Exhibit 10.1

EXECUTION VERSION

SECURITIES PURCHASE AGREEMENT

This Securities Purchase Agreement (this “ Agreement ”) is dated as of December 2, 2013, by and between OncoMed Pharmaceuticals, Inc., a Delaware corporation (the “ Company ”), and Celgene Corporation (“ Celgene ”).

RECITALS

A. The Company and Celgene are executing and delivering this Agreement in reliance upon the exemption from securities registration afforded by Section 4(2) of the Securities Act of 1933, as amended (the “ Securities Act ”), and Rule 506 of Regulation D (“ Regulation D ”) as promulgated by the United States Securities and Exchange Commission (the “ Commission ”) under the Securities Act.

B. Celgene wishes to purchase, and the Company wishes to sell, upon the terms and conditions stated in this Agreement, 1,470,588 of shares of common stock, par value $0.001 per share (the “ Common Stock ”), of the Company (the “ Shares ”).

C. Contemporaneously with the execution and delivery of this Agreement, the parties hereto are executing and delivering a Registration Rights Agreement, substantially in the form attached hereto as Exhibit A (the “ Registration Rights Agreement ”), pursuant to which, among other things, the Company will agree to provide certain registration rights with respect to the Shares under the Securities Act and the rules and regulations promulgated thereunder and applicable state securities laws.

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 Celgene hereby 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 shall have the meanings indicated in this Section 1.1 :

“ Action ” means any action, suit, inquiry, notice of violation, proceeding (including any partial proceeding such as a deposition) or investigation pending or, to the Company’s Knowledge, threatened in writing against the Company or any of its properties or any officer, director or employee of the Company acting in his or her capacity as an officer, director or employee before or by any federal, state, county, local or foreign court, arbitrator, governmental or administrative agency, regulatory authority, stock market, stock exchange or trading facility.

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

“ Agreement ” has the meaning set forth in the Preamble.

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

“ Business Day ” means any day except Saturday, 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.

“ California Courts ” means the state and federal courts sitting in the City of San Francisco.

“ Closing ” means the closing of the purchase and sale of the Shares pursuant to this Agreement.

“ Closing Date ” means the next Business Day following the date hereof.

“ Commission ” has the meaning set forth in the Recitals.

“ Common Stock ” has the meaning set forth in the Recitals, and also includes any other class of securities into which the Common Stock may hereafter be reclassified or changed into.

“ Common Stock Equivalents ” means any securities of the Company 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 exchangeable for, or otherwise entitles the holder thereof to receive, Common Stock or other securities that entitle the holder to receive, directly or indirectly, Common Stock.

“ Company ” has the meaning set forth in the Preamble.

“ Company Counsel ” means Latham & Watkins LLP.

“ Company Deliverables ” has the meaning set forth in Section 2.2(a) .

“ Company’s Knowledge ” means the knowledge of the executive officers of the Company.

“ Control ” (including the terms “controlling,” “controlled by” or “under common control with”) means the possession, direct or indirect, of the power to direct or cause the direction of the management and policies of a Person, whether through the ownership of voting securities, by contract or otherwise.

“ Disclosure Schedules ” has the meaning set forth in Section 3.1 .

“ DTC ” has the meaning set forth in Section 4.1(c) .

“ Effective Date ” means the date on which the initial Registration Statement required by Section 2(a) of the Registration Rights Agreement is first declared effective by the Commission.

“Effectiveness Deadline ” means the date on which the initial Registration Statement is required to be declared effective by the Commission under the terms of the Registration Rights Agreement.

“ Environmental Laws ” has the meaning set forth in Section 3.1(cc) .

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

“ GAAP ” means U.S. generally accepted accounting principles, consistently applied.

“ Intellectual Property ” means patents, patent applications, trademarks, trademark applications, service marks, tradenames, copyrights, trade secrets, licenses, domain names, mask works, or any other proprietary right or process.

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

“ Material Adverse Effect ” means a material adverse effect on the results of operations, assets, business or financial condition of the Company.

“ Material Contract ” means any contract of the Company that has been filed as an exhibit to the SEC Reports pursuant to Item 601(b)(4) or Item 601(b)(10) of Regulation S-K.

“ Material Permits ” has the meaning set forth in Section 3.1(n) .

“ OFAC ” has the meaning set forth in Section 3.1(hh) .

“ Person ” means an individual, corporation, partnership, limited liability company, trust, business trust, association, joint stock company, joint venture, sole proprietorship, unincorporated organization, governmental authority or any other form of entity not specifically listed herein.

“ Principal Trading Market ” means the Trading Market on which the Common Stock is primarily listed on and quoted for trading, which, as of the date of this Agreement and the Closing Date, shall be the NASDAQ Global Select Market.

“ Proceeding ” means an action, claim, suit, investigation or proceeding (including, without limitation, an investigation or partial proceeding, such as a deposition), whether commenced or threatened.

“ Purchase Price ” means $15.13 per share.

“ Celgene Deliverables ” has the meaning set forth in Section 2.2(b) .

“Registration Rights Agreement ” has the meaning set forth in the Recitals.

“ Registration Statement ” means a registration statement meeting the requirements set forth in the Registration Rights Agreement and covering the resale by Celgene of the Registrable Securities (as defined in the Registration Rights Agreement).

“ Regulation D ” has the meaning set forth in the Recitals.

“ Required Approvals ” has the meaning set forth 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 Report s” has the meaning set forth in Section 3.1(h) .

“ Secretary’s Certificate ” has the meaning set forth in Section 2.2(a)(v) .

“ Securities Act ” has the meaning set forth in the Recitals.

“ Shares ” has the meaning set forth in the Recitals.

“ Subsidiary ” means any subsidiary of the Company formed or acquired after the date hereof.

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“ Trading Day ” means (i) a day on which the Common Stock is listed or quoted and traded on its Principal Trading Market (other than the OTC Bulletin Board), or (ii) if the Common Stock is not listed on a Trading Market (other than the OTC Bulletin Board), a day on which the Common Stock is traded in the over-the-counter market, as reported by the OTC Bulletin Board, or (iii) if the Common Stock is not quoted on any Trading Market, a day on which the Common Stock is quoted in the over-the-counter market as reported in the “pink sheets” by Pink Sheets LLC (or any similar organization or agency succeeding to its functions of reporting prices); provided , that in the event that the Common Stock is not listed or quoted as set forth in (i), (ii) and (iii) hereof, then Trading Day shall mean a Business Day.

“ Trading Market ” means whichever of the New York Stock Exchange, the NYSE Amex Equities (formerly the American Stock Exchange), the NASDAQ Global Select Market, the NASDAQ Global Market, the NASDAQ Capital Market or the OTC Bulletin Board on which the Common Stock is listed or quoted for trading on the date in question.

“ Transaction Documents ” means this Agreement, the schedules and exhibits attached hereto, the Registration Rights Agreement and any other documents or agreements explicitly contemplated hereunder.

