SEC Form POS EX filed by Mustang Bio Inc.

As filed with the Securities and Exchange Commission on April 1, 2025.

Registration No. 333-284299

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Post-effective Amendment No. 1 to

FORM S-1

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

MUSTANG BIO, INC.

(Exact name of registrant as specified in its charter)

95 Sawyer Road

Waltham, MA 02453

(781) 652-4500

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Manuel Litchman, M.D.

President, Chief Executive Officer and Interim Chief Financial Officer

Mustang Bio, Inc.

95 Sawyer Road

Waltham, MA 02453

(781) 652-4500

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Rakesh Gopalan

David S. Wolpa

Alexander T. Yarbrough

Troutman Pepper Locke LLP 

301 S. College Street, 34^th Floor 

Charlotte, NC 28202 

(704) 998-4050 

Approximate date of commencement of proposed sale to the public: From time to time after this registration statement becomes effective.

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933 check the following box: x

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ¨

If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. x

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company, or an emerging growth company. See the definitions of “large accelerated filer,” “accelerated filer,” “smaller reporting company,” and “emerging growth company” in Rule 12b-2 of the Exchange Act.

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 7(a)(2)(B) of the Securities Act. ¨

This Post-Effective Amendment No. 1 shall become effective upon filing with the Securities and Exchange Commission in accordance with Rule 462(d) under the Securities Act of 1933, as amended.

EXPLANATORY NOTE

This Post-Effective Amendment No. 1 (this “Amendment”) to the Registration Statement on Form S-1 (File No. 333-284299) (the “Registration Statement”) of Mustang Bio, Inc. (the “Company”) is being filed as an exhibits-only filing solely to include the consent of KPMG LLP with respect to its report, dated March 28, 2025, relating to the consolidated financial statements of the Company contained in its Annual Report on Form 10-K for the year ended December 31, 2024, filed herewith as Exhibit 23.1. Accordingly, this Amendment consists only of the facing page, this explanatory note, Item 16 of Part II of the Registration Statement, the signature pages to the Registration Statement and Exhibit 23.1. The report of KPMG LLP was filed in Prospectus Supplement No. 3, dated April 1, 2025, filed with the Securities and Exchange Commission pursuant to Rule 424(b)(3). The prospectus, as supplemented, and the balance of Part II of the Registration Statement are unchanged hereby and have been omitted.

PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

Item 16. Exhibits and Financial Statement Schedules

The exhibits listed below are filed as part of this Registration Statement.

SIGNATURES

Pursuant to the requirements of the Securities Act, the Registrant has duly caused this post-effective amendment to the Registration Statement on Form S-1 to be signed on its behalf by the undersigned, thereunto duly authorized, in City of Worcester, Commonwealth of Massachusetts, on April 1, 2025.

Pursuant to the requirements of the Securities Act, this post-effective amendment to the Registration Statement on Form S-1 has been signed by the following persons in the capacities and on the dates indicated.