the Commission and no proceedings for that purpose have been instituted or, to the knowledge of the Company, are threatened by the Commission.  The Shares (i) have been registered pursuant to the Registration Statement, (ii) are being issued pursuant to the Registration Statement and (iii) are not “restricted securities” within the meaning of Rule 144.  Any certificate representing the Shares shall not contain any legend or other limitation on resale.  The Company proposes to file the Prospectus Supplement with the SEC pursuant to Rule 424(b).  At the time the Registration Statement and any amendments thereto became effective, at the date of this Agreement and at the Closing Date, the Registration Statement and any amendments thereto conformed and will conform in all material respects to the requirements of the Securities Act and did not and will not contain any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein not misleading; and the Prospectus and any amendments or supplements thereto, at the time the Prospectus or any amendment or supplement thereto was issued and at the Closing Date, conformed and will conform in all material respects to the requirements of the Securities Act and did not and will not contain an untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in light of the circumstances under which they were made, not misleading.

(g)           Capitalization.  The capitalization of the Company is as set forth on

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Schedule 3.1(g).  The Company has not issued any capital stock since its most recently filed periodic report under the Exchange Act, other than pursuant to the exercise of employee stock options, and the award of shares of Common Stock, under the Company’s stock incentive plans that were outstanding as of the date of the most recently filed periodic report under the Exchange Act and are reflected on Schedule 3.1(g).  No Person has any right of first refusal, preemptive right, right of participation, or any similar right to participate in the transactions contemplated by the Transaction Documents.  Except as set forth on Schedule 3.1(g), there are no outstanding options, warrants, scrip rights to subscribe to, calls or commitments of any character whatsoever relating to, or securities, rights or obligations convertible into or exercisable or exchangeable for, or giving any Person any right to subscribe for or acquire, any shares of Common Stock or Common Stock Equivalents, or contracts, commitments, understandings or arrangements by which the Company or any Subsidiary is or may become bound to issue additional shares of Common Stock or Common Stock Equivalents.  The issuance and sale of the Shares will not obligate the Company to issue shares of Common Stock or other securities to any Person and will not result in a right of any holder of Company securities to adjust the exercise, conversion, exchange or reset price under any of such securities.  All of the outstanding shares of capital stock of the Company are validly issued, fully paid and nonassessable, have been issued in compliance with all federal and state securities laws, and none of such outstanding shares was issued in violation of any preemptive rights or similar rights to subscribe for or purchase securities.  No further approval or authorization of any stockholder, the Board of Directors or others is required for the issuance and sale of the Shares.  There are no stockholders agreements, voting agreements, registration rights agreements or other similar agreements with respect to the Company’s capital stock to which the Company is a party or, to the knowledge of the Company, between or among any of the Company’s stockholders.

(h)           SEC Reports; Financial Statements.  The Company has filed or furnished all reports, schedules, forms, statements and other documents required to be filed or furnished by the Company under the Securities Act and the Exchange Act, including pursuant to Section 13(a) or 15(d) thereof, for the two years preceding the date hereof (the foregoing materials, including the exhibits thereto and documents incorporated by reference therein, together with the Prospectus and the Prospectus Supplement, being collectively referred to herein as the “SEC Reports”) on a timely basis.  As of their respective dates, the SEC Reports complied in all material respects with the requirements of the Securities Act and the Exchange Act, as applicable, and none of the SEC Reports, when filed or furnished, contained any untrue statement of a material fact or omitted to state a material fact required to be stated therein or necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading.  There are no outstanding comments from the Commission with respect to any SEC Report.  The Company does not have pending before the Commission any request for confidential treatment of information.  The financial statements of the Company included in the SEC Reports comply in all material respects with applicable accounting requirements and the rules and regulations of the Commission with respect thereto as in effect at the time of filing.  Such financial statements have been prepared in

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accordance with United States generally accepted accounting principles applied on a consistent basis during the periods involved (“GAAP”), except as may be otherwise specified in such financial statements or the notes thereto and except that unaudited financial statements may not contain all footnotes required by GAAP, and fairly present in all material respects the financial position of the Company and its consolidated Subsidiaries as of and for the dates thereof and the consolidated results of their operations and cash flows for the periods then ended, subject, in the case of unaudited statements, to normal, immaterial, year-end audit adjustments.

(i)            Material Changes; Undisclosed Events, Liabilities or Developments.

(i)            Since June 30, 2007, there has been no event, occurrence or development that could, individually or in the aggregate, have or reasonably be expected to result in a Material Adverse Effect.

(ii)           Except as set forth in the latest audited consolidated balance sheet included within the SEC Reports filed prior to the date of this Agreement or on Schedule 3.1(i)(ii), the Company and the Subsidiaries do not have any obligations or liabilities (whether absolute, contingent, accrued or otherwise) other than trade payables and accrued expenses incurred in the ordinary course of business consistent with past practice since the date of the latest audited consolidated balance sheet included within the SEC Reports filed prior to the date of this Agreement, that are material to the Company and its Subsidiaries taken as a whole.

(iii)          Since the date of the latest audited consolidated balance sheet included within the SEC Reports filed prior to the date of this Agreement, (A) the Company has not altered its method of accounting in any material respect, (B) the Company has not declared or made any dividend or distribution of cash or other property to its stockholders or purchased, redeemed or made any agreements to purchase or redeem any shares of its capital stock and (C) the Company has not issued any Common Stock or Common Stock Equivalents to any officer, director or any Affiliate of the Company, except pursuant to existing Company stock incentive plans.

