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): September 20, 2021

Mustang Bio, Inc.

(Exact Name of Registrant as Specified in Charter)

377 Plantation Street

Worcester, Massachusetts 01605

(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:

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). 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 September 20, 2021, Mustang Bio, Inc. (the “Company”) informed BDO USA, LLP (“BDO”) that the Company would be dismissing BDO as the Company’s independent registered public accounting firm. The Company’s Audit Committee and Board of Directors participated in and approved this decision. The audit committee intends to engage a nationally-recognized accounting firm after completion of its thorough selection process.

The reports of BDO on the consolidated financial statements of the Company for the fiscal years ended December 31, 2019 and 2020, did not contain an adverse opinion or a disclaimer of opinion, nor were such reports qualified or modified as to uncertainty, audit scope, or accounting principles.

During the Company’s fiscal years ended December 31, 2019 and 2020, and through September 20, 2021, the Company did not have any disagreements with BDO on any matter of accounting principles or practices, financial statement disclosure, or auditing scope or procedure, which disagreements, if not resolved to the satisfaction of BDO, would have caused it to make reference to the subject matter of the disagreements in connection with its reports on the consolidated financial statements for such time periods.

During the Company’s fiscal years ended December 31, 2019 and 2020, and through September 20, 2021, no “reportable events” as defined in Item 304(a)(1)(v) of Regulation S-K have occurred.

BDO has indicated to the Company that it concurs with the foregoing statements contained in the second, third and fourth paragraphs above as they relate to BDO and has furnished a letter to the Securities and Exchange Commission to this effect. A copy of the letter from BDO is attached to this Form 8-K as Exhibit 16.1.

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.