Exhibit 10.15

COMMON STOCK PURCHASE AGREEMENT

THIS COMMON STOCK PURCHASE AGREEMENT (this “Agreement”) is made as of September 3, 2014, by and between rEVO Biologics, Inc., a Delaware corporation (the “Company”), and LFB BIOTECHNOLOGIES S.A.S., a French Corporation (the “Purchaser”).

RECITALS

A. The Company is planning to issue and sell shares of the common stock, par value $0.01 per share, of the Company (the “Common Stock”) in an underwritten initial public offering (the “IPO”) pursuant to the Company’s registration statement on Form S-1 (File No. 333-197030) (the “Registration Statement”) and an underwriting agreement (the “Underwriting Agreement”) by and among the Company and Piper Jaffray & Co. and Guggenheim Securities, LLC, as representatives of the several underwriters listed therein (together, the “Underwriters”).

B. The Purchaser wishes to purchase, and the Company wishes to issue and sell, upon the terms and conditions stated herein, shares of Common Stock (the “Shares”) at the per share initial public offering price in the IPO (prior to any underwriting discounts and commissions, the “Per Share Purchase Price”) at an aggregate purchase price of $10.0 million (the “Subscription Amount”) contingent upon and concurrently with the closing of the IPO.

C. The Company and the Purchaser are executing and delivering this Agreement in reliance upon the exemption from securities registration afforded by Section 4(2) of 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.

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 hereby agree as follows:

ARTICLE 1

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:

“Closing Date” means the third (3rd) trading day after the date on which the Underwriting Agreement has been executed and delivered by all parties thereto.

“Company Covered Person” means, with respect to the Company as an “issuer” for purposes of Rule 506 promulgated under the Securities Act, any Person listed in the first paragraph of Rule 506(d)(1).

“Company’s Knowledge” means the actual knowledge of the executive officers (as defined in Rule 405 under the Securities Act) of the Company, after due inquiry.

“Material Adverse Effect” means a material adverse effect on the business, assets (including intangible assets), liabilities, financial condition, property, or results of operations of the Company.

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

“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.

“Transaction Documents” means this Agreement and any other documents or agreements executed in connection with the transactions contemplated hereunder.

ARTICLE 2

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 the Purchaser, and the Purchaser shall purchase from the Company, such number of shares of Common Stock equal to the quotient resulting from dividing (i) the Subscription Amount by (ii) the Per Share Purchase Price.

(b) Closing. The purchase and sale of the Shares shall be contingent on and take place concurrently with the closing of the IPO and remotely via the exchange of documents and signatures or at such other time and place as the parties may mutually agree upon, orally or in writing (which time and place are designated as the “Closing”).

2.2 Delivery. At the Closing, upon payment of the Subscription Agreement by wire transfer to a bank account designated by the Company or by such other methods as may be designated by the Company, the Company shall deliver to the Purchaser the Shares by electronic delivery to the Depository Trust Company (“DTC”) or its designated custodian.

ARTICLE 3

REPRESENTATIONS AND WARRANTIES

3.1 Representations and Warranties of the Company. The Company hereby represents and warrants as of the date hereof and the Closing Date (except for the representations and warranties that speak as of a specific date, which shall be made as of such date), to the Purchaser that, except as disclosed in the Registration Statement:

(a) Organization, Good Standing, Corporate Power and Qualification. The Company is a corporation duly organized, validly existing and in good standing under the laws of the State of Delaware and has all requisite corporate power and authority to carry on its business as presently conducted and as proposed to be conducted. The Company is duly qualified to transact business and is in good standing in each jurisdiction in which the failure to so qualify would have a Material Adverse Effect.

