UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): December 7, 2020

REPLIGEN CORPORATION

(Exact name of registrant as specified in charter)

41 Seyon Street, Bldg. 1, Suite 100, Waltham, MA 02453

(Address of Principal Executive Offices) (Zip Code)

(781) 250-0111

(Registrant’s telephone number, including area code)

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 (see General Instruction A.2. below):

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.  ☐

Underwriting Agreement

On December 7, 2020, Repligen Corporation (the “Company”) entered into an underwriting agreement (the “Underwriting Agreement”) with J.P. Morgan Securities LLC and Stifel, Nicolaus & Company, Incorporated, as representatives of the underwriters named therein (collectively, the “Underwriters”), relating to an underwritten public offering (the “Offering”) of 1,500,000 shares of the Company’s common stock, $0.01 par value per share (the “Common Stock”), at a price to the public of $181.00 per share (the “Offering Price”). After deducting the underwriting discounts and commissions and estimated offering expenses, the Company expects to receive net proceeds from the Offering of approximately $258.9 million. The Company has also granted the Underwriters a 30-day option to purchase up to an additional 225,000 shares of Common Stock at the Offering Price, less underwriting discounts and commissions.

The Offering was made pursuant to the Company’s effective automatic shelf registration statement on Form S-3 (File No. 333-231098), including the prospectus dated April 29, 2019, as supplemented by a prospectus supplement dated December 7, 2020 and filed on December 8, 2020. The Offering is expected to close on or about December 10, 2020, subject to the satisfaction of customary closing conditions.

A copy of the Underwriting Agreement is attached as Exhibit 1.1 to this Current Report on Form 8-K and is incorporated herein by reference. The foregoing description of the Underwriting Agreement does not purport to be complete and is qualified in its entirety by reference to such exhibit.

A copy of the legal opinion of Goodwin Procter LLP relating to the legality of the issuance and sale of the shares in the Offering is attached as Exhibit 5.1 to this Current Report on Form 8-K.

On December 7, 2020, the Company issued a press release announcing the commencement of the Offering. On December 7, 2020, the Company issued a press release announcing the pricing of the Offering. Copies of these press releases are attached to this Current Report on Form 8-K as Exhibits 99.1 and 99.2 and are incorporated herein by reference.

(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.