MUSTANG BIO, INC. 10-K

Item 1. Business ​ OVERVIEW Mustang Bio, Inc. (“Mustang,” “we,” “us” or the “Company”) is a clinical-stage biopharmaceutical company focused on translating today’s medical breakthroughs in cell and gene therapies into potential cures for hematologic cancers, solid tumors and rare genetic diseases. We aim to acquire rights to these technologies by licensing 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. Our pipeline is currently focused in three core areas: CAR T therapies for hematologic malignancies, CAR T therapies for solid tumors and gene therapies for rare genetic disorders. For each therapy we have partnered with world class research institutions. For our CAR T therapies we have partnered with the City of Hope National Medical Center (“COH”), Fred Hutchinson Cancer Center (“Fred Hutch”), Nationwide Children’s Hospital (“Nationwide”) and the Mayo Foundation for Medical Education and Research (“Mayo Clinic”). For our gene therapies, 5 ​ Table of Contents we have partnered with St. Jude Children’s Research Hospital (“St. Jude”) in the development of a first-in-class ex vivo lentiviral treatment of X-linked severe combined immunodeficiency (“XSCID”) and with Leiden University Medical Centre (“LUMC”) for RAG1 severe combined immunodeficiency (“RAG1-SCID”). CAR T Therapies Our pipeline of CAR T therapies is being developed under exclusive licenses from several world class research institutions. Our strategy is to license these technologies, support preclinical and clinical research activities by our partners and transfer the underlying technology to our cell processing facility located in Worcester, Massachusetts, in order to conduct our own clinical trials. We are developing CAR T therapies for hematologic malignancies in partnership with COH targeting CD123 (MB-102) and CS1 (MB-104) and with Fred Hutch targeting CD20 (MB-106). Phase 1 clinical trials sponsored by COH for MB-102 and MB-104 and by Fred Hutch for MB-106 are underway. In July 2019 the FDA approved our IND application to initiate a multi-center Phase 1/2 clinical trial of MB-102, and our clinical trial began enrollment in 2020 for the treatment of patients with blastic plasmacytoid dendritic cell neoplasm (“BPDCN”). In May 2021, the FDA approved our IND application to initiate a multi-center Phase 1/2 clinical trial of MB-106, and our clinical trial began enrollment in 2022 for treatment of patients with non-Hodgkin lymphoma (“NHL”) and chronic lymphocytic leukemia (“CLL”). We plan to file an IND for a multicenter Phase 1/2 trial for MB-104 for the treatment of patients with multiple myeloma once COH has established a safe and effective dose. We are also developing CAR T therapies for solid tumors in partnership with COH targeting IL13Rα2 (MB-101), HER2 (MB-103) and PSCA (MB-105). In addition, we have partnered with Nationwide for the C134 oncolytic virus (MB-108) in order to enhance the activity of MB-101 for the treatment of patients with glioblastoma (“GBM”). Phase 1 clinical trials sponsored by COH for MB-101, MB-103 and MB-105 are underway. A Phase 1 clinical trial sponsored by the University of Alabama at Birmingham (“UAB”) for MB-108 began during the third quarter of 2019, and we plan to file an IND for the combination of MB-101 and MB-108 – which is referred to as MB-109 – for the treatment of patients with relapsed or refractory GBM and anaplastic astrocytoma in 2023. In the third quarter of 2019, we announced that COH had started enrolling patients on a Phase 1 clinical trial of MB-101 in combination with nivolumab (trade name: Opdivo ® ) and ipilimumab (trade name: Yervoy ® ) in patients with recurrent malignant glioma (ClinicalTrials.gov Identifier: NCT04003649). In the fourth quarter of 2020 we announced that COH had initiated a Phase 1, two-arm clinical trial of MB-101 in patients with leptomeningeal brain tumors (e.g., glioblastoma, ependymoma or medulloblastoma; ClinicalTrials.gov Identifier: NCT04003649). Finally, the Company is collaborating with the Mayo Clinic to develop a novel technology that may be able to transform the administration of CAR T therapies and potentially be used as an off-the-shelf therapy. Mustang plans to file an IND application for a multicenter Phase 1 clinical trial once a lead construct has been identified. Gene Therapies In partnership with St. Jude, our XSCID gene therapy programs (MB-107 and MB-207) are being conducted under an exclusive license to develop a potentially curative treatment for XSCID, a rare genetic immune system condition in which affected patients do not live beyond infancy without treatment. This first-in-class ex vivo lentiviral gene therapy has been evaluated in two Phase 1/2 clinical trials involving two different autologous cell products: an ongoing multicenter trial of the MB-107 product in newly diagnosed infants sponsored by St. Jude and a single-center trial of the MB-207 product in previously transplanted patients sponsored by the National Institutes of Health (“NIH”). In 2022, the NIH study was suspended as a result of the study stopping rules. In January 2021 we received a safe to proceed “approval” from the U.S. Food and Drug Administration (“FDA”) for our MB-107 Investigational New Drug (“IND”) application allowing us to initiate a pivotal non-randomized multicenter Phase 2 clinical trial of MB-107 in newly diagnosed infants with XSCID who are under the age of two. In January 2022, the FDA issued a clinical hold, pending additional Chemistry, Manufacturing and Controls (“CMC”) data, on our IND application to conduct a pivotal non-randomized multicenter Phase 2 clinical trial of MB-207 in previously transplanted XSCID patients. To date, we have not received approval for the sale of our product candidates in any market and, therefore, have not generated any product sales from our product candidates. In addition, we have incurred substantial operating losses since our inception, and expect to continue to incur significant operating losses for the foreseeable future and may never become profitable. As of December 31, 2022, we have an accumulated deficit of $329.4 million. We are a majority-controlled subsidiary of Fortress. 6 ​ Table of Contents CORPORATE INFORMATION Mustang Bio, Inc. was incorporated in Delaware on March 13, 2015. Our executive offices are located at 377 Plantation Street, Worcester, Massachusetts 01605. Our telephone number is (781) 652-4500, and our email address is info@mustangbio.com . Our website address is www.mustangbio.com. The information set forth on our website is not a part of this report. We will make available free of charge through our website our annual reports on Form 10-K, quarterly reports on Form 10-Q and current reports on Form 8-K, and any amendments to these reports, as soon as reasonably practicable after we electronically file such material with, or furnish such material to, the SEC. We are not including the information on our website as a part of, nor incorporating it by reference into, this report. The SEC maintains a website that contains annual, quarterly, and current reports, proxy and information statements, and other information that issuers (including us) file electronically with the SEC. The SEC’s website address is https://www.sec.gov/. PRODUCTS UNDER DEVELOPMENT CAR T Therapies for Hematologic Malignancies MB-102 (CD123 CAR T Cell Program for BPDCN, AML and High-Risk MDS) CD123 is a subunit of the heterodimeric interleukin-3-receptor (“IL-3R”) which is widely expressed on human hematologic malignancies including blastic plasmacytoid dendritic cell neoplasm (“BPDCN”) and acute myeloid leukemia (“AML”). In addition, CD123 can be found on the surface of B cell acute lymphoblastic leukemia (“B-ALL”), hairy cell leukemia, myelodysplastic syndrome (“MDS”), chronic myeloid leukemia (“CML”) and Hodgkin lymphoma. Of these malignancies, we are currently investigating CD123 as a target for adoptive cellular immunotherapy in BPDCN, since high CD123 expression is associated with enhanced cell proliferation, increased resistance of these cells to apoptosis, and poor clinical prognosis. Depending on the early results in this patient population, we may broaden the inclusion criteria to include AML and high-risk MDS (“HR-MDS”). CD123 is overexpressed in the vast majority of cases of AML and HR-MDS and in essentially all cases of BPDCN. AML is a cancer of the myeloid line of blood cells characterized by rapid growth of abnormal white blood cells that accumulate in the bone marrow. AML is the most common form of acute leukemia. Although AML is a relatively rare disease, there are approximately 20,000 new cases per year in the U.S. and 10,000 deaths per year, accounting for approximately 1.8% of cancer deaths in the U.S. [Source: The Surveillance, Epidemiology, and End Results (“SEER”) Program of the National Cancer Institute]. AML standard of care involves chemotherapy to induce remission followed by additional chemotherapy or a hematopoietic stem cell transplant. Allogeneic stem cell transplantation (“allo-SCT”) is the preferred treatment for AML following a second remission. It can lead to a 5-year disease-free survival in 26% of patients. Unfortunately, however, currently only about half of relapsed patients are able to achieve a second remission with traditional chemotherapy agents. Patients who do not achieve a second remission are much less likely to benefit from transplantation and face a dismal outcome. MDS is a heterogeneous group of malignant hematopoietic stem cell disorders characterized by dysplastic and ineffective blood cell production and a variable risk of transformation to acute leukemia. Patients with MDS have varying reductions in the production of red blood cells, platelets, and