LICENSE AGREEMENT

Exhibit 10.18

WHENEVER CONFIDENTIAL INFORMATION IS OMITTED HEREIN (SUCH OMISSIONS ARE DENOTED BY AN ASTERISK *), SUCH CONFIDENTIAL INFORMATION HAS BEEN SUBMITTED SEPARATELY TO THE SECURITIES AND EXCHANGE COMMISSION PURSUANT TO A REQUEST FOR CONFIDENTIAL TREATMENT.

LICENSE AGREEMENT

by and between

THE SCRIPPS RESEARCH INSTITUTE,

a California nonprofit

public benefit corporation

and

REPLIGEN CORPORATION,

a Delaware corporation

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LICENSE AGREEMENT

This License Agreement is entered into and made effective as of this 6 ^th day of April, 2007 (the “Effective Date”), by and between THE SCRIPPS RESEARCH INSTITUTE, a California nonprofit public benefit corporation (“TSRI”) located at 10550 North Torrey Pines Road, La Jolla, California 92037, and Repligen Corporation, a Delaware corporation (“Licensee”) located at 41 Seyon Street, Waltham, Massachusetts, 02453 with respect to the facts set forth below.

RECITALS

A. TSRI is engaged in fundamental scientific biomedical and biochemical research including research relating to Friedrich’s ataxia (FA).

B. Licensee is engaged in research and development of products to prevent, diagnose and treat diseases and conditions in humans.

C. TSRI has disclosed to Licensee certain technology and TSRI has the right to grant a license to the technology, subject to certain rights of the U.S. Government resulting from the receipt by TSRI of certain funding from the U.S. Government.

D. TSRI desires to grant to Licensee, and Licensee wishes to acquire from TSRI, a sole worldwide right and license to certain patent rights and materials of TSRI, subject to the terms and conditions set forth herein.

AGREEMENT

NOW, THEREFORE, in consideration of the mutual covenants and conditions set forth herein, TSRI and Licensee hereby agree as follows:

1. Definitions . Capitalized terms shall have the meaning set forth herein.

1.1 Affiliate . The term “Affiliate” shall mean any entity which directly or indirectly controls, or is controlled by Licensee. The term “control” as used herein means (a) in the case of corporate entities, direct or indirect ownership of at least fifty percent (50%) of the stock or shares entitled to vote for the election of directors; or (b) in the case of non-corporate entities, direct or indirect ownership of at least fifty percent (50%) of the equity interest with the power to direct the management and policies of such non-corporate entities. Unless otherwise specified, the term Licensee includes Affiliates.

1.2 Confidential Information . The term “Confidential Information” shall mean any and all proprietary or confidential information of TSRI or Licensee which may be exchanged between the parties at any time and from time to time during the term of this Agreement. Information shall not be considered confidential to the extent that the receiving party can establish by competent proof that it:

(a) Is publicly disclosed through no fault of any party hereto, either before or after it becomes known to the receiving party; or

(b) Was known to the receiving party prior to the date of this Agreement, which knowledge was acquired independently and not from another party hereto (or such party’s employees); or

(c) Is subsequently disclosed to the receiving party in good faith by a third party who has a right to make such disclosure; or

(d) Has been published by a third party as a matter of right.

1.2.1 In the event that Confidential Information is required to be disclosed by law or court order, in which event the party required to make such disclosure shall limit the same to the minimum required to comply with the law or court order, and prior to making such disclosure that party shall notify the other party, not later than ten (10) days before the disclosure in order to allow that other party to comment and/or to obtain a protective or other order, including extensions of time and the like, with respect to such disclosure.

1.3 Field . The term “Field” shall mean the prevention, diagnosis and treatment of conditions or diseases in humans.

1.4 Licensed Patent Rights . The term “Licensed Patent Rights” shall mean rights arising out of or resulting from (a) the U.S./PCT Patent Application(s) set forth on Exhibit A; (b) the foreign patent applications of (a); (c) the patents proceeding from (a) and (b); (d) divisionals, continuations, reissues, reexaminations, and extensions of any patent or application set forth in (a)- (c) above; and (e) all claims of continuations-in-part that are entitled to the benefit of the priority date of (a).

