Company: MBIO
Filing Date: 2025-12-03
Form Type: DEF 14A
Source: 0001104659-25-118122
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Company: MUSTANG BIO, INC.
Filing Date: 2025-12-03
Form: DEF 14A
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UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 SCHEDULE 14A Proxy Statement Pursuant to Section 14(a) of the Securities Exchange Act of 1934

| ​                                          | ​ |
| Filed by Registrant                        | ☒ |
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| Filed by a Party other than the Registrant | ☐ |

Check the appropriate box:

| ☐ | Preliminary Proxy Statement |

| ☐ | Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2)) |

| ☒ | Definitive Proxy Statement |

| ☐ | Definitive Additional Materials |

| ☐ | Soliciting Material Under Rule 14a-12 |

MUSTANG BIO, INC. (Name of Registrant as Specified in its Charter) (Name of Person(s) Filing Proxy Statement, if other than the Registrant) Payment of Filing Fee (Check the appropriate box):

| ☒ | No fee required |

| ☐ | Fee paid previously with preliminary materials |

| ☐ | Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a6(i)(1) and 0-11 |

MUSTANG BIO, INC. 95 Sawyer Road, Suite 110 Waltham, Massachusetts 02453 Dear Stockholder: You are cordially invited to the Annual Meeting of Stockholders (the “Annual Meeting”) of Mustang Bio, Inc. (“Mustang” or the “Company”), to be held virtually at 9:00 a.m. Eastern Time, on Monday, December 22, 2025. The Annual Meeting can be accessed by visiting www.virtualshareholdermeeting.com/MBIO2025, where you will be able to listen to the meeting live, submit questions and vote online. At the Annual Meeting, the stockholders will be asked to (i) elect seven directors for a term of one year, (ii) ratify the appointment of KPMG LLP as our independent registered public accounting firm for the year ending December 31, 2025, (iii) approve an amendment to the Company’s 2019 Employee Stock Purchase Plan to increase the number of shares issuable by 250,000 shares and increase the number of shares subject to a Purchase Right thereunder to 10,000, (iv) approve an amendment to the Company’s 2016 Incentive Plan to increase the number of shares iss