“ Transfer Agent ” means Computershare Trust Company, N.A., the current transfer agent of the Company or any successor transfer agent for the Company.

ARTICLE II.

PURCHASE AND SALE

2.1 Closing .

(a) Amount . Subject to the terms and conditions set forth in this Agreement, at the Closing, the Company shall issue and sell to Celgene, and Celgene shall purchase from the Company, 1,470,588 shares of Common Stock.

(b) Closing . The Closing of the purchase and sale of the Shares shall take place at the offices of Latham & Watkins LLP, 140 Scott Drive, Menlo Park, California 94025, on the Closing Date or at such other locations or remotely by facsimile transmission or other electronic means as the parties may mutually agree.

(c) Form of Payment . On the Closing Date, Celgene shall pay to the Company $22,249,996.44 by wire transfer of immediately available funds and the Company shall irrevocably instruct the Transfer Agent to deliver to Celgene the Shares in book-entry form, free and clear of all restrictive and other legends (except as expressly provided in Section 4.1(b) hereof).

2.2 Closing Deliveries . (a) On or prior to the Closing, the Company shall issue, deliver or cause to be delivered to Celgene the following (the “ Company Deliverables ”):

(i) this Agreement, duly executed by the Company;

(ii) the Shares in book-entry form, free and clear of all restrictive and other legends (except as provided in Section 4.1(b) hereof);

(iii) a legal opinion of Company Counsel, dated as of the Closing Date, in form and substance reasonably satisfactory to Celgene, executed by such counsel and addressed to Celgene;

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(iv) the Registration Rights Agreement, duly executed by the Company;

(v) a certificate of the Secretary or Assistant Secretary of the Company (the “ Secretary’s Certificate ”), dated as of the Closing Date, (a) certifying the resolutions adopted by the Board of Directors of the Company or a duly authorized committee thereof approving the transactions contemplated by this Agreement and the other Transaction Documents and the issuance of the Securities, (b) certifying the current versions of the certificate of incorporation, as amended, and by-laws of the Company and (c) certifying as to the signatures and authority of persons signing the Transaction Documents and related documents on behalf of the Company, in the form attached hereto as Exhibit B ;

(vi) a certificate evidencing the formation and good standing of the Company issued by the Secretary of State of Delaware, as of a date within five (5) Business Days of the Closing Date; and

(vii) a certified copy of the articles of incorporation, as certified by the Secretary of State of Delaware as of a date within five (5) Business Days of the Closing Date.

(b) On or prior to the Closing, Celgene shall deliver or cause to be delivered to the Company the following (the “ Celgene Deliverables ”):

(i) this Agreement, duly executed by Celgene;

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

(iii) a lock-up agreement, duly executed by Celgene, in the form attached hereto as Exhibit C .

ARTICLE III.

REPRESENTATIONS AND WARRANTIES

3.1 Representations and Warranties of the Company . Except (i) as set forth in the schedules delivered herewith (the “ Disclosure Schedules ”), which Disclosure Schedules shall be deemed a part hereof and shall qualify any representation made herein to the extent of the disclosure contained in the corresponding section of the Disclosure Schedules, or (ii) disclosed in the SEC Reports, the Company hereby represents and warrants as of the date hereof to Celgene:

(a) Subsidiaries . The Company has no subsidiaries (as defined in Rule 405 under the Securities Act).

(b) Organization and Qualification . The Company is an entity duly incorporated or otherwise organized, validly existing and in good standing under the laws of the State of Delaware, with the requisite corporate power and authority to own or lease and use its properties and assets and to carry on its business as currently conducted. The Company is not in violation or default of any of the provisions of its certificate of incorporation or bylaws. The Company 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, would not have or reasonably be expected to result in a Material Adverse Effect, and no Proceeding has been instituted, is pending, or, to the Company’s Knowledge, has been threatened in writing in any such jurisdiction revoking, limiting or curtailing or seeking to revoke, limit or curtail such power and authority or qualification.

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(c) Authorization; Enforcement; Validity . The Company has the requisite corporate power and authority to enter into and to consummate the transactions contemplated by each of the Transaction Documents to which it is a party and otherwise to carry out its obligations hereunder and thereunder. The Company’s execution and delivery of each of the Transaction Documents to which it is a party and the consummation by it of the transactions contemplated hereby and thereby (including, but not limited to, the sale and delivery of the Shares) have been duly authorized by all necessary corporate action on the part of the Company, and no further corporate action is required by the Company, its Board of Directors or its stockholders in connection therewith other than in connection with the Required Approvals. Each of the Transaction Documents to which it is a party has been (or upon delivery will have been) duly executed by the Company and is, or when delivered in accordance with the terms hereof, will constitute the legal, valid and binding obligation of the Company.

(d) No Conflicts . The execution, delivery and performance by the Company of the Transaction Documents to which it is a party and the consummation by the Company of the transactions contemplated hereby or thereby (including, without limitation, the issuance of the Shares) do not and will not (i) conflict with or violate any provisions of the Company’s certificate of incorporation or bylaws, (ii) conflict with, or constitute a default (or an event that with notice or lapse of time or both would result in a default) under, result in the creation of any Lien upon any of the properties or assets of the Company or give to others any rights of termination, amendment, acceleration or cancellation (with or without notice, lapse of time or both) of, any Material Contract, or (iii) subject to 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 is subject (including federal and state securities laws and regulations and the rules and regulations, assuming the correctness of the representations and warranties made by Celgene herein, of any self-regulatory organization to which the Company or its securities are subject), or by which any property or asset of the Company is bound or affected, except in the case of clauses (ii) and (iii) such as would not, individually or in the aggregate, have or reasonably be 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 other Person in connection with the execution, delivery and performance by the Company of the Transaction Documents (including the issuance of the Securities), other than (i) the filing with the Commission of one or more Registration Statements in accordance with the requirements of the Registration Rights Agreement, (ii) filings required by applicable state securities laws, (iii) the filing of a Notice of Sale of Securities on Form D with the Commission under Regulation D of the Securities Act, (iv) the filing of any requisite notices and/or application(s) to the Principal Trading Market for the issuance and sale of the Securities and the listing of the Shares thereon in the time and manner required thereby, (v) the filings required in accordance with Section 4.5 of this Agreement and (vi) those that have been made or obtained prior to the date of this Agreement (collectively, the “ Required Approvals ”).

(f) Issuance of the Securities . The Shares have been duly authorized and, when issued and paid for in accordance with the terms of the Transaction Documents, will be validly issued, fully paid and nonassessable and free and clear of all Liens, other than restrictions on transfer provided for in the Transaction Documents or imposed by applicable securities laws, and shall not be subject to preemptive or similar rights. Assuming the accuracy of the representations and warranties of Celgene in this Agreement, the Securities will be issued in compliance with all applicable federal and state securities laws.