1.5 Licensed Product . The term “Licensed Product” shall mean any product, the manufacture, use, importation, sale or offer for sale of which in or into a particular country is covered by a Valid Claim within the Licensed Patent Rights. Whether a product is a “Licensed Product” shall be determined on a country-by-country basis.

1.6 Licensed Process . The term “Licensed Process” shall mean any process, the performance of which is covered by a Valid Claim of Licensed Patent Rights. Whether a process is a “Licensed Process” shall be determined on a country-by-country basis.

1.7 Licensed Service . The term “Licensed Service” shall mean the performance of a service by Licensee or a sublicensee for a third party, which performance uses or incorporates a Licensed Product or Licensed Process. Whether a service is a “Licensed Service” shall be determined on a country-by-country basis.

1.8 Major Market Country . The term “Major Market Country” shall mean any of the following countries: the United States of America, the United Kingdom, France, Germany, Spain, Italy, Japan, Canada, or Australia.

1.9 Net Sales . The term “Net Sales” shall mean the gross amount invoiced by Licensee, or sublicensee, or any of them on all sales of Licensed Products, Licensed Processes and Licensed Services less (a) discounts, chargebacks and rebates actually allowed, whether in cash or trade; (b) credits for claims, allowances, retroactive price reductions or returned goods;

(c) prepaid freight and insurance; and (d) sales taxes or other governmental charges actually paid in connection with sales of Licensed Products (but excluding what are commonly known as income taxes and value-added taxes). Net Sales shall include all consideration charged by Licensee or sublicensees in exchange for any Licensed Products, Licensed Processes, or Licensed Services, including without limitation any monetary payments or any other property whatsoever. For purposes of determining Net Sales, a sale shall be deemed to have occurred when an invoice therefore shall be generated or the Licensed Product shipped for delivery, Licensed Process, completed, or Licensed Service provided. Sales of Licensed Products by Licensee to any Affiliate or sublicensee which is a reseller thereof shall be excluded, and only the subsequent sale of such Licensed Products by Affiliates or sublicensees of Licensee to unrelated parties shall be deemed to generate Net Sales hereunder.

1.10 Valid Claim . The term “Valid Claim” shall mean a claim of an issued patent within the Licensed Patent Rights that has not lapsed, expired, been canceled, or become abandoned, and has not been held invalid by a court or other appropriate body of competent jurisdiction, unappealable or unappealed within the time allowed for appeal and which has not been admitted to be invalid or unenforceable through reissue or disclaimer or otherwise. The term Valid Claim shall also include the claims of a pending patent application within the Licensed Patent Rights for a period of six (6) years from the date of first examination (i.e., first office action) of that patent application.

1.11 Novartis Research Products Nonexclusive License . “Novartis Research Products Nonexclusive License” shall mean the non-exclusive, worldwide license rights (without the right to sublicense) granted by Scripps to Novartis under the Licensed Patent Rights to make and use (but not sell) “Research Products”. “Research Products” is defined to mean any product, process or device which is designed or utilized for discovering, improving or testing a Therapeutic Product, Preventative medicine, or Diagnostic Product. “Diagnostic Product” means any product, process or device that is designed or utilized for diagnosis of a disease or condition in humans or vertebrate animals. “Preventative medicine” means any product, process or device that is designed or utilized to prevent the occurrence of any disease state in humans or vertebrate animals. “Therapeutic Product” means any product, process or device which is designed or utilized for treatment or mitigation of an existing disease state in humans or vertebrate animals.

