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): July 27, 2018

Mustang Bio, Inc.

(Exact Name of Registrant as Specified in Charter)

2 Gansevoort Street, 9th Floor

New York, New York 10014

(Address of Principal Executive Offices)

(781) 652-4500

(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:

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 x

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. x

On July 27, 2018, Mustang Bio, Inc. (the “Company”) launched an at-the-market offering (the “Offering”) of up to $75,000,000 worth of shares of the Company’s common stock, par value $0.0001 per share, pursuant to an At Market Issuance Sales Agreement by and among the Company, B. Riley FBR, Inc., Cantor Fitzgerald & Co., National Securities Corporation, and Oppenheimer & Co. Inc., dated July 27, 2018. A copy of the At Market Issuance Sales Agreement is attached hereto as Exhibit 1.1 and is incorporated by reference herein.

Alston & Bird LLP, counsel to the Company, delivered an opinion as to the validity of the Offering, a copy of which is attached hereto as Exhibit 5.1 and is incorporated by reference herein.

The following exhibit is furnished as part of this report:

SIGNATURE

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.