(g) Capitalization . The number of shares and type of all authorized, issued and outstanding capital stock, options and other securities of the Company (whether or not presently convertible into or exercisable or exchangeable for shares of capital stock of the Company) is set forth in Schedule 3.1(g)

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hereto. The Company has not issued any capital stock since the date of its most recently filed SEC Report other than to reflect stock option and warrant exercises. 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 that have not been effectively waived as of the Closing Date. Except as set forth on Schedule 3.1(g) or as specifically disclosed in the most recently filed SEC Report, 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 contracts, commitments, understandings or arrangements by which the Company 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 (other than Celgene) 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 applicable 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. Except as set forth on Schedule 3.1(g) or as specifically disclosed in the most recently filed SEC Report, there are no stockholders agreements, voting agreements or other similar agreements with respect to the Company’s capital stock to which the Company is a party or, to the Company’s Knowledge, between or among any of the Company’s stockholders.

(h) SEC Reports; Disclosure Materials . The Company has filed all reports, schedules, forms, statements and other documents required to be filed by it under the Exchange Act, including pursuant to Section 13(a) or 15(d) thereof, for the two years preceding the date hereof (or such shorter period as the Company was required by law or regulation to file such material) (the foregoing materials, including the exhibits thereto and documents incorporated by reference therein, and also including the Company’s prospectus dated July 17, 2013 filed with the Commission pursuant to Rule 424(b) under the Securities Act, being collectively referred to herein as the “ SEC Reports ,” and the SEC Reports, together with the Disclosure Schedules, being collectively referred to as the “ Disclosure Materials ”) on a timely basis or has received a valid extension of such time of filing and has filed any such SEC Reports prior to the expiration of any such extension, except where the failure to file on a timely basis would not have or reasonably be expected to result in a Material Adverse Effect (including, for this purpose only, any failure which would prevent Celgene from using Rule 144 to resell any Securities). As of their respective filing dates, or to the extent corrected by a subsequent restatement, the SEC Reports complied in all material respects with the requirements of the Securities Act and the Exchange Act and the rules and regulations of the Commission promulgated thereunder, and none of the SEC Reports, when filed, 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 light of the circumstances under which they were made, not misleading. The Company has never been an issuer subject to Rule 144(i) under the Securities Act. Each of the Material Contracts to which the Company is a party or to which the property or assets of the Company are subject has been filed as an exhibit to the SEC Reports.

(i) Financial Statements . 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 (or to the extent corrected by a subsequent restatement). Such financial statements have been prepared in accordance with GAAP applied on a consistent basis during the periods involved, 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 as of and for the dates thereof and the results of operations and cash flows for the periods then ended, subject, in the case of unaudited statements, to normal, immaterial year-end audit adjustments.

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(j) Material Changes . Except as specifically disclosed in SEC Reports filed prior to the date hereof, (i) there have been no events, occurrences or developments that have had or would reasonably be expected to have, either individually or in the aggregate, a Material Adverse Effect, (ii) the Company has not incurred any material liabilities (contingent or otherwise) other than (A) trade payables and accrued expenses incurred in the ordinary course of business consistent with past practice and (B) liabilities not required to be reflected in the Company’s financial statements pursuant to GAAP or disclosed in filings made with the Commission, (iii) the Company has not altered materially its method of accounting or the manner in which it keeps its accounting books and records, (iv) the Company has not declared or made any dividend or distribution of cash, shares of capital stock or other property to its stockholders or purchased, redeemed or made any agreements to purchase or redeem any shares of its capital stock (other than in connection with repurchases of unvested stock issued to employees of the Company), and (v) the Company has not issued any equity securities to any officer, director or Affiliate, except Common Stock issued in the ordinary course as dividends on outstanding preferred stock or issued pursuant to existing Company stock option or stock purchase plans or executive and director compensation arrangements disclosed in the SEC Reports.

(k) Litigation . There is no Action which (i) adversely affects or challenges the legality, validity or enforceability of any of the Transaction Documents or the Securities or (ii) except as specifically disclosed in the SEC Reports, would, if there were an unfavorable decision, individually or in the aggregate, have or reasonably be expected to result in a Material Adverse Effect. Neither the Company nor, to the Company’s Knowledge, any 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 Company’s Knowledge there is not pending or contemplated, any investigation by the Commission involving the Company or any current or former 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 under the Exchange Act or the Securities Act.

(l) Employment Matters . No material labor dispute exists or, to the Company’s Knowledge, is imminent with respect to any of the employees of the Company which would have or reasonably be expected to result in a Material Adverse Effect. None of the Company’s employees is a member of a union that relates to such employee’s relationship with the Company, and the Company is not a party to a collective bargaining agreement, and the Company believes that its relationship with its employees is good. No executive officer of the Company (as defined in Rule 501(f) of the Securities Act) has notified the Company that such officer intends to leave the Company or otherwise terminate such officer’s employment with the Company. To the Company’s Knowledge, no executive officer 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 a third party, and to the Company’s Knowledge, the continued employment of each such executive officer does not subject the Company to any liability with respect to any of the foregoing matters. The Company is 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 would not, individually or in the aggregate, have or reasonably be expected to result in a Material Adverse Effect.

(m) Compliance . The Company is not, and with respect only to clauses (ii), (iii) and (iv) below has not for the past two years been, (i) 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 under), nor has the Company received written notice of a claim that it is in default under or that it is in violation of, any Material Contract (whether or not such default or violation has been waived) except as would not, individually or in the aggregate, have or reasonably be expected to result in a Material Adverse

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Effect, (ii) in violation in any material respect of any order of any court, arbitrator or governmental body having jurisdiction over the Company or its business, products, properties or assets, (iii) in violation in any material respect of, or in receipt of written notice that it is in violation of, any statute, rule or regulation of any governmental authority applicable to the Company or its business, products, properties or assets or (iv) subject to any injunctions on production at any facility of the Company or clinical holds, other than any partial clinical holds that subsequently have been lifted, on any clinical investigations by the Company.

(n) Regulatory Permits . The Company possesses all material certificates, authorizations and permits issued by the appropriate federal, state, local or foreign regulatory authorities necessary to conduct its respective business as currently conducted and as described in the SEC Reports (“ Material Permits ”), and the Company has not received any notice of Proceedings relating to the revocation or modification of any such Material Permits.

(o) Title to Assets . The Company has good and marketable title in fee simple to all real property owned by it. The Company has good and marketable title to all tangible personal property owned by it that is material to the business of the Company, in each case free and clear of all Liens except such as do not materially affect the value of such property and do not interfere with the use made and proposed to be made of such property by the Company. Any real property and facilities held under lease by the Company are held by the Company under valid, subsisting and enforceable leases with such exceptions as are not material and do not interfere with the use made and proposed to be made of such property and buildings by the Company.