(iv)          Except for the issuance of the Shares contemplated by this Agreement, no event, liability or development has occurred or exists with respect to the Company or its Subsidiaries or their respective business, properties, operations or financial condition, that would be required to be disclosed by the Company under applicable securities laws and that has not been so disclosed.

(j)            Litigation.  There is no action, suit, inquiry, notice of violation, proceeding or investigation pending or, to the knowledge of the Company, threatened against or affecting the Company, any Subsidiary or any of their respective properties before or by any court, arbitrator, governmental or administrative agency or regulatory authority (federal, state, county, local or foreign) (collectively, an “Action”) which (i) adversely affects or challenges the legality, validity or enforceability of any of the Transaction

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Documents or the Shares or (ii) could, individually or in the aggregate, if there were an unfavorable decision, have or reasonably be expected to result in a Material Adverse Effect. Neither the Company nor any Subsidiary, nor any current director or officer thereof, is or has been the subject of any Action involving a claim of violation of or liability under federal or state securities laws or a claim of breach of fiduciary duty.  There has not been, and to the knowledge of the Company, there is not pending or contemplated, any investigation by the Commission involving the Company or any current director or officer of the Company.  The Commission has not issued any stop order or other order suspending the effectiveness of any registration statement filed by the Company or any Subsidiary under the Exchange Act or the Securities Act.

(k)           Labor Relations.  No labor dispute exists or, to the knowledge of the Company, is imminent with respect to any of the employees of the Company which, individually or in the aggregate, has had or could reasonably be expected to result in a Material Adverse Effect.  None of the Company’s or its Subsidiaries’ employees is a member of a union that relates to such employee’s relationship with the Company or such Subsidiary, and neither the Company nor any of its Subsidiaries is a party to a collective bargaining agreement, and the Company and its Subsidiaries believe that their relationships with their employees are good.  No executive officer, to the knowledge of the Company, is, or is now expected to be, in violation of any material term of any employment contract, confidentiality, disclosure or proprietary information agreement or non-competition agreement, or any other contract or agreement or any restrictive covenant in favor of any third party, and the continued employment of each such executive officer does not subject the Company or any of its Subsidiaries to any liability with respect to any of the foregoing matters. The Company and its Subsidiaries are in compliance with all U.S. federal, state, local and foreign laws and regulations relating to employment and employment practices, terms and conditions of employment and wages and hours, except where the failure to be in compliance could not, individually or in the aggregate, have or reasonably be expected to result in a Material Adverse Effect.

(l)            Compliance.  Neither the Company nor any Subsidiary (i) is in default under or in violation of (and no event has occurred that has not been waived that, with notice or lapse of time or both, would result in a default by the Company or any Subsidiary under), nor has the Company or any Subsidiary received notice of a claim that it is in default under or that it is in violation of, any indenture, loan or credit agreement or any other agreement or instrument to which it is a party or by which it or any of its properties is bound (whether or not such default or violation has been waived), (ii) is in violation of any order of any court, arbitrator or governmental body, or (iii) is or has been since January 1, 2006, in violation of any statute, rule or regulation of any governmental authority, including without limitation all foreign, federal, state and local laws applicable to its business and all such laws that affect the environment, except in each case as could not, individually or in the aggregate, have or reasonably be expected to result in a Material Adverse Effect.

(m)          Regulatory Permits.  The Company and the Subsidiaries possess all certificates, authorizations and permits issued by the appropriate federal, state, local or

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foreign regulatory authorities necessary to conduct their respective businesses as described in the SEC Reports (collectively, the “Material Permits”), except where the failure to possess such permits could not, individually or in the aggregate, have or reasonably be expected to result in a Material Adverse Effect.  Neither the Company nor any Subsidiary has received any notice of proceedings relating to the revocation or modification of any Material Permit.

(n)           Title to Assets.  The Company and the Subsidiaries have good and marketable title in fee simple to all real property owned by them and good and marketable title in all personal property owned by them that is material to the business of the Company and the Subsidiaries, in each case free and clear of all Liens, except for (i) Liens that do not materially affect the value of such property and do not materially interfere with the use made and proposed to be made of such property by the Company and the Subsidiaries, (ii) Liens for the payment of federal, state or other taxes, the payment of which is neither delinquent nor subject to penalties, and (iii) Liens that could not reasonably be expected, individually or in the aggregate, to have a Material Adverse Effect.  Any real property and facilities held under lease by the Company and the Subsidiaries are held by them under valid, subsisting and enforceable leases with which the Company and the Subsidiaries are in compliance.

(o)           Patents and Trademarks.  The Company and the Subsidiaries have, or have rights to use, all patents, patent applications, trademarks, trademark applications, service marks, trade names, trade secrets, inventions, copyrights, licenses and other intellectual property rights and similar rights necessary or material for use in connection with their respective businesses as described in the SEC Reports and which the failure to so have could, individually or in the aggregate, have or reasonably be expected to result in a Material Adverse Effect (collectively, the “Intellectual Property Rights”).  Neither the Company nor any Subsidiary has received a notice (written or otherwise) that any of the Intellectual Property Rights used by the Company or any Subsidiary violates or infringes upon the rights of any Person.  To the knowledge of the Company, all such Intellectual Property Rights are enforceable and there is no existing infringement by another Person of any of the Intellectual Property Rights.  With respect to intellectual property owned by the Company or its Subsidiaries, the Company and its Subsidiaries have taken reasonable security measures, except where disclosure has been required pursuant to applicable rules and regulations of the Patent and Trademark Office or corresponding international authorities, to protect the secrecy, confidentiality and value of all of their intellectual properties, except where failure to do so could not, individually or in the aggregate, have or reasonably be expected to have a Material Adverse Effect.

