Form 3 - Initial statement of beneficial ownership of securities

POWER OF ATTORNEY

KNOW ALL MEN BY THESE PRESENTS, that the undersigned hereby constitutes and appoints each of Kimberly Brown and Kenneth O'Brien the true and lawful attorney-in-fact and agent, with full power of substitution and resubstitution, for the undersigned and in the undersigned's name, place and stead, in any and all capacities (until revoked in writing) to execute for and on behalf of the undersigned, in any and all of the undersigned's capacities, any and all statements on Forms 3, 4 and 5 with respect to the undersigned's holdings of and transactions in securities issued by Repligen Corporation (the "Company") in accordance with Sections 16(a) of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), and any and all regulations promulgated thereunder, and to file the same, with all exhibits thereto, and any other documents in connection therewith, with the Securities and Exchange Commission, and with any other entity when and if such is mandated by the Exchange Act or by the Bylaws of the Financial Industry Regulatory Authority, granting unto said attorney-in-fact and agent full power and authority to do and perform each and every act and thing requisite and necessary fully to all intents and purposes as the undersigned might or could do in person thereby ratifying and confirming all that said attorney-in-fact and agent, or his or her substitute or substitutes, may lawfully do or cause to be done by virtue hereof.

This Power of Attorney shall remain in full force and effect until the undersigned is no longer required to file Forms 3, 4 and 5 with respect to the undersigned's holdings of and transactions in securities issued by the Company, unless earlier revoked by the undersigned in a signed writing delivered to the foregoing attorney-in-fact.

IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney to be

executed as of September 27, 2023.

/s/ Olivier Loeillot

Olivier Loeillot