(p) Intellectual Property . The Company owns exclusively, free and clear of all Liens, or has obtained valid and enforceable licenses for, all Intellectual Property described in the SEC Reports as being owned or licensed by the Company and all Intellectual Property listed in Schedule 3.1(p)(i) (collectively, the “ Company Intellectual Property ”), and the Company owns exclusively, free and clear of all Liens, or has obtained valid and enforceable licenses for, all Intellectual Property that is necessary or reasonably sufficient to the conduct of the business of the Company as now conducted. There is no material Intellectual Property owned or licensed to the Company other than the Company Intellectual Property. To the Company’s Knowledge: (i) there are no third parties who have rights to any Company Intellectual Property, except for the rights of third-party licensors under the agreements listed in Schedule 3.1(p)(ii) and the rights granted to, or retained by, third parties under the agreements listed in Schedule 3.1(p)(iii) ; and (ii) there is no infringement by third parties of any material Company Intellectual Property. Except as disclosed in the SEC Reports or listed in Schedule 3.1(p)(iv) , there is no pending or, to the Company’s Knowledge, threatened action, suit, proceeding or written claim by others: (A) challenging the Company’s rights in or to any Company Intellectual Property; (B) challenging the validity, enforceability or scope of any material, granted and issued, government-registered Company Intellectual Property; or (C) asserting that the Company infringes or otherwise violates, or would, upon the commercialization of any product or service described in the SEC Reports that is in pre-clinical or clinical development, infringe or violate, any Intellectual Property of others, and the Company has not received any written notice of such challenge or assertion with respect to any of the foregoing. The Company has complied or will comply in due time with the material terms of each agreement pursuant to which Company Intellectual Property has been licensed to the Company, and all such agreements are in full force and effect. Each employee and consultant has assigned to the Company all rights, if any, of such employee or consultant, respectively, in any Company Intellectual Property in connection with the Company’s relationship with such employee or consultant. Schedule 3.1(p)(i) lists all Company Intellectual Property owned by the Company that is the subject of an application or registration with any governmental authority. Schedule 3.1(p)(ii) lists all contracts (other than agreements with employees or consultants) pursuant to which the Company was granted or otherwise transferred rights to any Company Intellectual Property. Schedule 3.1(p)(iii) lists all material contracts pursuant to which the Company has granted or otherwise transferred to a third party any rights under Company Intellectual Property. All Company Intellectual Property owned by the Company and registered with any governmental

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authority (i) is in proper form in all material respects, (ii) has not been disclaimed and (iii) other than ordinary course activities consistent with past practice, has been duly maintained in accordance with applicable law in all material respects, including submission of all necessary filings and payment of fees in accordance with the legal and administrative requirements of the appropriate jurisdictions.

(q) Insurance . The Company is insured by insurers of recognized financial responsibility against such losses and risks and in such amounts as the Company believes to be prudent and customary in the businesses and locations in which the Company is engaged, including, but not limited to, directors and officers insurance coverage. The Company has not received any notice of cancellation of any such insurance, nor, to the Company’s Knowledge, will it be unable 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 significant increase in cost.

(r) Transactions With Affiliates and Employees . Except as set forth in the SEC Reports, none of the officers or directors of the Company and, to the Company’s Knowledge, none of the employees of the Company is presently a party to any transaction with the Company (other than for services as employees, officers and directors), that would be required to be disclosed pursuant to Item 404 of Regulation S-K promulgated under the Securities Act.

(s) Internal Accounting Controls . The Company maintains 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 and liability accountability, (iii) access to assets or incurrence of liabilities is permitted only in accordance with management’s general or specific authorization, and (iv) the recorded accountability for assets and liabilities is compared with the existing assets and liabilities at reasonable intervals and appropriate action is taken with respect to any differences.

(t) Sarbanes-Oxley; Disclosure Controls . The Company is in compliance in all material respects with all of the provisions of the Sarbanes-Oxley Act of 2002 which are applicable to it as an “emerging growth company,” as defined in Section 2(a) of the Securities Act, as of the Closing Date. The Company has established disclosure controls and procedures (as such term is defined in Rule 13a-15(e) and 15d-15(e) under the Exchange Act) 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.

(u) Certain Fees . No person or entity will have, as a result of the transactions contemplated by this Agreement, any valid right, interest or claim against or upon the Company or Celgene for any commission, fee or other compensation pursuant to any agreement, arrangement or understanding entered into by or on behalf of the Company, with respect to the offer and sale of the Shares.

(v) Private Placement . Assuming the accuracy of Celgene’s representations and warranties set forth in Section 3.2 of this Agreement, no registration under the Securities Act is required for the offer and sale of the Securities by the Company to Celgene under the Transaction Documents. The issuance and sale of the Shares hereunder does not contravene the rules and regulations of the Trading Market.

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(w) Investment Company . The Company is not, and immediately after receipt of payment for the Shares, will not be or be 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.

(x) Registration Rights . Other than Celgene or as set forth in the Company’s Amended and Restated Investor Rights Agreement, dated October 7, 2008, 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 those securities which are currently registered on an effective registration statement on file with the Commission.

(y) Listing and Maintenance Requirements . The Company’s Common Stock is registered pursuant to Section 12(b) or 12(g) of the Exchange Act, and the Company has taken no action designed to terminate 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 twelve (12) months or such applicable shorter period preceding the date hereof, received written notice from any Trading Market on which the Common Stock is 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 in compliance with all listing and maintenance requirements of the Principal Trading Market on the date hereof.

(z) Application of Takeover Protections; Rights Agreements . 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, poison pill (including any distribution under a rights agreement) or other similar anti-takeover provision under the Company’s charter documents or the laws of the State of Delaware that is or would reasonably be expected to become applicable to Celgene as a result of Celgene and the Company fulfilling its obligations or exercising their rights under the Transaction Documents, including, without limitation, the Company’s issuance of the Shares and Celgene’s ownership of the Shares.

(aa) No Integrated Offering . Assuming the accuracy of Celgene’s representations and warranties set forth in Section 3.2 , none of the Company nor, to the Company’s Knowledge, any of its Affiliates or any Person acting on its behalf has, directly or indirectly, at any time within the past six (6) months, made any offers or sales of any Company security or solicited any offers to buy any security under circumstances that would (i) eliminate the availability of the exemption from registration under Regulation D under the Securities Act in connection with the offer and sale by the Company of the Securities as contemplated hereby or (ii) cause the offering of the Securities pursuant to the Transaction Documents to be integrated with prior offerings by the Company for purposes of any applicable law, regulation or stockholder approval provisions, including, without limitation, under the rules and regulations of any Trading Market on which any of the securities of the Company are listed or designated.

(bb) Tax Matters . The Company (i) has accurately and timely prepared and filed all foreign, federal and state income and all other tax returns, reports and declarations required by any jurisdiction to which it is subject, (ii) has paid all taxes and other governmental assessments and charges that are material in amount, shown or determined to be due on such returns, reports and declarations, except those being contested in good faith, with respect to which adequate reserves have been set aside on the books of the Company and (iii) has set aside on its books provisions reasonably adequate for the payment of all taxes for periods subsequent to the periods to which such returns, reports or declarations apply, except, in the case of clauses (i) and (ii) above, where the failure to so pay or file any such tax, assessment, charge or return would not have or reasonably be expected to result in a Material Adverse Effect. There are no unpaid taxes in any material amount claimed to be due by the Company by the taxing authority of any jurisdiction.

