8-K

UNITED STATESSECURITIES AND EXCHANGE COMMISSIONWASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

REPLIGEN CORP

(Exact name of Registrant as Specified in Its Charter)

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 5.02 Departure of Directors or Certain Officers; Election of Directors; Appointment of Certain Officers; Compensatory Arrangements of Certain Officers.

On January 6, 2026, Repligen Corporation (the “Company”) announced that the Board of Directors (the “Board”) has elected Dr. Martin D. Madaus as Chair of the Board, effective March 13, 2026 (the “Effective Date”). Dr. Madaus will succeed Tony J. Hunt, who is currently serving as the Executive Chair of the Board, following his previously announced March 2026 retirement, which shall be on the Effective Date, at which time Mr. Hunt will retire as a member of the Board. The Board has previously determined Dr. Madaus is an independent member of the Board under the rules and regulations of the Securities and Exchange Commission and the Nasdaq Stock Market.

Item 7.01 Regulation FD Disclosure.

On January 6, 2026, the Company issued a press release announcing the appointment and retirement described above, a copy of which is attached hereto as Exhibit 99.1 and is incorporated into this Item 7.01 by reference.

The information in this Item 7.01, including Exhibit 99.1 attached hereto, is intended to be furnished and shall not be deemed “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”) or otherwise subject to the liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as expressly set forth by specific reference in such filing.

Item 9.01 Financial Statements and Exhibits.

(d) Exhibits

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

EX-99.1

Exhibit 99.1

REPLIGEN Executive chair tony hunt to retire; Dr. martin D. MadAus elected chair

WALTHAM, MA - Jan 6, 2026 – Repligen Corporation (NASDAQ:RGEN), a life sciences company focused on bioprocessing technology leadership, today announced that the Board has elected Dr. Martin D. Madaus as Chair of the Board, effective March 13, 2026. As previously communicated[1], Tony Hunt is retiring from his role as Executive Chair and member of the Board of Directors effective this March 13th. Mr. Hunt will continue to serve as an advisor to Repligen through March 2027.

“On behalf of Repligen, I want to thank Tony for over a decade of service to the Company, during which he expanded our unique and diversified portfolio of innovative products,” said Olivier Loeillot, Repligen President and CEO. “He left a strong foundation for us to build upon, and with Martin assuming the role of Chair of the Board, we are well-positioned for success. Martin’s deep expertise and strong leadership in bioprocessing and biopharma makes him exceptionally qualified to lead our Board.”

Dr. Martin D. Madaus added, “On behalf of the Board of Directors, our shareholders, employees, and other stakeholders, I want to commend Tony on his impressive tenure at Repligen. I am honored to be elected as Chair of the Repligen Board and look forward to guiding Repligen towards new heights.”

Tony Hunt said, “After more than a decade of leadership, I leave this Company immensely proud of the business we have created together. One that is rooted in clear strategy, disciplined execution and outstanding people. It has been a privilege and an honor to work alongside such a committed team, and I leave knowing the Company is in very capable hands. I am confident that Olivier and Martin will build on the success we have enjoyed and lead Repligen to a new phase of growth.”

Martin D. Madaus, D.V.M., Ph.D., has served as a director of Repligen since February 2023. Dr. Madaus has 36 years of industry experience, including five years as Chairman, President and CEO of Millipore Corporation, where he was integral to the company’s transformation into a life science leader, and its acquisition by Merck KGaA in 2010. Dr. Madaus serves on the boards of Azenta, Inc. and Hologic, Inc. He holds a D.V.M. from the University of Munich in Germany and a Ph.D. from the University of Veterinary Medicine of Hanover in Germany.

[1] Repligen June 14, 2024 8-K

About Repligen Corporation

Repligen Corporation is a global life sciences company that develops and commercializes highly innovative bioprocessing technologies and systems that enable efficiencies in the process of manufacturing biological drugs. We are “inspiring advances in bioprocessing” for the customers we serve; primarily biopharmaceutical drug developers and contract development and manufacturing organizations (CDMOs) worldwide. Our focus areas are Filtration and Fluid Management, Chromatography, Process Analytics and Proteins. Our corporate headquarters are located in Waltham, Massachusetts, and the majority of our manufacturing sites are in the U.S., with additional key sites in Estonia, France, Germany, Ireland, the Netherlands and Sweden. For more information about the our company see our website at www.repligen.com, and follow us on LinkedIn.

This press release may contain forward-looking statements within the meaning of the federal securities laws. Investors are cautioned that statements in this press release which are not strictly historical statements including, without limitation, statements identified by words like “believe,” “expect,” “may,” “will,” “should,” “seek,” or “could” and similar expressions, constitute forward-looking statements. Such forward-looking statements are subject to a number of risks and uncertainties that could cause actual results to differ materially from those anticipated, including risks discussed from time to time in our filings with the Securities and Exchange Commission. We expressly disclaim any responsibility to update any forward-looking statements, except as required by law.

Repligen Contact:

Jacob Johnson

VP, Investor Relations

781-419-0204

investors@repligen.com