mature granulocytes that may also exhibit functional defects; these abnormalities often result in anemia, bleeding, and increased risk of infection. The precise incidence of de novo MDS is not known; conservative estimates from cancer databases suggest that there are approximately 10,000 cases diagnosed annually in the U.S. The actual incidence of MDS is likely higher than that predicted by cancer databases, since the nonspecific symptoms may evade detection in early stages of the disease and suspected cases may not undergo definitive testing (i.e., bone marrow biopsy) due to comorbidities. Investigations that have analyzed reimbursement claims have estimated the incidence in the U.S. to be 30,000 to 40,000 new cases per year. MDS occurs most commonly in older adults, with a median age at diagnosis in most series of ≥65 years and a male predominance. MDS and AML lie along a disease continuum, with distinction between the two largely made based upon the percentage of myeloblasts, which are immature cells with large nuclei, nucleoli, and a scant rim of dark blue cytoplasm, suggesting an underlying malignant hematologic disorder. In the current World Health Organization (“WHO”) classification system, blast forms must account for less than 20% of the total cells of the bone marrow aspirate and peripheral blood to meet the criteria for MDS. MDS prognosis is often assessed using the revised International Prognostic Scoring System (“IPSS-R”), which takes into account cytogenetics, percentage of bone marrow blasts, and the degree of anemia, thrombocytopenia, and neutropenia. This System categorizes patients into very low, low, intermediate, high, and very high risk MDS. High risk and very high risk MDS are characterized by more 7 ​ Table of Contents unfavorable cytogenetics, bone marrow blast percentages greater than 5% but under the 20% threshold for AML, and worse cytopenias (anemia, thrombocytopenia, and neutropenia) – all of which cumulatively generate an IPSS-R score of >4.5 to 6 for high risk MDS and >6 for very high risk MDS. Furthermore, they are generally progressive in nature and can easily progress to AML. Treatment is stratified according to medical fitness in a manner similar to that for older patients with AML. Patients who are medically fit or of intermediate fitness are generally evaluated soon after diagnosis to determine their suitability for allo-SCT. For patients who are not candidates for intensive treatment, care is focused on relieving symptoms and improving the quality of life and might involve lower intensity treatment, for example, with azacitidine, decitabine, or targeted therapy. Patients with recurrent or refractory higher risk MDS may be encouraged to participate in clinical trials. Outside of a clinical trial, the management of patients with recurrent or refractory MDS is largely dependent on the patient’s prior therapy. BPDCN is categorized by the WHO under AML. Most often, BPDCN presents with features of both lymphoma and leukemia. There is little data about BPDCN and the only approved drug for this disease is tagraxofusp-erzs, which is indicated for the treatment of adult and pediatric patients with both treatment-naïve and previously-treated BPDCN. The average age at diagnosis is 60 to 70 years. BPDCN is very often misdiagnosed and under-reported. The skin is the most frequently involved site of disease (80 percent of cases). However, BPDCN usually progresses with bone marrow involvement and a decrease in red blood cell, white blood cell and platelet counts. The lymph nodes and spleen may also be involved. Common misdiagnoses for BPCDN include non-Hodgkin lymphoma (“NHL”), AML, leukemia cutis [a nonspecific term used for cutaneous (skin) manifestation of any type of leukemia], melanoma (a type of skin cancer), and lupus erythematosus (chronic inflammatory disease that occurs when the body’s immune system attacks its own tissues and organs). There are no data or randomized clinical trials that can define the best first treatment for patients with BPDCN. In addition to the emerging use of tagraxofusp-erzs, which was approved by the FDA in December 2018, treatment sometimes includes therapies that are used for AML, ALL, or lymphoma. The time for which a patient responds to these treatments is usually short. After a relapse, second remissions with conventional chemotherapy are difficult to achieve. allo-SCT, especially if offered in first remission, may result in longer remissions. The current recommendation is for BPDCN patients to be evaluated for an allo-SCT as soon as possible and to begin searching for a donor. The use of CAR T immunotherapy in relapsed BPDCN, AML, and HR-MDS patients may offer the potential to achieve a complete or longer lasting remission. COH investigators have developed CD123-targeted CAR T cells designed to be activated, to proliferate, and to kill CD123-expressing tumor cells [Mardiros A et al . Blood . 2013;122(18):3138-3148]. The therapy is designed to recognize and eliminate malignant cells, leading to remission in patients with relapsed or refractory BPDCN, AML, and HR-MDS, and could serve as a bridge to potentially curative allogeneic stem cell transplant. The manufacturing process genetically modifies T cells isolated from peripheral blood mononuclear cells in order to express a CD123-specific, hinge-optimized, CD28 co-stimulatory domain-expressing CAR. In October 2020, we announced the dosing of the first patient in a multicenter Phase 1/2 clinical trial of MB-102 in patients with relapsed or refractory BPDCN ( Clinicaltrials.gov Identifier: NCT04109482). This is also the first clinical trial under a Mustang IND in which a patient was dosed with cells processed in our manufacturing facility. In December 2022, we announced that the safety review team (“SRT”), after thoroughly reviewing the safety data from Dose Level 1 (100 x 10 6 CAR T cells), unanimously recommended dose escalation to Dose Level 2 (300 x 10 6 CAR T cells). We anticipate initiation of Dose Level 2 cohort in 2023. ​ MB-104 (CS1 CAR T for Multiple Myeloma and Light Chain Amyloidosis) CS1 (also known as CD319, CRACC and SLAMF7) was identified as a natural killer (“NK”) cell receptor regulating immune functions. It is also expressed on B cells, T cells, dendritic cells, NK-T cells, and monocytes. CS1 is overexpressed in multiple myeloma (“MM”) and light chain amyloidosis (“AL”), which makes it a good target for immunotherapy. A humanized anti-CS1 antibody, elotuzumab (Empliciti™), has shown promising results in clinical studies and was initially approved by the FDA in 2015 in combination with lenalidomide and dexamethasone for the treatment of patients with multiple myeloma who have received one to three prior therapies . Despite great advances in treatment, MM remains an incurable malignancy of plasma cells. AL is a protein deposition disorder that is a result of a plasma cell dysplasia, similar to MM. Immunotherapy is an attractive approach for AL because of the low burden of disease. Our academic partners at COH have developed a novel second generation CS1-specific CAR T cell therapy. In preclinical studies, they have demonstrated efficacy of these CAR T cells, both in vitro and in vivo , within the context of clinically relevant models of MM and AL. COH is evaluating the safety of this CS1-specific CAR T cell therapy in a Phase 1 trial that commenced in the first half of 2019 (ClinicalTrials.gov Identifier: NCT03710421). Once COH has established a safe and effective dose for MB-104 in this trial, we expect to file an IND for a multicenter Phase 1/2 trial for the treatment of patients with MM. 8 ​ Table of Contents MB-106 (CD20 CAR T for B cell non-Hodgkin lymphoma (NHL) and chronic lymphocytic leukemia (CLL)) CD20 is a promising target for immunotherapy of B-cell malignancies. CD20 is a B-cell lineage-specific phosphoprotein that is expressed in high, homogeneous density on the surface of more than 95% of B-cell NHL and CLL. CD20 is stable on the cell surface with minimal shedding, internalization, or modulation upon antibody binding and is present at only nanomolar levels as a soluble antigen. It is well established as an effective immunotherapy target, with extensive studies demonstrating improved tumor responses and survival of B-NHL patients treated with rituximab and other anti-CD20 antibodies. Importantly, CD20 continues to be expressed on the lymphoma cells of most patients with relapsed B-NHL despite repetitive rituximab treatments, and loss of CD20 expression is not a major contributor to treatment resistance. Thus, there is strong rationale for testing CD20 CAR T cells as an immunotherapy for NHL. More than 80,000 new cases of NHL are diagnosed each year in the United States, and over 20,000 patients die of this group of diseases annually. Most forms of NHL including follicular lymphoma, mantle cell lymphoma, marginal zone lymphoma, lymphoplasmacytic lymphoma, and small lymphocytic lymphoma (“SLL”), which account collectively for ~45% of all cases of NHL, are incurable with available therapies, except for allo-SCT. However, many NHL patients are not suitable candidates for allo-SCT, and this treatment is also limited by significant rates of morbidity and mortality due to graft-versus-host disease. Aggressive B-cell lymphomas such as diffuse large B-cell lymphoma account for an additional 30-35% of NHL. The majority of patients with aggressive B-NHL are successfully treated with combination chemotherapy, but a significant proportion relapse or have refractory disease, and the outcome of these patients is poor. Innovative new treatments are therefore urgently needed. Chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) is a mature B cell neoplasm