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(cc) Environmental Matters . To the Company’s Knowledge, the Company (i) is not in violation of any statute, rule, regulation, decision or order of any governmental agency or body or any court, domestic or foreign, relating to the use, disposal or release of hazardous or toxic substances or relating to the protection or restoration of the environment or human exposure to hazardous or toxic substances (collectively, “ Environmental Laws ”), (ii) does not own or operate any real property contaminated with any substance that is in violation of any Environmental Laws, (iii) is not liable for any off-site disposal or contamination pursuant to any Environmental Laws, and (iv) is not subject to any claim relating to any Environmental Laws; which violation, contamination, liability or claim has had or would have, individually or in the aggregate, a Material Adverse Effect; and there is no pending investigation or, to the Company’s Knowledge, investigation threatened in writing that might lead to such a claim.

(dd) No General Solicitation . Neither the Company nor, to the Company’s Knowledge, any person acting on behalf of the Company has offered or sold any of the Shares by any form of general solicitation or general advertising (within the meaning of Regulation D promulgated under the Securities Act).

(ee) Foreign Corrupt Practices . Neither the Company nor 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.

(ff) Off Balance Sheet Arrangements . There is no transaction, arrangement, or other relationship between the Company and an unconsolidated or other off balance sheet entity that is required to be disclosed by the Company in SEC Reports and is not so disclosed.

(gg) PFIC . The Company is not a “passive foreign investment company” within the meaning of Section 1297 of the U.S. Internal Revenue Code of 1986, as amended.

(hh) OFAC . Neither the Company nor any director, officer, agent, employee, Affiliate or Person acting on behalf of the Company is currently subject to any U.S. sanctions administered by the Office of Foreign Assets Control of the U.S. Treasury Department (“ OFAC ”); and the Company will not directly or indirectly use the proceeds of the sale of the Securities, or lend, contribute or otherwise make available such proceeds to any Subsidiary, joint venture partner or other Person or entity, towards any sales or operations in Cuba, Iran, Syria, Sudan, Myanmar or any other country sanctioned by OFAC or for the purpose of financing the activities of any Person currently subject to any U.S. sanctions administered by OFAC.

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

(a) Organization; Authority . Celgene is an entity duly organized, validly existing and in good standing under the laws of the jurisdiction of its organization with the requisite corporate or partnership power and authority to enter into and to consummate the transactions contemplated by the applicable Transaction Documents and otherwise to carry out its obligations hereunder and thereunder. The execution and delivery of this Agreement by Celgene and performance by Celgene of the transactions contemplated by this Agreement have been duly authorized by all necessary corporate action on the part of Celgene. Each Transaction Document to which it is a party has been duly executed by Celgene, and when delivered by Celgene in accordance with the terms hereof, will constitute the valid and legally binding obligation of

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Celgene, enforceable against it in accordance with its terms, except as such enforceability may be limited by applicable bankruptcy, insolvency, reorganization, moratorium, liquidation or similar laws relating to, or affecting generally the enforcement of, creditors’ rights and remedies or by other equitable principles of general application.

(b) No Conflicts . The execution, delivery and performance by Celgene of this Agreement and the Registration Rights Agreement and the consummation by Celgene of the transactions contemplated hereby and thereby will not (i) result in a violation of the organizational documents of Celgene, (ii) conflict with, or constitute a default (or an event which with notice or lapse of time or both would become a default) under, or give to others any rights of termination, amendment, acceleration or cancellation of, any agreement, indenture or instrument to which Celgene is a party, or (iii) result in a violation of any law, rule, regulation, order, judgment or decree (including federal and state securities laws) applicable to Celgene, except in the case of clauses (ii) and (iii) above, for such conflicts, defaults, rights or violations which would not, individually or in the aggregate, reasonably be expected to have a material adverse effect on the ability of Celgene to perform its obligations hereunder.

(c) Investment Intent . Celgene understands that the Shares are “restricted securities” and have not been registered under the Securities Act or any applicable state securities law and is acquiring the Shares 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 laws. Celgene is acquiring the Shares hereunder in the ordinary course of its business. Celgene does not presently have any agreement, plan or understanding, directly or indirectly, with any Person to distribute or effect any distribution of any of the Shares (or any securities which are derivatives thereof) to or through any person or entity; Celgene is not a registered broker-dealer under Section 15 of the Exchange Act or an entity engaged in a business that would require it to be so registered as a broker-dealer.

(d) Status . At the time Celgene was offered the Shares, it was, and at the date hereof it is an “accredited investor” as defined in Rule 501(a) under the Securities Act.

(e) General Solicitation . Celgene is not purchasing the Shares as a result of any advertisement, article, notice or other communication regarding Shares published in any newspaper, magazine or similar media or broadcast over television or radio or presented at any seminar or any other general advertisement.

(f) Experience . Celgene, 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 investment in the Shares, and has so evaluated the merits and risks of such investment. Celgene 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.

(g) Access to Information . Celgene acknowledges that it has had the opportunity to review the Disclosure Materials and has been afforded (i) the opportunity to ask such questions as it has deemed necessary of, and to receive answers from, representatives of the Company concerning the terms and conditions of the offering of the Shares and the merits and risks of investing in the Shares; (ii) access to information about the Company and its financial condition, results of operations, business, properties, management and prospects sufficient to enable Celgene to evaluate its investment; and (iii) the opportunity to obtain such additional information that the Company possesses or can acquire without unreasonable effort or expense that is necessary to make an informed investment decision with respect to the investment. Neither such inquiries nor any other investigation conducted by or on behalf of Celgene or its representatives or counsel shall modify, amend or affect Celgene’s right to rely on the truth, accuracy and completeness of the Disclosure Materials and the Company’s representations and warranties contained in the Transaction Documents. Celgene has sought such accounting, legal and tax advice as it has considered necessary to make an informed decision with respect to its acquisition of the Shares.

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(h) Brokers and Finders . No Person will have, as a result of the transactions contemplated by this Agreement, any valid right, interest or claim against or upon the Company or Celgene for any commission, fee or other compensation pursuant to any agreement, arrangement or understanding entered into by or on behalf of Celgene.

(i) Independent Investment Decision . Celgene has independently evaluated the merits of its decision to purchase Shares pursuant to the Transaction Documents Celgene has consulted such legal, tax and investment advisors as it, in its sole discretion, has deemed necessary or appropriate in connection with its purchase of the Shares.

The Company and Celgene acknowledge and agree that no party to this Agreement has made or makes any representations or warranties with respect to the transactions contemplated hereby other than those specifically set forth in this Article III and the Transaction Documents.

ARTICLE IV.