(p)           Insurance.  The Company and the Subsidiaries are insured by insurers of recognized financial responsibility against such losses and risks and in such amounts as are customary in the businesses in which the Company and the Subsidiaries are engaged, including, but not limited to, directors and officers insurance coverage.  Neither the Company nor any Subsidiary has any reason to believe that it will not be able to renew its existing insurance coverage as and when such coverage expires or to obtain similar coverage from similar insurers as may be necessary to continue its business without a

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significant increase in cost.

(q)           Transactions with Affiliates and Employees.  Except as set forth in the SEC Reports, none of the officers, directors or employees of the Company is presently a party to any transaction with the Company or any Subsidiary (other than for services as employees, officers and directors), including any contract, agreement or other arrangement providing for the furnishing of services to or by, providing for rental of real or personal property to or from, or otherwise requiring payments to or from any officer, director or such employee or, to the knowledge of the Company, any entity in which any officer, director, or any such employee has a substantial interest or is an officer, director, trustee or partner, in each case in excess of $120,000 other than for (i) payment of salary or consulting fees for services rendered, (ii) reimbursement for expenses incurred on behalf of the Company and (iii) other employee benefits, including stock option agreements under any stock option plan of the Company.

(r)            Sarbanes-Oxley; Internal Accounting Controls.  The Company is in material compliance with all provisions of the Sarbanes-Oxley Act of 2002 (including all rules and regulations promulgated thereunder) which are applicable to it as of the Closing Date.  The Company and the Subsidiaries maintain a system of internal accounting controls sufficient to provide reasonable assurance that (i) transactions are executed in accordance with management’s general or specific authorizations, (ii) transactions are recorded as necessary to permit preparation of financial statements in conformity with GAAP and to maintain asset accountability, (iii) access to assets is permitted only in accordance with management’s general or specific authorization, and (iv) the recorded accountability for assets is compared with the existing assets at reasonable intervals and appropriate action is taken with respect to any differences.  The Company has established disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) for the Company and designed such disclosure controls and procedures to ensure that information required to be disclosed by the Company in the reports it files or submits under the Exchange Act is recorded, processed, summarized and reported, within the time periods specified in the Commission’s rules and forms.  The Company’s certifying officers have evaluated the effectiveness of the Company’s disclosure controls and procedures as of the end of the period covered by the Company’s most recently filed periodic report under the Exchange Act (such date, the “Evaluation Date”).  The Company presented in its most recently filed periodic report under the Exchange Act the conclusions of the certifying officers about the effectiveness of the disclosure controls and procedures based on their evaluations as of the Evaluation Date.  Since the Evaluation Date, there have been no changes in the Company’s internal control over financial reporting (as such term is defined in the Exchange Act) that has materially affected, or is reasonably likely to materially affect, the Company’s internal control over financial reporting.

(s)           Certain Fees.  No brokerage or finder’s fees or commissions are or will be payable by the Company to any broker, financial advisor or consultant, finder, placement agent, investment banker, bank or other Person with respect to the transactions contemplated by the Transaction Documents.  The Purchaser shall not have any

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obligation with respect to any fees or with respect to any claims made by or on behalf of other Persons for fees of a type contemplated in this Section that may be due in connection with the transactions contemplated by the Transaction Documents.

(t)            Investment Company.  The Company is not, and is not an Affiliate of, and immediately after receipt of payment for the Shares, will not be or be an Affiliate of, an “investment company” within the meaning of the Investment Company Act of 1940, as amended. The Company shall conduct its business in a manner so that it will not become subject to the Investment Company Act of 1940, as amended.

(u)           Registration Rights.  No Person has any right to cause the Company to effect the registration under the Securities Act of any securities of the Company, other than the Purchaser pursuant to the Registration Rights Agreement.

(v)           Listing and Maintenance Requirements.  The Common Stock is registered pursuant to Section 12(b) of the Exchange Act, and the Company has taken no action designed to, or which to its knowledge is likely to have the effect of, terminating the registration of the Common Stock under the Exchange Act nor has the Company received any notification that the Commission is contemplating terminating such registration.  The Company has not, in the 12 months preceding the date hereof, received notice from any Trading Market on which the Common Stock is or has been listed or quoted to the effect that the Company is not in compliance with the listing or maintenance requirements of such Trading Market.  The Company is, and has no reason to believe that it will not in the foreseeable future continue to be, in compliance in all material respects with all such listing and maintenance requirements.

(w)          Application of Takeover Protections.  The Company and the Board of Directors have taken all necessary action, if any, in order to render inapplicable any control share acquisition, business combination or other similar anti-takeover provision under the Company’s certificate of incorporation (or similar charter documents) or the laws of its state of incorporation that is or could become applicable to the Purchaser as a result of the Purchaser and the Company fulfilling their obligations or exercising their rights under the Transaction Documents, including without limitation as a result of the Company’s issuance of the Shares and the Purchaser’s ownership of the Shares.  The Company does not have any “poison pill” or similar arrangements.