characterized by a progressive accumulation of monoclonal B lymphocytes. CLL is considered to be identical (i.e., one disease with different manifestations) to the NHL SLL. The malignant cells seen in CLL and SLL have identical pathologic and immunophenotypic features. The term CLL is used when the disease manifests primarily in the blood, whereas the term SLL is used when involvement is primarily nodal. CLL is the most common leukemia in adults in Western countries, accounting for approximately 25 to 35 percent of all leukemias in the United States. It is estimated that 18,740 new cases of CLL will be diagnosed in the United States in 2023. CLL is considered to be mainly a disease of older adults, with a median age at diagnosis of approximately 70 years; however, it is not unusual to make this diagnosis in younger individuals (e.g., from 30 to 39 years of age). The incidence increases rapidly with increasing age. The natural history of CLL is extremely variable, with survival times from initial diagnosis that range from approximately 2 to 20 years, and a median survival of approximately 10 years. Most patients will have a complete or partial response to initial therapy. However, conventional therapy for CLL is not curative and most patients experience relapse. In addition, many patients will require a change in therapy due to intolerance. Since patients with CLL are generally elderly with a median age older than 70 years, and due to the relatively benign course of the disease in the majority of patients, only selected patients are candidates for intensive treatments such as allo-SCT. Innovative new treatments with a favorable safety profile are therefore urgently needed for patients with relapsed and refractory disease. Under their IND, Fred Hutch is currently conducting a Phase 1/2 clinical study to evaluate the anti-tumor activity and safety of administering CD20-directed third-generation CAR T cells incorporating both 4-1BB and CD28 co-stimulatory signaling domains (MB-106) to patients with relapsed or refractory B-cell NHL or CLL (ClinicalTrials.gov Identifier: NCT03277729). Secondary endpoints of this study include safety and toxicity, preliminary antitumor activity as measured by overall response rate and complete remission rate, progression-free survival, and overall survival. The study is also assessing CAR T cell persistence and the potential immunogenicity of the cells. Finally, the study was designed so that Mustang together with Fred Hutch could determine a recommended Phase 2 dose. Fred Hutch intends to enroll approximately 50 subjects in the study, which is being led by Principal Investigator Mazyar Shadman, M.D., M.P.H., Assistant Member of Fred Hutch’s Clinical Research Division. The Fred Hutch IND was amended in 2019 to incorporate an optimized manufacturing process that had been developed in collaboration with Mustang. In May 2021, we announced that the FDA had approved our IND application allowing for initiation of a multi-center Phase 1/2 clinical study of MB-106 in patients with relapsed or refractory B cell NHL or CLL (Clinicaltrials.gov Identifier: NCT05360238). In November 2021, Mustang was awarded a grant of approximately $2 million from NCI of the National Institutes of Health. This two-year award will partially fund the Mustang-sponsored multicenter trial to assess the safety, tolerability and efficacy of MB-106. 9 ​ Table of Contents CAR T Therapies for Solid Tumors MB-103 (HER2 CAR T for GBM & Metastatic Breast Cancer to Brain) HER2/neu (“HER2”) is a growth-promoting protein on the outside of all breast cells. Breast cancer cells with higher-than-normal levels of HER2 are called HER2-positive (“HER2+”). These cancers tend to grow and spread faster than other breast cancers. Breast cancer is the most commonly diagnosed cancer in women, with over 42,000 women in the United States expected to die from advanced metastatic disease in 2023. Approximately 20% to 25% of breast cancers overexpress HER2, which is an established therapeutic target of both monoclonal antibodies (mAbs) and receptor tyrosine kinase inhibitors. With the advent of effective mAbs directed against HER2, the median overall survival of patients with metastatic HER2+ breast cancer has improved. However, management of metastatic disease in the brain and/or CNS – observed in up to 50% of HER2+ breast cancer patients – continues to be a clinical challenge in large part due to the inability of mAbs to sufficiently cross the blood-brain barrier. Although small-molecule inhibitors of HER2 exist and have been clinically approved, their single-agent efficacy in the context of metastatic disease to the brain has been limited. While HER2-targeted therapy in combination with conventional agents has shown some promise for the treatment of patients with metastatic breast cancer, control of brain metastases remains a significant unmet clinical need, as most patients survive less than two years following CNS involvement. Recent advances in cellular immunotherapy approaches have underscored the potential for potent antitumor immune responses and clinical benefit against solid cancers, and these approaches may be effective in the treatment of HER2+ cancers – in particular breast cancer – that have metastasized to the brain. Likewise, HER2 has been suggested as a suitable target for GBM, wherein elevated HER2 protein levels have been correlated with impaired survival. CAR T cell immunotherapy is being actively investigated for the treatment of solid tumors, including HER2+ cancers. Our academic partners at COH have developed a second-generation HER2-specific CAR T cell therapy for the treatment of brain and/or leptomeningeal metastases from HER2+ cancers, as well as for the treatment of refractory/relapsed HER2+ GBM. COH’s preclinical data demonstrate effective targeting of breast cancer brain metastases with intraventricular delivery of CAR T cells expressing HER2-CARs that contain the 4-1BB costimulatory domain. COH is evaluating the safety of this HER2-specific CAR T cell therapy in two ongoing Phase 1 clinical trials that commenced in the fourth quarter of 2018 (ClinicalTrials.gov Identifier: NCT03389230 for HER2+ GBM; ClinicalTrials.gov Identifier: NCT03696030 for HER2+ brain metastases). MB-105 (PSCA CAR T for Prostate & Pancreatic Cancers) PSCA is a glycosylphosphatidylinositol-anchored cell membrane glycoprotein. In addition to being highly expressed in the prostate it is also expressed in the bladder, placenta, colon, kidney, and stomach. This gene is upregulated in a large proportion of prostate cancers and is also detected in cancers of the bladder and pancreas. The gene includes a polymorphism that results in an upstream start codon in some individuals; this polymorphism is thought to be associated with a risk for certain gastric and bladder cancers. Prostate cancer may be amenable to T cell-based immunotherapy since several tumor antigens, including prostate stem-cell antigen (“PSCA”), are widely overexpressed in metastatic disease. Our academic partners at COH have developed a second-generation PSCA-specific CAR T cell therapy that has demonstrated robust in vitro and in vivo anti-tumor activity in patient-derived, clinically relevant, bone-metastatic prostate cancer xenograft models. COH is evaluating the safety of this PSCA-specific CAR T cell therapy in an ongoing Phase 1 trial treating patients with PSCA+ metastatic castration-resistant prostate cancer (ClinicalTrials.gov Identifier: NCT03873805). In October 2020,we announced initial data from this Phase 1 clinical trial in patients with PSCA-positive castration-resistance prostate cancer (“CRPC”). In the presentation at the 2020 Annual Prostate Cancer Foundation Scientific Retreat, the COH principal investigator reported results from a highly refractory patient treated with MB-105 who experienced a 94 percent reduction in prostate-specific antigen (“PSA”), a nearly complete reduction of measurable soft tissue metastasis by computerized tomography, and improvement in bone metastases by magnetic resonance imaging. MB-109: Combination MB-101 (IL13Rα2 CAR T Cell Program for Glioblastoma) and MB-108 (HSV-1 oncolytic virus C134) as a Potential Treatment for IL13Rα2+ Relapsed or Refractory Glioblastoma (GBM) and Anaplastic Astrocytoma (AA). An attractive novel approach to control glioblastoma is adoptive cellular immunotherapy utilizing CAR T cells. CAR T cells can be engineered to recognize very specific antigenically distinct tumor populations and to migrate through the brain parenchyma to kill malignant cells. In addition, oncolytic viruses (“OVs”) have been developed to effectively infect and kill cancer cells in the tumor, as well as modify the microenvironment to increase tumor immunogenicity and immune cell trafficking within the tumor. Due to these properties, OVs have been studied in combination with other treatments to enhance the effectiveness of immunotherapies. 