MUSTANG BIO, INC. 10-K

Item 9A. Controls and Procedures. ​ Disclosure Controls and Procedures Controls and Procedures Disclosure controls and procedures (as defined in Exchange Act Rules 13a-15(e) and 15d-15(e)) are designed only to provide reasonable assurance that they will meet their objectives. Under the supervision and with the participation of our management, including our principal executive and financial officer, we conducted an evaluation of the effectiveness, as of December 31, 2025, of the design and operation of our disclosure controls and procedures, as such term is defined in Exchange Act Rules 13a-15(e) and 15d-15(e). Based on this evaluation, our principal executive and financial officer concluded that, as of such date, our disclosure controls and procedures were effective to ensure that information required to be disclosed by us in our Exchange Act reports is recorded, processed, summarized, and reported within the time periods specified in the SEC’s rules and forms, and that such information is accumulated and communicated to our management, including our principal executive officer and principal financial officer, as appropriate to allow timely decisions regarding required disclosure. Internal Control over Financial Reporting Management’s Report on Internal Control over Financial Reporting. Our management is responsible for establishing and maintaining adequate internal control over financial reporting, as such term is defined in Exchange Act Rules 13a-15(f) and 15d-15(f). Internal control over financial reporting refers to the process designed by, or under the supervision of, our principal executive and financial officer, and effected by our Board, management and other personnel, to provide 64 ​ Table of Contents reasonable assurance regarding the reliability of financial reporting and the preparation of financial statements for external purposes in accordance with generally accepted accounting principles, and includes those policies and procedures that: (1) pertain to the maintenance of records that in reasonable detail accurately and fairly reflect the transactions and dispositions of our assets; (2) provide reasonable assurance that transactions are recorded as necessary to permit preparation of financial statements in accordance with generally accepted accounting principles in the United States (“GAAP”), and that our receipts and expenditures are being made only in accordance with authorization of our management and directors; and (3) provide reasonable assurance regarding prevention or timely detection of unauthorized acquisitions, use or disposition of our assets that could have a material effect on the financial statements. Internal control over financial reporting has inherent limitations. Internal control over financial reporting is a process that involves human diligence and compliance and is subject to lapses in judgment and breakdowns resulting from human failures. Internal control over financial reporting also can be circumvented by collusion or improper management override. Because of such limitations, there is a risk that material misstatements may not be prevented or detected on a timely basis by internal control over financial reporting. However, these inherent limitations are known features of the financial reporting process. Therefore, it is possible to design into the process safeguards to reduce, though not eliminate, this risk. Our management assessed the effectiveness of our internal control over financial reporting as of December 31, 2025. In making the assessment, management used the criteria set forth by the Committee of Sponsoring Organizations of the Treadway Commission (“COSO”) in Internal Control - Integrated Framework (2013) . Based on our assessment, our management has concluded that, as of December 31, 2025, our internal controls over financial reporting were effective based upon those criteria. Changes in Internal Controls over Financial Reporting. There were no changes in our internal control over financial reporting during our most recent fiscal quarter that have materially affected, or are reasonably likely to materially affect, our internal control over financial reporting. Item 9B. Other Information ​ During the three months ended December 31, 2025, none of our directors or officers adopted or terminated a “Rule 10b5-1 trading arrangement” or “non-Rule 10b5-1 trading arrangement,” as each term is defined in Item 408(a) of Regulation S-K. ​ Item 9C. Disclosure Regarding Foreign Jurisdiction that Prevents Inspections. ​ None. ​ ​ ​ 65 ​ Table of Contents PART III Item 10. Directors, Executive Officers and Corporate Governance ​ The following table sets forth information regarding our executive officers and directors, including their ages as of the date of this Form 10-K. ​ Name Age Position(s) Executive Officers Manuel Litchman, M.D. 72 President, Chief Executive Officer, Interim Chief Financial Officer and Director ​ ​ ​ ​ ​ Non-Employee Directors Michael S. Weiss 60 Chairman of the Board of Directors and Executive Chairman Adam J. Chill 58 Director Neil Herskowitz 69 Director David Jin ​ 35 ​ Director Lindsay A. Rosenwald, M.D. 70 Director Michael J. Zelefsky, M.D. 65 Director ​ Information about our Executive Officers ​ Manuel Litchman, M.D. - President, Chief Executive Officer, Interim Chief Financial Officer and Director Dr. Litchman has served as our President and Chief Executive Officer, and as a member of our Board since April 2017 and as Interim Chief Financial Officer since November 2024. Dr. Litchman has also served on the board of Cascade Prodrug, LLC, a private biotechnology company, since August 2025. Dr. Litchman joined us from Arvinas, LLC, where he served as President and Chief Executive Officer. While at Arvinas, Dr. Litchman oversaw the advancement of the company’s pipeline of protein-degradation therapeutics for the treatment of cancers and other diseases toward Investigational New Drug applications and secured multi-target discovery collaborations with Merck and Genentech. Prior to Arvinas, Dr. Litchman spent more than 18 years with Novartis Pharmaceuticals Corporation, where he held positions of increasing responsibility related to the development of Novartis’ oncology pipeline. Most recently, Dr. Litchman served as Senior Vice President and Executive Global Program Head, CTL019, Cell & Gene Therapies Unit, where he led a collaboration with the University of Pennsylvania investigating chimeric antigen receptor modified T cells (“CAR Ts”) directed against CD19 on B cell malignancies. Prior to the CTL019 collaboration, Dr. Litchman served as Novartis’ Vice President and Head, Oncology Business Development & Licensing. Earlier in his career, Dr. Litchman was a senior equity analyst at Ursus Capital and directed oncology/immunology clinical research at Hoffmann-La Roche Inc. Dr. Litchman received his M.D. from Yale University School of Medicine, and his B.A. from Princeton University. He completed his internal medicine residency and hematology-oncology fellowship at New York-Presbyterian/Weill Cornell Medical Center. Based on Dr. Litchman’s biotechnology and pharmaceutical industry experience and in-depth understanding of our business, we believe that Dr. Litchman has the appropriate set of skills to serve as a member of the Board. Information about our Non-Employee Directors ​ Michael S. Weiss – Chairman of the Board of Directors and Executive Chairman Mr. Weiss has served as Chairman of our Board since May 2015 and has also served as our Executive Chairman since January 2017. He previously served as our interim President & Chief Executive Officer from March 2015 to April 2017. He is also a board member and the Executive Vice Chairman, Strategic Development of Fortress Biotech, Inc., a position he has held since February 2014. Since December 2011, Mr. Weiss has served in multiple capacities at TG Therapeutics, Inc., and is currently its Chairman, President and Chief Executive Officer. Mr. Weiss earned his J.D. from Columbia Law School and his B.S. in Finance from The University at Albany. He began his professional career as a lawyer with Cravath, Swaine & Moore LLP. From 2002 to 2009, Mr. Weiss was the Chairman and Chief Executive Officer of Keryx Biopharmaceuticals, Inc. Additionally, Mr. Weiss co-founded and served as Co-Portfolio Manager and Managing Partner of Opus Point Partners, LLC from 2009 to 2019. Based on Mr. Weiss’s biotechnology and pharmaceutical industry experience, as well as his extensive management experience, we believe that Mr. Weiss has the appropriate set of skills to serve as a member of the Board. Effective January 1, 2017, our Board approved and authorized the execution of a Board Advisory Agreement with Caribe BioAdvisors, LLC (the “Advisor”), which is owned by Michael S. Weiss, to provide the Board with the advisory services of Mr. Weiss as Chairman of the 66 ​ Table of Contents Board and Executive Chairman. Pursuant to the Advisory Agreement, the Advisor is paid an annual cash fee of $60,000, in addition to any and all annual equity incentive grants paid to members of the Board. Adam J. Chill – Director Mr. Chill has served as a member of our Board since June 2017. Mr. Chill is the President of and a Portfolio Manager at Kingsbrook Partners LP, an alternative asset management firm he co-founded in March 2009. From February 2001 to March 2009, Mr. Chill was a Portfolio Manager and Managing Director at Highbridge Capital Management, LLC, an alternative asset management firm owned by J.P. Morgan Asset Management. At Highbridge, Mr. Chill was responsible for structuring, negotiating and monitoring Highbridge’s portfolio of structured investments in public and private companies worldwide. From April 2000 to February 2001, Mr. Chill worked at Angelo, Gordon & Co., an alternative asset management firm. From October 1992 to April 2000, Mr. Chill was a corporate attorney specializing in securities and mergers and acquisitions at Stroock & Stroock & Lavan LLP. Mr. Chill is a co-founder of the Bayit Association of New Jersey. Mr. Chill received his B.A., magna cum laude, from Yeshiva University and his J.D. from Columbia University School of Law, where he was a Harlan Fiske Stone Scholar. Based on Mr. Chill’s extensive investment experience and knowledge of the biotechnology industry, we believe that Mr. Chill has the appropriate set of skills to serve as a member of the Board. Neil Herskowitz – Director Mr. Herskowitz has served as a member of our Board since August 2015. Mr. Herskowitz has served as the managing member of the ReGen Group of companies, located in New York, since 1998, which include ReGen Capital Investments LLC and Riverside Claims Investments LLC. He has also served as the President of its affiliate, Riverside Claims LLC, since June 2004. Mr. Herskowitz serves as a member of the board of directors for our affiliate, Avenue Therapeutics, Inc. Mr. Herskowitz received a B.B.A. in Finance from Bernard M. Baruch College in 1978. Based on Mr. Herskowitz’s financial industry experience and in-depth understanding of our business, we believe that Mr. Herskowitz has the appropriate set of skills to serve as a member of the Board. David Jin – Director Mr. Jin has served as a member of our Board since October 2024. Mr. Jin has served as the Chief Financial Officer of Fortress since August 2022 and Head of Corporate Development since May 2020. He also serves as Chief Operating Officer, Interim Chief Financial Officer and Corporate Secretary of Avenue Therapeutics, Inc. (a Fortress partner company) and as a member of the board of directors of Crystalys Therapeutics. Since August 2022, Mr. Jin has served as Treasurer of Fortress’ private subsidiaries, including Cyprium Therapeutics, Urica Therapeutics, Helocyte, and Cellvation. From March 2022 to August 2022, he served as Interim Chief Executive Officer at Avenue Therapeutics. Previously, he was on the investment team in the Private Equity & Real Assets group at Barings, Director of Corporate Development at Sorrento Therapeutics, Vice President of Healthcare Investment Banking at FBR & Co., and was in the management consulting group at IMS Health (now IQVIA). He holds a B.S. in Industrial Engineering & Management Sciences with a double-major in Mathematical Methods in the Social Sciences from Northwestern University. Based on Mr. Jin’s financial experience and knowledge of the biotechnology industry, we believe that Mr. Jin has the appropriate set of skills to serve as a member of the Board. Lindsay A. Rosenwald, M.D. – Director Dr. Rosenwald has served as a member of our Board since our inception. Dr. Rosenwald has been a member of the Board of Directors of Fortress Biotech, Inc. since October 2009 and has served as its Chairman, President and Chief Executive Officer since December 2013. He also serves on the board of directors of Avenue Therapeutics, Inc. and Journey Medical Corporation. Prior to that, from 1991 to 2008, he served as the Chairman of Paramount BioCapital, Inc. Over the last 30 years, Dr. Rosenwald has acted as a biotechnology entrepreneur and has been involved in the founding and recapitalization of numerous public and private biotechnology and life sciences companies. Dr. Rosenwald received his B.S. in finance from Pennsylvania State University and his M.D. from Temple University School of Medicine. We believe that Dr. Rosenwald’s extensive biotechnology, pharmaceutical and finance expertise, as well as his medical background and in-depth understanding of our businesses, makes him an exemplary candidate to continue serving on our Board. Michael J. Zelefsky, M.D. – Director Dr. Zelefsky has served as a member of our Board since June 2017. Dr. Zelefsky has served as a Member at NYU Langone since 2023 and before that was a Member at the Memorial Sloan-Kettering Cancer Center Department of Radiation Oncology since 2005. He has served as Chief of Memorial Sloan-Kettering’s Brachytherapy Services since 2000 and has been a Professor of Radiation Oncology at Weill Cornell Medical College, Cornell University since 1994. He is a recognized expert in radiation therapy and has helped develop and enhance Memorial Sloan-Kettering’s prostate brachytherapy program during his tenure. Dr. Zelefsky received a Bachelor of Arts in Biology (summa cum laude) from Yeshiva University in 1982 and a Medical Doctor degree from Albert Einstein College of Medicine in 1986. Dr. Zelefsky is currently 67 ​ Table of Contents Editor-in-Chief of Brachytherapy and has previously served as president of the American Brachytherapy Society. Based on Dr. Zelefsky’s extensive experience and background in oncology, we believe that Dr. Zelefsky has the appropriate set of skills to serve as a member of the Board. Family Relationships There is no family relationship between and among any of our executive officers or directors. ​ Board Structure and Leadership Our Bylaws provide that our Board shall consist of between one and nine directors, and such number of directors within this range may be determined from time to time by resolution of our board of directors or our stockholders. Currently, we have seven directors. The Board does not have a formal policy regarding the separation of the roles of Chief Executive Officer and Chairman of the Board, as the Board believes that it is in the best interests of the Company to make that determination based on the direction of the Company and the current membership of the Board. The Board has determined that having a director who is also the Chief Executive Officer serve as the Chairman is not in the best interest of the Company’s stockholders at this time. During 2025, our Board held six meetings. During 2025, each director attended at least 75% of the meetings of the Board and the meetings of those committees on which each director served, in each case during the period that such person was a director. The permanent committees established by our Board are the Audit Committee and the Compensation Committee, descriptions of which are set forth in more detail below. Our directors are expected to attend each Annual Meeting of Stockholders. Director Independence ​ We adhere to the corporate governance standards adopted by Nasdaq. Nasdaq rules require our Board to make an affirmative determination as to the independence of each director. Consistent with these rules, our Board completed its annual review of director independence and considered relationships and transactions during 2025 between each director or any member of his immediate family, on the one hand, and the Company and our subsidiaries and affiliates, on the other hand. The purpose of this review was to determine whether any such relationships or transactions were inconsistent with a determination that the director is independent. Based on this review, our Board determined that Adam Chill, Neil Herskowitz, and Michael Zelefsky, M.D., are independent under the criteria established by Nasdaq and our Board. Fortress Biotech, Inc. (“Fortress”) beneficially owns capital stock representing more than 50% of the voting power of our outstanding voting stock eligible to vote in the election of directors. As a result, we qualify as a “controlled company” and avail ourselves of certain “controlled company” exemptions under the Nasdaq corporate governance rules. As a controlled company, we are not required to have a majority of “independent directors” on our Board as defined under the Nasdaq rules, or have a compensation, nominating or governance committee composed entirely of independent directors. Despite qualifying as a controlled company, we have a separately constituted Compensation Committee consisting entirely of independent directors. ​ Board Committees The permanent committees established by our Board are the Audit Committee and the Compensation Committee, descriptions of which are set forth in more detail below. Audit Committee The Audit Committee currently consists of Adam J. Chill, Neil Herskowitz, and Michael J. Zelefsky, M.D. Mr. Chill chairs the Audit Committee. The Audit Committee held four meetings during the fiscal year ended December 31, 2025. The duties and responsibilities of the Audit Committee are set forth in the Charter of the Audit Committee which was recently reviewed by our Audit Committee. A copy of the Charter of the Audit Committee is available on our website, located at ir.mustangbio.com. Among other things, the duties and responsibilities of the Audit Committee include reviewing and monitoring our financial statements and internal accounting procedures, the selection of, consultation with and review of the services provided by our independent registered public accounting and identifying and assessing any related party transactions in collaboration with counsel, accountants and management. Our Audit Committee has sole discretion over the retention, compensation, evaluation and oversight of our independent registered public accounting firm. 68 ​ Table of Contents The SEC and Nasdaq have established rules and regulations regarding the composition of audit committees and the qualifications of audit committee members. Our Board has examined the composition of our Audit Committee and the qualifications of our Audit Committee members in light of the current rules and regulations governing audit committees. Based upon this examination, our Board has determined that each member of our Audit Committee is independent and is otherwise qualified to be a member of our Audit Committee in accordance with the rules of the SEC and Nasdaq. Additionally, the SEC requires that at least one member of the Audit Committee have a “heightened” level of financial and accounting sophistication. Such a person is known as the “audit committee financial expert” under the SEC’s rules. Our Board has determined that Mr. Chill is an “audit committee financial expert,” as the SEC defines that term, and is an independent member of our Board and our Audit Committee. Please see Mr. Chill’s biography in Item 10. Directors, Executive Officers, and Corporate Governance. Compensation Committee The Compensation Committee currently consists of Adam J. Chill, Neil Herskowitz and Michael J. Zelefsky, M.D. Mr. Herskowitz chairs the Compensation Committee. The Compensation Committee held one meeting during the fiscal year ended December 