2. Grant of License .

2.1 Grant of License for Licensed Products . TSRI hereby grants and Licensee accepts, subject to the terms and conditions of this Agreement, a sole license under the Licensed Patent Rights to make and have made, to use and have used and to import Licensed Products in the Field. In addition, TSRI hereby grants and Licensee accepts, subject to the terms and conditions of this Agreement, an exclusive license under the Licensed Patent Rights to offer to sell, to sell and have sold Licensed Products in the Field.

2.2 Grant of License for Licensed Processes . TSRI hereby grants and Licensee accepts, subject to the terms and conditions of this Agreement, a sole license under the Licensed Patent Rights to use and have used Licensed Processes in the Field. In addition, TSRI hereby grants and Licensee accepts, subject to the terms and conditions of this Agreement, an exclusive

license under the Licensed Patent Rights to offer to sell, to sell and have sold Licensed Processes in the Field.

2.3 Grant of License for Licensed Services . TSRI hereby grants and Licensee accepts, subject to the terms and conditions of this Agreement, a sole license under the Licensed Patent Rights to use and have used Licensed Services in the Field. In addition, TSRI hereby grants and Licensee accepts, subject to the terms and conditions of this Agreement, an exclusive license under the Licensed Patent Rights to offer to sell, to sell and have sold Licensed Services in the Field.

2.4 Sublicensing . Licensee shall have the right to grant and authorize sublicenses to any party with respect to the rights conferred upon Licensee under this Agreement, provided, however, that any such sublicense shall be subject in all respects to the provisions contained in this Agreement (excluding the payments specified in Sections 3.1 and 3.2 below). Sublicensees shall not further sublicense without TSRI’s prior written consent, which approval shall not be unreasonably withheld. Licensee shall forward to TSRI a copy of any and all fully executed agreements within thirty (30) days of execution.

2.5 No Other License . This Agreement confers no license or rights by implication, estoppel, or otherwise under any patent applications or patents of TSRI other than Licensed Patent Rights regardless of whether such patents are dominant or subordinate to Licensed Patent Rights. TSRI and Licensee hereby agree and acknowledge that nothing in this Agreement, including without limitation the provisions of Sections 2.6, 2.7, and 2.8, create, expressly or implicitly, any obligation for Licensee to grant any rights or licenses, or to provide any materials or perform any services, to or for TSRI or any Third Party, including without limitation, the United States Government or Novartis.

2.6 Governmental Interest . Licensee and TSRI acknowledge that TSRI has received, and expects to continue to receive, funding from the United States Government in support of TSRI’s research activities. Licensee and TSRI acknowledge and agree that their respective rights and obligations pursuant to this Agreement shall be subject to the rights of the United States Government, which may exist, arise or result from TSRI’s receipt of research support from the United States Government, including but not limited to, 37 C.F.R. 401, the NIH Grants Policy Statement and the NIH Guidelines for Obtaining and Disseminating Biomedical Research Resources.

2.7 Reservation of Rights . TSRI reserves the right to use for any research or educational purposes any Licensed Patent Rights and materials licensed hereunder, without TSRI being obligated to pay Licensee any royalties or other compensation. In addition, TSRI reserves the right to grant non-exclusive research and educational use licenses to other nonprofit or academic institutions to Licensed Patent Rights licensed hereunder, without the other nonprofit entity being obligated to pay Licensee any royalties or other compensation. TSRI shall have no obligation to notify or inform Licensee of such use or licenses.

2.8 Novartis Non-Exclusive License . The licenses granted under Sections 2.1 and 2.2 of this Agreement are subject to the non-exclusive license rights granted to Novartis pursuant to the Novartis Research Products Nonexclusive License.

3. Royalties

3.1 License Issue Royalty . In consideration for TSRI entering into this Agreement, Licensee agrees to pay and shall pay to TSRI a noncreditable, nonrefundable license issue royalty in the amount of Three Hundred Thousand U.S. Dollars (U.S.$300,000) (“License Issue Royalty”) within fifteen (15) days of the Effective Date. Failure of Licensee to make this payment shall render this Agreement null and void ( ab initio) .