10 ​ Table of Contents Preliminary anti-tumor activity has been observed in clinical studies administering the OV (MB-108) and CAR T cell therapy (MB-101) as single agents; however, the combination has not yet been explored. To determine if the combination of both therapies will result in a synergistic effect, investigators from COH developed preclinical studies in orthotopic GBM models in nude mice. Dr. Christine Brown from City of Hope presented these preclinical studies at the American Association for Cancer Research 2022 annual meeting. It was observed that co-treatment with C134 OV and IL13Rα2-directed CAR-T cells gave no adverse reaction and, more notably, that pre-treatment with C134 re-shaped the tumor microenvironment by increasing immune cell infiltrates and enhanced the efficacy of sub-therapeutic doses of CAR-T cell therapy delivered either intraventricularly or intratumorally. These preclinical studies aimed to provide a deeper understanding of this combination approach to support the potential benefit of a combination study that will evaluate C134 OV (MB-108) and IL13Rα2-directed CAR-T cells (MB-101). We received Pre-IND Written Responses from the FDA in May 2022, and we expect to file an IND for the combination trial of C134 oncolytic virus (MB-108) and IL13Rα2-directed CAR- T cells (MB-101) in 2023. In the planned Phase 1 clinical study, we intend to evaluate the combination of CAR-T cells (MB-101) and the C134 oncolytic virus (MB-108) in patients with IL13Rα2+ high-grade gliomas. The proposed design of this study will investigate increasing doses of intratumorally administered MB-108 followed by dual intratumoral (ICT) and intraventricular (ICV) administration of MB-101. ​ MB-101 (IL13Rα2 CAR T Cell Program for Glioblastoma) ​ GBM is the most common brain and central nervous system (“CNS”) cancer, accounting for 49.1% of malignant primary brain and CNS tumors, 54% of all gliomas, and 16% of all primary brain and CNS tumors. More than 13,000 new glioblastoma cases were predicted in the U.S. for 2022. Malignant brain tumors are the second leading cause of cancer-related deaths in adolescents and young adults aged 15-39 and the most common cancer occurring among 15-19-year-olds in the U.S. While GBM is a rare disease [2-3 cases per 100,000 persons per year in the U.S. and European Union (“EU”)], it is quite lethal, with five-year survival rates historically under 10%. Standard of care therapy consists of maximal surgical resection, radiation, and chemotherapy with temozolomide, which, while rarely curative, is shown to extend median overall survival from 4.5 to 15 months. GBM remains difficult to treat due to the inherent resistance of the tumor to conventional therapies. Immunotherapy approaches targeting brain tumors offer promise over conventional treatments. IL13R α 2 is an attractive target for CAR T therapy, as it has limited expression in normal tissue but is overexpressed on the surface of greater than 50% of GBM tumors. CAR-T cells are designed to express membrane-tethered IL-13 receptor ligand (“IL-13”) mutated at a single site (glutamic acid at position 13 to a tyrosine; E13Y) with high affinity for IL13Rα2 and reduced binding to IL13Rα1 in order to reduce healthy tissue targeting (Kahlon KS et al. Cancer Research. 2004;64:9160-9166). We are developing an optimized CAR-T product incorporating enhancements in CAR-T design and T cell engineering to improve antitumor potency and T cell persistence. These include a second-generation hinge-optimized CAR containing mutations in the IgG4 linker to reduce off-target Fc interactions (Jonnalagadda M et al. Molecular Therapy. 2015;23(4):757-768.), a 4-1BB (CD137) co-stimulatory signaling domain for improved survival and maintenance of CAR T cells, and the extracellular domain of CD19 as a selection/tracking marker. In order to further improve persistence, either central memory T-cells (T CM ) or enriched CD62L+ naïve and memory T cells (T N/MEM ) are isolated and enriched. Our manufacturing process limits ex vivo expansion, which is designed to reduce T cell exhaustion and maintain a T CM or T N/MEM phenotype. Based on experiments with CAR-Ts in mouse xenograft models of GBM, these CAR-modified T CM and T N/MEM cells have been shown to be more potent and persistent than earlier generations of CAR-T cells. Our academic partners at COH have completed a Phase 1 study to assess the feasibility and safety of using T CM or T N/MEM enriched IL13Rα2-specific CAR-engineered T cells for clinical study participants with recurrent/refractory malignant glioma (ClinicalTrials.gov Identifier: NCT02208362). As of May 2022 COH had enrolled and treated 65 patients. Preliminary data for patients enrolled in Arm 2 of the protocol (the “Intracavitary Arm”) were presented at the annual meeting of the American Association for Cancer Research in April 2018. The data indicated that the CAR-T cells were well tolerated, and no dose-limiting toxicities had been observed. In 2016 COH reported that a patient had achieved a complete response to treatment based on the imaging and clinical features set forth by the Response Assessment in Neuro-Oncology Criteria (“RANO”). This result was published as a case report in the New England Journal of Medicine (Brown CE et al. NEJM. 2016;375:2561-9). As described in the paper, this patient diagnosed with recurrent multifocal glioblastoma received multiple infusions of IL13Rα2-specific CAR-T cells over 220 days through two intracranial delivery routes – infusions into the resected tumor cavity followed by infusions into the ventricular system. Intracranial infusions of IL13Rα2-targeted CAR-T cells were not associated with any toxic effects of grade 3 or higher. After CAR-T cell treatment, regression of all intracranial and spinal tumors was observed, along with corresponding increases in levels of cytokines and immune cells in the cerebrospinal fluid. This clinical response was sustained for 7.5 months after the initiation of CAR T-cell therapy; however, the patient’s disease eventually recurred at four new locations that were distinct and non-adjacent to the original tumors, and biopsy of one of these lesions showed decreased expression of IL13Rα2. With 11 ​ Table of Contents enrollment in this Phase 1 study completed, COH has established the recommended Phase 2 dose, schedule and route of administration, as well as the optimal T cell selection. Results from this COH study have laid the foundation for 3 new MB-101 studies: 1. MB-101 with or without nivolumab and ipilimumab in treating patients with recurrent or refractory glioblastoma (currently enrolling patients; ClinicalTrials.gov Identifier: NCT04003649) sponsored by COH; 2. MB-101 in treating patients with recurrent or refractory glioblastoma with a substantial component of leptomeningeal disease (currently enrolling patients; ClinicalTrials.gov Identifier: NCT04661384) sponsored by COH; 3. MB101 in combination with the C134 oncolytic virus (MB108) in treating patients with recurrent or refractory glioblastoma or anaplastic astrocytoma (IND filing expected in 2023). This combination therapy, to be administered in a phase 1 two-center trial under Mustang IND, will be referred to as MB-109. Technology to Convert GBM from an Immunologically Cold Tumor to an Immunologically Hot Tumor MB-108 (HSV-1 oncolytic virus C134) MB-108 is a next-generation oncolytic herpes simplex virus (“oHSV”) that is conditionally replication competent; that is, it can replicate in tumor cells, but not in normal cells, thus killing the tumor cells directly through this process. Replication of C134 in the tumor itself not only kills the infected tumor cells but causes the tumor cell to act as a factory to produce new virus. These virus particles are released as the tumor cell dies and can then proceed to infect other tumor cells in the vicinity and continue the process of tumor kill. In addition to this direct oncolytic activity, the virus promotes an immune response against surviving tumor cells, which increases the antitumor effect of the therapy. The virus expresses a gene from another virus from the same overall virus family, human cytomegalovirus, which allows it to replicate better in the tumor cells than its first-generation predecessors. However, the virus has also been genetically engineered to minimize the production of any toxic effects for the patient receiving the therapy. To improve this virus over its first-generation predecessors, modifications have focused on improving viral replication and spread within the tumor bed and on enhancing bystander damage to uninfected tumor cells. These effects cumulatively should result in converting an immunologically cold tumor to an immunologically hot tumor, which Mustang anticipates will increase the efficacy of its IL13Rα2-directed CAR T for the treatment of GBM and anaplastic astrocytoma. UAB is the clinical trial site for the Phase 1 trial of MB-108, and the site has initiated a Phase 1 trial that began enrolling patients in 2019 (ClinicalTrials.gov Identifier: NCT03657576). The primary objective of this study is to determine the safety and tolerability of stereotactic intracerebral injections of escalating doses of MB-108 and to determine the maximally tolerated dose (“MTD”) of the oncolytic virus. Secondary objectives are to obtain preliminary information about the potential benefit of MB-108 in the treatment of patients with recurrent malignant gliomas, including relevant data on markers of efficacy, including time to tumor progression and patient survival. This trial has been on clinical hold since September 2022 due to toxicity, and UAB expects FDA clearance in 2023 in order to resume enrolling patients at a lower dose level. In Vivo CAR T Platform Technology Mustang is collaborating with the Mayo Clinic to develop a novel technology that may be able to transform the administration of CAR T therapies and potentially be used as an off-the-shelf therapy. The technology, developed by Larry R. Pease, Ph.D., principal investigator and former director of the Center for Immunology and Immune Therapies at Mayo Clinic, is a new platform to administer CAR T therapy using a two-step approach. First, a peptide is administered to the patient to drive the proliferation of the patient’s resident T cells. This is followed by the administration of a viral CAR construct directly into the lymph nodes of the patient. In turn, the viral construct infects the activated T cells and effectively forms CAR T cells in vivo in the patient. Successful