31, 2025. The duties and responsibilities of the Compensation Committee are set forth in the Charter of the Compensation Committee which was recently reviewed by our Compensation Committee. A copy of the Charter of the Compensation Committee is available on our website, located at ir.mustangbio.com. As discussed in its Charter, among other things, the duties and responsibilities of the Compensation Committee include approving any corporate goals and objectives relating to the compensation of our executive officers, evaluating the performance of our executive officers, and administering all of our executive compensation programs, including, but not limited to, our incentive and equity-based plans. The Compensation Committee evaluates the performance of all of our executive officers on an annual basis and reviews and approves on an annual basis all compensation programs and awards relating to such officers. The Compensation Committee applies discretion in the determination of individual executive compensation packages to ensure compliance with our compensation philosophy. Our Chief Executive Officer makes recommendations to the Compensation Committee with respect to the compensation packages for officers other than himself. Nasdaq has established rules and regulations regarding the composition of compensation committees and the qualifications of compensation committee members. Our Board has examined the composition of our Compensation Committee and the qualifications of our Compensation Committee members in light of the current rules and regulations governing compensation committees. Based upon this examination, our Board of Directors has determined that each member of our Compensation Committee is independent and is otherwise qualified to be a member of our Compensation Committee in accordance with such rules. Nominating Process We do not currently have a nominating committee or any other committee serving a similar function. Although we do not have a written charter in place to select director nominees, our Board has adopted resolutions regarding the director nomination process. We believe that the current process in place functions effectively to select director nominees who will be valuable members of our Board. We identify potential nominees to serve as directors through a variety of business contacts, including current executive officers, directors, community leaders and stockholders. We may, to the extent deemed appropriate by the Board, retain a professional search firm and other advisors to identify potential nominees. We will also consider candidates recommended by stockholders for nomination to our Board. A stockholder who wishes to recommend a candidate for nomination to our Board must submit such recommendation to our Corporate Secretary, at our offices located at 95 Sawyer Road, Suite 110, Waltham, MA 02453. Any recommendation must be received not less than 50 calendar days nor more than 90 calendar days before the anniversary date of the previous year’s annual meeting. On April 7, 2017, we entered into an Executive Employment Agreement with Dr. Litchman, pursuant to which, among other things, we agreed to use our best efforts to cause Dr. Litchman to be nominated and reelected to the Board. Except as described herein, there are no arrangements or understandings between any of our executive officers or directors and any other person pursuant to which any of them are elected as an officer or director. We believe that our Board as a whole should encompass a range of talent, skill, and expertise enabling it to provide sound guidance with respect to our operations and interests. Our independent directors evaluate all candidates to our Board by reviewing their biographical information and qualifications. If the directors determine that a candidate is qualified to serve on our Board, such candidate is interviewed by at least one of the directors and our Chief Executive Officer. Other members of the Board also have an opportunity to interview qualified candidates. The directors then determine, based on the background information and the information obtained in the interviews, whether to 69 ​ Table of Contents recommend to the Board that the candidate be nominated for approval by the stockholders to fill a directorship. With respect to an incumbent director whom the directors are considering as a potential nominee for re-election, the directors review and consider the incumbent director’s service during his or her term, including the number of meetings attended, level of participation, and overall contribution to the Board. The manner in which the directors evaluate a potential nominee will not differ based on whether the candidate is recommended by our directors or stockholders. We consider the following qualifications, among others, when making a determination as to whether a person should be nominated to our Board: the independence of the director nominee; the nominee’s character and integrity; financial literacy; level of education and business experience, including experience relating to biopharmaceutical companies; whether the nominee has sufficient time to devote to our Board; and the nominee’s commitment to represent the long-term interests of our stockholders. We review candidates in the context of the current composition of the Board and the evolving needs of our business. We believe that each of the current members of our Board has the requisite business, biopharmaceutical, financial or managerial experience to serve as a member of the Board, as described above in their biographies under the heading “Information about our Executive Officers” and “Information about our Non-Employee Directors.” We also believe that each of the current members of our Board has other key attributes that are important to an effective board, including integrity, high ethical standards, sound judgment, analytical skills, and the commitment to devote significant time and energy to service on the Board and its committees. Code of Business Conduct and Ethics We have adopted a Code of Ethics (the “Code”), which applies to all of our directors and employees, including our principal executive officer and principal financial officer. The Code includes guidelines dealing with the ethical handling of conflicts of interest, compliance with federal and state laws, financial reporting, and our proprietary information. The Code also contains procedures for dealing with and reporting violations of the Code. We have posted a copy of the Code on our website, located at www.mustangbio.com. Insider Trading Policy; Policy Prohibiting Hedging and Speculative Trading We have adopted an Insider Trading Policy that governs the purchase, sale, and other dispositions of our securities on the basis of material non-public information by directors, officers, employees, consultants and contractors. We believe these policies and procedures are reasonably designed to promote compliance with insider trading laws, rules and regulations, and applicable Nasdaq listing standards. A copy of our Insider Trading Policy is filed as an exhibit to this Form 10-K. Pursuant to our Insider Trading Policy, our officers, directors, and employees are also prohibited from engaging in speculative trading, including hedging transactions or short sale transactions with respect to our securities. Delinquent Section 16(a) Reports ​ Section 16 of the Exchange Act requires our directors, certain officers, and beneficial owners of more than ten percent of our common stock to file reports with the SEC indicating their holdings of and transactions in our equity securities, and to provide copies of such reports to us. Based solely on a review of our records, publicly available information, and written representations by the persons required to file such reports, we believe that during the fiscal year ended December 31, 2025, there were no delinquent Section 16(a) filings. ​ ​ Item 11. Executive Compensation ​ Named Executive Officers As determined in accordance with SEC rules, our named executive officers (“NEOs”), which includes all executive officers serving during 2025, are the individuals set forth below: ● Manuel Litchman, M.D., our President, Chief Executive Officer, and Interim Chief Financial Officer. ​ 70 ​ Table of Contents The following table sets forth information concerning compensation paid by us to our NEOs for their services rendered to us in all capacities during the years ended December 31, 2025, and 2024. Summary Compensation Table ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Non-Equity ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Stock ​ ​ Option ​ ​ Incentive Plan ​ ​ All Other ​ ​ ​ ​ ​ ​ ​ ​ Salary ​ Bonus ​ ​ Awards (1) ​ ​ Awards ​ ​ Compensation (2) ​ ​ Compensation ​ ​ Total Name and Principal Position ​ ​ ​ Year ​ ​ ​ ​ ($) ​ ​ ​ ($) ​ ​ ​ ​ ($) ​ ​ ​ ​ ($) ​ ​ ​ ​ ($) ​ ​ ​ ​ ($) ​ ​ ​ ​ ($) Manuel Litchman, M.D. ​ 2025 ​ $ 485,500 ​ $ — ​ $ — ​ $ — ​ $ — ​ $ 12,763 (3) ​ $ 498,263 President, Chief Executive Officer, and Interim Chief Financial Officer ​ 2024 ​ ​ 485,500 ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ 12,542 (3) ​ ​ 498,042 ____________________ (1) The amounts in the “Stock Awards” column reflect the aggregate grant date fair value of restricted stock units granted during the year computed in accordance with the provisions of FASB ASC Topic 718. The assumptions used in calculating these amounts are incorporated by reference to Note 8 to the financial statements included in this Form 10-K . No Stock Awards were granted in 2025 and 2024. (2) In 2025 and 2024, the Compensation Committee decided to not pay annual cash incentive bonuses . See the “Annual Cash Incentive Bonus” section below for additional details. (3) All other compensation for Dr. Litchman is comprised of Company matching 401(k) contributions. Narrative to Summary Compensation Table Employment Agreements Dr. Litchman In April 2017, we entered into an employment agreement with Dr. Litchman, our President, Chief Executive Officer and Interim Chief Financial Officer, pursuant to which he received an initial annual base salary of $395,000. As part of his annual review in January 2023, the Board increased Dr. Litchman’s annual base salary to $485,500 effective as of April 1, 2023. There were no increases to Dr. Litchman’s annual base salary in 2025 and 2024. The employment agreement further provides eligibility for an incentive bonus linked to the realization of certain corporate milestones to be established annually by the Board or the Compensation Committee. Dr. Litchman’s target annual bonus is equal to fifty percent (50%) of his annual salary, and the Board or the Compensation Committee will determine the actual payout amount each year. The employment agreement provides that if we terminate Dr. Litchman without cause or if he resigns for good reason, as those terms are defined in the employment agreement, he will be entitled to: (i) severance payments at a rate equal to his base salary then in effect for a period of 12 months following his termination date; (ii) a pro-rata share of the annual incentive bonus for the year in which the termination occurred, to be paid when and if such bonus would have been paid under the employment agreement; (iii) accelerated partial vesting of all unvested time-based equity awards with respect to the same number of shares that would have vested if Dr. Litchman had continued in employment for one year following the termination date; and (iv) if Dr. Litchman timely elects continued health insurance coverage under COBRA, the entire premium necessary to continue such coverage for Dr. Litchman and Dr. Litchman’s eligible dependents until the conclusion of the time when Dr. Litchman is receiving continuation of base salary payments or until Dr. Litchman becomes eligible for group health insurance coverage under another employer’s plan, whichever occurs first, provided however that we have the right to terminate such payment of COBRA premiums on behalf of Dr. Litchman and instead pay him a lump sum amount equal to the COBRA premium times the number of months remaining in the specified period if we determine in our discretion that continued payment of COBRA premiums is or may be discriminatory under Section 105(h) of the Internal Revenue Code. In addition, if Dr. Litchman is terminated without cause or resigns for good reason within twelve months following a change in control, he will be entitled to the severance benefits described in (i), (ii) and (iv) of the immediately preceding sentence, as well as 100% accelerated vesting of the options and other equity awards granted to him. In the event Dr. Litchman’s employment is terminated due to his death or disability, he or his estate will receive continuing salary payments for ninety days and a pro-rata share of the annual incentive bonus for the year in which the termination occurred, to be paid when and if such bonus would have been paid under the employment agreement. In each case, the severance benefits are conditioned upon Dr. Litchman’s execution and non-revocation of a release of claims against us and compliance with certain non-solicitation and non-competition covenants during his employment and for a period of six months thereafter. Also, the severance benefits are subject to reduction to avoid the imposition of excise taxes under Sections 280G and 4999 of the Code, if such reduction would result in a better after-tax result for Dr. Litchman. ​ 71 ​ Table of Contents Annual Cash Incentive Bonus In 2025, Dr. Litchman was eligible to earn a target annual cash incentive equal to 50% of his base salary per the terms of his Employment Agreement. Dr. Litchman’s annual cash incentive bonus is based upon our performance against pre-established corporate goals and objectives, which included a combination of clinical and nonclinical goals related to our products as well as other corporate development goals, and his individual performance based upon subjective performance reviews. In 2025, the Compensation Committee decided not to pay the 2025 annual cash incentive bonus to preserve our cash resources. Equity Awards The Company maintains the Mustang Bio, Inc. 2016 Incentive Plan (the “2016 Plan”), pursuant to which it may, from time to time, grant equity awards to its service providers, including its executive officers and directors. However, no equity awards were granted in 2025. ​ Outstanding Equity Awards at Fiscal Year-Ended December 31, 2025 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Option Awards ​ Stock Awards ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Market Value ​ ​ Number of ​ Number of ​ ​ ​ ​ ​ ​ Number of ​ of Shares or ​ ​ securities ​ securities ​ ​ ​ ​ ​ ​ Shares or ​ Units of Stock ​ ​ underlying ​ underlying ​ Option ​ ​ ​ Units of ​ That Have ​ ​ unexercised ​ unexercised ​ exercise ​ Option ​ Stock That ​ Not ​ ​ options (#) ​ options (#) ​ price ​ Expiration ​ Have Not ​ Vested (1) Name ​ ​ ​ exercisable ​ ​ ​ unexercisable ​ ​ ​ ($) ​ ​ ​ Date ​ ​ ​ Vested (#) ​ ​ ​ ($) Manuel Litchman M.D. 868 (2) ​ 520 (2) ​ $ 4,297.50 4/24/2027 71 (3) ​ $ 70 __________________ (1) Market value is based on $0.981 per share, the closing price of our common stock on the Nasdaq Capital Market on December 31, 2025, the last trading day of the fiscal year . (2) The unvested portion of the option will vest and become exercisable upon the occurrence of the following milestones being achieved, in each case subject to Dr. Litchman’s continuous service to the Company on the date of such occurrences: (A) 25% of such shares will vest upon the dosing of the first patient in the first Phase 2 clinical trial of a second Company product candidate; (B) 25% of such shares will vest upon our achievement of a fully-diluted market capitalization of $500,000,000; and (C) 25% of such shares will vest upon our achievement of a fully-diluted market capitalization of $1 billion . Notwithstanding the foregoing, in the event that a Phase 2 clinical trial for the Company product candidates referenced in subsection (A) of this paragraph is bypassed, the corresponding percentage of the Performance Option grant that would have otherwise vested pursuant to subsection (A) of this paragraph will vest upon the earlier of (x) the dosing of the first patient in the first Phase 3 clinical trial for that Company product candidate, or (y) the filing of a Biologics License Application or New Drug Application with the U.S. Food and Drug Administration, or alternatively the filing of an equivalent regulatory filing with a foreign regulatory agency, with respect to that Company product candidate. (3) These restricted stock units vest as follows: (i) 46 shares will vest on April 24, 2026; and (ii) 25 shares will vest on April 24, 2027, subject in each case to Dr. Litchman’s continuous service to the Company through that date. ​ Clawback Policy ​ Pursuant to Nasdaq listing requirements, we have adopted a policy providing for the recovery of erroneously awarded incentive-based compensation received by our executive officers or the executive officers of one of our subsidiaries during an applicable recovery period (the “Clawback Policy”) in compliance with Section 10D of the Exchange Act. Under the Clawback Policy, in the event that financial results upon which a cash or equity-based incentive award was based becomes the subject of a financial restatement that is required because of material non-compliance with financial reporting requirements, the Compensation Committee will conduct a review of awards covered by the Clawback Policy and recoup any erroneously awarded incentive-based compensation to ensure that the ultimate award reflects the financial results as restated. The Clawback Policy covers any cash or equity-based incentive compensation award that was paid, earned or granted to covered executive officers during the last completed three fiscal years immediately preceding the date on which we are required to prepare the accounting restatement. 72 ​ Table of Contents Stock Option Grant Policy ​ We did not grant stock options or similar instruments to our NEOs during 2025. We have no set policy or practice regarding the timing of stock option awards or similar instruments in relation to the disclosure of material nonpublic information. In general, the timing of stock option awards is dictated by the event or circumstance giving rise to the award and the schedules of the directors responsible for approving the award. If, in the future, a stock option grant is made at a time that material nonpublic information exists , the directors approving the award would be responsible for considering the anticipated effect of that information on our stock price and would take such effect into account when sizing and pricing the award. ​ Director Compensation ​ Directors who are also employees are not compensated separately for serving on the Board or any of its committees. For 2025, our only employee director was Dr. Litchman, and he is therefore not included in the Director Compensation Table below. Each of our non-employee directors is eligible to receive cash and equity compensation for his or her services. The Compensation Committee periodically conducts reviews of peer company director compensation practices, including before considering changes to our director compensation program and amounts. Director Compensation Program In January 2016, the Board adopted a Non-Employee Directors Compensation Plan for our non-employee directors, which determines the cash and equity compensation payable to our non-employee directors. The Non-Employee Directors Compensation Plan provides for our non-employee directors to receive the following compensation: Cash Compensation : ● $50,000 annual retainer; and ● $10,000 additional annual retainer for the Audit Committee Chair. However, for Mr. Weiss, in lieu of the cash compensation described above, $60,000 of annual cash compensation is paid to the Advisor according to the Advisory Agreement. Equity Compensation : ● Initial Equity Grant: 50,000 shares of restricted stock, which shares shall vest and become non-forfeitable in equal annual installments over three years, beginning on the third (3 rd ) anniversary of the grant date, subject to the director’s continued service on the Board on such date. ● Re-Election Equity Grant: The greater of (i) a number of shares of restricted stock having a fair market value on the grant date of $50,000, or (ii) 10,000 shares of restricted stock, which shares shall vest and become non-forfeitable on the third (3 rd ) anniversary of the grant date, subject to the director’s continued service on the Board on such date. However, in 2025 the Board decided not to grant director equity awards due to timing of the annual shareholders meeting. In addition, each non-employee director receives reimbursement for reasonable travel expenses incurred in attending meetings of our Board and meetings of committees of our Board. ​ 73 ​ Table of Contents Director Compensation Table The following table sets forth the cash and other compensation we paid to the non-employee members of our Board for all services in all capacities during 2025. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Fees Earned or ​ ​ ​ Stock ​ ​ ​ ​ ​ ​ ​ Paid in Cash ​ Awards ​ Total Name ​ ($) (1) ​ ($) (2) ​ ($) Michael S. Weiss (3) ​ $ 60,000 ​ $ — ​ $ 60,000 Adam J. Chill ​ ​ 60,000 ​ ​ — ​ ​ 60,000 Neil Herskowitz ​ ​ 50,000 ​ ​ — ​ ​ 50,000 David Jin ​ ​ 50,000 ​ ​ — ​ ​ 50,000 Lindsay A. Rosenwald, M.D. ​ ​ 50,000 ​ ​ — ​ ​ 50,000 Michael J. Zelefsky, M.D. ​ ​ 50,000 ​ ​ — ​ ​ 50,000 ____________________ (1) Represents the cash retainer for serving on our Board and committees of the Board. (2) No stock awards were granted in 2025. As of December 31, 2025, each of Mr. Herskowitz, Dr. Rosenwald, Mr. Weiss, Mr. Chill and Dr. Zelefsky had 157 shares of unvested restricted stock pursuant to prior awards. (3) Pursuant to the Advisory Agreement, the Advisor is paid an annual cash fee of $60,000, for the services of Mr. Weiss as Chairman of the Board and Executive Chairman in addition to any and all annual equity incentive grants paid to members of the Board. ​ ​ Item 12. Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters ​ Securities Authorized for Issuance Under Equity Compensation Plans ​ The following table contains information about our equity compensation plans as of December 31, 2025. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Equity Compensation Plan Information ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of securities ​ ​ ​ ​ ​ ​ ​ remaining available ​ ​ ​ ​ Weighted- ​ for future issuance ​ ​ ​ ​ average ​ under equity ​ ​ Number of securities to be ​ exercise price of ​ compensation plans ​ ​ issued upon exercise of ​ outstanding ​ (excluding securities ​ ​ outstanding options, ​ options, warrants ​ reflected in Plan Category ​ warrants and rights ​ and rights (1) ​ column (a)) ​ ​ ​ ​ (a) ​ ​ ​ (b) ​ ​ ​ (c) Equity compensation plans approved by security holders 1,617 ​ $ 4,297.50 2,506,958 Equity compensation plans not approved by security holders — ​ — — Total 1,617 ​ $ 4,297.50 2,506,958 ​ (1) The calculation of the weighted-average exercise price of outstanding options, warrants and rights in this column does not include outstanding restricted stock units, as they do not have an exercise price. ​ Our equity compensation plans consist of the 2016 Plan, and the Mustang Bio, Inc. 2019 Employee Stock Purchase Plan, which were each approved by our stockholders. We do not have any equity compensation plans or arrangements that have not been approved by our stockholders. ​ ​ ​ ​ 74 ​ Table of Contents Security Ownership of Our Directors, Executive Officers, and 5% Beneficial Owners ​ The following table shows information, as of March 17, 2026, concerning the beneficial ownership of our common stock by: ● each person we know to be the beneficial owner of more than 5% of our common stock; ● each of our current directors; ● each of our NEOs shown in our Summary Compensation Table; and ● all current directors and executive officers as a group. As of March 17, 2026, there were 6,732,092 shares of our common stock, 845,385 shares of our Class A common stock, and 250,000 shares of our Class A Preferred Stock outstanding. In order to calculate a stockholder’s percentage of beneficial ownership, we include in the calculation those shares underlying options or warrants beneficially owned by that stockholder that are vested or that will vest within 60 days of March 16, 2026. Shares of restricted stock are deemed to be outstanding. Options or warrants held by other stockholders that are not attributed to the named beneficial owner are disregarded in this calculation. Beneficial ownership is determined in accordance with the rules of the SEC and includes voting or investment power with respect to the shares of our common stock. Unless we have indicated otherwise, each person named in the table below has sole voting power and investment power for the shares listed opposite such person’s name, except to the extent authority is shared by spouses under community property laws. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Shares Under ​ ​ ​ ​ ​ ​ ​ ​ ​ Exercisable ​ ​ ​ ​ ​ ​ ​ ​ ​ Options and ​ ​ ​ ​ ​ ​ ​ ​ ​ Unvested ​ Total Shares ​ ​ ​ ​ ​ ​ ​ Restricted Stock ​ Beneficially ​ ​ ​ Name of Beneficial Owner (1) ​ Shares owned ​ Units (2) ​ Owned ​ % of total CS ​ Michael S. Weiss (3) ​ 991 ​ — ​ 991 ​ * % Manuel Litchman, M.D ​ 1,563 ​ 939 ​ 2,502 ​ * % Lindsay A. Rosenwald, M.D (3) ​ 1,008 ​ — ​ 1,008 ​ * % Neil Herskowitz ​ 145 ​ — ​ 145 ​ * % Adam J. Chill ​ 375 ​ — ​ 375 ​ * % Michael J. Zelefsky, M.D ​ 379 ​ — ​ 379 ​ * % David Jin ​ 286 ​ — ​ 286 ​ * % All current executive officers and directors as a group (7 persons) ​ 4,747 ​ 939 ​ 5,686 ​ * % 5% or Greater Stockholders: ​ ​ ​ ​ ​ ​ ​ ​ ​ Fortress Biotech, Inc (4) ​ 536,577 ​ — ​ 536,577 ​ 8.0 % _________________ * Less than 1% of our common stock outstanding (1) The address of each of the directors and executive officers is c/o Mustang Bio, Inc., 95 Sawyer Road, Suite 110, Waltham, MA 02453, and the address of Fortress Biotech, Inc. is c/o Fortress Biotech, Inc., 1111 Kane Concourse, Suite 301, Bay Harbor Island, FL 33154 (2) Includes only options exercisable within 60 days of March 17, 2026 and unvested restricted stock units. (3) Includes 666 warrants issued by Fortress to each of Mr. Weiss and Dr. Rosenwald that cover shares of our common stock that are owned by Fortress. These do not represent equity compensation by us to either Mr. Weiss or Dr. Rosenwald . (4) Includes shares underlying 666 warrants issued to each of Mr. Weiss and Dr. Rosenwald, and excludes 250,000 of Class A Preferred Stock, which are convertible into 333 shares of Common Stock. 75 ​ Table of Contents The following table shows information, as of March 17, 2026, concerning the beneficial ownership of our Class A Common Stock: ​ ​ Class A Common Stock Beneficially Owned Name and Address of Beneficial Owner (1) Number of Shares and Nature of Beneficial Ownership (2) Percentage of Total Class A Common Stock City of Hope 845,385 100% ​ ____________________ (1) The address of City of Hope is 1500 East Duarte Road, Duarte, California 91010. (2) Converts into 1,127 shares of common stock. ​ The following table shows information, as of March 17, 2026, concerning the beneficial ownership of our Class A Preferred Stock: ​ Class A Preferred Stock Beneficially Owned Name and Address of Beneficial Owner (1) Number of Shares and Nature of Beneficial Ownership (2) Percentage of Total Class A Preferred Stock Fortress Biotech, Inc 250,000 100% ​ ____________________ (1) The address of Fortress Biotech Inc. is c/o Fortress Biotech, Inc., 1111 Kane Concourse, Suite 301, Bay Harbor Island, FL 33154. (2) Converts into 333 shares of common stock . ​ Item 13. Certain Relationships and Related Transactions, and Director Independence ​ Except as set forth below, since January 1, 2024, we have not been a party to any transaction in which the amount involved exceeded or will exceed $120,000, and in which any of our directors, NEOs, or beneficial owners of more than 5% of our capital stock, or an affiliate or immediate family member thereof, had or will have a direct or indirect material interest, and other than compensation, termination, and change-in-control arrangements. The written charter of the Audit Committee authorizes, and Nasdaq rules require, the Audit Committee to review and approve related-party transactions. In reviewing related-party transactions, the Audit Committee applies the basic standard that transactions with affiliates should be made on terms no less favorable to us than could have been obtained from unaffiliated parties. Therefore, the Audit Committee reviews the benefits of the transactions, terms of the transactions and the terms available from unrelated third parties, as applicable. All transactions other than compensatory arrangements between us and our officers, directors, principal stockholders and their affiliates will be approved by the Audit Committee or a majority of the disinterested directors and will continue to be on terms no less favorable to us than could be obtained from unaffiliated third parties. Founders Agreement and Management Services Agreement with Fortress Effective March 13, 2015, we entered a Founders Agreement with Fortress, which was amended and restated on May 17, 2016, and again on July 26, 2016 (the “Mustang Founders Agreement”). The Mustang Founders Agreement provides that, in exchange for the time and capital expended in the formation of our company and the identification of specific assets the acquisition of which result in the formation of a viable emerging growth life science company, Fortress loaned $2.0 million, representing the up-front fee required to acquire our license agreement with COH. The Mustang Founders Agreement has a term of 15 years, which upon expiration automatically renews for successive one-year periods unless terminated by Fortress and the Company or a Change in Control (as defined in the Mustang Founders Agreement) occurs. Concurrently with the second amendment on July 26, 2016, to the Mustang Founders Agreement, Fortress entered into an Exchange Agreement whereby Fortress exchanged its 7.25 million Class B Common shares for 9,333 common shares and 250,000 Class A Preferred shares. Class A Preferred Stock is identical to common stock other than as to voting rights, conversion rights and the Annual Stock Dividend right (as described below). Each share of Class A Preferred Stock is entitled to vote the number of votes that is equal to one and one-tenth (1.1) times a fraction, the numerator of which is the sum of (A) the shares of our outstanding common stock and (B) the whole shares of our 76 ​ Table of Contents common stock into which the shares of outstanding Class A common stock and Class A Preferred Stock are convertible and the denominator of which is the number of shares of outstanding Class A Preferred Stock. Thus, the Class A Preferred Stock will at all times constitute a voting majority. Each share of Class A Preferred Stock is convertible, at Fortress’ option, into one fully paid and nonassessable share of our common stock, subject to certain adjustments. As holders of Class A Preferred Stock, Fortress will receive on each January 1 (each a “Annual Stock Dividend Payment Date”) until the date all outstanding Class A Preferred Stock is converted into common stock, pro rata per share dividends paid in additional fully paid and nonassessable shares of common stock (“Annual Stock Dividends”) such that the aggregate number of shares of common stock issued pursuant to such Annual Stock Dividend is equal to two and one-half percent (2.5%) of our fully-diluted outstanding capitalization on the date that is one (1) business day prior to any Annual Stock Dividend Payment Date. As additional consideration under the Mustang Founders Agreement, we are required to: (i) pay an equity fee in shares of common stock, payable within five (5) business days of the closing of any equity or debt financing that occurs after the effective date of the Mustang Founders Agreement and ending on the date when Fortress no longer has majority voting control in our voting equity, equal to two and one-half (2.5%) of the gross amount of any such equity or debt financing; and (ii) pay a cash fee equal to four and one-half percent (4.5%) of our annual net sales, payable on an annual basis, within ninety (90) days of the end of each calendar year. In the event of a Change in Control, we will pay a one-time change in control fee equal to five (5x) times the product of (A) net sales for the twelve (12) months immediately preceding the change in control and (B) four and one-half percent (4.5%). Effective as of March 13, 2015, we entered into a Management Services Agreement (the “MSA”) with Fortress, pursuant to which Fortress renders advisory and consulting services to us. The MSA has an initial term of five years and is automatically renewed for successive five-year terms unless terminated in accordance with its provisions. Services provided under the MSA may include, without limitation, (i) advice and assistance concerning any and all aspects of our operations, clinical trials, financial planning and strategic transactions and financings and (ii) conducting relations on our behalf with accountants, attorneys, financial advisors and other professionals (collectively, the “Services”). We are obligated to utilize clinical research services, medical education, communication and marketing services and investor relations/public relation services of companies or individuals designated by Fortress, provided those services are offered at market prices. However, we are not obligated to take or act upon any advice rendered by Fortress and Fortress shall not be liable for any of its actions or inactions based upon their advice. Pursuant to the MSA and our Certificate of Incorporation, Fortress and its affiliates, including all members of our Board, will have no fiduciary or other duty to communicate or present any corporate opportunities to us or to refrain from engaging in business that is similar to that of our company. In consideration for the Services, we pay Fortress an annual consulting fee of $0.5 million (the “Annual Consulting Fee”), payable in advance in equal quarterly installments on the first business day of each calendar quarter in each year, provided, however, that such Annual Consulting Fee shall be increased to $1.0 million for each calendar year in which we have net assets in excess of $100 million at the beginning of the calendar year. We record fifty percent of the Annual Consulting Fee in research and development expense and fifty percent in general and administrative expense in the Statement of Operations. For the years ended December 31, 2025 and 2024, we recorded expense of $0.5 million and $0.5 million, respectively, related to this agreement. For the year ended December 31, 2025, the Company issued 127,140 shares of common stock to Fortress, which equaled 2.5% of the sum of the gross proceeds of $0.6 million from the sale of shares of common stock under Mustang’s At-the-Market Offering, $8.0 million gross proceeds from the February 2025 Public Offering, and $7.1 million from the July 2025 Series C-2 warrant exercises. The Company recorded an expense of approximately $0.4 million in general and administrative expenses related to these shares for the year ended December 31, 2025. ​ For the year ended December 31, 2024, the Company issued 23,450 shares of common stock to Fortress, which equaled 2.5% of the sum of the gross proceeds of $2.6 million from the sale of shares of common stock under Mustang’s At-the-Market Offering, $4.0 million gross proceeds from the May 2024 Public Offering, $2.5 million from the June 2024 PIPE, and $4.0 million from the October 2024 warrant exercise. The Company recorded an expense of approximately $0.3 million in general and administrative expenses related to these shares for the year ended December 31, 2024. ​ Payables and Accrued Expenses Related Party In the normal course of business, Fortress pays certain expenses on behalf of the Company. Such expenses are recorded as payables and accrued expenses - related party. ​ 77 ​ Table of Contents Director Compensation Dr. Rosenwald and David Jin Pursuant to the terms of our Non-Employee Directors Compensation Plan, Dr. Rosenwald and Mr. Jin will receive a cash fee of $50,000 per year paid quarterly and an annual stock award of the greater of (i) a number of shares of common stock having a fair market value on the grant date of $50,000 or (ii) 10,000 shares of common stock, which shares shall vest and become non-forfeitable on the third anniversary of the grant date, subject to continued service on the board of directors on such date. However, no restricted stock awards were granted in 2025 or 2024. Dr. Rosenwald is Chairman, President and Chief Executive Officer of Fortress and Mr. Jin is Chief Financial Officer and Head of Corporate Development of Fortress. We are a controlled subsidiary of Fortress. For the year ended December 31, 2025, we recognized $50,000 and $50,000 for Dr. Rosenwald and Mr. Jin, respectively, in expense related to the director compensation. For the year ended December 31, 2024, we recognized $50,000 and $12,500 for Dr. Rosenwald and Mr. Jin, respectively, in expense in our Statements of Operations related to the director compensation. No restricted stock awards were granted in 2025 and 2024. Mr. Weiss - Advisory Agreement with Caribe BioAdvisors, LLC The Board approved and authorized our entrance into an advisory agreement, dated January 1, 2017 (the “Advisory Agreement”), with Caribe BioAdvisors, LLC (the “Advisor”), owned by Michael S. Weiss, the Chairman of the Board, to provide the board advisory services of Mr. Weiss as Chairman of the Board. Pursuant to the Advisory Agreement, the Advisor will be paid an annual cash fee of $60,000, paid quarterly and an annual stock award of the greater of (i) a number of shares of common stock having a fair market value on the grant date of $50,000 or (ii) 10,000 shares of common stock, which shares shall vest and become non-forfeitable on the third anniversary of the grant date, subject to continued service on the Board on such date. For the year ended December 31, 2025, we recognized $60,000 in expense related to the Advisory Agreement. For the year ended December 31, 2024, we recognized $60,000 in expense in our Statements of Operations related to the Advisory Agreement. No restricted stock awards were granted in 2025 and 2024. It em 14. Principal Accounting Fees and Services ​ Audit Fees, Audit-Related Fees, Non-Audit Fees, Tax Fees and Other Fees Audit Fees For the year ended December 31, 2025, KPMG LLP billed us an aggregate of approximately $413,000 in fees and professional services rendered in connection with the audit of our annual financial statements included in our Annual Reports on Form 10-K for the 2025 fiscal year, the review of our financial statements included in our Quarterly Reports on Form 10-Q during that fiscal year, and overages incurred for final billings for the 2024 audit. For the year ended December 31, 2024, KPMG LLP billed us an aggregate of approximately $412,000 in fees and professional services rendered in connection with the audit of our annual financial statements included in our Annual Reports on Form 10-K for the 2024 fiscal year and the review of our financial statements included in our Quarterly Reports on Form 10-Q during that fiscal year. Audit-Related Fees For the year ended December 31, 2025, and 2024, KPMG LLP billed us an aggregate of approximately $293,000 and $255,000, respectively, in fees for audit-related services rendered in connection with securities offerings and registration statements, in addition to the fees described above under the heading “Audit Fees.” Tax Fees During the fiscal years ended December 31, 2025 and 2024 we were not billed by KPMG LLP for fees for professional services rendered for tax compliance, tax advice, and tax planning services. 