(x)            Disclosure.  Except with respect to the material terms and conditions of the transactions contemplated by the Transaction Documents, the Company confirms that neither it nor, to the Company’s knowledge, any other Person acting on its behalf has provided the Purchaser or its agents or counsel with any information that it believes constitutes or might constitute material, non-public information which is not otherwise disclosed in the Prospectus Supplement.  The Company understands and confirms that the Purchaser will rely on the foregoing representation in effecting transactions in securities of the Company.  All information or document furnished by or on behalf of the Company to the Purchaser regarding the Company, its business and the transactions contemplated hereby, including the Disclosure Schedules to this Agreement, is true and correct and does not contain any untrue statement of a material fact or omit to state any

14

material fact necessary in order to make the statements made therein, in light of the circumstances under which they were made, not misleading. The press releases disseminated by the Company during the twelve months preceding the date of this Agreement taken as a whole do not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary in order to make the statements therein, in light of the circumstances under which they were made and when made, not misleading.  The Company acknowledges and agrees that the Purchaser does not make or has not made any representations or warranties with respect to the transactions contemplated hereby other than those specifically set forth in Section 3.2 hereof.

(y)           No Integrated Offering.  Neither the Company, nor any of its Affiliates, nor any Person acting on its or their behalf has, directly or indirectly, made any offers or sales of any security or solicited any offers to buy any security, under circumstances that would cause this offering of the Shares to be integrated with prior offerings by the Company for purposes of any applicable shareholder approval provisions of any Trading Market on which any of the securities of the Company are listed or designated or otherwise.

(z)            Solvency.  Based on the consolidated financial condition of the Company as of the Closing Date, after giving effect to the receipt by the Company of the proceeds from the sale of the Shares hereunder, (i) the fair saleable value of the Company’s assets exceeds the amount that will be required to be paid on or in respect of the Company’s existing debts and other liabilities (including known contingent liabilities) as they mature, (ii) the Company’s assets do not constitute unreasonably small capital to carry on its business as now conducted and as proposed to be conducted including its capital needs taking into account the particular capital requirements of the business conducted by the Company, and projected capital requirements and capital availability thereof, and (iii) the current cash flow of the Company, together with the proceeds the Company would receive, were it to liquidate all of its assets, after taking into account all anticipated uses of the cash, would be sufficient to pay all amounts on or in respect of its liabilities when such amounts are required to be paid.  The Company does not intend to incur debts beyond its ability to pay such debts as they mature (taking into account the timing and amounts of cash to be payable on or in respect of its debt).  The Company has no knowledge of any facts or circumstances which lead it to believe that it will file for reorganization or liquidation under the bankruptcy or reorganization laws of any jurisdiction within one year from the Closing Date.  Neither the Company nor any Subsidiary is in default with respect to any Indebtedness.

(aa)         Tax Status.  Except for matters that could not, individually or in the aggregate, have or reasonably be expected to result in a Material Adverse Effect, the Company and each Subsidiary has filed all necessary federal, state and foreign income and franchise tax returns and has paid or accrued all taxes shown as due thereon through the date hereof, and the Company has no knowledge of a tax deficiency which has been asserted or threatened against the Company or any Subsidiary.

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(bb)         Foreign Corrupt Practices.  Neither the Company, nor to the knowledge of the Company, any agent or other person acting on behalf of the Company, has (i) directly or indirectly, used any funds for unlawful contributions, gifts, entertainment or other unlawful expenses related to foreign or domestic political activity, (ii) made any unlawful payment to foreign or domestic government officials or employees or to any foreign or domestic political parties or campaigns from corporate funds, (iii) failed to disclose fully any contribution made by the Company (or made by any person acting on its behalf of which the Company is aware) which is in violation of law, or (iv) violated in any material respect any provision of the Foreign Corrupt Practices Act of 1977, as amended.

(cc)         Accountants.  The Company’s accounting firm is Ernst & Young LLP.  To the knowledge and belief of the Company, such accounting firm (i) is a registered public accounting firm as required by the Exchange Act and (ii) shall express its opinion with respect to the financial statements to be included in the Company’s Annual Report on Form 10-K for the year ending June 30, 2008.

(dd)         Acknowledgment Regarding Purchaser’s Purchase of Shares.  The Company acknowledges and agrees that the Purchaser is acting solely in the capacity of an arm’s length purchaser with respect to the Transaction Documents and the transactions contemplated thereby.  The Company further acknowledges that the Purchaser is not acting as a financial advisor or fiduciary of the Company (or in any similar capacity) with respect to the Transaction Documents and the transactions contemplated thereby and any advice given by the Purchaser or any of its representatives or agents in connection with the Transaction Documents and the transactions contemplated thereby is merely incidental to the Purchaser’s purchase of the Shares. The Company further represents to the Purchaser that the Company’s decision to enter into this Agreement and the other Transaction Documents has been based solely on the independent evaluation of the transactions contemplated hereby by the Company and its representatives.

(ee)         Acknowledgement Regarding Purchaser’s Trading Activity.  Anything in this Agreement or elsewhere herein to the contrary notwithstanding, it is understood and acknowledged by the Company (i) that the Purchaser has not been asked by the Company to agree, nor has the Purchaser agreed, to desist from purchasing or selling, long and/or short, securities of the Company, or “derivative” securities based on securities issued by the Company or to hold the Shares for any specified term; (ii) that past or future open market or other transactions by the Purchaser or any entity in which the Purchaser has an interest, specifically including, without limitation, Short Sales or “derivative” transactions, before or after the closing of this or future transactions, may negatively impact the market price of the Company’s publicly-traded securities; (iii) that the Purchaser, and counter-parties in “derivative” transactions to which the Purchaser is a party or in which the Purchaser has an interest, directly or indirectly, presently may have a “short” position in the Common Stock; and (iv) that the Purchaser shall not be deemed to have any affiliation with or control over any arm’s length counter-party in any “derivative” transaction. The Company further understands and acknowledges that (a) the Purchaser or any entity in which the Purchaser has an interest may engage in hedging activities at various times, and (b) such hedging activities (if any) could reduce the value

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of the existing stockholders’ equity interests in the Company at and after the time that the hedging activities are being conducted.  The Company acknowledges that such aforementioned hedging activities do not constitute a breach of any of the Transaction Documents.

