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Note 3 - Clinical Trial and Sponsored Research Agreements

Research and Development Expenses – All Licenses

City of Hope

CD123 License (MB-102)

For the three and six months ended, June 30, 2021, the Company recorded $0.3 million related to a non-refundable milestone payment for the 24th patient treated in connection with the CD123 clinical study. There were no such expenses for the three and six months ended June 30, 2022.

Mayo Clinic – CAR T Technology License

For the three and six months ended June 30, 2021, the Company recorded $0.8 million in research and development expenses – licenses acquired. There were no such expenses for the three and six months ended June 30, 2022.

Research and Development Expenses - Sponsored Research and Clinical Trial Agreements

For the three and six months ended June 30, 2022 and 2021, the Company recorded the following expense in research and development for sponsored research and clinical trial agreements in the Unaudited Statements of Operations pursuant to the terms of this agreement:

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CD123 (MB-102) Clinical Research Support Agreement

Since February 2017, the Company has been party to a clinical research support agreement for the CD123-directed CAR T program (the “CD123 CRA”) with COH whereby, the Company has agreed to contribute approximately $0.1 million per patient in connection with the ongoing investigator-initiated study.

IL13Rα2 (MB-101) Clinical Research Support Agreements

Since February 2017, the Company has been party to a clinical research support agreement for the IL13Rα2-directed CAR T program (the “IL13Rα2 CRA”) with COH whereby, the Company has agreed to contribute $0.1 million related to patient costs in connection with the on-going investigator-initiated study.

Since October 2020, the Company has been party to a clinical research support agreement for the IL13Rα2-directed CAR T program for adult patients with leptomeningeal glioblastoma, ependymoma or medulloblastoma (the “IL13Rα2 Leptomeningeal CRA”) with COH whereby, the Company has agreed to contribute $0.1 million per patient in connection

with the ongoing investigator-initiated study. Further, the Company agreed to fund approximately $0.2 million annually pertaining to the clinical development of the IL13Rα2-directed CAR T program for this patient population.

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Since March 2021, the Company has been party to a clinical research support agreement for an Institutional Review Board-approved, investigator-initiated protocol entitled: “Single Patient Treatment with Intraventricular Infusions of IL13Rα2-targeting and HER2-targeting Chimeric Antigen Receptor (CAR)-T cells for a Single Patient (UPN 181) with Recurrent Multifocal Malignant Glioma.” Pursuant to the terms of this agreement, the Company will contribute up to $0.2 million in connection with the ongoing investigator-initiated study.

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CS1 (MB-104) Clinical Research  Support Agreement

Since June 2020, the Company has been party to a clinical research and support agreement with COH in connection with an investigator-sponsored study conducted under an Institutional Review Board-approved for MB-104 whereby, the Company has agreed to reimburse COH for costs associated with this trial, when incurred, not to exceed $2.4 million. The agreement will expire upon the delivery of a final study report or earlier. Since inception, the Company has reimbursed COH $1.5 million.

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HER2 (MB-103) Clinical Research Support Agreement

Since September 2020, the Company has been party to a clinical research support agreement with COH in connection with an investigator-sponsored study conducted under an Institutional Review Board-approved, investigator-initiated protocol entitled: “Phase I Study of Cellular Immunotherapy using Memory-Enriched T Cells Lentivirally Transduced to Express a HER2-Specific, Hinge-Optimized, 41BB-Costimulatory Chimeric Receptor and a Truncated CD19 for Patients with Recurrent/Refractory Malignant Glioma” for MB-103. Under the terms of the agreement the Company will reimburse COH for costs associated with this trial not to exceed $3.0 million. The agreement will expire upon the delivery of a final study report or earlier. Since inception, the Company has reimbursed COH $2.5 million.

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PSCA (MB-105) Clinical Research Support Agreement

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Since October 2020, the Company has been party to a clinical research support agreement with COH in connection with an investigator-sponsored study conducted under an Institutional Review Board-approved, investigator-initiated protocol entitled: “A Phase 1 Study to Evaluate PSCA-Specific Chimeric Antigen Receptor (CAR)-T Cells for Patients with Metastatic Castration Resistant Prostate Cancer” for MB-105. The Company has agreed to reimburse COH for costs associated with this trial not to exceed $2.3 million.  The agreement will expire upon the delivery of a final study report or earlier. Since inception, the Company has reimbursed COH $0.3 million.

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CD20 (MB-106) Clinical Trial Agreement with Fred Hutchinson Cancer Research Center

Since July 3, 2017, in conjunction with the CD20 Technology License from Fred Hutchinson Cancer Research Center (“Fred Hutch”), the Company has been party to an investigator-initiated clinical trial agreement (the “CD20 CTA”) to provide partial funding for a Phase 1/2 clinical trial at Fred Hutch evaluating the safety and efficacy of the CD20 Technology in patients with relapsed or refractory B-cell non-Hodgkin lymphomas. In connection with the CD20 CTA, the Company agreed to fund up to $5.3 million of costs associated with the clinical trial, which commenced during the fourth quarter of 2017. In November 2020, the CD20 CTA was amended to include additional funding of approximately $1.8 million, which includes $0.8 million for the treatment of five patients with chronic lymphocytic leukemia. In January 2022, the CD20 CTA was amended to include additional funding of $2.2 million increasing the total payment obligation of the Company in connection with the CD20 CTA not to exceed $9.3 million. Since inception, the Company has reimbursed Fred Hutch $6.1 million.

XSCID (MB-107) Data Transfer Agreement with St. Jude Children’s Research Hospital

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Since June 2020, the Company has been party to a Data Transfer Agreement with St. Jude Children’s Research Hospital (“St. Jude”) under which Mustang will reimburse St. Jude for costs associated with St. Jude’s clinical trial for the treatment of infants with X-linked severe combined immunodeficiency (“XSCID”) whereby, the Company will continue to

reimburse St. Jude for costs incurred in connection with this trial. Since inception, the Company has reimbursed St. Jude $2.7 million.

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RAG1-SCID (MB-110) Sponsored Research Support Agreement (“SRA”) with Leiden University Medical Centre

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Since September 8, 2021, in connection with the Leiden License, the Company has been party to a Sponsored Research Support Agreement (“SRA”) with Leiden University Medical Centre (“LUMC”) under which the Company will fund research in the amount of approximately $0.5 million annually over a period of 5 years. The research performed pursuant to this agreement will support technology the Company has licensed from Leiden for the use of a gene therapy under development for the treatment of severe immunodeficiency caused by mutations in the RAG1 gene.

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Sponsored Research Support Agreement with Mayo Clinic  

Since June 2021, the Company has been party to an SRA with the Mayo Clinic under which the Company will fund research in the amount of $2.1 million over a period of two years. The research performed pursuant to this agreement will support technology the Company has licensed from Mayo Clinic for a novel technology that may be able to transform the administration of CAR T therapies and has the potential to be used as an off-the-shelf therapy. Since inception, the Company has funded $0.9 million.