OTHER AGREEMENTS OF THE PARTIES

4.1 Transfer Restrictions .

(a) Compliance with Laws . Notwithstanding any other provision of this Article IV , Celgene acknowledges and agrees that the Shares may be disposed of only pursuant to an effective registration statement under, and in compliance with the requirements of, the Securities Act, or pursuant to an available exemption from, or in a transaction not subject to, the registration requirements of the Securities Act, and in compliance with any applicable state and federal securities laws. In connection with any transfer of the Securities other than (i) pursuant to an effective registration statement, (ii) to the Company or (iii) pursuant to Rule 144, the Company may require the transferor thereof to provide to the Company an opinion of counsel selected by the transferor and reasonably acceptable to the Company, the form and substance of which opinion shall be reasonably satisfactory to the Company, to the effect that such transfer does not require registration of such transferred Securities under the Securities Act. As a condition of transfer, any such transferee shall agree in writing to be bound by the terms of this Agreement and the Registration Rights Agreement and shall have the rights of Celgene under this Agreement and the Registration Rights Agreement with respect to such transferred Securities.

(b) Legends . The book-entry form of the Securities shall bear any legend as required by the “blue sky” laws of any state and a restrictive legend in substantially the following form, until such time as they are not required under Section 4.1(c) :

THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “SECURITIES ACT”), OR APPLICABLE STATE SECURITIES LAWS. THE SECURITIES MAY NOT BE OFFERED FOR SALE, SOLD, TRANSFERRED OR ASSIGNED (I) IN THE ABSENCE OF (A) AN EFFECTIVE REGISTRATION STATEMENT FOR THE SECURITIES UNDER THE SECURITIES ACT OR (B) AN AVAILABLE EXEMPTION FROM, OR IN A TRANSACTION NOT SUBJECT TO, THE REGISTRATION REQUIREMENTS OF THE SECURITIES ACT AND IN ACCORDANCE WITH APPLICABLE STATE SECURITIES LAWS OR BLUE SKY LAWS AS EVIDENCED BY A LEGAL OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE

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COMPANY AND ITS TRANSFER AGENT OR (II) UNLESS SOLD PURSUANT TO RULE 144 UNDER THE SECURITIES ACT. NOTWITHSTANDING THE FOREGOING, THE SECURITIES MAY BE PLEDGED IN CONNECTION WITH A BONA FIDE MARGIN ACCOUNT OR OTHER LOAN OR FINANCING ARRANGEMENT SECURED BY THE SECURITIES.

(c) Removal of Legends . The legend set forth in Section 4.1(b) above shall be removed and the Company shall issue to such holder the applicable Shares in book-entry form free and clear of such legend or any other legends by electronic delivery at the applicable balance account at the Depository Trust Company (“ DTC ”), if (i) such Securities are registered for resale under the Securities Act, (ii) such Securities are sold or transferred pursuant to Rule 144 (if the transferor is not an Affiliate of the Company), or (iii) such Securities are eligible for sale under Rule 144, without the requirement for the Company to be in compliance with the current public information required under Rule 144 as to such securities and without volume or manner-of-sale restrictions. The Company agrees that it shall cause Company Counsel (i) after the Effective Date, to issue to the Transfer Agent, if required by the Transfer Agent, a “blanket” legal opinion or other letter to allow sales without restriction pursuant to the effective registration statement and (ii) provide all other opinions of Company Counsel as may reasonable be required by the Transfer Agent in connection with the removal of legends pursuant to this Section 4.1(c) following receipt of the certificates and documents contemplated below. Following Rule 144 becoming available for the resale of a Purchaser’s Securities, without the requirement for the Company to be in compliance with the current public information required under Rule 144 as to such securities and without volume or manner-of-sale restrictions, the Company, upon the request of such Purchaser and delivery of the certificates and documents contemplated below, shall cause Company Counsel or other counsel satisfactory to the Transfer Agent to issue to the Transfer Agent a legal opinion stating that such Securities of such Purchaser are eligible for sale under Rule 144 without the requirement for the Company to be in compliance with the current public information required under Rule 144 as to such securities and without volume or manner-of-sale restrictions. Any fees (with respect to the Transfer Agent, Company Counsel or otherwise) associated with the issuance of such opinion or the removal of such legend shall be borne by the Company. Following the Effective Date, or at such earlier time as a legend is no longer required for certain Securities, the Company will promptly upon written request from Celgene instruct the Transfer Agent to remove the restrictive notation from the book entries evidencing such Securities. The Company may not make any notation on its records or give instructions to the Transfer Agent that enlarge the restrictions on transfer set forth in this Section 4.1(c) .

(d) Acknowledgement . Celgene hereunder acknowledges its primary responsibilities under the Securities Act and accordingly will not sell or otherwise transfer the Shares or any interest therein without complying with the requirements of the Securities Act. While the Registration Statement remains effective, Celgene may sell the Shares accordance with the plan of distribution contained in the Registration Statement and if it does so it will comply therewith and with the related prospectus delivery requirements unless an exemption therefrom is available. Celgene agrees that if it is notified by the Company in writing at any time that the Registration Statement registering the resale of the Shares is not effective or that the prospectus included in such Registration Statement no longer complies with the requirements of Section 10 of the Securities Act, Celgene will refrain from selling such Shares until such time as Celgene is notified by the Company that such Registration Statement is effective or such prospectus is compliant with Section 10 of the Securities Act, unless Celgene is able to, and does, sell such Shares pursuant to an available exemption from the registration requirements of Section 5 of the Securities Act.

4.2 Integration . The Company shall not, and shall use its commercially reasonable efforts to ensure that no Affiliate of the Company shall, 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 will be integrated with the offer or sale of the Shares in a manner that would require the registration under the Securities Act of the

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sale of the Shares to Celgene, or that will be integrated with the offer or sale of the Securities for purposes of the rules and regulations of any Trading Market such that it would require stockholder approval prior to the closing of such other transaction unless stockholder approval is obtained before the closing of such subsequent transaction.

4.3 Shareholder Rights Plan . No claim will be made or enforced by the Company or, with the consent of the Company, any other Person, that Celgene is an “ Acquiring Person ” 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 Celgene could be deemed to trigger the provisions of any such plan or arrangement, in either case solely by virtue of purchasing the Shares under the Transaction Documents.

4.4 Principal Trading Market Listing . In the time and manner required by the Principal Trading Market, the Company shall prepare and file with such Principal Trading Market an additional shares listing application covering all of the Shares and shall use its commercially reasonable efforts to take all steps necessary to cause all of the Shares to be approved for listing on the Principal Trading Market as contemplated by the Registration Rights Agreement.

4.5 Form D; Blue Sky . The Company agrees to timely file a Form D with respect to the Securities as required under Regulation D and to provide a copy thereof. The Company, on or before the Closing Date, shall take such action as the Company shall reasonably determine is necessary in order to obtain an exemption for or to qualify the Securities for sale to Celgene under applicable securities or “Blue Sky” laws of the states of the United States (or to obtain an exemption from such qualification) and shall provide evidence of such actions promptly.