implementation may lead to an off-the-shelf product with no need to isolate and expand patient T cells ex vivo . Preclinical proof-of-concept has been established, and the ongoing development of this technology will take place at Mayo Clinic. Mustang plans to file an IND application for a multicenter Phase 1 clinical trial once a lead construct has been identified. ​ 12 ​ Table of Contents Gene Therapies for Rare Genetic Disorders MB-107 and MB-207 (Ex vivo Lentiviral Therapy for X-linked Severe Combined Immunodeficiency (XSCID)) XSCID is a rare genetic immune system condition that occurs almost exclusively in males, in which affected patients do not live beyond infancy without treatment. Mustang Bio’s first-in-class ex vivo lentiviral gene therapy for XSCID has been administered as two distinct cellular products using the same lentiviral vector in two phase 1/2 clinical trials: (1) an ongoing multicenter trial of MB-107 in newly diagnosed patients being led by St. Jude and including also UCSF Benioff Children’s Hospital San Francisco (“UCSF”) and Seattle Children’s Hospital (“Seattle Children’s”) (ClinicalTrials.gov Identifier: NCT01512888) and (2) a single center trial of MB-207 at the NIH in patients who have previously undergone hematopoietic stem cell transplantation (ClinicalTrials.gov Identifier: NCT01306019). MB-207 (previously transplanted patients): The last peer-reviewed presentation by the NIH Principal Investigator, Dr. Harry Malech, occurred at the 61st Annual Meeting of the American Society of Hematology (“ASH”) in December 2019, at which time 24 patients had been treated in total. Eleven patients under the age of two years had been treated at St. Jude and UCSF and thirteen patients 3 to 34 years of age had been treated at the NIH . The existing data from these 24 patients were encouraging. In the initial stage of accrual to the Phase 1/2 NIH trial, eight patients (referred to as Cohort A) were followed for 3 to 7 years. Among Cohort A, seven patients aged 3 to 23 years increased host T cells chimerism from 0-2% to 28-93% and had normal T cell proliferation response. These seven patients also normalized their IgM levels, and four of these patients were able to discontinue immunoglobulin replacement therapy. In addition, gradual clinical benefit was observed in the clearance of chronic norovirus and associated abdominal complaints, malabsorption, and growth retardation, with six of seven affected patients being cured of their disease. Five of six patients resolved their protein-losing enteropathy. While the Cohort A results were impressive, the relatively inefficient transduction of hematopoietic stem/progenitor cells (“HSPCs”) required large quantities of vector. This resulted in relatively low vector copy number in myeloid cells in some patients, with delayed immune cell recovery and persistent clinical disease, especially in the last patient treated (patient 8). To address this, NIH developed a refined enhanced transduction (“ET”) procedure and incorporated two transduction enhancers: LentiBOOST™ 1mg/mL and dimethyl prostaglandin 2 (dmPGE2; 1µM) into the manufacturing process from MB-207. In addition to the Cohort A results, the NIH presentation at the 2019 ASH Annual Meeting included data from six ET patients (referred to as Cohort B) treated from February to June 2019, including re-treatment of patient 8. Prior to undergoing gene therapy, the patients, who were aged 12 to 36 years, had significant problems with donor T cell infiltration of liver, bone marrow and kidneys and had nearly absent B and NK cells. The ET procedure achieved much greater transduction efficiencies than were observed in Cohort A, with greater than 10-fold less vector, and resulted in faster immune reconstitution and more significant clinical benefit by 3 months. As noted by the investigators, longer follow-up will be required to know if the increased vector marking using the ET regimen will prove to be stable and safe long term. In all NIH patients, the low-dose, nonmyeloablative busulfan pretreatment conditioning was well tolerated, and of a low enough intensity to avoid the need for transfusions of red blood cells or platelets. No evidence of malignant transformation was observed. In a press release dated February 2, 2021, we further disclosed that, of the 6 Cohort A patients who were alive at the time of the 2019 NIH data readout and who did not undergo repeat therapy, 3 patients were able to discontinue chronic intravenous immunoglobulin (IVIG) and experienced sustained restoration of humoral responses to immunization. The remaining 3 patients had reduced IVIG requirements. All chronic norovirus infections were resolved, and the quality of life of all patients had improved significantly. The original 6 patients in Cohort B also continued to do well, with the longest follow-up being 22 months. Two additional patients were successfully treated with transduction enhancers, for a total of 8 patients in Cohort B. As was the case in Cohort A, no serious adverse events related to treatment were reported other than hematologic related to low-dose busulfan conditioning, and there was no evidence of malignant transformation. As a result of the study stopping rules, the NIH study was suspended in 2022 due to the presence of clonal expansion in the myeloid lineage in 10% of the treated patients, although to date there have been no observations of insertional mutagenesis or malignancies. All patients continue to be followed and remain clinically stable with no significant hematological anomalies. Upon review of these data, the FDA agree that the risk-benefit ration of both MB-107 and MB-207 remains favorable to support moving forward with the Mustang-sponsored multicenter clinical trials once Mustang has appropriately addressed other items flagged by the Agency. The IND for MB-207 was submitted to the FDA in December 2021. In January 2022, the FDA issued a clinical hold, pending additional CMC data. In order to lift this clinical hold and receive an FDA safe-to-procced for the IND, we believe the most critical activities will be 13 ​ Table of Contents to (1) perform process validation manufacturing runs using healthy donor material and (2) ensure qualification of all assays related to the product release. Following completion of these activities and the earliest release of the clinical hold by FDA, we expect to enroll the first patient in a pivotal multicenter Phase 2 clinical trial in 2023. ​ MB-207 received Orphan Drug Designation from the FDA in September 2020. The FDA also granted Rare Pediatric Disease Designation for MB-207 in August 2020. If Mustang’s BLA for MB-207 is approved, the Company may be eligible to receive a priority review voucher for this product as well, which can also be redeemed to obtain priority review for any subsequent marketing application and may be sold or transferred. The European Medicines Agency (“EMA”) granted Advanced Therapy Medicinal Product (“ATMP”) classification to MB-207 in April 2020 and Orphan Drug designation in April 2021. ​ MB-107 (newly diagnosed patients): ​ Interim Phase 1/2 data on treatment of newly diagnosed infants under the age of two with the same LV vector used in MB-107 were updated at an oral presentation at the American Society of Gene & Cell Therapy (“ASGCT”) 25 th Annual Meeting held from May 16-19, 2022. The data included 23 infants with XSCID treated with the LV vector at a median age of 3 months (range: 2 months to 14 months) with a median follow-up of 2.4 years (range: 1.4 months to 5.4 years), making it the largest known cohort of infants treated with LV gene therapy with the longest follow-up. Transduced autologous bone marrow CD34+ cells were generated for all patients with a median vector copy number (VCN) of 0.81/cell (range: 0.16-1.81), and a median CD34+ cell dose of 9.61x10 6 /kg (range 4.40-18.95). Prior to the infusion of cells, patients received busulfan targeted to a cumulative area-under-the-curve (cAUC) of 22 mg*hr/L. Severe adverse events occurred in three patients (two patients with pancytopenia and hemolytic anemia, and one patient with delayed neutrophil engraftment), and all resolved. ​ Seventeen of 18 patients with a follow-up of > 6 months achieved robust immune reconstitution [median CD3+ 2,545/µL, CD4+ 1,568/µL, CD4+/CCR7+/CD45R0- 1,416/µL]. In these 17 patients, T cells matured appropriately as assessed by normal T cell receptor excision circles (TRECs) and TCRvβ repertoire diversity and were functional as judged by phytohemagglutinin activation (“PHA”). All patients were alive with stable vector marking in all cell lineages. In addition, 15 patients had discontinued intravenous immunoglobulin, and 12 patients had been successfully immunized. No evidence of clonal expansion or malignant transformation was observed. ​ The MB-107 timeline has been extended due to unanticipated issues related to the materials used in manufacturing. These issues were communicated to the FDA and the Company received a written response on August 26, 2022. The FDA response provided additional direction enabling us to effectively continue to work with our outside suppliers. We are working towards enrolling the first patient in a pivotal multicenter Phase 2 clinical trial under our IND in 2023. ​ MB-107 received Orphan Drug Designation in August 2020 and Rare Pediatric Disease and Regenerative Medicine Advanced Therapy (“RMAT”) designations in August 2019. Finally, the FDA designated MB-107 a Rare Pediatric Disease in August 2020. ​ The FDA grants Rare Pediatric Disease Designation for serious and life-threatening diseases that primarily affect children ages 18 years or younger and affect fewer than 200,000 people in the United States. If Mustang’s