(ff)           Regulation M Compliance.   The Company has not, and to its knowledge no one acting on its behalf has, (i) taken, directly or indirectly, any action designed to cause or to result in the stabilization or manipulation of the price of any security of the Company to facilitate the sale or resale of any of the Shares, (ii) sold, bid for, purchased, or, paid any compensation for soliciting purchases of, any of the Shares, or (iii) paid or agreed to pay to any Person any compensation for soliciting another to purchase any other securities of the Company.

(gg)         FDA.  As to each product subject to the jurisdiction of the U.S. Food and Drug Administration (“FDA”) under the Federal Food, Drug and Cosmetic Act, as amended, and the regulations thereunder (“FDCA”) that is manufactured, packaged, labeled, tested, distributed, sold, and/or marketed by the Company or any of its Subsidiaries (each such product, a “Pharmaceutical Product”), such Pharmaceutical Product is being manufactured, packaged, labeled, tested, distributed, sold and/or marketed by the Company in compliance with all applicable requirements under FDCA and similar laws, rules and regulations relating to registration, investigational use, premarket clearance, licensure, or application approval, good manufacturing practices, good laboratory practices, good clinical practices, product listing, quotas, labeling, advertising, record keeping and filing of reports, except where the failure to be in compliance would not have a Material Adverse Effect.  There is no pending, completed or, to the Company’s knowledge, threatened, action (including any lawsuit, arbitration, or legal or administrative or regulatory proceeding, charge, complaint, or investigation) against the Company or any of its Subsidiaries, and none of the Company or any of its Subsidiaries has received any notice, warning letter or other communication from the FDA or any other governmental entity, which (i) contests the premarket clearance, licensure, registration, or approval of, the uses of, the distribution of, the manufacturing or packaging of, the testing of, the sale of, or the labeling and promotion of any Pharmaceutical Product, (ii) withdraws its approval of, requests the recall, suspension, or seizure of, or withdraws or orders the withdrawal of advertising or sales promotional materials relating to, any Pharmaceutical Product, (iii) imposes a clinical hold on any clinical investigation by the Company or any of its Subsidiaries, (iv) enjoins production at any facility of the Company or any of its Subsidiaries, (v) enters or proposes to enter into a consent decree of permanent injunction with the Company or any of its Subsidiaries, or (vi) otherwise alleges any violation of any laws, rules or regulations by the Company or any of its Subsidiaries, and which, either individually or in the aggregate, would have a Material Adverse Effect.  The properties, business and operations of the Company have been and are being conducted in all material respects in accordance with all applicable laws, rules and regulations of the FDA.  The Company has not been informed by the FDA that the FDA will prohibit the marketing, sale, license or use in the United States of any product proposed to be developed, produced or marketed by the Company nor has the FDA expressed any concern as to approving or clearing for

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marketing any product being developed or proposed to be developed by the Company.

3.2           Representations and Warranties of the Purchaser.  The Purchaser hereby represents and warrants as of the date hereof to the Company as follows:

(a)           Organization; Authority.  The Purchaser is an entity duly organized, validly existing and in good standing under the laws of the jurisdiction of its organization with full right, corporate or partnership power and authority to enter into and to consummate the transactions contemplated by this Agreement and otherwise to carry out its obligations hereunder and thereunder.  The execution and delivery of this Agreement and performance by the Purchaser of the transactions contemplated by this Agreement have been duly authorized by all necessary corporate or similar action on the part of the Purchaser.  Each Transaction Document to which it is a party has been duly executed by the Purchaser, and when delivered by the Purchaser in accordance with the terms hereof, will constitute the valid and legally binding obligation of the Purchaser, enforceable against it in accordance with its terms, except (i) as limited by general equitable principles and applicable bankruptcy, insolvency, reorganization, moratorium and other laws of general application affecting enforcement of creditors’ rights generally, (ii) as limited by laws relating to the availability of specific performance, injunctive relief or other equitable remedies and (iii) insofar as indemnification and contribution provisions may be limited by applicable law.

(b)           Own Account.  The Purchaser is acquiring the Shares as principal for its own account and not with a view to or for distributing or reselling such Shares or any part thereof in violation of the Securities Act or any applicable state securities law, has no present intention of distributing any of such Shares in violation of the Securities Act or any applicable state securities law and has no direct or indirect arrangement or understandings with any other persons to distribute or regarding the distribution of such Shares in violation of the Securities Act or any applicable state securities law (this representation and warranty not limiting the Purchaser’s right to sell the Shares immediately pursuant to Rule 144 or another applicable exemption from the registration requirements of the Securities Act or pursuant to a registration statement filed pursuant to the Registration Rights Agreement or otherwise in compliance with applicable federal and state securities laws).  The Purchaser is acquiring the Shares hereunder in the ordinary course of its business.

(c)           Purchaser Status.  At the time the Purchaser was offered the Shares, it was, and at the date hereof it is either: (i) an “accredited investor” as defined in Rule 501(a)(1), (a)(2), (a)(3), (a)(7) or (a)(8) under the Securities Act or (ii) a “qualified institutional buyer” as defined in Rule 144A(a) under the Securities Act.  The Purchaser is not required to be registered as a broker-dealer under Section 15 of the Exchange Act.  Neither BVF Partners L.P. nor BVF Inc. will beneficially own or control the Shares to be purchased by the Purchaser.