(b) Authorization. All corporate action required to be taken by the Company’s Board of Directors and stockholders in order to authorize the Company to enter into the Transaction Documents, and to issue the Shares at the Closing, has been taken or will be taken prior to the Closing. All action on the part of the officers of the Company necessary for the execution and delivery of the Transaction Documents, the performance of all obligations of the Company under the Transaction Documents to be performed as of the Closing, and the issuance and delivery of the Shares has been taken or will be taken prior to the Closing. The Transaction Documents, when executed and delivered by the Company, shall constitute valid and legally binding obligations of the Company, enforceable against the Company in accordance with their respective terms except (i) as limited by applicable bankruptcy,

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insolvency, reorganization, moratorium, fraudulent conveyance, or other laws of general application relating to or affecting the enforcement of creditors’ rights generally, and (ii) as limited by laws relating to the availability of specific performance, injunctive relief, or other equitable remedies.

(c) Valid Issuance of Shares.

(i) The Shares, when issued, sold and delivered in accordance with the terms and for the consideration set forth in this Agreement, will be validly issued, fully paid and nonassessable and free of restrictions on transfer other than restrictions on transfer under the Transaction Documents, applicable state and federal securities laws and liens or encumbrances created by or imposed by a Purchaser. Assuming the accuracy of the representations of the Purchaser in Section 3.2 and subject to the filings described in Subsection 3.1(d), the Shares will be issued in compliance with all applicable federal and state securities laws.

(ii) No “bad actor” disqualifying event described in Rule 506(d)(1)(i)-(viii) of the Securities Act (a “Disqualification Event”) is applicable to the Company or, to the Company’s knowledge, any Company Covered Person, except for a Disqualification Event as to which Rule 506(d)(2)(ii–iv) or (d)(3), is applicable.

(d) Governmental Consents and Filings. Assuming the accuracy of the representations made by the Purchaser in Section 3.2, no consent, approval, order or authorization of, or registration, qualification, designation, declaration or filing with, any federal, state or local governmental authority is required on the part of the Company in connection with the consummation of the transactions contemplated by this Agreement, except for filings pursuant to Regulation D of the Securities Act, and applicable state securities laws, which have been made or will be made in a timely manner.

(e) Compliance with Other Instruments. The Company is not in violation or default (i) of any provisions of its certificate of incorporation or bylaws, (ii) of any instrument, judgment, order, writ or decree, (iii) under any note, indenture or mortgage, or (iv) under any Material Contract, or (v) to its knowledge, of any provision of federal or state statute, rule or regulation applicable to the Company, the violation of which would have a Material Adverse Effect. The execution, delivery and performance of the Transaction Documents and the consummation of the transactions contemplated by the Transaction Documents will not result in any such violation or be in conflict with or constitute, with or without the passage of time and giving of notice, either (i) a default under any such provision, instrument, judgment, order, writ, decree, contract or agreement; or (ii) an event which results in the creation of any lien, charge or encumbrance upon any assets of the Company or the suspension, revocation, forfeiture, or nonrenewal of any material permit or license applicable to the Company.

(f) 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 any Purchaser for any commission, fee or other compensation pursuant to any agreement, arrangement or understanding entered into by or on behalf of the Company.

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

(a) Authorization. The Purchaser has full power and authority to enter into the Transaction Documents. The Transaction Documents when executed and delivered by the Purchaser, will constitute valid and legally binding obligations of the Purchaser, enforceable in accordance with their terms, except as limited by applicable bankruptcy, insolvency, reorganization, moratorium, fraudulent conveyance and any other laws of general application affecting enforcement of creditors’ rights generally, and as limited by laws relating to the availability of specific performance, injunctive relief or other equitable remedies.

(b) Purchase Entirely for Own Account. This Agreement is made with the Purchaser in reliance upon the Purchaser’s representation to the Company, which by the Purchaser’s execution of this Agreement, the Purchaser hereby confirms, that the Shares to be acquired by the Purchaser will be acquired for investment for the Purchaser’s own account, not as a nominee or agent, and not with a view to the resale or distribution of any part thereof, and that the Purchaser has no present intention of selling, granting any participation in, or otherwise distributing the same. By executing this Agreement, the Purchaser further represents that the Purchaser does not presently have any contract, undertaking, agreement or arrangement with any Person to sell, transfer or grant participations to such Person or to any third Person, with respect to any of the Shares. The Purchaser has not been formed for the specific purpose of acquiring the Shares.