78 ​ Table of Contents All Other Fees During the fiscal years ended December 31, 2025 and 2024, we were not billed by KPMG LLP for any fees for services, other than those described above, rendered to us for each of those fiscal years. Pre-Approval of Services ​ Our Audit Committee has established a policy setting forth the procedures under which services provided by our independent registered public accounting firm will be pre-approved by our Audit Committee. The potential services that might be provided by our independent registered public accounting firm fall into two categories: ● Services that are permitted, including the audit of our annual financial statements, the review of our quarterly financial statements, related attestations, benefit plan audits and similar audit reports, financial and other due diligence on acquisitions, and federal, state, and non-US tax services; and ● Services that may be permitted, subject to individual pre-approval, including compliance and internal-control reviews, indirect tax services such as transfer pricing and customs and duties, and forensic auditing. Services that our independent registered public accounting firm may not legally provide include such services as bookkeeping, certain human resources services, internal audit outsourcing, and investment or investment banking advice. All proposed engagements of our independent registered public accounting firm, whether for audit services or permissible non-audit services, are pre-approved by our Audit Committee. We jointly prepare a schedule with our independent registered public accounting firm that outlines services which we reasonably expect we will need from our independent registered public accounting firm and categorize them according to the classifications described above. Each service identified is reviewed and approved or rejected by our Audit Committee. ​ PART IV Item 15. Exhibits, Financial Statement Schedules ​ (a) Financial Statements. The following financial statements are filed as part of this Form 10-K: ​ Report of Independent Registered Public Accounting Firm ( KPMG LLP , New York, NY ; PCAOB ID: 185 ) F-2 Financial Statements: Balance Sheets as of December 31, 2025 and 2024 F-4 Statements of Operations for the Years Ended December 31, 2025 and 2024 F-5 Statements of Changes in Stockholders’ Equity for the Years Ended December 31, 2025 and 2024 F-6 Statements of Cash Flows for the Years Ended December 31, 2025 and 2024 F-7 Notes to Financial Statements F-8 - F-26 ​ (b) Exhibits. ​ Exhibit No. Description 1.1 ​ At the Market Offering Agreement, dated May 31, 2024, between the Company, Band H.C. Wainwright & Co., LLC (incorporated by reference to the Exhibit 1.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on June 6, 2024). ​ 2.1 ​ Bill of Sale and Surrender Agreement, dated January 31, 2025, by and between Mustang Bio, Inc. and AbbVie Bioresearch Center Inc. (incorporated by reference to the Exhibit 2.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on February 27, 2025). ​ 79 ​ Table of Contents Exhibit No. Description 3.1 Amended and Restated Certificate of Incorporation of Mustang Bio, Inc. (formerly Mustang Therapeutics, Inc.), dated July 26, 2016 (incorporated by reference to the Exhibit 3.1 of the Registrant’s Form 10-12G (File No. 000-55668) filed with the SEC on July 28, 2016). ​ 3.2 Certificate of Amendment of the Amended and Restated Certificate of Incorporation of Mustang Bio, Inc., dated June 14, 2018 (incorporated by reference to the Exhibit 3.1 of the Registrant’s Quarterly Report on Form 10-Q (File No. 001-38191) filed with the SEC on June 14, 2018). 3.3 Certificate of Amendment of the Amended and Restated Certificate of Incorporation of Mustang Bio, Inc., dated September 30, 2019 (incorporated by reference to the Exhibit 3.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on September 30, 2019). ​ ​ 3.4 ​ Certificate of Amendment of the Amended and Restated Certificate of Incorporation of Mustang Bio, Inc., dated December 4, 2020 (incorporated by reference to the Exhibit 3.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on December 4, 2020). ​ ​ ​ 3.5 Certificate of Amendment of the Amended and Restated Certificate of Incorporation of Mustang Bio, Inc., dated June 17, 2021 (incorporated by reference to the Exhibit 3.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on June 22, 2021). ​ ​ ​ ​ 3.6 ​ Certificate of Amendment of the Amended and Restated Certificate of Incorporation of Mustang Bio, Inc., dated July 5, 2022 (incorporated by reference to the Exhibit 3.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on July 5, 2022). ​ 3.7 ​ Certificate of Amendment of the Amended and Restated Certificate of Incorporation of Mustang Bio, Inc., dated April 3, 2023 (incorporated by reference to the Exhibit 3.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on April 3, 2023). ​ 3.8 ​ Certificate of Amendment to the Amended and Restated Certificate of Incorporation of Mustang Bio, Inc., dated January 15, 2025 (incorporated by reference to the Exhibit 3.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on January 17, 2025). ​ 3.9 ​ Amended and Restated Bylaws of Mustang Bio, Inc. (incorporated by reference to the Exhibit 3.2 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on April 3, 2023). 4.1 Form of warrant agreement (incorporated by reference to the Exhibit 4.2 of the Registrant’s Form 10-12G (File No. 000-55668) filed with the SEC on July 28, 2016). 4.2 Description of Securities of Mustang Bio, Inc. (incorporated by reference to Exhibit 4.2 of the Registrant’s Form 10-K (File No. 001-38191) filed with the SEC on March 28, 2025). 4.3 ​ Common Stock Warrant issued by Mustang Bio, Inc. to NSC Biotech Venture Fund I, LLC, dated July 5, 2016 (incorporated by reference to the Exhibit 10.5 of the Registrant’s Form 10-12G (File No. 000-55668) filed with the SEC on July 28, 2016). ​ 4.4 ​ Warrant to Purchase Common Stock issued to Runway Growth Finance Corp., dated March 4, 2022 (incorporated by reference to the Exhibit 4.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on March 8, 2022). ​ 4.5 ​ Form of Pre-funded Warrant (incorporated by reference to the Exhibit 4.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on October 30, 2023). ​ 4.6 ​ ​ Form of Warrant (incorporated by reference to the Exhibit 4.2 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on October 30, 2023). ​ 80 ​ Table of Contents Exhibit No. Description 4.7 ​ Form of Wainwright Warrant (incorporated by reference to the Exhibit 4.3 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on October 30, 2023). ​ 4.8 ​ Form of May 2024 Pre-Funded Warrant (incorporated by reference to the Exhibit 4.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on May 2, 2024). ​ 4.9 ​ Form of May 2024 Series A-1, A-2, and A-3 Warrant (incorporated by reference to the Exhibit 4.2 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on May 2, 2024). ​ 4.10 ​ Form of May 2024 Placement Agent Warrant (incorporated by reference to the Exhibit 4.3 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on May 2, 2024). ​ 4.11 ​ Form of June 2024 Pre-Funded Warrant (incorporated by reference to the Exhibit 4.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on June 24, 2024). ​ 4.12 ​ Form of June 2024 Warrant (incorporated by reference to the Exhibit 4.2 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on June 24, 2024). ​ 4.13 ​ Form of June 2024 Wainwright Warrant (incorporated by reference to the Exhibit 4.3 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on June 24, 2024). ​ 4.14 ​ Form of Series B-1 Warrant (incorporated by reference to the Exhibit 4.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on October 25, 2024). ​ 4.15 ​ Form of October 2024 Wainwright Warrant (incorporated by reference to the Exhibit 4.3 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on October 25, 2024). ​ 4.16 ​ Form of Pre-Funded Warrant (incorporated by reference to the Exhibit 4.1 of the Registrant’s Current Report on Form 8-K (file No. 001-38191) filed with the SEC on February 11, 2025). ​ 4.17 ​ Form of Series C-1 and C-2 Warrant (incorporated by reference to the Exhibit 4.2 of the Registrant’s Current Report on Form 8-K (file No. 001-38191) filed with the SEC on February 11, 2025). ​ 4.18 ​ Form of Placement Agent Warrant (incorporated by reference to the Exhibit 4.3 of the Registrant’s Current Report on Form 8-K (file No. 001-38191) filed with the SEC on February 11, 2025). ​ 10.1 Second Amended and Restated Founders Agreement between Fortress Biotech, Inc. and Mustang Bio, Inc., dated July 26, 2016 (incorporated by reference to the Exhibit 10.1 of the Registrant’s Form 10-12G (File No. 000-55668) filed with the SEC on July 28, 2016). 10.2 Management Services Agreement between Fortress Biotech, Inc. and Mustang Bio, Inc., dated March 13, 2015 (incorporated by reference to the Exhibit 10.2 of the Registrant’s Form 10-12G (File No. 000-55668) filed with the SEC on July 28, 2016). 10.3 Sponsored Research Agreement by and between Mustang Bio, Inc. and City of Hope, dated March 17, 2015 (incorporated by reference to the Exhibit 10.7 of the Registrant’s Form 10-12G (File No. 000-55668) filed with the SEC on July 28, 2016). 10.4 Mustang Bio, Inc. Non-Employee Directors Compensation Plan (incorporated by reference to the Exhibit 10.9 of the Registrant’s Form 10-12G (File No. 000-55668) filed with the SEC on July 28, 2016). † ​ 10.5 Board Advisory Services Agreement by and between Mustang Bio, Inc. and Caribe BioAdvisors, LLC, dated January 1, 2017 (incorporated by reference to the Exhibit 10.11 of the Registrant’s Annual Report on Form 10-K (File No. 000-55668) filed with the SEC on March 31, 2017). † 81 ​ Table of Contents Exhibit No. Description 10.6 Exclusive License Agreement (IV/ICV) by and between Mustang Bio, Inc. and City of Hope, dated February 17, 2017 (incorporated by reference to the Exhibit 10.5 of the Registrant’s Quarterly Report on Form 10-Q (File No. 000-55668) filed with the SEC on August 14, 2017). # 10.7 Amended and Restated Exclusive License Agreement ( IL13R a 2 ) by and between Mustang Bio, Inc. and City of Hope, dated February 17, 2017 (incorporated by reference to the Exhibit 10.15 of the Registrant’s Annual Report on Form 10-K (File No. 000-55668) filed with the SEC on March 31, 2017). # ​ 10.8 Amended and Restated Exclusive License Agreement (Spacer) by and between Mustang Bio, Inc. and City of Hope, dated February 17, 2017 (incorporated by reference to the Exhibit 10.16 of the Registrant’s Annual Report on Form 10-K (File No. 000-55668) filed with the SEC on March 31, 2017). # ​ 10.9 Employment Agreement between Manuel Litchman and Mustang Bio, Inc., effective as of April 24, 2017 (incorporated by reference to the Exhibit 10.1 of the Registrant’s Current Report on Form 8-K (File No. 000-55668) filed with the SEC on April 24, 2017). † ​ 10.10 Mustang Bio, Inc. 2016 Incentive Plan, dated May 17, 2016 (incorporated by reference to Exhibit 10.8 to the Registrant’s Form 10-12G filed on July 28, 2016). † ​ ​ ​ 10.11 ​ Amendment to Mustang Bio, Inc. 2016 Incentive Plan, filed with the Registrant’s Definitive Proxy Statement for the Annual Meeting of Stockholders on June 14, 2018, filed on April 30, 2018. † ​ 10.12 ​ Second Amendment to the Mustang Bio, Inc. 2016 Equity Incentive Plan, dated June 17, 2021 (incorporated by reference to the Exhibit 10.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on June 22, 2021). † ​ ​ ​ 10.13 ​ Third Amendment to Mustang Bio, Inc. 2016 Equity Incentive Plan, dated June 21,2022 (incorporated by reference to the Exhibit 10.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on June 24, 2022). † ​ 10.14 ​ Fourth Amendment to the Mustang Bio, Inc. 2016 Equity Incentive Plan, dated December 22, 2025 (incorporated by reference to Exhibit 10.2 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on December 23, 2025). † ​ 10.15 ​ Form of Option Agreement (incorporated by reference to Exhibit 10.28 of the Registrant’s Annual Report on Form 10-K (File No. 001-38191) filed with the SEC on March 11, 2024). † ​ 10.16 ​ Form of Restricted Stock Unit Agreement (incorporated by reference to Exhibit 10.29 of the Registrant’s Annual Report on Form 10-K (File No. 001-38191) filed with the SEC on March 11, 2024). † ​ 10.17 ​ Form of Director Stock Award Agreement (incorporated by reference to Exhibit 10.30 of the Registrant’s Annual Report on Form 10-K (File No. 001-38191) filed with the SEC on March 11, 2024). † ​ 10.18 ​ Mustang Bio, Inc. 2019 Employee Stock Purchase Plan (incorporated by reference to the Exhibit 10.1 of the Registrant’s Quarterly Report on Form 10-Q (File No. 001-38191) filed with the SEC on August 9, 2019).† ​ 10.19 ​ Amendment to the Mustang Bio, Inc. 2019 Employee Stock Purchase Plan, dated June 17, 2021 (incorporated by reference to the Exhibit 10.2 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on June 22, 2021). † ​ 10.20 ​ Amendment No. 2 to the Mustang Bio, Inc. 2019 Employee Stock Purchase Plan, dated June 21, 2023 (incorporated by reference to the Exhibit 10.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on June 21, 2023). † ​ 82 ​ Table of Contents Exhibit No. Description 10.21 ​ Amendment No. 3 to the Mustang Bio, Inc. 2019 Employee Stock Purchase Plan, dated December 22, 2025 (incorporated by reference to the Exhibit 10.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on December 23, 2025). † ​ 10.22 ​ Form of Securities Purchase Agreement, dated October 26, 2023, by and between the Company and the purchaser party thereto (incorporated by reference to the Exhibit 10.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on October 30, 2023). ​ 10.23 ​ Form of Securities Purchase Agreement, dated April 29, 2024, by and between the Company and the purchaser party thereto (incorporated by reference to the Exhibit 10.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on May 2, 2024). ​ 10.24 ​ Warrant Agreement Amendment, dated April 29, 2024, by and between the Company and the holder thereto (incorporated by reference to the Exhibit 10.2 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on May 2, 2024). ​ 10.25 ​ Form of Securities Purchase Agreement, dated June 19, 2024, by and between the Company and the purchaser party thereto (incorporated by reference to the Exhibit 10.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on June 24, 2024). ​ 10.26 ​ Form of Securities Purchase Agreement, dated February 5, 2025 (incorporated by reference to the Exhibit 10.1 of the Registrant’s Current Report on Form 8-K (file No. 001-38191) filed with the SEC on February 11, 2025). ​ 10.27 ​ Asset Purchase Agreement, dated June 27, 2024, by and between the Company and uBriGene (Boston) Biosciences, Inc. (incorporated by reference to the Exhibit 1.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on July 3, 2024). ​ 10.28 ​ Form of Investor Inducement Agreement (incorporated by reference to the Exhibit 10.1 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on October 25, 2024). ​ 10.29 ​ Form of Indemnification Agreement (incorporated by reference to the Exhibit 10.2 of the Registrant’s Current Report on Form 8-K (File No. 001-38191) filed with the SEC on October 25, 2024). ​ 19.1 ​ Insider Trading Policy (incorporated by reference to Exhibit 19.1 of the Registrant’s Form 10-K (File No. 001-38191) filed with the SEC on March 28, 2025). ​ 23.1 ​ Consent of Independent Registered Public Accounting Firm, KPMG, LLP, Boston , Massachusetts. ** ​ ​ ​ 31.1 Certification of Principal Executive and Financial Officer, pursuant to Rule 13a-14(a) of the Exchange Act, as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002. ** 32.1 Certification of Principal Executive and Financial Officer, pursuant to Rule 13a-14(b) of the Exchange Act and 18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley Act of 2002. *** 97 ​ Compensation Clawback Policy (incorporated by reference to Exhibit 97 of the Registrant’s Annual Report on Form 10-K (File No. 001-38191) filed with the SEC on March 11, 2024). ​ ​ ​ 101 The following financial information from Mustang Bio, Inc.’s Annual Report on Form 10-K for the year ended December 31, 2025, formatted in Inline Extensible Business Reporting Language (iXBRL): (i) the Balance Sheets, (ii) the Statements of Operations, (iii) the Statement of Stockholders’ Equity, (iv) the Statements of Cash Flows, and (v) Notes to the Financial Statements (filed herewith). ​ 104 ​ ​ Cover Page Interactive Data File (formatted as Inline XBRL and contained in exhibit 101) # Confidential treatment has been requested with respect to omitted portions of this exhibit. 83 ​ Table of Contents ​ † Indicates management contract or compensatory plan or arrangement. ​ ** Filed herewith. ​ *** Furnished herewith. ​ Item 16. Form 10-K Summary. ​ None. ​ ​ ​ 84 ​ Table of Contents ​ INDEX TO FINANCIAL STATEMENTS ​ Report of Independent Registered Public Accounting Firm (KPMG LLP, New York, NY; PCAOB ID: 185) F-2 Balance Sheets as of December 31, 2025 and 2024 F-4 Statements of Operations for the Years Ended December 31, 2025 and 2024 F-5 Statements of Changes in Stockholders’ Equity for the Years Ended December 31, 2025 and 2024 F-6 Statements of Cash Flows for the Years Ended December 31, 2025 and 2024 F-7 Notes to Financial Statements F-8 – F-26 ​ ​ ​ F-1 ​ Table of Contents ​ Report of Independent Registered Public Accounting Firm To the Stockholders and Board of Directors Mustang Bio, Inc.: ​ Opinion on the Financial Statements We have audited the accompanying balance sheets of Mustang Bio, Inc. (the Company) as of December 31, 2025 and 2024, the related statements of operations, stockholders’ equity, and cash flows for the years then ended, and the related notes (collectively, the financial statements). In our opinion, the financial statements present fairly, in all material respects, the financial position of the Company as of December 31, 2025 and 2024, and the results of its operations and its cash flows for the years then ended, in conformity with U.S. generally accepted accounting principles. Basis for Opinion These financial statements are the responsibility of the Company’s management. Our responsibility is to express an opinion on these financial statements based on our audits. We are a public accounting firm registered with the Public Company Accounting Oversight Board (United States) (PCAOB) and are required to be independent with respect to the Company in accordance with the U.S. federal securities laws and the applicable rules and regulations of the Securities and Exchange Commission and the PCAOB. ​ We conducted our audits in accordance with the standards of the PCAOB. Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement, whether due to error or fraud. The Company is not required to have, nor were we engaged to perform, an audit of its internal control over financial reporting. As part of our audits, we are required to obtain an understanding of internal control over financial reporting but not for the purpose of expressing an opinion on the effectiveness of the Company’s internal control over financial reporting. Accordingly, we express no such opinion. ​ Our audits included performing procedures to assess the risks of material misstatement of the financial statements, whether due to error or fraud, and performing procedures that respond to those risks. Such procedures included examining, on a test basis, evidence regarding the amounts and disclosures in the financial statements. Our audits also included evaluating the accounting principles used and significant estimates made by management, as well as evaluating the overall presentation of the financial statements. We believe that our audits provide a reasonable basis for our opinion. ​ Critical Audit Matter Critical audit matters are matters arising from the current period audit of the financial statements that were communicated or required to be communicated to the audit committee and that: (1) relate to accounts or disclosures that are material to the financial statements and (2) involved our especially challenging, subjective, or complex judgments. We determined that there are no critical audit matters. ​ /s/ KPMG LLP We have served as the Company’s auditor since 2021. ​ Boston, Massachusetts March 19, 2026 ​ ​ ​ F-2 ​ Table of Contents MUSTANG BIO, INC. BALANCE SHEETS (in thousands, except for share and per share amounts) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ ​ ​ ​ 2025 ​ ​ ​ 2024 ​ ​ ​ ​ ​ ASSETS ​ ​ ​ ​ Current Assets: ​ ​ ​ ​ Cash and cash equivalents ​ $ 17,266 ​ $ 6,839 Other receivables ​ ​ 217 ​ ​ 402 Prepaid expenses and other current assets ​ 110 ​ 200 Property, plant and equipment, held for sale ​ — ​ 1,165 Total current assets ​ 17,593 ​ 8,606 ​ ​ ​ ​ ​ Property, plant and equipment, net ​ — ​ 371 Other assets ​ — ​ 250 Operating lease right-of-use asset, net ​ ​ — ​ ​ 81 Total Assets ​ $ 17,593 ​ $ 9,308 ​ ​ ​ ​ ​ LIABILITIES AND STOCKHOLDERS’ EQUITY ​ ​ ​ ​ Current Liabilities: ​ ​ ​ ​ Accounts payable and accrued expenses ​ $ 5,411 ​ $ 9,486 Payables and accrued expenses - related party ​ ​ 2,503 ​ ​ 2,667 Operating lease liabilities - short-term ​ ​ — ​ ​ 456 Total current liabilities ​ 7,914 ​ 12,609 ​ ​ ​ ​ ​ Deferred income ​ 150 ​ 150 Operating lease liabilities - long-term ​ ​ — ​ ​ 422 Total Liabilities ​ 8,064 ​ 13,181 ​ ​ ​ ​ ​ Commitments and Contingencies (Note 7) ​ ​ ​ ​ ​ ​ ​ ​ ​ Stockholders’ Equity (Deficit) ​ ​ ​ ​ Preferred stock ($ 0.0001 par value), 2,000,000 shares authorized, 250,000 shares of Class A preferred stock issued and outstanding as of December 31, 2025 and December 31, 2024, respectively ​ — ​ — Common stock ($ 0.0001 par value), 200,000,000 shares authorized as of December 31, 2025 and December 31, 2024, respectively ​ ​ ​ ​ Class A common shares, 845,385 shares issued and outstanding as of December 31, 2025 and December 31, 2024, respectively ​ — ​ — Common shares, 6,453,701 , and 985,972 shares issued and outstanding as of December 31, 2025 and December 31, 2024, respectively ​ 1 ​ 5 Common stock issuable, 278,385 and 69,046 shares as of December 31, 2025 and December 31, 2024, respectively ​ 273 ​ 611 Additional paid-in capital ​ 407,899 ​ 392,234 Accumulated deficit ​ ( 398,644 ) ​ ( 396,723 ) Total Stockholders’ Equity (Deficit) ​ 9,529 ​ ( 3,873 ) Total Liabilities and Stockholders’ Equity (Deficit) ​ $ 17,593 ​ $ 9,308 ​ See accompanying notes to financial statements. F-4 Table of Contents MUSTANG BIO, INC. STATEMENTS OF OPERATIONS (in thousands, except for share and per share amounts) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31, ​ ​ ​ ​ ​ 2025 ​ ​ ​ 2024 ​ ​ ​ Operating expenses: ​ ​ ​ ​ Research and development ​ $ ( 1,516 ) ​ $ 8,418 ​ Asset impairment ​ ​ — ​ ​ 3,692 ​ General and administrative ​ 3,948 ​ 4,135 ​ Total operating expenses ​ 2,432 ​ 16,245 ​ Loss from operations ​ ( 2,432 ) ​ ( 16,245 ) ​ ​ ​ ​ ​ ​ ​ Other income ​ ​ ​ ​ ​ Other income ​ ​ — ​ ​ 314 ​ Interest income, net ​ 511 ​ 179 ​ Total other income ​ 511 ​ 493 ​ Net Loss ​ $ ( 1,921 ) ​ $ ( 15,752 ) ​ ​ ​ ​ ​ ​ ​ Net loss per Class A common and common shares outstanding, basic and diluted ​ $ ( 0.39 ) ​ $ ( 38.57 ) ​ ​ ​ ​ ​ ​ ​ Weighted average number of Class A common and common shares outstanding, basic and diluted ​ 4,908,164 ​ 609,696 ​ ​ See accompanying notes to financial statements. ​ ​ F-5 Table of Contents MUSTANG BIO, INC. STATEMENTS OF STOCKHOLDERS’ EQUITY (in thousands, except share amounts) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Common ​ Additional ​ ​ ​ ​ Total ​ ​ Class A Preferred Stock ​ Class A Common Shares ​ Common Shares ​ Stock ​ Paid-in ​ Accumulated ​ Stockholders’ ​ ​ ​ ​ Shares ​ ​ ​ Amount ​ ​ ​ Shares ​ ​ ​ Amount ​ ​ ​ Shares ​ ​ ​ Amount ​ ​ ​ Issuable ​ ​ ​ Capital ​ ​ ​ Deficit ​ ​ ​ Equity Balances at December 31, 2023 250,000 ​ $ — 845,385 ​ $ — 166,974 ​ $ 1 ​ ​ ​ $ 591 ​ ​ ​ $ 380,502 ​ ​ ​ $ ( 380,971 ) ​ ​ ​ $ 123 Common stock issuable - Annual Stock Dividend to Fortress — ​ — — ​ — — ​ — ​ ​ ​ 611 ​ ​ ​ — ​ ​ ​ — ​ ​ ​ 611 Issuance of common shares - Annual Stock Dividend to Fortress — ​ — — ​ — 18,564 ​ — ​ ( 477 ) ​ 477 ​ — ​ ​ ​ — Issuance of common shares, equity fee on At-the-Market Offering ​ — ​ ​ — ​ — ​ ​ — ​ 13,266 ​ ​ — ​ ​ ( 114 ) ​ ​ 443 ​ ​ — ​ ​ 329 Issuance of common shares, net of offering costs - Equity Offerings ​ — ​ ​ — ​ — ​ ​ — ​ 83,700 ​ ​ — ​ ​ — ​ ​ 5,160 ​ ​ — ​ ​ 5,160 Issuance of common shares, net of offering costs - At-the-Market Offering ​ — ​ ​ — ​ — ​ ​ — ​ 140,402 ​ ​ 1 ​ ​ — ​ ​ 2,534 ​ ​ — ​ ​ 2,535 Issuance of common shares under ESPP ​ — ​ ​ — ​ — ​ ​ — ​ 938 ​ ​ — ​ ​ — ​ ​ 48 ​ ​ — ​ ​ 48 Stock-based compensation expenses — ​ — — ​ — 119 ​ — ​ — ​ ( 450 ) ​ — ​ ( 450 ) Abeyance Shares released (1) — ​ — — ​ — 69,672 ​ — ​ — ​ — ​ — ​ — Exercise of warrants (1) ​ — ​ ​ — ​ — ​ ​ — ​ 491,816 ​ ​ 3 ​ ​ — ​ ​ 3,520 ​ ​ — ​ ​ 3,523 Reverse Split ( 1 -for-50) adjustment ​ — ​ ​ — ​ — ​ ​ — ​ 521 ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — Net loss ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ ( 15,752 ) ​ ​ ( 15,752 ) Balances at December 31, 2024 250,000 ​ $ — 845,385 ​ $ — 985,972 ​ $ 5 ​ $ 611 ​ $ 392,234 ​ $ ( 396,723 ) ​ $ ( 3,873 ) Common stock issuable - Annual Stock Dividend to Fortress ​ — ​ ​ — ​ — ​ ​ — ​ — ​ ​ — ​ ​ 273 ​ ​ — ​ ​ — ​ ​ 273 Issuance of common shares - Annual Stock Dividend to Fortress — ​ — — ​ — 69,046 ​ — ​ ( 611 ) ​ 611 ​ — ​ — Issuance of common shares, equity fee on At-the-Market and equity offerings — ​ — — ​ — 127,140 ​ — ​ — ​ 395 ​ — ​ 395 Issuance of common shares, net of offering costs - Equity Offerings ​ — ​ ​ — ​ — ​ ​ — ​ 495,000 ​ ​ — ​ ​ — ​ ​ 6,782 ​ ​ — ​ ​ 6,782 Issuance of common shares, net of offering costs - At-the-Market Offering ​ — ​ ​ — ​ — ​ ​ — ​ 54,440 ​ ​ — ​ ​ — ​ ​ 599 ​ ​ — ​ ​ 599 Issuance of common shares under ESPP ​ — ​ ​ — ​ — ​ ​ — ​ 200 ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — Stock-based compensation expenses ​ — ​ ​ — ​ — ​ ​ — ​ 68 ​ ​ — ​ ​ — ​ ​ 129 ​ ​ — ​ ​ 129 Abeyance Shares released (1) ​ — ​ ​ — ​ — ​ ​ — ​ 185,880 ​ ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ — Exercise of warrants ​ — ​ ​ — ​ — ​ ​ — ​ 4,536,162 ​ 1 ​ ​ — ​ ​ 7,144 ​ ​ — ​ ​ 7,145 Reverse Split ( 1 -for-50) adjustment ​ — ​ ​ — ​ — ​ ​ — ​ ( 207 ) ​ ( 5 ) ​ ​ — ​ ​ 5 ​ ​ — ​ ​ — Net loss ​ — ​ ​ — ​ — ​ ​ — ​ — ​ ​ — ​ ​ — ​ ​ — ​ ​ ( 1,921 ) ​ ​ ( 1,921 ) Balances at December 31, 2025 250,000 ​ $ — 845,385 ​ $ — 6,453,701 ​ $ 1 ​ $ 273 ​ $ 407,899 ​ $ ( 398,644 ) ​ $ 9,529 ​ (1) In connection with the induced warrant exercise in October 2024, a certain warrant holder was induced to exercise for cash 337,552 shares of common stock related to the Series A-3 warrants at the exercise price of $ 11.85 per share. Of the 337,552 shares on the exercise date, 255,552 were held in abeyance and not considered outstanding. The balance of the shares held in abeyance will be held in abeyance until notice from the shareholder that the balance, or portion thereof, may be issued in compliance with a beneficial ownership limitation provision in the warrants. As of December 31, 2025, all shares held in abeyance have been issued. See accompanying notes to financial statements. ​ F-6 Table of Contents MUSTANG BIO, INC. STATEMENTS OF CASH FLOWS (in thousands) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31, ​ ​ ​ ​ 2025 ​ ​ ​ 2024 Cash Flows from Operating Activities: ​ ​ ​ ​ Net loss ​ $ ( 1,921 ) ​ $ ( 15,752 ) Adjustments to reconcile net loss to net cash used in operating activities: ​ ​ ​ ​ ​ ​ Issuance of common shares - equity fee on equity offerings to Fortress Biotech ​ 395 ​ 329 Common shares issuable - Annual Stock Dividend to Fortress Biotech ​ ​ 273 ​ ​ 611 Research and development - licenses acquired ​ ​ — ​ ​ 250 Stock-based compensation expenses ​ 129 ​ ( 450 ) Depreciation expense ​ 34 ​ 671 Amortization of operating lease right-of-use assets ​ ​ 7 ​ ​ 152 Settlement of payables ​ ( 2,104 ) ​ ( 2,383 ) Loss on disposal of property and equipment ​ ​ — ​ ​ 29 Asset impairment ​ ​ — ​ ​ 3,692 Gain on lease termination ​ ​ ( 394 ) ​ ​ ( 314 ) Changes in operating assets and liabilities: ​ ​ ​ ​ ​ Prepaid expenses and other assets ​ 90 ​ 586 Other receivables ​ ​ 435 ​ ​ 494 Accounts payable and accrued expenses ​ ( 1,971 ) ​ ( 591 ) Payable and accrued expenses - related party ​ ( 164 ) ​ 1,833 Deferred income ​ ​ — ​ ​ ( 120 ) Lease liabilities ​ ​ ( 73 ) ​ ​ ( 447 ) Net cash used in operating activities ​ ( 5,264 ) ​ ( 11,410 ) ​ ​ ​ ​ ​ Cash Flows from Investing Activities: ​ ​ ​ ​ Proceeds from the sale of property and equipment ​ ​ 1,165 ​ ​ — Net cash from investing activities ​ 1,165 ​ — ​ ​ ​ ​ ​ Cash Flows from Financing Activities: ​ ​ ​ ​ Proceeds from issuance of common shares, net of offering costs - equity offering ​ ​ 6,782 ​ ​ 5,159 Proceeds from issuance of common shares, net of offering costs - At-the-Market offering ​ ​ 599 ​ ​ 2,535 Proceeds from warrant exercises ​ ​ 7,145 ​ ​ 3,523 Proceeds from issuance of common shares under ESPP ​ ​ — ​ ​ 48 Net cash provided by financing activities ​ 14,526 ​ 11,265 ​ ​ ​ ​ ​ Net change in cash and cash equivalents ​ 10,427 ​ ( 145 ) Cash and cash equivalents, beginning of the period ​ 6,839 ​ 6,984 Cash and cash equivalents, end of the period ​ $ 17,266 ​ $ 6,839 ​ ​ ​ ​ ​ Supplemental disclosure of noncash activities: ​ ​ ​ ​ Issuance of common shares - Founders Agreement and equity fee to Fortress ​ $ 611 ​ $ 591 ​ ​ ​ ​ ​ ​ ​ Supplemental disclosure of noncash activities related to the uBriGene Repurchase Transaction (see Note 4): ​ ​ ​ ​ ​ ​ Fair value of assets received ​ $ — ​ $ 2,209 Fair value of supplies received expensed to research and development ​ $ — ​ $ 2,509 Accounts receivable written off ​ $ — ​ $ ( 6,967 ) Accounts payable written off ​ $ — ​ $ 3,644 Deferred purchase consideration ​ $ — ​ $ ( 1,295 ) ​ See accompanying notes to financial statements. F-7 Table of Contents Notes to Financial Statements Note 1 - Organization and Description of Business Mustang Bio, Inc. (the “Company” or “Mustang”) was incorporated in Delaware on March 13, 2015. Mustang is a clinical-stage biopharmaceutical company focused on translating today’s medical breakthroughs into potential cures for difficult-to-treat cancers and autoimmune diseases. The Company may acquire rights to these technologies by licensing the rights or otherwise acquiring an ownership interest in the technologies, funding their research and development and eventually either out-licensing or bringing the technologies to market. The Company is a majority-controlled subsidiary of Fortress Biotech, Inc. (“Fortress” or “Parent”). The Company’s common stock is listed on the Nasdaq Capital Market and trades under the symbol “MBIO.” Reverse Stock Split On January 15, 2025, the Company filed an amendment (the “Reverse Split Amendment”) to its Amended and Restated Certificate of Incorporation with the Secretary of State of the State of Delaware to effect the 1 -for- 50 reverse stock split of the Company's shares of common stock ("Reverse Stock Split"). As a result of the Reverse Stock Split, every 50 shares of common stock outstanding immediately prior to effectiveness of the Reverse Stock Split were combined and converted into one share of common stock without any change in the par value per share. The Reverse Stock Split became effective on January 15, 2025, and the common stock was quoted on the Nasdaq Stock Market on a post-split basis at the open of business on January 16, 2025. No fractional shares were issued in connection with the Reverse Stock Split. Stockholders who would have otherwise been entitled to a fraction of one share of common stock as a result of the Reverse Stock Split instead received a proportional cash payment . All share and per share information has been retroactively adjusted to give effect to the Reverse Stock Split for all periods presented, unless otherwise indicated. ​ Liquidity and Capital Resources The Company has incurred substantial operating losses and expects to continue to incur significant operating losses for the foreseeable future and may never become profitable. To date, the Company has funded its operations primarily with the proceeds from equity securities. As of December 31, 2025, the Company had an accumulated deficit of $ 398.6 million and cash and cash equivalents of $ 17.3 million. The Company has previously disclosed in its financial statements for the year ended December 31, 2024, and its most recent quarterly report on Form 10-Q for the period ended September 30, 2025, that substantial doubt existed regarding its ability to continue as a going concern. Although it has a history of negative cash flows from operations and operating losses, the Company has raised approximately $ 14.5 million in net proceeds from the February 2025 Equity Offering, the ATM Agreement and the July 2025 warrant exercises (see Note 8) during the year ended December 31, 2025. In addition to these net proceeds, the Company has been actively negotiating settlements of aged payables and has recognized approximately $ 2.1 million in savings during the year ended December 31, 2025, and it has significantly reduced its operating costs. The Company expects to continue generating operating losses and negative operating cash flows as it develops its products through to potential approval, however, based on the improvement in its cash position for the year ended December 31, 2025, the Company believes it has sufficient cash and cash equivalents to fund its operations for at least twelve months from the date of this annual report on Form 10-K. Therefore, the Company has concluded that substantial doubt about its ability to continue as a going concern no longer exists. ​ F-8 Table of Contents Note 2 - Significant Accounting Policies Basis of Presentation The Company’s financial statements have been prepared in conformity with accounting principles generally accepted in the United States of America (“GAAP”). The Company has no subsidiaries. All inter-company transactions between Fortress and Mustang are classified as due from or due to related party in the financial statements. Segment Reporting Operating segments are defined as components of an enterprise about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources in assessing performance. The Company views its operations and manages its business in one segment, which reflects the research and development of potential cures for difficult-to-treat cancers. The Company’s chief operating decision maker (“CODM”) is its chief executive officer. The CODM assesses performance for the research and development segment and decides how to allocate resources based on net loss, which is reported on the Statements of Operations. The CODM uses net loss to evaluate costs to develop its pipeline. The accounting policies of the segment are the same as those described in this Note 2. Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period. Actual results could differ from those estimates. Cash and Cash Equivalents The Company considers highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. Cash and cash equivalents at December 31, 2025 and 2024, consisted of cash and certificates of deposit in institutions in the United States. The Company maintains its cash and cash equivalent balances with high-quality financial institutions and, consequently, the Company believes that such funds are currently adequately protected against credit risk. At times, portions of the Company’s cash and cash equivalents may be uninsured or in deposit accounts that exceed Federal Deposit Insurance Corporation (FDIC) limits, though the Company customarily invests a significant portion of its cash in Insured Cash Sweep (“ICS”) accounts to maximize FDIC insurance coverage across its holdings. As of December 31, 2025, the Company had not experienced losses on these accounts, and management believes the Company is not exposed to significant risk on such accounts. Other Receivables – Related Party Other receivables include amounts due to the Company from Fortress and is recorded at the invoiced amount. Property, plant and equipment, net Property, plant and equipment, net, consisting primarily of leasehold improvements, are carried at cost less accumulated depreciation. Depreciation for leasehold improvements is computed over the shorter of the estimated useful lives or the term of the respective leases. Depreciation for all other property and equipment assets is recorded over the useful lives of the respective assets, generally five years , using the straight-line method. Property, plant and equipment, held for sale Property, plant and equipment, held for sale represent assets that have met the criteria of “held for sale” accounting, as specified by Accounting Standards Codification (“ASC”) 360, “Long-lived Assets.” In February 2025, the Company F-9 Table of Contents completed the sale of the lab and cell processing equipment, furniture and fixtures and computer equipment that were recorded as assets held for sale as of December 31, 2024. ​ Impairment of Long-Lived Assets ​ The Company reviews long-lived assets, including tangible assets and other intangible assets with definitive lives, for impairment whenever events or changes in circumstances indicate that the asset’s carrying amount may not be recoverable. The Company conducts its long-lived asset impairment analyses in accordance with ASC 360-10, "Impairment or Disposal of Long-Lived Assets. ASC 360-10-15 requires the Company to group assets and liabilities at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities and evaluate the asset group against the sum of the undiscounted future cash flows. If the undiscounted cash flows do not indicate the carrying amount of the asset group is recoverable, an impairment charge is measured as the amount by which the carrying amount of the asset group exceeds its fair value based on discounted cash flow analysis or appraisals. ​ Research and Development Costs Research and development costs are expensed as incurred. Advance payments for goods and services that will be used in future research and development activities are expensed when the activity has been performed or when the goods have been received rather than when the payment is made. Upfront and milestone payments due to third parties that perform research and development services on the Company’s behalf will be expensed as services are rendered or when the milestone is achieved. Research and development costs primarily consist of personnel related expenses, including salaries, benefits, travel, and other related expenses, stock-based compensation, payments made to third parties for license and milestone costs related to in-licensed products and technology, payments made to third party contract research organizations for preclinical and clinical studies, investigative sites for clinical trials, consultants, the cost of acquiring and manufacturing clinical trial materials, costs associated with regulatory filings, laboratory costs and other supplies. Additionally, consideration received or due from research and development vendors, inclusive of credits on existing invoices, is recorded as a reduction of research and development expenses in the period that the related amounts are probable and reasonably estimable. In accordance with Accounting Standards Codification (“ASC”) 730-10-25-1, Research and Development, costs incurred in obtaining technology licenses are charged to research and development expense if the technology licensed has not reached commercial feasibility and has no alternative future use. The licenses purchased by the Company require substantial completion of research and development, regulatory and marketing approval efforts to reach commercial feasibility and has no alternative future use. Accordingly, the total purchase price for the licenses acquired is reflected as research and development expenses in the Company’s Statements of Operations. Annual Stock Dividend to Fortress In July 2016, in connection with the Amended and Restated Articles of Incorporation, the Company issued 250,000 Class A preferred shares to Fortress. The Class A preferred shares entitle the holder to a stock dividend equal to 2.5 % of the fully diluted outstanding equity of the Company (the “Annual Stock Dividend”). The Annual Stock Dividend was part of the consideration payable for formation of the Company and the identification of certain assets, including the license contributed to Mustang by Fortress (see Note 3). The Company considers the Annual Stock Dividend as contingent consideration for the license contributed to Mustang by Fortress. Since the ultimate amount of the Annual Stock Dividend is highly uncertain and cannot be reasonable estimable, in accordance with ASC 450-20, Loss Contingencies , the Company records the Annual Stock Dividend in Research and development expense in the Company’s Statements of Operations, when the shares are issued. Fair Value Measurement The Company follows accounting guidance on fair value measurements for financial assets and liabilities measured at fair value on a recurring basis. Under the accounting guidance, fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants F-10 Table of Contents at the measurement date. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or a liability. The accounting guidance requires fair value measurements be classified and disclosed in one of the following three categories: ​ Level 1: Quoted prices in active markets for identical assets or liabilities. Level 2: Observable inputs other than Level 1 prices, for similar assets or liabilities that are directly or indirectly observable in the marketplace. Level 3: Unobservable inputs which are supported by little or no market activity and that are financial instruments whose values are determined using pricing models, discounted cash flow methodologies, or similar techniques, as well as instruments for which the determination of fair value requires significant judgment or estimation. ​ The fair value hierarchy also requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and consider factors specific to the asset or liability. Leases Arrangements meeting the definition of a lease are classified as operating or financing leases and are recorded on the balance sheet as both a right of use asset and lease liability, calculated by discounting fixed lease payments over the lease term at the rate implicit in the lease or the Company's incremental borrowing rate. Lease liabilities are increased by interest and reduced by payments each period, and the right of use asset is amortized over the lease term. For operating leases, interest on the lease liability and the amortization of the right of use asset result in straight-line rent expense over the lease term. Variable lease expenses are recorded when incurred. In calculating the right of use asset and lease liability, the Company elects to combine lease and non-lease components. The Company excludes short-term leases having initial terms of 12 months or less from the new guidance as an accounting policy election and recognizes rent expense on a straight-line basis over the lease term. As of December 31, 2025, the Company is no longer party to any operating or financing leases. Stock-Based Compensation The Company expenses stock-based compensation to employees over the requisite service period based on the estimated grant-date fair value of the awards and forfeiture rates. The Company estimates the fair value of stock option grants using the Black-Scholes option pricing model. The assumptions used in calculating the fair value of stock-based awards represent management’s best estimates and involve inherent uncertainties and the application of management’s judgment. Income Taxes The Company records income taxes using the asset and liability method. Deferred income tax assets and liabilities are recognized for the future tax effects attributable to temporary differences between the financial statement carrying amounts of existing assets and liabilities and their respective income tax bases, and operating loss and tax credit carryforwards. The Company establishes a valuation allowance if management believes it is more likely than not that the deferred tax assets will not be recovered based on an evaluation of objective verifiable evidence. For tax positions that are more likely than not of being sustained upon audit, the Company recognizes the largest amount of the benefit that is greater than 50% likely of being realized. For tax positions that are not more likely than not of being sustained upon audit, the Company does not recognize any portion of the benefit. F-11 Table of Contents Net Loss per Share Basic and diluted net loss per share is computed by dividing net loss by the weighted average number of common shares outstanding, including prefunded warrants and shares held in abeyance, during the period, without consideration of potential dilutive securities. For periods in which the Company generated a net loss, the Company does not include potential shares of common stock in diluted net loss per share when the impact of these items is anti-dilutive. The Company has generated a net loss for all periods presented, therefore diluted net loss per share is the same as basic net loss per share since the inclusion of potentially dilutive securities would be anti-dilutive. ​ The table below summarizes potentially dilutive securities that were not considered in the computation of diluted net loss per share because they would be anti-dilutive. ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31, ​ ​ ​ ​ 2025 ​ ​ ​ 2024 Warrants 4,678,646 ​ 1,576,919 Options 1,521 1,521 Class A preferred shares (1) 333 333 Unvested restricted stock awards 720 1,195 Unvested restricted stock units 96 226 Total 4,681,316 1,580,194 ​ (1) Class A Preferred Shares are reflected on an as-if converted basis. The Company considers Class A common stock and Class A preferred stock to be additional classes of common stock for the purpose of calculating net loss per share, as they do not have preferential rights when compared to the Company’s common stock, and therefore losses are allocated to these additional classes using the two-class method. The two-class method is an earnings allocation formula that treats participating securities as having rights that would otherwise have been available to common stockholders. At December 31, 2025, the Class A common stock and Class A preferred stock have rights to convert to a total of 1,461 common shares. ​ In connection with the exercise of certain existing warrants in October 2024 (see Note 8), the Company recorded a deemed dividend of approximately $ 7.8 million for the issuance of new warrants. For the year ended December 31, 2024, net loss attributable to common stockholders consisted of net loss, as adjusted for deemed dividends. ​ Comprehensive Loss The Company has no components of other comprehensive loss, and therefore, comprehensive loss equals net loss. Recent Accounting Pronouncements In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures , which expands disclosures in an entity’s income tax rate reconciliation table and disclosures regarding cash taxes paid both in the U.S. and foreign jurisdictions. The update will be effective for annual periods beginning after December 15, 2024. The Company adopted the accounting standard on its annual report on Form 10-K for the year ended December 31, 2025, and determined that the guidance does not have a material impact on its financial statements. ​ In November 2024, the FASB issued ASU 2024-03, Income Statement-Reporting Comprehensive Income-Expense Disaggregation Disclosures (Topic 220-40). The amendments in this update require new disclosures to disaggregate prescribed natural expenses underlying any income statement caption. ASU 2024-03 is effective for annual periods in fiscal years beginning after December 15, 2026, and interim periods thereafter. Early adoption is permitted. ASU 2024-03 applies on a prospective basis for periods beginning after the effective date. However, retrospective application to any or all prior periods presented is permitted. The Company is currently assessing the impact ASU 2024-03 will have on the financial statements and disclosures. ​ ​ F-12 Table of Contents Note 3 - Related Party Agreements Founders Agreement and Management Services Agreement with Fortress Effective March 13, 2015, the Company entered a Founders Agreement with Fortress, which was amended and restated on May 17, 2016, and again on July 26, 2016 (the “Mustang Founders Agreement”). The Mustang Founders Agreement provides that, in exchange for the time and capital expended in the formation of Mustang and the identification of specific assets the acquisition of which result in the formation of a viable emerging growth life science company, Fortress loaned $ 2.0 million, representing the up-front fee required to acquire the Company’s license agreement with COH. The Mustang Founders Agreement has a term of 15 years , which upon expiration automatically renews for successive one-year periods unless terminated by Fortress and the Company or a Change in Control (as defined in the Mustang Founders Agreement) occurs. Concurrently with the second amendment on July 26, 2016, to the Mustang Founders Agreement, Fortress entered into an Exchange Agreement whereby Fortress exchanged its 7.25 million Class B Common shares for 9,333 common shares and 250,000 Class A Preferred shares. Class A Preferred Stock is identical to common stock other than as to voting rights, conversion rights and the Annual Stock Dividend right (as described below). Each share of Class A Preferred Stock is entitled to vote the number of votes that is equal to one and one-tenth ( 1.1 ) times a fraction, the numerator of which is the sum of (A) the shares of outstanding Mustang common stock and (B) the whole shares of Mustang common stock into which the shares of outstanding Class A Common Stock and Class A Preferred Stock are convertible and the denominator of which is the number of shares of outstanding Class A Preferred Stock. Thus, the Class A Preferred Stock will at all times constitute a voting majority. Each share of Class A Preferred Stock is convertible, at Fortress’ option, into one fully paid and nonassessable share of Mustang common stock, subject to certain adjustments. As holders of Class A Preferred Stock, Fortress will receive on each January 1 (each a “Annual Stock Dividend Payment Date”) until the date all outstanding Class A Preferred Stock is converted into common stock, pro rata per share dividends paid in additional fully paid and nonassessable shares of common stock (“Annual Stock Dividends”) such that the aggregate number of shares of common stock issued pursuant to such Annual Stock Dividend is equal to two and one-half percent ( 2.5 %) of Mustang’s fully-diluted outstanding capitalization on the date that is one (1) business day prior to any Annual Stock Dividend Payment Date. The Company records the value of all shares issued for the Annual Stock Dividend as research and development – licenses expense in its Statements of Operations. Pursuant to the Amended and Restated Articles of Incorporation, the Company issued 278,385 shares of common stock to Fortress for the Annual Stock Dividend, representing 2.5 % of the fully-diluted outstanding equity of Mustang on January 1, 2026. The value of these shares is shown in the Statement of Stockholders’ Equity at December 31, 2025, as Common stock issuable – Annual Stock Dividend. The Company recorded an expense of approximately $ 0.3 million in research and development expense related to these issuable shares during the year ended December 31, 2025. Pursuant to the Amended and Restated Articles of Incorporation, the Company issued 69,046 shares of common stock to Fortress for the Annual Stock Dividend, representing 2.5 % of the fully-diluted outstanding equity of Mustang on January 1, 2025. The value of these shares is shown in the Statement of Stockholders’ Equity at December 31, 2024, as Common stock issuable – Annual Stock Dividend. The Company recorded an expense of approximately $ 0.6 million in research and development expense acquired related to these issuable shares during the year ended December 31, 2024. As additional consideration under the Mustang Founders Agreement, Mustang will also: (i) pay an equity fee in shares of common stock, payable within five (5) business days of the closing of any equity or debt financing for Mustang that occurs after the effective date of the Mustang Founders Agreement and ending on the date when Fortress no longer has majority voting control in the Company’s voting equity, equal to two and one-half ( 2.5 %) of the gross amount of any such equity or debt financing, with the number of shares issuable based on the share price of the equity round or, in the instance of debt financing, the closing price of the Company’s common shares on the day prior to the closing; and (ii) pay a cash fee equal to four and one-half percent ( 4.5 %) of the Company’s annual net sales, payable on an annual basis, within ninety (90) days of the end of each calendar year. In the event of a Change in Control, the Company will pay a one-time change in control fee equal to five (5x) times the product of (A) net sales for the twelve (12) months immediately preceding the change in control and (B) four and one-half percent ( 4.5 %). The Company records the value of all shares issued for the equity fee component of the Mustang Founders Agreement as Stock-based compensation expense in its Statements of Operations. F-13 Table of Contents For the year ended December 31, 2025, the Company issued 127,140 shares of common stock to Fortress, which equaled 2.5 % of the sum of the gross proceeds of $ 0.6 million from the sale of shares of common stock under Mustang’s At-the-Market Offering, $ 8.0 million gross proceeds from the February 2025 Equity Offering, and $ 7.1 million from the July 2025 Series C-2 warrant exercises. The Company recorded an expense of approximately $ 0.4 million in general and administrative expenses related to these shares for the year ended December 31, 2025. ​ For the year ended December 31, 2024, the Company issued 23,450 shares of common stock to Fortress, which equaled 2.5 % of the sum of the gross proceeds of $ 2.6 million from the sale of shares of common stock under Mustang’s At-the-Market Offering, $ 4.0 million gross proceeds from the May 2024 Public Offering, $ 2.5 million from the June 2024 PIPE, and $ 4.0 million from the October 2024 warrant exercise. The Company recorded an expense of approximately $ 0.3 million in general and administrative expenses related to these shares for the year ended December 31, 2024. ​ Effective as of March 13, 2015, the Company entered into a Management Services Agreement (the “MSA”) with Fortress, pursuant to which Fortress renders advisory and consulting services to the Company. The MSA has an initial term of five years and is automatically renewed for successive five-year terms unless terminated in accordance with its provisions. Services provided under the MSA may include, without limitation, (i) advice and assistance concerning any and all aspects of the Company’s operations, clinical trials, financial planning and strategic transactions and financings and (ii) conducting relations on behalf of the Company with accountants, attorneys, financial advisors and other professionals (collectively, the “Services”). The Company is obligated to utilize clinical research services, medical education, communication and marketing services and investor relations/public relation services of companies or individuals designated by Fortress, provided those services are offered at market prices. However, the Company is not obligated to take or act upon any advice rendered from Fortress and Fortress shall not be liable for any of its actions or inactions based upon their advice. Pursuant to the MSA and the Company’s Certificate of Incorporation, Fortress and its affiliates, including all members of the Company’s Board of Directors, will have no fiduciary or other duty to communicate or present any corporate opportunities to the Company or to refrain from engaging in business that is similar to that of the Company. In consideration for the Services, the Company will pay Fortress an annual consulting fee of $ 0.5 million (the “Annual Consulting Fee”), payable in advance in equal quarterly installments on the first business day of each calendar quarter in each year, provided, however, that such Annual Consulting Fee shall be increased to $ 1.0 million for each calendar year in which the Company has net assets in excess of $ 100 million at the beginning of the calendar year. The Company records fifty percent of the Annual Consulting Fee in research and development expense and fifty percent in general and administrative expense in the Statement of Operations. For the years ended December 31, 2025 and 2024, the Company recorded expense of $ 0.5 million and $ 0.5 million, respectively, related to this agreement. Payables and Accrued Expenses Related Party In the normal course of business, Fortress pays certain expenses on behalf of the Company. Such expenses are recorded as payables and accrued expenses - related party. Director Compensation Dr. Rosenwald and David Jin Pursuant to the terms of the Director Compensation Plan, Dr. Rosenwald and Mr. Jin will receive a cash fee of $ 50,000 per year paid quarterly and an annual stock award of the greater of (i) a number of shares of common stock having a fair market value on the grant date of $ 50,000 or (ii) 10,000 shares of common stock, which shares shall vest and become non-forfeitable on the third anniversary of the grant date, subject to continued service on the Board on such date. For the year ended December 31, 2025, the Company recognized $ 50,000 and $ 50,000 for Dr. Rosenwald and Mr. Jin, respectively, in expense in its Statements of Operations related to the director compensation. For the year ended December 31, 2024, the Company recognized $ 50,000 and $ 12,500 for Dr. Rosenwald and Mr. Jin, respectively, in expense in its Statements of Operations related to the director compensation. No restricted stock awards were granted in 2025 and 2024. F-14 Table of Contents Mr. Weiss - Advisory Agreement with Caribe BioAdvisors, LLC The Board of the Company by unanimous written consent approved and authorized the execution of an advisory agreement dated January 1, 2017 (the “Advisory Agreement”), with Caribe BioAdvisors, LLC (the “Advisor”), owned by Michael S. Weiss, the Chairman of the Board, to provide the board advisory services of Mr. Weiss as Chairman of the Board. Pursuant to the Advisory Agreement, the Advisor will be paid an annual cash fee of $ 60,000 , paid quarterly and an annual stock award of the greater of (i) a number of shares of common stock having a fair market value on the grant date of $ 50,000 or (ii) 10,000 shares of common stock, which shares shall vest and become non-forfeitable on the third anniversary of the grant date, subject to continued service on the Board on such date. For the year ended December 31, 2025, the Company recognized $ 60,000 in expense in its Statements of Operations related to the advisory agreement. For the year ended December 31, 2024, the Company recognized $ 60,000 in expense in its Statements of Operations related to the advisory agreement. No restricted stock awards were granted in 2025 and 2024. Note 4 – Asset Purchase Agreements In May 2023, the Company agreed to sell its Worcester, Massachusetts cell-processing facility assets to uBriGene (Boston) Biosciences, Inc. (“uBriGene”) under an Asset Purchase Agreement, as later amended. The sale closed on July 28, 2023, for $ 6.0 million in cash, and the Company recorded a gain of $ 1.4 million in connection with the equipment and facility assets transferred (excluding the facility lease) and recorded $ 0.3 million of the base consideration as deferred income that would have been recognized upon transfer of the facility lease. The Company and uBriGene submitted a voluntary joint notice to the U.S. Committee on Foreign Investment in the United States (“CFIUS”). Following CFIUS’s review, the Company, together with uBriGene and CFIUS, entered into a National Security Agreement (“NSA”) on May 13, 2024, requiring the Company and uBriGene to terminate of all related agreements and abandon the original transaction. The NSA also obligated uBriGene to sell or otherwise dispose of the equipment assets purchased within 180 days after the execution of the NSA. ​ In June 2024, the Company entered into a new Asset Purchase Agreement with uBriGene to repurchase the previously transferred equipment assets and supplies for total consideration of approximately $ 4.7 million. The Company agreed to pay uBriGene a total purchase price of $ 1.4 million consisting of (i) an upfront payment of $ 0.1 million due and (ii) $ 1.3 million due twelve ( 12 ) months after the closing date (the “Deferred Amount”). In the event that on the date the Deferred Amount is payable, the