BLA for MB-107 is approved, the Company may be eligible to receive a priority review voucher, which can be redeemed to obtain priority review for any subsequent marketing application and may be sold or transferred. This program is intended to encourage development of new drugs and biologics for the prevention and treatment of rare pediatric diseases. ​ The EMA, granted Priority Medicines (“PRIME”) designation to MB-107 in July 2021, and ATMP classification to MB-107 in April 2020 and Orphan Drug designation in November 2020. MB-110 (Ex vivo Lentiviral Therapy for RAG1 Severe Combined Immunodeficiency (SCID)) Under an exclusive license and in partnership with LUMC, MB-110, a first-in-class ex vivo treatment for RAG1 SCID, is under development. Severe combined immunodeficiency (“SCID”) due to complete recombinase-activating gene-1 (RAG1) deficiency is a rare, genetic disorder due to null mutations in the RAG1 gene resulting in less than 1% of wild type V(D)J recombination activity. Neonatal patients present with life-threatening, severe, recurrent infections by opportunistic fungal, viral and bacterial micro-organisms, as well as skin rashes, chronic diarrhea, failure to thrive and fever. Immunologic observations include profound T and B cell lymphopenia, low or absent serum immunoglobulins, and normal natural killer cell counts. As is the case with other types of SCID, RAG1-SCID is fatal in infancy unless immune reconstitution is achieved with hematopoietic stem cell transplantation (HSCT). MB-110, which includes low-dose conditioning prior to reinfusion of the patients’ own gene-modified blood stem cells, is currently being evaluated in a Phase 1/2 multicenter clinical trial in Europe. The ongoing clinical trial has enrolled its first patient, and additional clinical 14 ​ Table of Contents sites are expected to be added in the near future. The RAG1-SCID program has been granted Orphan Drug Designation by the European Medicines Agency. ​ Mustang also established an ongoing partnership with Frank J. Staal, Ph.D., professor of Molecular Stem Cell Biology and molecular immunologist at LUMC, whose laboratory developed the MB-110 therapy. Dr. Staal will continue the development of additional LV gene therapies in his lab, to which Mustang Bio has rights under the agreement. INTELLECTUAL PROPERTY AND PATENTS General Our goal is to obtain, maintain and enforce patent protection for our products, formulations, processes, methods and other proprietary technologies, preserve our trade secrets, and operate without infringing on the proprietary rights of other parties, both in the U.S. and in other countries. Our policy is to actively seek to obtain, where appropriate, the broad intellectual property protection for our product candidates, proprietary information and proprietary technology through a combination of contractual arrangements and patents, both in the U.S. and elsewhere in the world. We also depend upon the skills, knowledge and experience of our scientific and technical personnel, as well as that of our advisors, consultants and other contractors (“know-how”). To help protect our proprietary know-how which is not patentable, and for inventions for which patents may be difficult to enforce, we rely on trade secret protection and confidentiality agreements to protect our interests. To this end, we require all employees, consultants, advisors and other contractors to enter into confidentiality agreements which prohibit the disclosure of confidential information and, where applicable, require disclosure and assignment to us of the ideas, developments, discoveries and inventions that they generate or make, and which are important to our business. Patents and other proprietary rights are crucial to the development of our business. We will be able to protect our proprietary technologies from unauthorized use by third parties only to the extent that our proprietary rights are covered by valid and enforceable patents, supported by regulatory exclusivity or are effectively maintained as trade secrets. We have a few patents and patent applications related to our compounds and other technology, but we cannot guarantee the scope of protection of the issued patents, or that such patents will survive a validity or enforceability challenge, or that any of the pending patent applications will issue as patents. Generally, patent applications in the U.S. are maintained in secrecy for a period of 18 months or more. The patent positions of biotechnology and pharmaceutical companies are highly uncertain and involve complex legal and factual questions. Therefore, we cannot predict the breadth of claims allowed in biotechnology and pharmaceutical patents, or their enforceability. To date, there has been no consistent policy regarding the breadth of claims allowed in biotechnology patents. Third parties or competitors may challenge or circumvent our patents or patent applications, if issued. If our competitors prepare and file patent applications in the U.S. that claim technology also claimed by us, we may have to participate in interference or derivation proceedings declared by the U.S. Patent and Trademark Office (“USPTO”) to determine priority of invention, which could result in substantial cost, even if the eventual outcome is favorable to us. Because of the extensive time required for development, testing and regulatory review of a potential product, it is possible that before we commercialize any of our products, any related patent may expire or remain in existence for only a short period following commercialization, thus reducing any advantage of the patent. However, the life of a patent covering a product that has been subject to regulatory approval may have the ability to be extended through the patent restoration program, although any such extension could still be minimal. Additionally, statutory caps impose further limitation on any such extensions. If a patent is issued to a third party containing one or more preclusive or conflicting claims, and those claims are ultimately determined to be valid and enforceable, we may be required to obtain a license, if available, under such patent or to develop or obtain alternative technology. In the event of litigation involving a third party claim, an adverse outcome in the litigation could subject us to significant liabilities to such third party, require us to seek a license for the disputed rights from such third party, and/or require us to cease use of the technology. Further, our breach of an existing license or failure to obtain a license to technology required to commercialize our products may seriously harm our business. We also may need to commence litigation to enforce any patents issued to us or to determine the scope and validity of third party proprietary rights. Litigation would not only involve substantial costs but would also involve substantial time commitments on the part of our key executives and research and development personnel. In March 2015, we licensed intellectual property related to CAR T technology from COH. The portfolio of rights licensed from COH now includes patents and application directed to CARs targeting IL13Rα2, CD123, CS1, HER2, and PSCA, as well as rights related to modified CAR hinge regions and methods of preparing CAR T cells in particular subpopulations of cell and administering CAR T cells. The intellectual property licensed thereunder relating to IL13Rα2-targeting CARs includes granted patents in the U.S., Australia, China, Europe, 15 ​ Table of Contents Russia, Japan, Hong Kong, Israel, and Mexico, and this patent family further includes pending applications in the U.S., Australia, Brazil, Canada, China, Europe, South Korea, Russia, Japan, Israel, Mexico, and New Zealand. Any patents issuing from the IL13Rα2-targeting CAR will expire no sooner than 2035. The licensed intellectual property relating to relating to CD123-targeting CARs includes issues patents in the U.S., China, Europe, Hong Kong, Israel, Japan, South Korea, and Mexico, and this patent family further includes pending applications in the U.S., Australia, Brazil, China, Europe, Hong Kong, Israel, Japan, South Korea, Mexico, and New Zealand. Any patents issuing from the CD123-targeting CAR will expire no sooner than 2033. The licensed intellectual property relating to relating to CS1-targeting CARs includes issues patents in the U.S., Australia, Israel, and Russia, as well as pending applications in the U.S., Australia, Brazil, Canada, China, Europe, Hong Kong, Israel, South Korea, Mexico, Japan, Russia, and New Zealand. Any patents issuing from the CS1-targeting CAR will expire no sooner than 2035, and some patents relating to particular methods involving CS1-targeting CARs will expire no sooner than 2038. The licensed intellectual property relating to relating to HER2-targeting CARs includes issues patents in Japan and Russia, as well as pending applications in the U.S., Australia, Brazil, Canada, China, Europe, Hong Kong, Israel, Japan, South Korea, Russia, Mexico, and New Zealand. Any patents issuing from the HER2-targeting CAR will expire no sooner than 2036. The licensed intellectual property relating to relating to PSCA-targeting CARs includes issues patents in Europe and Hong Kong, as well as pending applications in the U.S., Australia, Brazil, Canada, China, Europe, Hong Kong, Israel, Japan, South Korea, Russia, and New Zealand. The licensed intellectual property relating to relating modified CAR hinge regions includes issues patents in China, Europe, and Japan, as well as pending applications in the U.S., Australia, China, and Europe. The patents issuing from the modified CAR hinge region family will expire no sooner than 2034. The licensed intellectual