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

February 7, 2018

Date of Report (Date of earliest event reported)

Adverum Biotechnologies, Inc.

(Exact name of registrant as specified in its charter)

1035 O’Brien Drive

Menlo Park, CA 94025

(Address of principal executive offices, including zip code)

(650) 272-6269

(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 obligations of the registrant under any of the following provisions:

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.  ☒

On February 7, 2018, Adverum entered into an underwriting agreement with Cowen and Company, LLC and Piper Jaffray & Co., as representatives of the underwriters, relating to the offering, issuance and sale of 8,888,900 shares of Adverum’s common stock, par value $0.0001 per share, at the public offering price of $6.75 per share. Pursuant to the underwriting agreement, the underwriters have agreed to purchase the shares of common stock from Adverum at a price of $6.345 per share, which will result in approximately $55.9 million of net proceeds to Adverum after deducting estimated offering expenses. The offering is expected to close on or about February 12, 2018, subject to customary closing conditions. The underwriters have a 30-day option to purchase up to an additional 1,333,335 shares of common stock. All of the shares in the offering are being sold by Adverum.

The offering is being made pursuant to Adverum’s effective shelf registration statement on Form S-3 (Registration No. 333-219890) previously filed with the Securities and Exchange Commission, and a final prospectus supplement thereunder dated February 8, 2018. A preliminary prospectus relating to the offering was filed with the Securities and Exchange Commission on February 7, 2018.

The underwriting agreement contains customary representations, warranties and agreements by Adverum, customary conditions to closing, indemnification obligations of Adverum and the underwriters, including for liabilities under the Securities Act of 1933, as amended, other obligations of the parties and termination provisions. The representations, warranties and covenants contained in the underwriting agreement were made only for purposes of the underwriting agreement and as of specific dates, were solely for the benefit of the parties to the underwriting agreement and may be subject to limitations agreed upon by the contracting parties.

The underwriting agreement is filed as Exhibit 1.1 hereto. The foregoing description of the terms of the underwriting agreement is qualified in its entirety by reference to Exhibit 1.1. A copy of the opinion of Cooley LLP relating to the legality of the issuance and sale of the shares in the offering is attached as Exhibit 5.1 hereto.

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.