Company has net assets below $ 20 million, the Company may, upon written notice to uBriGene, elect to delay its payment obligation by an additional six ( 6 ) months, and the Deferred Amount will accrue interest at a rate of 5 % per annum beginning on that date twelve months after closing and until the Deferred Amount is paid in full. As of December 31, 2025, the Company’s net assets were below $ 20.0 million and the Deferred Amount of approximately $ 1.3 million, including approximately $ 33,000 of accrued interest, continued to be deferred and remained recorded in Accrued Other Expenses (see Note 6). ​ The $ 4.7 million purchase consideration was allocated to the repurchased equipment and supplies based on a relative fair value basis. The Company used a third-party to perform a valuation of the repurchase equipment, which resulted in fair value less costs to sell of approximately $ 2.2 million. The remaining $ 2.5 million was allocated to the supplies repurchased, the Company determined that there was no alternative future use, and therefore, the $ 2.5 million was recorded as research and development expense at closing. The repurchased equipment was classified as held for sale at the acquisition date. In February 2025, the Company completed the sale of these assets to an unrelated third party. ​ Note 5 – Property, Plant and Equipment, Net and Held for Sale, and Asset Impairment In June 2024, the Company concluded it had a triggering event requiring assessment of impairment for certain leasehold improvements and the related right-of-use asset. The Company assessed the carrying value of the asset group consisting of the leasehold improvements and right-of-use asset in accordance with ASC 360, given the significant changes to the Company’s operations, operating cash and the repurchase of equipment. The assessment of the recoverability of the asset group concluded that there was impairment on the carrying value of the asset group of approximately $ 2.6 million, which was allocated on a pro rata basis using the relative carrying amounts of the assets. Approximately $ 2.2 million of the F-15 Table of Contents impairment loss was allocated to the leasehold improvements, with the remaining $ 0.4 million allocated to the right-of-use asset. ​ In February 2025, the Company terminated the lease of its Plantation Street Facility. The remaining lease liability of approximately $ 0.8 million was reversed, and the remaining leasehold improvements of approximately $ 0.3 million and right of use assets of approximately $ 0.1 million were written off, resulting in a net gain of $ 0.4 million recorded in research and development expense in the Statements of Operations. ​ In conjunction with the termination of the lease, the Company also completed the sale of the remaining equipment for approximately $ 1.2 million, which had been classified as held for sale on the Balance Sheet at December 31, 2024. ​ Note 6 - Accounts Payable and Accrued Expenses At December 31, 2025 and 2024, accounts payable and accrued expenses consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ($ in thousands) ​ 2025 ​ ​ ​ 2024 Accounts payable ​ $ 3,510 ​ $ 7,464 Accrued research and development ​ ​ 250 ​ ​ 330 Accrued compensation ​ ​ 24 ​ ​ 93 Other (1) ​ ​ 1,627 ​ ​ 1,599 Total accounts payable and accrued expenses ​ $ 5,411 ​ $ 9,486 ​ ​ (1) Other includes approximately $ 1.3 million of accrued consideration for the uBriGene Asset Purchase Agreement, see Note 4. ​ ​ ​ Note 7 - Commitments and Contingencies Leases On February 7, 2025, the Company entered into the First Amendment to the Lease Agreement with WCS – 377 Plantation Street, Inc. (the “Landlord”), pursuant to which the Company’s lease of its Plantation Street Facility was terminated. Following the termination of the lease, the Company is no longer party to any leases for office space or equipment. Upon termination of the lease, the Company moved its headquarters to 95 Sawyer Road, Suite 110, Waltham, MA, which is office space leased by Fortress. Fortress allocates a small portion of its rent and office related costs to the Company on a monthly basis which is recorded in general and administrative expenses in the Statements of Operations. Upon termination of the lease, the Company wrote off the remaining right of use assets, operating lease liabilities, and associated leasehold improvements and recorded a net gain of approximately $ 0.4 million in research and development expenses in the Statements of Operations. As of December 31, 2025, the Company had no operating lease liabilities or right of use assets. At December 31, 2024, the Company had operating lease liabilities of $ 0.9 million and right of use assets of $ 0.1 million, which were included in the Balance Sheet. ​ F-16 Table of Contents The following summarizes quantitative information about the Company’s operating leases, which were terminated in February 2025, and the nominal rent allocation from Fortress: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Year Ended ​ ​ December 31, ​ December 31, ($ in thousands) ​ ​ ​ 2025 ​ 2024 Lease cost ​ ​ ​ ​ ​ Operating lease cost ​ $ 20 ​ $ 145 Variable lease cost ​ ​ 175 ​ ​ 324 Total ​ $ 195 ​ $ 469 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the Year Ended ​ ​ ​ December 31, ​ ​ ​ December 31, ​ ($ in thousands) ​ ​ ​ 2025 ​ ​ ​ 2024 Operating cash outflows from operating leases $ 86 ​ $ 534 ​ Gain on lease termination ​ $ 394 ​ ​ $ 314 ​ Weighted-average remaining lease term – operating leases ​ ​ — ​ ​ ​ 1.8 ​ Weighted-average discount rate – operating leases ​ ​ 9.0 % ​ ​ 9.0 % ​ ​ ​ ​ Note 8 - Stockholders’ Equity Common Stock The Company, in accordance with its certificate of incorporation, as amended in November 2020 and June 2021, which was retroactively applied, and July 2022, is authorized to issue (i) 200,000,000 common shares with a par value of $ 0.0001 per share, of which 1,000,000 shares are designated as Class A Common Stock and the remainder are undesignated Common Stock, and (ii) 2,000,000 shares of Preferred Stock, 250,000 of which are designated as Class A Preferred Stock and the remainder are undesignated Preferred Stock (see below Stock Issuances to Fortress and Note 4). In connection with the Company’s formation, Fortress subscribed for 7,000,000 shares of the Class B Common Stock and 2,666 shares of the Company’s Common Stock, pursuant to the Founders Agreement. Fortress paid the par value of $ 900 in 2016. The fair value of the Company’s common shares approximated par value as no licenses had been transferred at that time. In July 2016, the Class B Common Stock held by Fortress was exchanged for Class A Preferred Stock, and the Company amended and restated its Certificate of Incorporation to eliminate the Class B Common Stock and authorized a new series of Class A Preferred Stock. Dividends, if and when declared, are to be distributed pro-rata to the Class A Common Stock, Common Stock and Class A Preferred Common Stock. The holders of Common Stock are entitled to one vote per share of Common Stock held. The holders of Class A Common Stock are entitled to the number of votes equal to the number of whole shares of Common Stock into which the shares of Class A Common Stock held by such holder are convertible and for a period of ten years from its issuance, the holders of the Class A Common Stock have the right to appoint one member of the board of directors of Mustang. In March 2025, the right expired, and the holders of Class A Common Stock had not appointed such director. At-the-Market Offering of Common Stock On May 31, 2024, the Company entered into an At-the-Market Offering Agreement (the “Offering Agreement”) with Wainwright (the “Manager”) under which the Company may offer and sell, from time to time at its sole discretion, shares of its common stock through or to the Manager pursuant to the 2024 S-3. Under the Offering Agreement, the Company pays the Manager a commission of 3.0 % of the gross proceeds from the sales of any shares of common stock. The Company will also reimburse the Manager for certain expenses incurred in connection with the Offering Agreement. The Company and the Manager may each terminate the Sales Agreement at any time upon specified prior written notice. ​ During the year ended December 31, 2025, the Company issued approximately 54,000 shares of common stock at an average price of $ 11.55 per share for gross proceeds of $ 0.6 million under the Mustang ATM Agreement. In connection F-17 Table of Contents with these sales, the Company paid aggregate fees of approximately $ 27,000 for net proceeds of approximately $ 0.6 million. During the year ended December 31, 2024, the Company issued approximately 140,000 shares of common stock at an average price of $ 18.78 per share for gross proceeds of $ 2.6 million under the ATM Agreement. In connection with these sales, the Company paid aggregate fees of approximately $ 0.1 million for net proceeds of approximately $ 2.5 million. Pursuant to the Founders Agreement, the Company issued 1,361 shares of common stock to Fortress at a weighted average price of $ 11.55 per share for the year ended December 31, 2025. For the year ended December 31, 2024, the Company issued 3,509 shares of common stock to Fortress at a weighted average price of $ 18.78 per share for the year ended December 31, 2024. February 2025 Equity Offering ​ On February 5, 2025, the Company commenced a best efforts public offering (the “February 2025 Equity Offering”) of an aggregate of (i) 495,000 shares (the “Shares”) of its common stock, par value $ 0.0001 per share, (ii) pre-funded warrants (the “Pre-Funded Warrants”) to purchase up to an aggregate of 2,162,807 shares of common stock (the “Pre-Funded Warrant Shares”), (iii) Series C-1 warrants (the “Series C-1 Warrants”) to purchase up to an aggregate of 2,657,807 shares of common stock (the “Series C-1 Warrant Shares”), and (iv) Series C-2 warrants (the “Series C-2 Warrants,” and together with the Series C-1 Warrants, the “Warrants”) to purchase up to an aggregate of 2,657,807 shares of common stock (the “Series C-2 Warrant Shares,” and together with the Series C-1 Warrant Shares, the “Warrant Shares”). Each Share or Pre-Funded Warrant was sold together with one Series C-1 Warrant to purchase one share of common stock and one Series C-2 Warrant to purchase one share of common stock. The combined public offering price for each Share and accompanying Warrants was $ 3.01 , and the combined public offering price for each Pre-Funded Warrant and accompanying Warrant was $ 3.0099 . The Pre-Funded Warrants had an exercise price of $ 0.0001 per share, were exercisable immediately upon issuance and expired when exercised in full. Each Warrant has an exercise price of $ 3.01 per share and became exercisable beginning on the effective date of stockholder approval of the issuance of the Warrant Shares (the “Warrant Stockholder Approval”), which was obtained on March 23, 2025. The Series C-1 Warrants expire five years from the Warrant Stockholder Approval and the Series C-2 Warrants expire twenty-four months from the Warrant Stockholder Approval. The net proceeds of the February 2025 Equity Offering, after deducting the fees and expenses of the Placement Agent (as defined below), described in more detail below, and other offering expenses payable by the Company, but excluding the net proceeds, if any, from the exercise of the Warrants, were approximately $ 6.8 million. The February 2025 Equity Offering closed on February 10, 2025. ​ In July 2025, the remaining approximately 0.5 million of the Pre-Funded Warrants and approximately 2.4 million of the Series C-2 Warrants were exercised. In connection with these exercises, the Company received approximately $ 7.1 million in proceeds and issued approximately 2.9 million shares of its common stock. As of December 31, 2025, all of the Series C-1 Warrants and 284,452 of the Series C-2 Warrants remain outstanding. Pursuant to an Engagement Letter (the “Engagement Letter”) with H.C. Wainwright & Co., LLC (“Wainwright” or the “Placement Agent”), the Company agreed to pay the Placement Agent in connection with the February 2025 Equity Offering (i) a cash fee equal to 7.0 % of the aggregate gross proceeds raised in the February 2025 Equity Offering, (ii) a management fee equal to 1.0 % of the aggregate gross proceeds raised in the February 2025 Equity Offering, (iii) up to $ 100,000 for fees and expenses of the Placement Agent’s counsel and other out of pocket expenses, (iv) a non-accountable expense allowance of $ 25,000 , (v) up to $ 3,500 for road show expenses, and (vi) $ 15,950 for the clearing expenses. Also pursuant to the Engagement Letter, the Company, in connection with the February 2025 Equity Offering, agreed to issue to the Placement Agent or its designees warrants (the “Placement Agent Warrants”) to purchase up to an aggregate of 159,468 shares of common stock (the “Placement Agent Warrant Shares”) (which represented 6.0 % of the Shares and Pre-Funded Warrants sold in the February 2025 Equity Offering). The Placement Agent Warrants became exercisable beginning on the effective date of the Warrant Stockholder Approval, have an exercise price of $ 3.7625 ( 125 % of the combined public offering price per share of common stock and accompanying Warrants) and will terminate on the five-year anniversary of commencement of sales in the Offering. ​ F-18 Table of Contents May 2024 Equity Offering On April 29, 2024, the Company commenced a best efforts equity offering with an institutional investor (the “Investor”) (the “May 2024 Offering”) of an aggregate of (i) 23,200 shares of common stock, (ii) pre-funded warrants (the “May 2024 Pre-Funded Warrants”) to purchase up to an aggregate of 314,352 shares of common stock (the “May 2024 Pre-Funded Warrant Shares”), (iii) Series A-1 warrants (the “Series A-1 Warrants”) to purchase up to an aggregate of 337,552 shares of common stock (the “Series A-1 Warrant Shares”), (iv) Series A-2 warrants (the “Series A-2 Warrants”) to purchase up to an aggregate of 337,552 shares of common stock (the “Series A-2 Warrant Shares”), and (v) Series A-3 warrants (the “Series A-3 Warrants,” and together with the Series A-1 Warrants and Series A-2 Warrants, the “Warrants”) to purchase up to an aggregate of 337,552 shares of common stock (the “Series A-3 Warrant Shares”). Each share of common stock or May 2024 Pre-Funded Warrant was sold together with one Series A-1 Warrant to purchase one share of common stock, one Series A-2 Warrant to purchase one share of common stock, and one Series A-3 Warrant to purchase one share of common stock. The public offering price for each share of common stock and accompanying Warrants was $ 11.85 , and the public offering price for each May 2024 Pre-Funded Warrant and accompanying Warrants was $ 11.845 . The May 2024 Pre-Funded Warrants have an exercise price of $ 0.005 per share, were exercisable immediately and will expire when exercised in full. Each Warrant has an exercise price of $ 11.85 per share, will be exercisable beginning on the effective date of stockholder approval of the issuance of the shares upon exercise of the Warrants (the “Warrant Stockholder Approval”), which was obtained on July 30, 2024. The Series A-1 Warrant will expire on the five-year anniversary of the Warrant Stockholder Approval. The Series A-2 Warrant will expire on the twenty-four-month anniversary of the Warrant Stockholder Approval. The Series A-3 Warrant will expire on the nine-month anniversary of the Warrant Stockholder Approval. The Warrants contain customary anti-dilution adjustments to the exercise price, including for share splits, share dividends, rights offering and pro rata distributions. The net proceeds of the May 2024 Offering, after deducting the fees and expenses of the Placement Agent (as defined below), described in more detail below, and other offering expenses payable by us, but excluding the net proceeds, if any, from the exercise of the Warrants, was approximately $ 3.2 million. The May 2024 Offering closed on May 2, 2024. ​ In connection with the May 2024 Offering, the Company also entered into a warrant amendment agreement (the “Warrant Amendment Agreement”) with the Investor. Under the Warrant Amendment Agreement, the Company agreed to amend certain existing warrants to purchase up to 51,764 shares of common stock that were previously issued in October 2023 to the Investor, with an exercise price of $ 79.00 per share (the “Existing Warrants”), in consideration for their purchase of the securities in the May 2024 Offering, as follows: (i) lower the exercise price of the Existing Warrants to $ 11.85 per share, (ii) provide that the Existing Warrants, as amended, will not be exercisable until the receipt of Warrant Stockholder Approval for the exercisability of the Warrants in the May 2024 Offering, and (iii) extend the original expiration date of the Existing Warrants by five years following the receipt of such Warrant Stockholder Approval. The Warrant Amendment Agreement became effective on May 2, 2024. ​ June 2024 Registered Direct Offering and Concurrent Private Placement of Warrants (the “June 2024 Offering”) ​ On June 19, 2024, the Company entered into a Securities Purchase Agreement (the “Purchase Agreement”) with an institutional investor (the “June 2024 Investor”), pursuant to which the Company agreed to issue and sell, in a registered direct offering priced at-the-market under the rules of Nasdaq (the “Registered Direct Offering”), (i) 60,500 shares of common stock, at a price per Share of $ 20.50 and (ii) pre-funded warrants (the “Pre-Funded Warrants”) to purchase up to 62,100 shares of our common stock, at a price per Pre-Funded Warrant equal to $ 20.495 , the price per share of common stock, less $ 0.005 . The Pre-Funded Warrants were sold in lieu of shares of common stock to the June 2024 Investor . The Pre-Funded Warrants have an exercise price of $ 0.005 per share, became exercisable upon issuance and remain exercisable until exercised in full. The net proceeds from the June 2024 Offering, after deducting the fees and expenses of the Placement Agent and other offering expenses payable by us, but excluding the net proceeds, if any, from the exercise of the Warrants, was approximately $ 2.1 million. The June 2024 Offering closed on June 21, 2024. F-19 Table of Contents In a concurrent private placement, pursuant to the terms of the Purchase Agreement, the Company also agreed to issue and sell to the June 2024 Investor unregistered warrants (the “Private Placement Warrants”) to purchase up to 122,600 shares of common stock, at an offering price of $ 20.50 per Private Placement Warrant to purchase one share of common stock (the “Private Placement” and, together with the Registered Direct Offering, the “Offerings”) (which offering price was included in the purchase price per share of common stock or Pre-Funded Warrant). The Private Placement Warrants have an exercise price of $ 20.50 per share (subject to customary adjustments as set forth in the Private Placement Warrants), were exercisable upon issuance and will expire five years from the date of issuance. The Private Placement Warrants contain customary anti-dilution adjustments to the exercise price, including for share splits, share dividends, rights offering and pro rata distributions. The resale of the shares of common stock issuable upon the exercise of the Private Placement Warrants was subsequently registered in July 2024 on a Form S-1 (File No. 333-280927). Wainwright acted as the exclusive placement agent in connection with the Offerings under an Engagement Letter, dated as of June 18, 2024, between us and Wainwright (the “Engagement Letter”). Pursuant to the Engagement Letter, the Company issued to Wainwright (or its designees) warrants to purchase up to 7,355 shares of common stock (the “Wainwright Warrants” and, together with the Private Placement Warrants, the “2024 Warrants”). The Wainwright Warrants have substantially the same terms as the Private Placement Warrants, except that the Wainwright Warrants will expire five years from the commencement of the sales of the Offerings and have an exercise price of $ 25.625 per share (subject to customary adjustment as set forth in the Wainwright Warrants), representing 