property relating to relating to method of preparing or administering CAR T cells includes issues patents in China, Europe, and Japan, as well as pending applications in the U.S., Australia, Brazil, Canada, China, Europe, Hong Kong, Japan, Israel, Mexico, Russia, and New Zealand. The patents relating to these technologies will expire no sooner than 2035 or, in the case of the administration methods, 2036. Also, in March 2015, we executed a sponsored research agreement with COH, pursuant to which research is performed in the laboratory of Drs. Stephen Forman and Christine Brown. The sponsored research agreement gives us the right to first negotiation under specified maximum terms regarding any future inventions arising from the laboratory. In May 2017, we licensed intellectual property related to CAR T technology for targeting CD20 from Fred Hutch. The intellectual property includes an international application under the Patent Cooperation Treaty (i.e., a PCT application), which has now matured into several issued patents, including issued patents in the U.S. and Europe, as well as pending applications in the U.S., Australia, Brazil, Canada, China, Europe, Hong Kong, Israel, Japan, South Korea, Mexico, New Zealand, and Russia. These applications contain claims relating to various CD20-targeting CAR constructs and CAR T cells, as well as methods of making and using the same. The national stage applications claiming priority to the PCT application were filed in May 2018 in order to begin substantive examination of the claims. Patents maturing from these national stage applications will expire no sooner than March 2037. In March 2017, we licensed intellectual property related to antibodies and binding agents that specifically bind to PSCA from the University of California Los Angeles (“UCLA”). The intellectual property includes multiple granted patents and pending applications from around the world including the U.S., Europe, Japan, China, and Canada. The granted patents and patents maturing from the pending applications will expire no sooner than March 2027. In August 2018, we licensed from St. Jude Children’s Research Hospital XSCID Technology related to an ex vivo lentiviral vector gene therapy program to provide a normal copy of the IL2RG gene to patients born with XSCID. In February 2019, we licensed Material and Technical Information related to the HSV-1 oncolytic virus C134 from Nationwide in Columbus, Ohio. In August 2019, we licensed from CSL Behring (Calimmune) the Cytegrity TM stable producer cell line developed and used by St. Jude. The Cytegrity TM stable producer cell line will be used to produce the viral vector for MB-107. In September 2020, we entered into an exclusive, worldwide licensing agreement with SIRION Biotech for the rights to SIRION’s LentiBOOST TM technology for the development of MB-207. This license includes right to granted patents and pending applications in the U.S., Europe, Japan, and Israel. In December 2021 this licensing agreement was amended to include CD20-directed CAR Ts in addition to lentiviral stem cell gene therapy for the treatment of XSCID. ​ In November 2021, we entered into an exclusive, worldwide licensing agreement with Leiden University Medical Centre for a first-in-class ex vivo lentiviral gene therapy for the treatment of RAG1 severe combined immunodeficiency (“RAG1-SCID”). In August 2021, we entered into an exclusive license agreement with Mayo Clinic for a novel technology that may be able to transform the administration of CAR T therapies and potentially allow such therapies to be used as an off-the-shelf therapy. 16 ​ Table of Contents In addition to the technology the Company has in-licensed, Mustang has also developed its own proprietary intellectual property, both alone and in conjunction with COH. In particular, Mustang filed a U.S. provisional application directed to optimized methods for manufacturing cell-based therapeutics, and Mustang and COH, as co-applicants, filed a U.S. provisional application directed to methods of treating hematological cancers. In addition to the technology the company has in-licensed, Mustang has also developed its own proprietary intellectual property, both alone and in conjunction with COH. In particular, Mustang owns pending applications in the U.S. and Europe directed to methods for manufacturing cell-based therapeutics, and pending applications in the U.S., Taiwan, and PCT relating to anti-idiotype antibodies. Mustang and COH also own as co-applicants pending application in the U.S., Taiwan, and PCT directed to methods of treating hematological cancers with a combination therapy. Other Intellectual Property Rights We depend upon trademarks, trade secrets, knowhow and continuing technological advances to develop and maintain our competitive position. To maintain the confidentiality of trade secrets and proprietary information, we require our employees, scientific advisors, consultants and collaborators, upon commencement of a relationship with us, to execute confidentiality agreements and, in the case of parties other than our research and development collaborators, to agree to assign their inventions to us. These agreements are designed to protect our proprietary information and to grant us ownership of technologies that are developed in connection with their relationship with us. These agreements may not, however, provide protection for our trade secrets in the event of unauthorized disclosure of such information. In addition to patent protection, we may utilize orphan drug regulations or other provisions of the Food, Drug and Cosmetic Act of 1938, as amended (the “FDCA”), to provide market exclusivity for certain of our product candidates. Orphan drug regulations provide incentives to pharmaceutical and biotechnology companies to develop and manufacture drugs for the treatment of rare diseases, currently defined as diseases that exist in fewer than 200,000 individuals in the U.S., or diseases that affect more than 200,000 individuals in the U.S. but for which the sponsor does not realistically anticipate will generate a net profit. Under these provisions, a manufacturer of a designated orphan drug can seek tax benefits, and the holder of the first approval of a designated orphan product from the FDA will be granted a seven-year period of marketing exclusivity for such FDA approved orphan product. LICENSE, CLINICAL TRIAL AND SPONSORED RESEARCH AGREEMENTS St. Jude Children’s Research Hospital XSCID License On August 2, 2018, the Company entered into an exclusive worldwide license agreement with St. Jude for the development of a first-in-class ex vivo lentiviral gene therapy for the treatment of XSCID. The Company paid $1.0 million in consideration for the exclusive license in addition to an annual maintenance fee of $0.1 million (beginning in 2019). St. Jude is eligible to receive payments totaling $13.5 million upon the achievement of five development and commercialization milestones. Royalty payments in the mid-single digits are due on net sales of licensed products. XSCID Non-interventional Services Agreement In December 2019, the Company entered into a Non-Interventional Services Agreement with Children's CGMP, LLC ("Children’s"), an affiliate of St. Jude Children's Research Hospital, pursuant to which Children’s provides lentiviral vector for non-clinical XSCID research purposes, as well as related advisory services. Pursuant to the agreement, we agreed to fund approximately $0.8 million upon execution of the agreement. XSCID Data Transfer Agreement In June 2020, the Company entered into a Data Transfer Agreement for the XSCID program (the “XSCID DTA”). Pursuant to the terms of the XSCID DTA, we made an upfront payment of approximately $1.1 million and will reimburse St. Jude for additional costs in connection with the on-going investigator-initiated study. 17 ​ Table of Contents City of Hope In February 2017, the Company and COH amended and restated their license agreement, dated March 17, 2015 (the “Original Agreement”), by entering into three separate amended and restated exclusive license agreements, one relating to the CD123-directed CAR T program, one relating to the IL13Rα2-directed CAR T program, and one relating to the Spacer technology (described below). The total potential consideration payable to COH by the Company, in equity or cash, did not in the aggregate change materially from the Original Agreement. As of December 31, 2022, COH owns 845,385 shares of Class A common stock representing approximately 0.8% of ownership, and has the right to appoint a director to the Board of Directors (the “Board”). The Company considers COH to be a related party, due to the foregoing rights and ownership, as well as the high proportion of the Company’s assets that are licensed from COH. In addition, the Company entered into a sponsored research agreement with COH under which the Company has funded continued research in the amount of $2.0 million per year, payable in four equal installments, which ended in the first quarter of 2020. The research covered under this arrangement is for the IL13Rα2-directed CAR T program, the CD123-directed CAR T program, and the Spacer technology. CD123 License In February 2017, the Company entered into an Amended and Restated Exclusive License Agreement with COH to acquire intellectual property rights pertaining to patent rights related to the CD123-directed CAR T program (the “CD123 License”). Pursuant to the CD123 License, the Company and COH acknowledged that an upfront fee had already been paid under the Original Agreement. In addition, COH is eligible to receive an annual maintenance fee of $25,000 and milestone payments totaling up to approximately $14.5 