(c) Disclosure of Information. The Purchaser has had an opportunity to discuss the Company’s business, management, financial affairs and the terms and conditions of the offering of the Shares with the Company’s management and has had an opportunity to review the Company’s facilities. The foregoing, however, does not limit or modify the representations and warranties of the Company in Section 3.1 or the right of the Purchaser to rely thereon.

(d) Restricted Securities. The Purchaser understands that the Shares have not been, and will not be, registered under the Securities Act, by reason of a specific exemption from the registration provisions of the Securities Act which depends upon, among other things, the bona fide nature of the investment intent and the accuracy of the Purchaser’s representations as expressed herein. The Purchaser understands that the Shares are “restricted securities” under applicable U.S. federal and state securities laws and that, pursuant to these laws, the Purchaser must hold the Shares indefinitely unless they are registered with the Commission and qualified by state authorities, or an exemption from such registration and qualification requirements is available. The Purchaser acknowledges that the Company has no obligation to register or qualify the Shares, for resale. The Purchaser further acknowledges that if an exemption from registration or qualification is available, it may be conditioned on various requirements including, but not limited to, the time and manner of sale, the holding period for the Shares, and on requirements relating to the Company which are outside of the Purchaser’s control, and which the Company is under no obligation and may not be able to satisfy. The Purchaser acknowledges that the Company filed the Registration Statement in connection with the IPO. The Purchaser understands that this transaction is not intended to be part of the IPO, and that the Purchaser will not be able to rely on the protection of Section 11 of the Securities Act with respect to the Shares and the transaction contemplated hereunder.

(e) Legends. The Purchaser understands that the Shares and any securities issued in respect of or exchange for the Shares, may be notated with one or all of the following legends:

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(i) “THE SHARES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AND HAVE BEEN ACQUIRED FOR INVESTMENT AND NOT WITH A VIEW TO, OR IN CONNECTION WITH, THE SALE OR DISTRIBUTION THEREOF. NO SUCH TRANSFER MAY BE EFFECTED WITHOUT AN EFFECTIVE REGISTRATION STATEMENT RELATED THERETO OR AN OPINION OF COUNSEL IN A FORM SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED UNDER THE SECURITIES ACT OF 1933.”

(ii) Any legend set forth in, or required by, the other Transaction Documents.

(iii) Any legend required by the securities laws of any state to the extent such laws are applicable to the Shares represented by the certificate, instrument, or book entry so legended.

(f) Accredited Investor. The Purchaser is an accredited investor as defined in Rule 501(a) of Regulation D promulgated under the Securities Act.

(g) “Bad Actor” Status. The Purchaser represents that it is not a “bad actor” within the meaning of Rule 506(d) promulgated under the Securities Act.

(h) Foreign Investors. The Purchaser hereby represents that it has satisfied itself as to the full observance of the laws of its jurisdiction in connection with any invitation to subscribe for the Shares or any use of this Agreement, including (i) the legal requirements within its jurisdiction for the purchase of the Shares, (ii) any foreign exchange restrictions applicable to such purchase, (iii) any governmental or other consents that may need to be obtained, and (iv) the income tax and other tax consequences, if any, that may be relevant to the purchase, holding, redemption, sale, or transfer of the Shares. The Purchaser’s subscription and payment for and continued beneficial ownership of the Shares will not violate any applicable securities or other laws of the Purchaser’s jurisdiction.

(i) No General Solicitation. Neither the Purchaser, nor any of its officers, directors, employees, agents, stockholders or partners has either directly or indirectly, including, through a broker or finder (a) engaged in any general solicitation, or (b) published any advertisement in connection with the offer and sale of the Shares.

(j) Access to Information. The Purchaser acknowledges that it has received all the information it considers necessary or appropriate for deciding whether to purchase the Shares 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 respective financial condition, results of operations, business, properties, management and prospects sufficient to enable it 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 the Purchaser or its representatives or counsel shall modify, amend or affect the Purchaser’s right to rely on the truth, accuracy and completeness of the Registration Statement and the Company’s representations and warranties contained in the Transaction Documents.