ARTICLE V.

CONDITIONS PRECEDENT TO CLOSING

5.1 Conditions Precedent to the Obligation to Purchase Securities . The obligation of Celgene to acquire Shares at the Closing is subject to the fulfillment, on or prior to the Closing Date, of each of the following conditions, any of which may be waived by Celgene:

(a) Representations and Warranties . The representations and warranties of the Company contained herein shall be true and correct.

(b) Performance . The Company shall have performed, satisfied and complied with all covenants, agreements and conditions required by the Transaction Documents to be performed, satisfied or complied with by it at or prior to the Closing.

(c) No Injunction . No statute, rule, regulation, executive order, decree, ruling or injunction shall have been enacted, entered, promulgated or endorsed by any court or governmental authority of competent jurisdiction that prohibits the consummation of any of the transactions contemplated by the Transaction Documents.

(d) Consents . The Company shall have obtained in a timely fashion any and all consents, permits, approvals, registrations and waivers necessary for consummation of the purchase and sale of the Shares (including all Required Approvals), all of which shall be and remain so long as necessary in full force and effect.

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(e) No Suspensions of Trading in Common Stock . The Common Stock shall not have been suspended, as of the Closing Date, by the Commission or the Principal Trading Market from trading on the Principal Trading Market nor shall suspension by the Commission or the Principal Trading Market have been threatened, as of the Closing Date, either (A) in writing by the Commission or the Principal Trading Market or (B) by falling below the minimum listing maintenance requirements of the Principal Trading Market.

(f) Company Deliverables . The Company shall have delivered the Company Deliverables in accordance with Section 2.2(a) .

(g) Compliance Certificate . The Company shall have delivered to Celgene a certificate, dated as of the Closing Date and signed by its Chief Executive Officer or its Chief Financial Officer, dated as of the Closing Date, certifying to the fulfillment of the conditions specified in Sections 5.1(a) and (b)  in the form attached hereto as Exhibit D .

5.2 Conditions Precedent to the Obligations of the Company to sell Securities . The Company’s obligation to sell and issue the Shares at the Closing to Celgene is subject to the fulfillment to the satisfaction of the Company on or prior to the Closing Date of the following conditions, any of which may be waived by the Company:

(a) Representations and Warranties . The representations and warranties made by Celgene in Section 3.2 hereof shall be true and correct.

(b) Performance . Celgene shall have performed, satisfied and complied respects with all covenants, agreements and conditions required by the Transaction Documents to be performed, satisfied or complied with by Celgene at or prior to the Closing Date.

(c) No Injunction . No statute, rule, regulation, executive order, decree, ruling or injunction shall have been enacted, entered, promulgated or endorsed by any court or governmental authority of competent jurisdiction that prohibits the consummation of any of the transactions contemplated by the Transaction Documents.

(d) Consents . The Company shall have obtained in a timely fashion any and all consents, permits, approvals, registrations and waivers necessary for consummation of the purchase and sale of the Securities, all of which shall be and remain so long as necessary in full force and effect.

(e) Celgene Deliverables . Celgene shall have delivered the Celgene Deliverables in accordance with Section 2.2(b) .

ARTICLE VI.

MISCELLANEOUS

6.1 Fees and Expenses . The Company and Celgene shall each pay the fees and expenses of their respective advisers, counsel, accountants and other experts, if any, and all other expenses incurred by such party in connection with the negotiation, preparation, execution, delivery and performance of this Agreement. The Company shall pay all Transfer Agent fees and stamp taxes levied in connection with the sale and issuance of the Shares to Celgene.

6.2 Entire Agreement . The Transaction Documents, together with the exhibits and schedules thereto, contain the entire understanding of the parties with respect to the subject matter hereof and supersede all prior agreements, understandings, discussions and representations, oral or written, with respect to sale of the Shares, which the parties acknowledge have been merged into such documents, exhibits and schedules. At or after the Closing, and without further consideration, the Company and Celgene will execute and deliver to the other such further documents as may be reasonably requested in order to give practical effect to the intention of the parties under the Transaction Documents.

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6.3 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 on the earliest of (a) the date of transmission, if such notice or communication is delivered via facsimile (provided the sender receives a machine-generated confirmation of successful transmission) at the facsimile number specified in this Section 6.3 prior to 5:00 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 specified in this Section 6.3 on a day that is not a Trading Day or later than 5:00 P.M., New York City time, on any Trading Day, (c) the Trading Day following the date of mailing, if sent by U.S. nationally recognized overnight courier service with next day delivery specified, or (d) upon actual receipt by the party to whom such notice is required to be given. The address for such notices and communications shall be as follows:

or such other address as may be designated in writing hereafter, in the same manner, by such Person.

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6.4 Amendments; Waivers . No provision of this Agreement may be waived, modified, supplemented or amended except in a written instrument signed, in the case of an amendment, by the Company and Celgene. 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 of either party to exercise any right hereunder in any manner impair the exercise of any such right.

6.5 Construction . 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. The language used in this Agreement will be deemed to be the language chosen by the parties to express their mutual intent, and no rules of strict construction will be applied against any party. This Agreement shall be construed as if drafted jointly by the parties, and no presumption or burden of proof shall arise favoring or disfavoring any party by virtue of the authorship of any provisions of this Agreement or any of the Transaction Documents.

6.6 Successors and Assigns . The provisions of this Agreement shall inure to the benefit of and be binding upon the parties and their successors and permitted assigns. This Agreement, or any rights or obligations hereunder, may not be assigned by the Company without the prior written consent of Celgene.

6.7 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.

6.8 Governing Law . All questions concerning the construction, validity, enforcement and interpretation of this Agreement shall be governed by and construed and enforced in accordance with the internal laws of the State of California, without regard to the principles of conflicts of law thereof. Each party agrees that all 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, employees or agents) shall be commenced exclusively in the California Courts. Each party hereto hereby irrevocably submits to the exclusive jurisdiction of the California Courts 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 Proceeding, any claim that it is not personally subject to the jurisdiction of any such California Court, or that such Proceeding has been commenced in an improper or inconvenient forum. Each party hereto hereby irrevocably waives personal service of process and consents to process being served in any such 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 manner permitted by law. EACH PARTY HERETO HEREBY IRREVOCABLY WAIVES, TO THE FULLEST EXTENT PERMITTED BY APPLICABLE LAW, ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY LEGAL PROCEEDING ARISING OUT OF OR RELATING TO THIS AGREEMENT OR THE TRANSACTIONS CONTEMPLATED HEREBY.

6.9 Survival . The representations, warranties, agreements and covenants contained herein shall survive the Closing and the delivery of the Shares.

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6.10 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 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” 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 signature page were an original thereof.