125 % of the purchase price per share of common stock in the Registered Direct Offering. Induced Warrant Exercise On October 24, 2024, we entered into an inducement offer letter agreement (the “Inducement Letter”) with a certain investor (the “Holder”) that held outstanding Series A-3 warrants (the “Existing Warrants”) to purchase up to an aggregate of 337,552 shares of our common stock, originally issued to the Holder on May 2, 2024. Pursuant to the Inducement Letter, the Holder agreed to exercise for cash the Series A-3 warrants at the exercise price of $ 11.85 per share in exchange for our agreement to issue in a private placement new Series B Common Stock purchase warrants to purchase up to (i) 337,552 shares of common stock (the “New Series B-1 Warrant Shares”) and (ii) 337,552 shares of common stock (the “New Series B-2 Warrant Shares” and collectively, the “New Warrants”). Each Warrant has an exercise price of $ 13.50 per share and will be exercisable beginning on the effective date of stockholder approval of the issuance of the shares upon exercise of the Warrants (the “Warrant Stockholder Approval”), which was obtained on February 11, 2025 . The New Series B-1 Warrant will expire on the five-year anniversary of the Warrant Stockholder Approval. The New Series B-2 Warrant will expire on the twelve-month anniversary of the Warrant Stockholder Approval. The closing of the transaction contemplated pursuant to the Inducement Letter occurred on October 25, 2024 (the “Closing Date”). We received aggregate gross proceeds of approximately $ 4.0 million from the exercise of the Existing Warrants by the Holder, before deducting placement agent fees and other expenses payable by us of approximately $ 0.4 million. We engaged Wainwright to act as our exclusive agent in connection with the transaction summarized above and paid Wainwright a cash fee equal to 7.0 % of the aggregate gross proceeds from the exercise of the Existing Warrants. In addition, we (i) reimbursed Wainwright for $ 50,000 of the fees and expenses of Wainwright’s legal counsel and other of its out-of-pocket expenses, (ii) reimbursed Wainwright for its non-accountable expenses in the amount of $ 25,000 , and (iii) paid a management fee equal to 1.0 % of the gross proceeds raised. We also issued to Wainwright or its designees (“PA Warrant Holders”) placement agent warrants (the “Wainwright Warrants”) to purchase up to 20,251 shares of Common Stock (the “Wainwright Warrant Shares”). The Wainwright Warrants have the same terms as the New Series B-1 Warrants, except that the Wainwright Warrants have an exercise price equal to $ 14.815 per share. The issuance of the New Warrants was accounted for as an equity issuance cost associated with the exercise of the Existing Warrants, which had no net impact on equity as the New Warrants conveyed were determined to be equity classified. ​ F-20 Table of Contents Registration Statements ​ On May 31, 2024, the Company filed a shelf registration statement on Form S-3 (File No. 333-279891) (the “2024 S-3”), which was declared effective on June 12, 2024. Under the 2024 S-3, the Company may sell up to a total of $ 40.0 million of its securities. As of December 31, 2025, approximately $ 34.2 million of the 2024 S-3 remains available for sales of securities. As of the filing of this Form 10-K, the Company is subject to the General Instruction I.B.6 to Form S-3, known as the “baby shelf rules,” which limit the number of securities it can sell under its registration statements on Form S-3. Stock Issuances to Fortress During the year, the Company issues shares of common stock to Fortress in connection with the Founders Agreement, see Note 3. Stock Warrants A summary of warrant activities for the years ended December 31, 2025 and 2024, is presented below: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Average ​ ​ ​ ​ ​ ​ ​ Remaining ​ ​ ​ ​ Weighted Average ​ Contractual Life (in ​ ​ Warrants ​ Exercise Price ​ years) Outstanding as of December 31, 2023 89,618 ​ $ 67.16 5.34 Granted ​ 2,234,669 ​ ​ 10.93 ​ 2.10 Exercised ( 747,368 ) ​ 5.35 — Outstanding as of December 31, 2024 1,576,919 ​ $ 14.56 3.14 Granted 7,637,889 ​ 2.17 1.99 Exercised ( 4,536,162 ) ​ 1.57 — Outstanding as of December 31, 2025 4,678,646 ​ $ 6.93 3.37 ​ Upon the exercise of warrants, the Company will issue new shares of common stock. In connection with the February 2025 Equity Offering on February 10, 2025, the Company issued Pre-Funded Warrants to purchase up to 2,162,807 shares of common stock and issued two series of warrants to purchase up to 5,315,614 shares of common stock. In connection with this offering, Wainwright received Placement Agent Warrants to purchase up to 159,468 shares of common stock. ​ During the year ended December 31, 2025, all of the Pre-Funded Warrants were exercised at an exercise price of $ 0.0001 per share and 2,373,355 of the Series C-2 Warrants were exercised at an exercise price of $ 3.01 per share. ​ In connection with the May 2024 Offering, the Company issued pre-funded warrants to purchase up to 314,352 shares of common stock and issued three series of warrants (the “Series A-1,” “Series A-2,” and “Series A-3”) to purchase up to 1,012,656 shares of common stock. In connection with these offerings, Wainwright received Placement Agent Warrants to purchase up to 20,251 shares of common stock. ​ In connection with the June 2024 Registered Direct Offering, the Company issued pre-funded warrants to purchase up to 62,100 shares of common stock, and in the concurrent Private Placement, the Company issued unregistered warrants to purchase up to 122,600 shares of common stock. The resale of the underlying shares of common stock were subsequently registered in July 2024 on Form S-1 (File No. 333-280927). In connection with these offerings, Wainwright received Placement Agent Warrants to purchase up to 7,355 shares of common stock. ​ In connection with the induced warrant exercise in October 2024, the holder of the Series A-3 warrants from the May 2024 Offering agreed to exercise for cash 337,552 warrants in partial consideration for the Company to issued two series of unregistered warrants (the “New Series B-1” and “New Series B-2”) to purchase up to 675,104 shares of common stock. Upon exercise of the Series A-3 warrants, the Company issued to the holder 82,000 of the 337,552 shares of common stock. Due to beneficial ownership limitation provisions in the inducement letter agreement, the remaining 255,552 shares F-21 Table of Contents were initially unissued and held in abeyance for the benefit of the holder until notice from the holder that the shares may be issued in compliance with the agreement. As of December 31, 2024, 185,880 shares remained in abeyance. In connection with the issuance of the New Series B-1 and New Series B-2 warrants, a pproximately $ 7.8 million of the aggregate fair value was deemed to be a dividend and recorded to additional paid-in-capital because the Company had an accumulated deficit on the exercise date. The deemed dividend was included in the net loss attributable to Class A common and common stockholders in the calculation of net loss per share in the Statements of Operations (see Note 2). The resale of the underlying shares of common stock were subsequently registered in November 2024 on Form S-3 (File No. 333-283420). In connection with these offerings, Wainwright received Placement Agent Warrants to purchase up to 20,251 shares of common stock. ​ The key inputs used for the Black-Scholes Model calculation on October 25, 2024, to measure the fair value of the New Warrants, were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ New Series B-1 ​ New Series B-2 ​ ​ Warrants ​ Warrants Stock Price ​ 14.50 ​ ​ 14.50 ​ Risk-free interest rate ​ 4.1 % ​ 4.3 % Expected dividend yield ​ — ​ ​ — ​ Expected term in years ​ 5 ​ ​ 1 ​ Expected volatility ​ 122.2 % ​ 213.2 % ​ Equity Incentive Plan The Company has in effect the 2016 Incentive Plan (the “Incentive Plan”). The Incentive Plan was adopted in 2016 and enables the grant of stock-based awards to directors, officers, employees and consultants. The plan initially authorized grants with respect to 2,666 shares of common stock and expires 10 years from adoption and limits the term of each option to no more than 10 years from the date of grant. ​ In June 2018, the Company’s stockholders approved an amendment to the Incentive Plan to increase the number of authorized shares issuable by 4,000 shares, for a total of 6,666 shares. In June 2021, the Company’s stockholders approved an amendment to the Incentive Plan to increase the number of authorized shares issuable by 4,000 shares, for a total of 10,666 shares. In June 2022, the Company’s stockholders approved an amendment to the Incentive Plan to increase the number of authorized shares issuable by 4,000 shares, for a total of 14,666 shares. In December 2025, the Company’s stockholders approved an amendment to the Incentive Plan to increase the number of authorized shares issuable by 2,500,000 shares, for a total of 2,514,666 shares. ​ As of December 31, 2025, 2,506,958 shares are available for issuance under the Incentive Plan. ​ Stock Options The following table summarizes stock option activities for the years ended December 31, 2025 and 2024: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Average ​ ​ ​ ​ ​ ​ ​ Remaining ​ ​ ​ ​ Weighted Average ​ Contractual Life (in ​ ​ Stock Options ​ Exercise Price ​ years) Outstanding at December 31, 2024 1,521 ​ $ 4,297.50 2.31 Outstanding at December 31, 2025 1,521 ​ $ 4,297.50 1.31 Options vested and exercisable at December 31, 2025 951 ​ $ 4,297.50 1.31 ​ As of December 31, 2025, the Company had no unrecognized stock-based compensation expense related to options. The Company accounts for forfeited awards as they occur as permitted. F-22 Table of Contents Restricted Stock Awards Certain employees and directors have been awarded restricted stock. The restricted stock vesting consists of milestone and time-based vesting. The following table summarizes restricted stock award activities for the years ended December 31, 2025 and 2024: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Average ​ ​ ​ ​ Grant Date Fair ​ ​ Number of Shares ​ Value Nonvested at December 31, 2023 1,285 ​ $ 577.50 Vested ​ ( 90 ) ​ ​ 2,722.50 Nonvested at December 31, 2024 1,195 ​ $ 415.95 Vested ​ ( 475 ) ​ ​ 523.50 Nonvested at December 31, 2025 720 ​ $ 345.00 ​ As of December 31, 2025, the Company had unrecognized stock-based compensation expense related to restricted stock of approximately $ 42,000 , which is expected to be recognized over a weighted average period of approximately 0.5 years. Restricted Stock Units The following table summarizes restricted stock units’ activities for the year ended December 31, 2025 and 2024: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Weighted Average ​ ​ ​ ​ Grant Date Fair ​ ​ Number of Units ​ Value Nonvested at December 31, 2023 1,911 ​ $ 948.25 Forfeited ​ ( 1,320 ) ​ ​ 911.70 Vested ​ ( 365 ) ​ ​ 1,205.20 Nonvested at December 31, 2024 226 ​ $ 746.70 Forfeited ​ ( 12 ) ​ ​ 1,321.25 Vested ( 118 ) ​ 1,042.90 Nonvested at December 31, 2025 96 ​ $ 310.81 ​ As of December 31, 2025, the Company had unrecognized stock-based compensation expense related to restricted stock units of approximately $ 4,000 , which is expected to be recognized over a weighted average period of approximately one year . The following table summarizes stock-based compensation expense for the years ended December 31, 2025 and 2024 (in thousands). ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31, ​ ​ ​ ​ 2025 ​ ​ ​ 2024 General and administrative ​ $ 139 ​ $ 200 Research and development (1) ​ ( 10 ) ​ ( 650 ) Total stock-based compensation expense ​ $ 129 ​ $ ( 450 ) ​ ​ Employee Stock Purchase Plan In connection with our Employee Stock Purchase Plan (“ESPP”), eligible employees of Mustang and Fortress can purchase the Company’s Common Stock at the end of a predetermined offering period at 85 % of the lower of the fair market value at the beginning or end of the offering period. In December 2025, the Company’s stockholders approved an amendment to the ESPP to increase the number of shares issuable by 250,000 shares. As of December 31, 2025, 2,762 shares have been purchased, and 256,571 shares are available for future sale under the Company’s ESPP. F-23 Table of Contents ​ Note 9 - Income Taxes The Company has accumulated net losses since inception and has not recorded an income tax provision or benefit during the years ended December 31, 2025 and 2024. ​ The Company adopted ASU 2023-09, Income Taxes (Topic 740): Improvements to Income Tax Disclosures , on a prospective basis. As a result, the 2025 rate reconciliation is presented in accordance with the new disclosure requirements, while the 2024 reconciliation continues to be presented under the disclosure requirements in effect for that period. ​ A reconciliation of income tax computed at the federal statutory rate to the provision for income taxes pursuant to the disclosure requirements of ASU 2023-09 for the year ended December 31, 2025, was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31, ($ in thousands) ​ ​ ​ 2025 ​ ​ Amount Percent U.S. federal statutory tax rate ​ $ ( 396 ) ​ 21.0 % State and local income taxes, net of federal income tax effect (1) ​ ​ 21 ​ ( 1.1 ) % Change in valuation allowance ​ ( 130 ) ​ 6.9 % Non-deductible items: ​ ​ ​ ​ ​ Share-based compensation ​ 70 ​ ( 3.7 ) % Non-deductible compensation ​ ​ 170 ​ ( 9.0 ) % Stock issuance costs ​ 83 ​ ( 4.4 ) % Other adjustments: ​ ​ ​ ​ ​ ​ Federal net operating loss ​ 274 ​ ( 14.5 ) % Other true-ups ​ ​ ( 65 ) ​ 3.5 % Provision for income taxes and effective income tax rate ​ ​ 27 ​ ( 1.4 ) % ​ (1) During the year ended December 31, 2025, state taxes in Massachusetts, New York and New York City comprised greater than 50% of the tax effect in this category. ​ A reconciliation of the statutory U.S. federal rate to the Company’s effective tax rate for the year ended December 31, 2024, was as follows: ​ ​ ​ ​ ​ ​ ​ For the year ended December 31, ​ ​ ​ ​ 2024 Statutory federal income tax rate 21 % State taxes, net of federal tax benefit 16 % Non-deductible items ( 1 ) % Tax credits 1 % Other ( 10 ) % Change in valuation allowance ( 27 ) % Income taxes provision (benefit) — ​ ​ F-24 Table of Contents The components of the net deferred tax asset as of December 31, 2025 and 2024 are the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ For the year ended December 31, ($ in thousands) ​ ​ ​ 2025 ​ ​ ​ 2024 Deferred tax assets: ​ ​ ​ ​ Net operating loss carryovers ​ $ 103,701 ​ $ 95,131 Stock compensation and other ​ 1,267 ​ 1,537 Change in fair value of warrant liabilities ​ 60 ​ 59 Amortization of license ​ 8,735 ​ 9,672 Lease liability ​ ​ — ​ ​ 326 Accruals and reserves ​ 135 ​ 1,922 Startup costs ​ 4 ​ 4 Tax credits ​ ​ 19,046 ​ ​ 19,046 174 Capitalization ​ 16,835 ​ 24,437 Other ​ ​ 56 ​ ​ — Total deferred tax assets ​ ​ 149,839 ​ ​ 152,134 Less: valuation allowance ​ ( 149,839 ) ​ ( 152,104 ) Deferred tax assets, net ​ $ — ​ $ 30 ​ ​ ​ ​ ​ ​ ​ Deferred tax liability: ​ ​ ​ ​ ​ ​ Right of use asset ​ ​ — ​ ​ ( 30 ) Total deferred tax assets, net ​ $ — ​ $ — ​ The Company has determined, based upon available evidence, that it is more likely than not that the net deferred tax asset will not be realized and, accordingly, has provided a full valuation allowance against its net deferred tax assets as of December 31, 2025 and 2024. A valuation allowance of approximately $ 149.8 million and $ 152.1 million, respectively, was recorded for the years ended December 31, 2025 and 2024. As of December 31, 2025, the Company had federal and state net operating loss carryforwards of approximately $ 306.9 million and $ 654.8 million, respectively. Approximately $ 283.3 million and $ 0.6 million of the federal and state net operating loss carryforwards, respectively, can be carried forward indefinitely. As of December 31, 2025, the Company had federal and state income tax credits of approximately $ 15.0 million and $ 5.1 million, respectively, which will begin to expire in 2034 . Under the provisions of Section 382 of the Internal Revenue Code, a corporation that undergoes an “ownership change”, as defined therein, is subject to limitations on its use of pre-change NOLs and income tax credits carryforwards to offset future tax liabilities. Certain tax attributes may be subject to an annual limitation as a result of the Company’s January 2017 capital raise, as it appears to constitute an ownership change under Section 382. Additionally, under Section 382, annual use of the Company’s net operating loss carryforwards to offset taxable income may be limited based on cumulative changes in ownership. The Company has not completed an analysis to determine whether any such limitations have been triggered as of December 31, 2025. The Company has no income tax effect due to the recognition of a full valuation allowance on all of its deferred tax assets as it believes that it is more likely than not that the deferred tax assets will not be realized regardless of whether an “ownership change” has occurred. At December 31, 2025 and December 31, 2024, the Company did not have any significant uncertain tax positions. The Company will recognize interest and penalties related to uncertain tax positions in income tax expense. As of December 31, 2025 and 2024, the Company had no accrued interest or penalties related to uncertain tax positions and no amounts have been recognized in the Company’s statement of operations. The Company is subject to U.S. federal and various state taxes. Because of net operating losses, all federal tax years since inception remain open for the assessment of income taxes. The expiration of the statute of limitations related to the various state income and franchise tax returns varies by state. ​ On July 4, 2025, President Donald J. Trump signed the “One Big Beautiful Bill Act” (OBBBA) into law. Key corporate tax provisions include the restoration of 100% bonus depreciation, immediate expensing for domestic research and experimental expenditures, changes to interest limitation rules, and expanded aggregation requirements for compensation F-25 Table of Contents deductibility limits. In accordance with ASC 740, the Company recognized the effects of the new tax law in the period enacted. As a result, the Company immediately expensed current-year domestic research and experimental expenditures and elected to continue amortizing its existing domestic capitalized research and experimental expenditures over their remaining useful lives. Due to the Company having a full valuation allowance, there were no impacts to the effective tax rate. ​ Under ASC 2023-09, entities must disclose income taxes paid (net of refunds received), disaggregated between federal and state. This also requires disclosing income taxes paid (net of refunds) by individual jurisdictions that represent more than 5% of total income taxes paid (net of refunds). Because the company does not have significant payments for the year ended December 31, 2025, no amounts are disclosed. ​ ​ ​ ​ ​ ​ F-26 Table of Contents ​ SIGNATURES Pursuant to the requirements of Section 13 or 15(d) of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized. ​ Mustang Bio, Inc. By: /s/ Manuel Litchman, M.D. Name: Manuel Litchman, M.D. Title: President, Chief Executive Officer and Interim Chief Financial Officer ​ March 19, 2026 ​ Pursuant to the requirements of the Securities Exchange Act of 1934, this Form 10-K has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated. ​ Signature Title Date /s/ Manuel Litchman President, Chief Executive Officer, Interim Chief Financial Officer and Director Manuel Litchman, M.D. (Principal Executive and Financial Officer) March 19, 2026 ​ /s/ Michael S. Weiss Chairman of the Board of Directors and Executive Michael S. Weiss Chairman March 19, 2026 ​ ​ ​ ​ ​ /s/ Adam Chill Adam Chill Director March 19, 2026 /s/ Neil Herskowitz Neil Herskowitz Director March 19, 2026 ​ ​ ​ ​ ​ /s/ David Jin David Jin Director March 19, 2026 /s/ Lindsay A. Rosenwald Lindsay A. Rosenwald, M.D. Director March 19, 2026 /s/ Michael Zelefsky Michael Zelefsky, M.D. Director March 19, 2026 ​ ​ ​ ​ ​ 96