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(k) 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 any Purchaser for any commission, fee or other compensation pursuant to any agreement, arrangement or understanding entered into by or on behalf of the Purchaser.

ARTICLE 4

CONDITIONS PRECEDENT TO CLOSING

4.1 Conditions Precedent to the Obligations of the Purchaser to Purchase Shares at the Closing. The obligation of the Purchaser to acquire Shares at the Closing is subject to the fulfillment to the Purchaser’s satisfaction, on or prior to the Closing Date, of each of the following conditions, any of which may be waived by the Purchaser:

(a) Representations and Warranties. The representations and warranties of the Company contained herein shall be true and correct in all material respects (except for those representations and warranties which are qualified as to materiality, in which case such representations and warranties shall be true and correct in all respects) as of the date of this Agreement and as of the Closing Date, as though made on and as of the Closing Date, except for such representations and warranties that speak as of a specific date.

(b) IPO Shares. The Underwriters shall have purchased, concurrent with the purchase of the Shares by the Purchaser hereunder, the Firm Shares (as defined in the Underwriting Agreement) at the per share purchase price set forth in the Underwriting Agreement.

(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.

4.2 Conditions Precedent to the Obligations of the Company to sell Shares at the Closing. The Company’s obligation to sell and issue the Shares to the Purchaser at the Closing 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 the Purchaser in Section 3.2 hereof shall be true and correct in all material respects as of the date of this Agreement, and as of the Closing Date as though made on and as of the Closing Date, except for representations and warranties that speak as of a specific date.

(b) IPO Shares. The Underwriters shall have purchased, concurrent with the purchase of the Shares by the Purchaser hereunder, the Firm Shares (as defined in the Underwriting Agreement) at the per share purchase price set forth in the Underwriting Agreement.

(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.

ARTICLE 5

MISCELLANEOUS

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5.1 Termination. This Agreement shall automatically terminate upon the earliest to occur of (i) the written consent of the Company and the Purchaser, (ii) the withdrawal by the Company of the Registration Statement, or (iii) following the execution of the Underwriting Agreement, the termination of such Underwriting Agreement in accordance with its terms.

5.2 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 such matters, 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 the Purchaser 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.

5.3 Notices. All notices and other communications hereunder shall be in writing and shall be deemed to have been duly given if mailed or transmitted and confirmed by any standard form of telecommunication. The address for such notices and communications shall be as follows: (i) if to the Company, rEVO Biologics, Inc., 175 Crossing Blvd., Framingham, MA 01702, Attention: President, fax: 508-370-3797, with a copy to Goodwin Procter LLP, 53 State Street, Boston, MA 02109, Attention: Stuart Cable, fax: 617-523-1231, (ii) if to the Purchaser, Laboratoire français du Fractionnement et des Biotechnologies, 3 avenue des Tropiques, ZA de Courtaboeuf, 91940, Attention: General Counsel, fax: + 33 1 70 99 40 63.

5.4 Amendments; Waivers; No Additional Consideration. No amendment or waiver of any provision of this Agreement, nor any consent or approval to any departure therefrom, shall in any event be effective unless the same shall be in writing and signed by the parties hereto.

5.5 Construction. The headings herein are included for convenience of reference only and are not intended to be part of, or to affect the meaning or interpretation of, this Agreement.

5.6 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 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.

5.7 Governing Law. This Agreement shall be governed by and construed in accordance with the laws of the State of Delaware, without regard to the principles of conflicts of law thereof.

5.8 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.

5.9 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.

5.10 Remedies. In addition to being entitled to exercise all rights provided herein or granted by law, including recovery of damages, the Purchaser and the Company will be entitled to specific

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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 obligations described in the foregoing sentence and hereby agree to waive in any action for specific performance of any such obligation (other than in connection with any action for a temporary restraining order) the defense that a remedy at law would be adequate.

[signatures to follow]

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

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