3.2 Equity . In addition to the License Issue Royalty specified in 3.1 above, Licensee shall issue to TSRI Eighty Seven Thousand Four Hundred Sixty-Four (87,464) shares of Licensee’s common stock, equal to Three Hundred Thousand U.S. Dollars (U.S. $300, 000) within fifteen (15) days of the Effective Date as reported on the Nasdaq Global Market or such other market on which such shares are then traded. Each share of Licensee common stock shall be valued at the closing price of such shares on the trading day immediately prior to the Effective Date. If the value of the shares is not equal to Three Hundred Thousand U.S. Dollars (U.S. $300,000) on the one-year anniversary of the Effective Date, Licensee shall make a cash payment to TSRI equal to the difference between the actual total value of the shares on such date and Three Hundred Thousand U.S. Dollars (U.S. $300,000) within thirty (30) days after the one year anniversary of the Effective Date.

3.3 Minimum Annual Royalty . Subject to the credits described in this Section 3.3, within thirty days following each anniversary of the Effective Date, Licensee agrees to pay and shall pay to TSRI a nonrefundable minimum annual royalty in the amount of [**Confidential Treatment Requested**] for the twelve (12) month period immediately preceding such anniversary date. Each such minimum annual royalty shall be offset (i.e., reduced by) by any amounts paid, as specified in 3.4, 3.5, 3.6, 4.1, and 4.2. hereunder by Licensee during the twelve (12) month period immediately preceding the relevant anniversary date.

3.4 Running Royalties for Licensed Products . Licensee agrees to pay and shall pay to TSRI a running royalty on a country by country basis in the amount of [**Confidential Treatment Requested**] of Net Sales of Licensed Products. Licensee shall be entitled to a credit against royalties due hereunder, of [**Confidential Treatment Requested**] of any royalties paid to any third parties by Licensee, its Affiliates or sublicensees which is necessary in order for Licensee or its Affiliates or sublicensees to make, use, sell, offer for sale, or import any Licensed Product without infringing any patent or other rights of such third party. The application of such credit shall be limited so that it shall not reduce by more than [**Confidential Treatment Requested**] the royalties paid hereunder for any given period.

3.5 Running Royalties for Licensed Processes . Licensee agrees to pay and shall pay to TSRI a running royalty on a country by country basis in the amount of [**Confidential Treatment Requested**] of Net Sales of products made using a Licensed Process. Licensee shall be entitled to a credit against royalties due hereunder, of [**Confidential Treatment Requested**] of any royalties paid to any third parties by Licensee, its Affiliates or sublicensees which is necessary in order for Licensee or its Affiliates or sublicensees to make, use, sell, offer for sale or perform any Licensed Process without infringing any patent or other rights of such third party. The application of such credit shall be limited so that it shall not reduce by more than [**Confidential Treatment Requested**] the royalties paid hereunder for any given period.

3.6 Running Royalties for Licensed Services . Licensee agrees to pay and shall pay to TSRI [**Confidential Treatment Requested**] of any and all Net Sales for Licensed Services. Licensee shall be entitled to a credit against royalties due hereunder, of [**Confidential Treatment Requested**] of any royalties paid to any third parties by Licensee, its Affiliates or sublicensees which is necessary in order for Licensee or its Affiliates or sublicensees to make, use, sell, offer for sale or perform any Licensed Service without infringing any patent or other rights of such third party. The application of such credit shall be limited so that it shall not reduce by more than [**Confidential Treatment Requested**] the royalties paid hereunder for any given period.

3.7 Multiple Royalties . No multiple royalties shall be due because any Licensed Product, Licensed Process or Licensed Service is covered by more than one of the Licensed Patent Rights. In such case, Licensee shall pay the highest of the royalties owed to TSRI pursuant to Sections 3.4-3.6 above.