(d)           Experience of Purchaser.  The Purchaser, either alone or together with its representatives, has such knowledge, sophistication and experience in business and financial matters so as to be capable of evaluating the merits and risks of the prospective

18

investment in the Shares, and has so evaluated the merits and risks of such investment.  The Purchaser is able to bear the economic risk of an investment in the Shares and, at the present time, is able to afford a complete loss of such investment.

ARTICLE IV.
OTHER AGREEMENTS OF THE PARTIES

4.1           Furnishing of Information.  For so long as the Purchaser owns any Shares, (a) the Company covenants to timely file (or obtain extensions in respect thereof and file within the applicable grace period) all reports required to be filed by the Company after the date hereof pursuant to the Exchange Act even if the Company is not then subject to the reporting requirements of the Exchange Act and (b) if the Company is not required to file reports pursuant to the Exchange Act, it will prepare and furnish to the Purchaser and make publicly available in accordance with Rule 144(c) such information as is required for the Purchaser to sell the Shares under Rule 144.  The Company further covenants that it will take such further action as any holder of Shares may reasonably request, to the extent required from time to time to enable such Person to sell such Shares without registration under the Securities Act within the requirements of the exemption provided by Rule 144.

4.2           Integration.  The Company shall not sell, offer for sale or solicit offers to buy or otherwise negotiate in respect of any security (as defined in Section 2 of the Securities Act) that would be integrated with the offer or sale of the Shares for purposes of the rules and regulations of any Trading Market such that it would require shareholder approval prior to the closing of such other transaction unless shareholder approval is obtained before the closing of such subsequent transaction.

4.3           Securities Laws Disclosure; Publicity.  The Company shall, by 8:30 a.m. (New York City time) on the Trading Day immediately following the date hereof, issue a Current Report on Form 8-K, disclosing the material terms of the transactions contemplated hereby, and filing the Transaction Documents as exhibits thereto as well as the Prospectus Supplement.  The Company and the Purchaser shall consult with each other in issuing any other press releases with respect to the transactions contemplated hereby, and neither the Company nor the Purchaser shall issue any such press release or otherwise make any such public statement without the prior consent of the Company, with respect to any press release or public statement of the Purchaser, or without the prior consent of the Purchaser, with respect to any press release or public statement of the Company.  Notwithstanding the foregoing, the Company shall not publicly disclose the name of the Purchaser or any of its Affiliates, or include the name of the Purchaser or any of its Affiliates in any filing with the Commission (including the Form 8-K and the Prospectus Supplement referred to above) or any regulatory agency or Trading Market, without the prior written consent of the Purchaser, except that the Purchaser’s consent shall not be required with respect to subsequent regulatory filings by the Company if the disclosure in such subsequent regulatory filings is identical to the disclosure previously approved in writing by the Purchaser.

4.4           Shareholder Rights Plan.  No claim will be made or enforced by the Company or, with the consent of the Company, any other Person, that the Purchaser is an “Acquiring Person”

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under any control share acquisition, business combination, poison pill (including any distribution under a rights agreement) or similar anti-takeover plan or arrangement in effect or hereafter adopted by the Company, or that the Purchaser could be deemed to trigger the provisions of any such plan or arrangement, by virtue of receiving Shares under the Transaction Documents or under any other agreement between the Company and the Purchaser.

4.5           Non-Public Information.  Except with respect to the material terms and conditions of the transactions contemplated by the Transaction Documents, the Company covenants and agrees that neither it nor any other Person acting on its behalf will provide the Purchaser or its agents or counsel with any information that the Company believes constitutes material non-public information, unless prior thereto the Purchaser shall have executed a written agreement regarding the confidentiality and use of such information.  The Company understands and confirms that the Purchaser shall be relying on the foregoing covenant in effecting transactions in securities of the Company.

4.6           Use of Proceeds.  The Company shall use the net proceeds from the sale of the Shares hereunder for working capital purposes and shall not use such proceeds for (a) the satisfaction of any portion of the Company’s debt (other than payment of trade payables in the ordinary course of the Company’s business and prior practices) or (b) the redemption of any Common Stock or Common Stock Equivalents.

4.7           Indemnification of Purchaser.  Subject to the provisions of this Section 4.7, the Company will indemnify and hold the Purchaser and its directors, officers, shareholders, members, partners, employees and agents (and any other Persons with a functionally equivalent role of a Person holding such titles notwithstanding a lack of such title or any other title), each Person who controls the Purchaser (within the meaning of Section 15 of the Securities Act and Section 20 of the Exchange Act), and the directors, officers, shareholders, agents, members, partners or employees (and any other Persons with a functionally equivalent role of a Person holding such titles notwithstanding a lack of such title or any other title) of such controlling persons (each, a “Purchaser Party”) harmless from any and all losses, liabilities, obligations, claims, contingencies, damages, costs and expenses, including all judgments, amounts paid in settlements, court costs and reasonable attorneys’ fees and costs of investigation that any Purchaser Party may suffer or incur (collectively, “Losses”) as a result of or relating to (a) any breach of any of the representations or warranties made by the Company in this Agreement or in the other Transaction Documents (without regard to any “materiality” or Material Adverse Effect” qualifiers contained therein), to the extent that the amount of the Losses arising from all such breaches exceeds $500,000, (b) any breach of any of the covenants or agreements made by the Company in this Agreement or in the other Transaction Documents (without regard to any “materiality” or Material Adverse Effect” qualifiers contained therein) and (c) any action instituted against any Purchaser Party in any capacity, or any of them or their respective Affiliates, by any stockholder of the Company who is not an Affiliate of the Purchaser, with respect to any of the transactions contemplated by the Transaction Documents (unless such action is based upon a breach of the Purchaser’s representations, warranties or covenants under the Transaction Documents or any agreements or understandings the Purchaser may have with any such stockholder or any violations by the Purchaser of state or federal securities laws or any conduct by the Purchaser which constitutes fraud, gross negligence, willful misconduct or