6.11 Severability . If any provision of this Agreement is held to be invalid or unenforceable in any respect, the validity and enforceability of the remaining terms and provisions of this Agreement shall not in any way be affected or impaired thereby and the parties will attempt to agree upon a valid and enforceable provision that is a reasonable substitute therefor, and upon so agreeing, shall incorporate such substitute provision in this Agreement.

[REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

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

EXHIBITS:

EXHIBIT A

FORM OF REGISTRATION RIGHTS AGREEMENT

EXHIBIT B

FORM OF SECRETARY’S CERTIFICATE

The undersigned hereby certifies that he is the duly elected, qualified and acting Assistant Secretary of OncoMed Pharmaceuticals, Inc., a Delaware corporation (the “ Company ”), and that as such he is authorized to execute and deliver this certificate in the name and on behalf of the Company and in connection with the Securities Purchase Agreement, dated as of                     , 2013, by and between the Company and Celgene Corporation (the “Securities Purchase Agreement” ), and further certifies solely in his official capacity, in the name and on behalf of the Company, the items set forth below. Capitalized terms used but not otherwise defined herein shall have the meaning set forth in the Securities Purchase Agreement.

Latham & Watkins LLP, special counsel to the Company, is entitled to rely on this certificate in connection with the opinion that such firm is rendering pursuant to the Securities Purchase Agreement.

IN WITNESS WHEREOF, the undersigned has hereunto set his hand as of this          day of             , 2013.

EXHIBIT A

Resolutions

EXHIBIT B

Certificate of Incorporation

EXHIBIT C

Bylaws

EXHIBIT C

FORM OF LOCK-UP AGREEMENT

December      , 2013

Jefferies LLC

Leerink Swann LLC

As Representatives of the several

Underwriters listed in the Underwriting

Agreement referred to below

c/o Jefferies LLC

520 Madison Avenue

New York, New York 10022

and

c/o Leerink Swann LLC

1 Federal Street, 37 ^th Floor

Boston, Massachusetts 02110

Ladies & Gentlemen:

The undersigned is an owner of record or beneficially of certain shares of common stock, par value $0.001 per share, of the Company (“ Shares ”) or of securities convertible into or exchangeable or exercisable for Shares. The Company conducted its initial public offering of Shares (the “ Offering ”) for which Jefferies LLC (“ Jefferies ”) and Leerink Swann LLC (“ Leerink ”) acted as the representatives of the several underwriters listed in the Underwriting Agreement, dated as of July 17, 2013 (the “ Underwriting Agreement ”). The undersigned acknowledges that the underwriters will rely on the representations and agreements of the undersigned contained in this letter agreement.

Annex A sets forth definitions for capitalized terms used in this letter agreement that are not defined in the body of this agreement. Those definitions are a part of this agreement.

In consideration of the foregoing, and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the undersigned hereby agrees that, during the remainder of the Lock-up Period, the undersigned will not (and will use best efforts to cause any Immediate Family Member not to), subject to the exceptions set forth in this letter agreement, without the prior written consent of Jefferies and Leerink, which may withhold their consent in their sole discretion:

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The foregoing restrictions shall not apply to (i) the transfer of Shares or Related Securities by gift, or by will or intestate succession to the legal representative, heir, beneficiary or any Family Member or to a trust whose beneficiaries consist exclusively of one or more of the undersigned and/or a Family Member, (ii) transfers or dispositions of the undersigned’s Shares or Related Securities to any corporation, partnership, limited liability company or other entity all of the beneficial ownership interests of which are held by the undersigned or any Family Member, (iii) distributions of the undersigned’s Shares or Related Securities to partners, members or stockholders of the undersigned, (iv) the transfer of Shares by operation of law, including pursuant to a domestic order or a negotiated divorce settlement and (v) transfers of Shares or Related Securities pursuant to a bona fide third party tender offer, merger, consolidation or other similar transaction made to holders of the Shares or Related Securities involving a change of control of the Company, provided that in the event that the tender offer, merger, consolidation or other such transaction is not completed, the undersigned shall remain subject to the restrictions contained herein; provided, however , that in any such case except for clause (v), it shall be a condition to such transfer or distribution that:

Furthermore, notwithstanding the restrictions imposed by this letter agreement, the undersigned may, without the prior written consent of Jefferies and Leerink, (i) exercise an option to purchase Shares granted under any stock incentive plan or stock purchase plan of the Company, provided that the underlying Shares shall continue to be subject to the restrictions on transfer set forth in this letter agreement, (ii) establish a trading plan pursuant to Rule 10b5-1 under the Exchange Act for the transfer of Shares, provided that such plan does not provide for any transfers of Shares during the Lock-up Period, and (iii) transfer or dispose of Shares acquired in the Offering or on the open market following the Offering, provided that no filing under the Exchange Act or other public announcement shall be required or shall be made voluntarily in connection with such transfer or disposition pursuant to this clause (iii) during the Lock-up Period.

The undersigned also agrees and consents to the entry of stop transfer instructions with the Company’s transfer agent and registrar against the transfer of Shares or Related Securities held by the undersigned and the undersigned’s Immediate Family Members, if any, except in compliance with the foregoing restrictions.

The undersigned confirms that the undersigned has not, and has no knowledge that any Immediate Family Member has, directly or indirectly, taken any action designed to or that might reasonably be expected to cause or result in the stabilization or manipulation of the price of any

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security of the Company to facilitate the sale of the Shares. The undersigned will not, and will cause any Immediate Family Member not to take, directly or indirectly, any such action.

The undersigned hereby represents and warrants that the undersigned has full power, capacity and authority to enter into this letter agreement. This letter agreement is irrevocable and will be binding on the undersigned and the successors, heirs, personal representatives and assigns of the undersigned.

This letter agreement shall be governed by, and construed in accordance with, the laws of the State of New York.

[Remainder of Page Intentionally Blank; Signature Page Follows]

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(Indicate capacity of person signing if

signing as custodian or trustee, or on behalf

of an entity)

Annex A

Certain Defined Terms

Used in Lock-up Agreement

For purposes of the letter agreement to which this Annex A is attached and of which it is made a part:

in each case whether effected directly or indirectly.

Capitalized terms not defined in this Annex A shall have the meanings given to them in the body of this letter agreement.

EXHIBIT D

FORM OF OFFICER’S CERTIFICATE

The undersigned, the [Chief Executive Officer][Chief Financial Officer] of Oncomed Pharmaceuticals Inc., a Delaware corporation (the “ Company ”), pursuant to Section 5.1(g) of the Securities Purchase Agreement, dated as of                     , by and between the Company and Celgene Corporation (the “ Securities Purchase Agreement ”), hereby represents, warrants and certifies as follows (capitalized terms used but not otherwise defined herein shall have the meaning set forth in the Securities Purchase Agreement):

Latham & Watkins LLP, special counsel to the Company, is entitled to rely on this certificate in connection with the opinion that such firm is rendering pursuant to the Securities Purchase Agreement.

IN WITNESS WHEREOF, the undersigned has executed this certificate this          day of                     , 2013.