Sec Form 4 Filing - Achenbach Brian @ MUSTANG BIO, INC. - 2021-12-08

FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Achenbach Brian 2. Issuer Name and Ticker or Trading Symbol MUSTANG BIO, INC. [ MBIO] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) SVP, Fin. & Corp. Controller (Last) (First) (Middle) 377 PLANTATION STREET 3. Date of Earliest Transaction (MM/DD/YY) 12/08/2021 (Street) WORCESTER, MA01605 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price COMMON STOCK 12/08/2021 A 22,500( 1 ) A $ 0 149,103( 4 ) D COMMON STOCK 12/14/2021 S( 2 ) 4,374 D $ 1.83( 3 ) 144,729( 4 ) D

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Achenbach Brian 377 PLANTATION STREET WORCESTER, MA01605 SVP, Fin. & Corp. Controller Signatures /s/ Brian Achenbach 12/16/2021 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Each restricted stock unit represents the right to receive one share of Common Stock of Mustang Bio, Inc. The restricted stock units will vest at different times over a period of 4 years. ( 2 )4,374 shares were sold in connection with the vesting of 13,750 shares on December 4, 2021, these shares were sold by the Company's restricted stock administrator in order to satisfy Mr. Achenbach's tax withholding obligations. Mr. Achenbach had no discretion with respect to such sale, which was transacted automatically in accordance with the Company's corporate policies regarding the vesting of restricted stock. ( 3 )Represents the weighted average sales price. ( 4 )Includes restricted share units, which vest over various time periods.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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