20

malfeasance).  If any action shall be brought against any Purchaser Party in respect of which indemnity may be sought pursuant to this Agreement, such Purchaser Party shall promptly notify the Company in writing, and the Company shall have the right to assume the defense thereof with counsel of its own choosing reasonably acceptable to the Purchaser Party.  Any Purchaser Party shall have the right to employ separate counsel in any such action and participate in the defense thereof, but the fees and expenses of such counsel shall be at the expense of such Purchaser Party except to the extent that (i) the employment thereof has been specifically authorized by the Company in writing, (ii) the Company has failed after a reasonable period of time to assume such defense and to employ counsel, or (iii) in such action there is, in the reasonable opinion of such separate counsel, a material conflict on any material issue between the position of the Company and the position of such Purchaser Party, in which case the Company shall be responsible for the reasonable fees and expenses of no more than one such separate counsel (and local counsel).  The Company will not be liable to any Purchaser Party under this Agreement for any settlement by a Purchaser Party effected without the Company’s prior written consent, which shall not be unreasonably withheld or delayed.

4.8           Listing of Common Stock.  The Company hereby agrees to use commercially reasonable efforts to maintain the listing of the Common Stock on a Trading Market and, agrees that no later than the Closing Date, all of the Shares will be listed on such Trading Market.  The Company further agrees, if the Company applies to have the Common Stock traded on any other Trading Market, it will include in such application all of the Shares, and will take such other action as is necessary to cause all of the Shares to be listed on such other Trading Market as promptly as possible.  The Company will take all action reasonably necessary to continue the listing and trading of its Common Stock on a Trading Market and will comply in all respects with the Company’s reporting, filing and other obligations under the bylaws or rules of the Trading Market.

ARTICLE V.
MISCELLANEOUS

5.1           Fees and Expenses.  Except as expressly set forth in the Transaction Documents to the contrary, each party shall pay the fees and expenses of its advisers, counsel, accountants and other experts, if any, and all other expenses incurred by such party incident to the negotiation, preparation, execution, delivery and performance of this Agreement.  The Company shall pay all Transfer Agent fees, stamp taxes and other taxes and duties levied in connection with the delivery of the Shares to the Purchaser.

5.2           Entire Agreement.  The Transaction Documents, together with the exhibits and schedules thereto, the Prospectus and the Prospectus Supplement, contain the entire understanding of the parties with respect to the subject matter hereof and supersede all prior agreements and understandings, oral or written, with respect to such matters, which the parties acknowledge have been merged into such documents, exhibits and schedules.

5.3           Notices.  Any and all notices or other communications or deliveries required or permitted to be provided hereunder shall be in writing and shall be deemed given and effective

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on the earliest of (a) the date of transmission, if such notice or communication is delivered via facsimile at the facsimile number set forth on the signature pages attached hereto prior to 5:30 p.m. (New York City time) on a Trading Day, (b) the next Trading Day after the date of transmission, if such notice or communication is delivered via facsimile at the facsimile number set forth on the signature pages attached hereto on a day that is not a Trading Day or later than 5:30 p.m. (New York City time) on any Trading Day, (c) the 2nd Trading Day following the date of mailing, if sent by U.S. nationally recognized overnight courier service, or (d) upon actual receipt by the party to whom such notice is required to be given.  The addresses for such notices and communications shall be as follows:

(a)  If to the Company:

ImmunoGen, Inc.

830 Winter Street

Waltham, MA 02451

Fax:  (781) 895-0613

Attn:  General Counsel

with a copy (which shall not constitute notice) to:

Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.

One Financial Center

Boston, MA 02111

Fax:  (617) 542-2241

Attn:  Jonathan L. Kravetz, Esq.

(b)  If to the Purchaser:

Ziff Brothers Investments

350 Park Avenue

New York, NY  10022

Attention:  General Counsel

Fax:  (212) 292-6659

with a copy (which shall not constitute notice) to:

Fried, Frank, Harris, Shriver & Jacobson LLP
One New York Plaza
New York, New York 10004
Attention:  Jonathan Adler, Esq.

Fax:  (212) 859-4000

5.4           Amendments; Waivers.  No provision of this Agreement may be waived or amended except in a written instrument signed by the Company and the Purchaser or, in the case of a waiver, by the party against whom enforcement of any such waived provision is sought.  No waiver of any default with respect to any provision, condition or requirement of this Agreement shall be deemed to be a continuing waiver in the future or a waiver of any subsequent default or a waiver of any other provision, condition or requirement hereof, nor shall any delay or omission

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of any party to exercise any right hereunder in any manner impair the exercise of any such right.

5.5           Headings.  The headings herein are for convenience only, do not constitute a part of this Agreement and shall not be deemed to limit or affect any of the provisions hereof.

5.6           Successors and Assigns.  This Agreement shall be binding upon and inure to the benefit of the parties and their successors and permitted assigns.  The Company may not assign this Agreement or any rights or obligations hereunder without the prior written consent of the Purchaser (other than by merger).  The Purchaser may assign any or all of its rights under this Agreement to any Person to whom the Purchaser assigns or transfers any Shares.