3.8 Arms-Length Transactions. On sales of Licensed Products, Licensed Processes or Licensed Services which are made in other than an arm’s-length transaction, the value of the Net Sales attributed under this Section 3 to such a transaction shall be that which would have been received in an arm’s-length transaction, based on sales of like quality and quantity products on or about the time of such transaction. “Arm’s-length transaction” means a sale between unaffiliated parties.

3.9 Duration of Royalty Obligations . The royalty obligations of Licensee as to each Licensed Product, Licensed Process or Licensed Service shall terminate on a country-by-country basis concurrently with the expiration or termination of the last Valid Claim within Licensed Patent Rights that covers such Licensed Product or Licensed Process or Licensed Service.

4. Non-royalty Revenues .

4.1 Sublicense Revenues . Any and all revenues, other than royalties, research and development funding (excluding Licensed Services), and equity investments made by such sublicensees in Licensee’s stock, pursuant to a stock purchase agreement that is separate from the sublicense agreement, to the extent such stock was sold by Licensee for a price that is above the then-current fair market value (for avoidance of doubt, the amount above fair market value shall be included within Sublicense Revenue as defined herein). Sublicense Revenue shall be reported and paid to TSRI by Licensee within thirty (30) days of receipt by Licensee as provided herein. Licensee shall pay to TSRI a non-creditable, non-refundable percentage of these Sublicense Revenues according to the following schedule (“Sublicense Payments”):

Any non-cash consideration received by Licensee from sublicensees shall be valued at its fair market value as of the date of receipt.

4.2 Product Development Milestones . Licensee agrees to pay and shall pay to TSRI the following non-creditable, non-refundable product development milestones within thirty (30) days of the first achievement of each milestone with a Licensed Product. All such milestones shall be payable a maximum of one time each regardless of how many times each is achieved in a particular country and regardless of in how many countries each is achieved.

4.3 Certain Additional Terms . After Licensee executes its first sublicense pursuant to Section 2.4, all amounts that Licensee thereafter pays to TSRI under Section 4.2 shall be fully credited only against the Sublicense Payments due from Licensee to TSRI under Section 4.1 for product development milestone payments that Licensee subsequently receives from its sublicensees under sublicense agreements (“Sublicensee Milestone Payments”). The payments

that Licensee makes to TSRI under Section 4.2 shall not be credited or applied against any other Sublicense Payments due from Licensee to TSRI under Section 4.1. In order to receive such credit, Licensee shall itemize in detail on its accounting of Sublicense Revenues under Section 4.1 the original amount of Sublicense Payments due under Section 4.1 for Sublicensee Milestone Payments for each sublicense, and the specific amounts paid to TSRI under Section 4.2 after the date of Licensee’s first sublicense that Licensee wants credited against its Sublicense Payments due under Section 4.1 for Sublicensee Milestone Payments for each sublicense. If any amounts required to be paid to TSRI under Section 4.2 are due before Licensee executes its first sublicense, but are not actually paid by Licensee to TSRI until after Licensee executes its first sublicense, then those amounts actually paid by Licensee to TSRI under Section 4.2 shall not be entitled to be credited or applied against Sublicense Payments due under Section 4.1 for Sublicensee Milestone Payments for any sublicense.

5. Royalty Payments .

5.1 Sales by Licensee . Royalties payable pursuant to Section 3 herein, shall be payable by Licensee quarterly, within sixty (60) days after the end of each calendar quarter, based upon Net Sales during the immediately preceding calendar quarter.

5.2 Sales by Sublicensees . Licensee agrees to pay and shall pay to TSRI, or cause its sublicensees to pay to TSRI all royalties pursuant to Section 3 herein resulting from the activities of its sublicensees, within ninety (90) days after the end of each calendar quarter.

6. Reports on Progress, Benchmarks, Sales or Payments .

6.1 Commercial Development Plan and Benchmarks . Prior to signing this Agreement, Licensee has provided to TSRI the Commercial Development Plan attached hereto as Exhibit B, under which Licensee intends to bring the subject matter of the Licensed Patent Rights to the point of commercia