5.7           No Third-Party Beneficiaries.  This Agreement is intended for the benefit of the parties hereto and their respective successors and permitted assigns and is not for the benefit of, nor may any provision hereof be enforced by, any other Person, except as otherwise set forth in Section 4.8.

5.8           Governing Law.  All questions concerning the construction, validity, enforcement and interpretation of the Transaction Documents shall be governed by and construed and enforced in accordance with the internal laws of the State of New York, without regard to the principles of conflicts of law thereof.  Each party agrees that all legal proceedings concerning the interpretations, enforcement and defense of the transactions contemplated by this Agreement and any other Transaction Documents (whether brought against a party hereto or its respective affiliates, directors, officers, shareholders, employees or agents) shall be commenced exclusively in the state and federal courts sitting in the City of New York.  Each party hereby irrevocably submits to the exclusive jurisdiction of the state and federal courts sitting in the City of New York, borough of Manhattan for the adjudication of any dispute hereunder or in connection herewith or with any transaction contemplated hereby or discussed herein (including with respect to the enforcement of any of the Transaction Documents), and hereby irrevocably waives, and agrees not to assert in any suit, action or proceeding, any claim that it is not personally subject to the jurisdiction of any such court, that such suit, action or proceeding is improper or is an inconvenient venue for such proceeding.  Each party hereby irrevocably waives personal service of process and consents to process being served in any such suit, action or proceeding by mailing a copy thereof via registered or certified mail or overnight delivery (with evidence of delivery) to such party at the address in effect for notices to it under this Agreement and agrees that such service shall constitute good and sufficient service of process and notice thereof.  Nothing contained herein shall be deemed to limit in any way any right to serve process in any other manner permitted by law.  If either party shall commence an action or proceeding to enforce any provisions of the Transaction Documents, then the prevailing party in such action or proceeding shall be reimbursed by the other party for its reasonable attorneys’ fees and other costs and expenses incurred with the investigation, preparation and prosecution of such action or proceeding.

5.9           Survival.  The representations and warranties contained herein shall survive the Closing and the delivery of the Shares.

5.10         Execution.  This Agreement may be executed in two or more counterparts, all of which when taken together shall be considered one and the same agreement and shall become

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effective when counterparts have been signed by each party and delivered to the other party, it being understood that both parties need not sign the same counterpart.  In the event that any signature is delivered by facsimile transmission or by e-mail delivery of a “.pdf” format data file, such signature shall create a valid and binding obligation of the party executing (or on whose behalf such signature is executed) with the same force and effect as if such facsimile or “.pdf” signature page were an original thereof.

5.11         Severability.  If any term, provision, covenant or restriction of this Agreement is held by a court of competent jurisdiction to be invalid, illegal, void or unenforceable, the remainder of the terms, provisions, covenants and restrictions set forth herein shall remain in full force and effect and shall in no way be affected, impaired or invalidated, and the parties hereto shall use their commercially reasonable efforts to find and employ an alternative means to achieve the same or substantially the same result as that contemplated by such term, provision, covenant or restriction.  It is hereby stipulated and declared to be the intention of the parties that they would have executed the remaining terms, provisions, covenants and restrictions without including any of such that may be hereafter declared invalid, illegal, void or unenforceable.

5.12         Replacement of Shares.  If any certificate or instrument evidencing any Shares is mutilated, lost, stolen or destroyed, the Company shall issue or cause to be issued in exchange and substitution for and upon cancellation thereof (in the case of mutilation), or in lieu of and substitution therefor, a new certificate or instrument (without any restrictive legends), but only upon receipt of evidence reasonably satisfactory to the Company of such loss, theft or destruction.  The applicant for a new certificate or instrument under such circumstances shall also pay any reasonable third-party costs (including customary indemnity) associated with the issuance of such replacement Shares.

5.13         Remedies.  In addition to being entitled to exercise all rights provided herein or granted by law, including recovery of damages, the Purchaser will be entitled to specific performance under the Transaction Documents.  The parties agree that monetary damages may not be adequate compensation for any loss incurred by reason of any breach of the Company’s obligations contained in the Transaction Documents and the Company hereby agrees to waive and not to assert in any action for specific performance of any such obligation the defense that a remedy at law would be adequate.

5.14         Saturdays, Sundays, Holidays, etc.  If the last or appointed day for the taking of any action or the expiration of any right required or granted herein shall not be a Business Day, then such action may be taken or such right may be exercised on the next succeeding Business Day.

5.15         Construction.  The parties agree that each of them and/or their respective counsel has reviewed and had an opportunity to revise the Transaction Documents and, therefore, the normal rule of construction to the effect that any ambiguities are to be resolved against the drafting party shall not be employed in the interpretation of the Transaction Documents or any amendments hereto.

5.16         Waiver of Jury Trial.  In any action, suit or proceeding in any jurisdiction brought by any party against any other party, the parties each knowingly and intentionally, to the greatest

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extent permitted by applicable law, hereby absolutely, unconditionally, irrevocably and expressly waives forever trial by jury.

(Signature Page Follows)

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IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be duly executed by their respective authorized signatories as of the date first indicated above.

[Signature Page to Securities Purchase Agreement]

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Exhibit C

1.             Mitchel Sayare

2.             David W. Carter

3.             Stephen C. McCluski

4.             Nicole Onetto

5.             Mark Skaletsky

6.             Joseph J. Villafranca

7.             Daniel M. Junius

8.             John M. Lambert

9.             John Tagliamonte

10.           Richard J. Wallace

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