million, upon and subject to the achievement of certain milestones. Royalty payments in the mid-single digits are due on net sales of licensed products. The Company is obligated to pay COH a percentage of certain revenues received in connection with a sublicense ranging from the mid-teens to mid-thirties, depending on the timing of the sublicense in the development of any product. In addition, equity grants made under the Original Agreement were acknowledged, and the anti-dilution provisions of the Original Agreement were carried forward. CD123 CRA (AML and BPDCN) In February 2017, the Company entered into a Clinical Research Support Agreement for CD123-directed CAR T program (the “CD123 CRA”). Pursuant to the terms of the CD123 CRA, the Company made an upfront payment of approximately $19,000 and will contribute an additional $97,000 per patient in connection with the on-going investigator-initiated study. Further, the Company agreed to fund approximately $76,000 annually pertaining to the clinical development of the CD123-directed CAR T therapy. IL13Rα2 License In February 2017, the Company entered into an Amended and Restated Exclusive License Agreement with COH to acquire intellectual property rights pertaining to patent rights related to the IL13Rα2-directed CAR T program (the “IL13Rα2 License”). Pursuant to the IL13Rα2 License, the Company and COH acknowledged that an upfront fee had already been paid under the Original Agreement. In addition, COH is eligible to receive an annual maintenance fee of $25,000 and milestone payments totaling up to approximately $14.5 million, upon and subject to the achievement of certain milestones. Royalty payments in the mid-single digits are due on net sales of licensed products. The Company is obligated to pay COH a percentage of certain revenues received in connection with a sublicense ranging from the mid-teens to mid-thirties, depending on the timing of the sublicense in the development of any product. In addition, equity grants made under the Original Agreement were acknowledged, and the anti-dilution provisions of the Original Agreement were carried forward. IL13Rα2 CRA (Glioblastoma) In February 2017, the Company entered into a Clinical Research Support Agreement for the IL13Rα2-directed CAR T program (the “IL13Rα2 GBM CRA”). Pursuant to the terms of the IL13Rα2 CRA, the Company made an upfront payment of approximately $9,000 and will contribute an additional $140,000 per patient in connection with the on-going investigator-initiated study. Further, the Company agreed to fund approximately $66,000 annually pertaining to the clinical development of the IL13Rα2-directed CAR T therapy. IL13Rα2 CRA (Leptomeningeal Glioblastoma) In October 2020, the Company entered into 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”). Pursuant to the terms of the IL13Rα2 Leptomeningeal CRA, the Company made an upfront payment of approximately $29,000 and will contribute an additional 18 ​ Table of Contents $150,000 per patient in connection with the on-going investigator-initiated study. Further, the Company agreed to fund approximately $200,000 annually pertaining to the clinical development of the IL13Rα2-directed CAR T therapy. Sponsored Research Agreement - IL13Rα2 and C134 Combination In October 2020, the Company entered into a Sponsored Research Agreement (“SRA”) with COH to conduct combination studies of a potential IL13Rα2 CAR and C134 oncolytic virus therapy. Pursuant to the SRA, the Company funded research in the amount of $0.3 million for the program. In November 2022, the SRA was amended to include additional funding of $0.6 million. Spacer License In February 2017, the Company entered into an Amended and Restated Exclusive License Agreement with COH to acquire intellectual property rights pertaining to patent rights related to Spacer (the “Spacer License”). Pursuant to the Spacer License, the Company and COH acknowledged that an upfront fee had already been paid under the Original Agreement. In addition, COH will receive an annual maintenance fee of $10,000. No royalties are due if the Spacer technology is used in conjunction with a CD123 CAR or an IL13Rα2 CAR, and royalty payments in the low single digits are due on net sales of licensed products if the Spacer technology is used in conjunction with other intellectual property. The Company is obligated to pay COH a percentage of certain revenues received in connection with a sublicense in the mid-thirties, but no such payments are due in connection with sublicenses that are granted in conjunction with the sublicense of other CARs that are licensed from COH to the Company. In addition, equity grants made under the Original Agreement were acknowledged, and the anti-dilution provisions of the Original Agreement were carried forward. IV/ICV License In February 2017, the Company entered into an exclusive license agreement (the “IV/ICV License”) with COH to acquire intellectual property rights in patent applications related to the intraventricular and intracerebroventricular methods of delivering T cells that express CARs. Pursuant to the IV/ICV License, in March 2017, the Company paid COH an upfront fee of $0.1 million. COH is eligible to receive a milestone payment totaling approximately $0.1 million, upon and subject to the achievement of a milestone, and an annual maintenance fee. Royalty payments in the low single digits are due on net sales of licensed products. The Company is obligated to pay COH a percentage of certain revenues received in connection with a sublicense in the mid-thirties, but no such payments are due in connection with sublicenses that are granted in conjunction with the sublicense of other CAR T programs that are licensed from COH to the Company. HER2 Technology License On May 31, 2017, the Company entered into an exclusive license agreement (the “HER2 Agreement”) with COH for the use of HER2 CAR T technology (“HER2 Technology”), which is currently being applied in the treatment of glioblastoma multiforme and in the treatment of HER2+ cancers – in particular breast cancer – that have metastasized to the brain. Pursuant to the HER2 Agreement, the Company paid an upfront fee of $0.6 million and owes an annual maintenance fee of $50,000 (which began in 2019). In addition, COH is eligible to receive milestone payments totaling up to $14.9 million, upon and subject to the achievement of certain milestones. Royalty payments in the mid-single digits are due on net sales of licensed products. The Company is obligated to pay COH a percentage of certain revenues received in connection with a sublicense ranging from the mid-teens to mid-thirties, depending on the timing of the sublicense in the development of any product. HER2 CRA (HER2+ glioblastoma and HER2+ brain metastases) In September 2020, the Company entered into a Clinical Research Support Agreement for the HER2-directed CAR T program (the “HER2 CRA”). Pursuant to the terms of the HER2 CRA, the Company made an upfront payment of approximately $29,000 and will contribute an additional $150,000 per patient in connection with the on-going investigator-initiated study. Further, the Company agreed to fund approximately $200,000 annually pertaining to the clinical development of the HER2-directed CAR T therapy. CS1 Technology License On May 31, 2017, the Company entered into an exclusive license agreement (the “CS1 Agreement”) with COH for the use of CS1-specific CAR T technology (“CS1 Technology”), which is currently being applied in the treatment of multiple myeloma. Pursuant to the CS1 Agreement, the Company paid an upfront fee of $0.6 million and owes an annual maintenance fee of $50,000 (which began in 2019). In addition, COH is eligible to receive milestone payments totaling up to $14.9 million, upon and subject to the achievement of certain milestones. Royalty payments in the mid-single digits are due on net sales of licensed products. The Company is obligated to pay COH 19 ​ Table of Contents a percentage of certain revenues received in connection with a sublicense ranging from the mid-teens to mid-thirties, depending on the timing of the sublicense in the development of any product. CS1 CRA (multiple myeloma) In June 2020, the Company entered into a Clinical Research Support Agreement for the CS1-directed CAR T program (the “CS1 CRA”). Pursuant to the terms of the CS1 CRA, the Company made an upfront payment of approximately $32,000 and will contribute an additional $130,000 per patient in connection with the on-going investigator-initiated study. Further, the Company agreed to fund approximately $200,000 annually pertaining to the clinical development of the CS1-directed CAR T therapy. PSCA Technology License On May 31, 2017, the Company entered into an exclusive license agreement (the “PSCA Agreement”) with COH for the use of PSCA CAR T technology (“PSCA Technology”), which is currently being applied in the treatment of PSCA+ metastatic castration-resistant prostate cancer. Pursuant to the PSCA Agreement, the Company paid an upfront fee of $0.3 million and owes an annual maintenance fee of $50,000 (which began in 2019). In addition, COH is eligible to receive milestone payments totaling up to $14.9 million, upon and subject to the achievement of certain milestones. Royalty payments in the mid-single digits are due on net sales of licensed products. The Company is obligated to pay COH a percentage of certain revenues received in connection with a sublicense ranging from the mid-teens to mid-thirties, depending on the timing of the sublicense in the development of any product. PSCA CRA In October 2020, the Company entered into a Clinical Research Support Agreement for the PSCA-directed CAR T program (the “PSCA CRA”). Pursuant to the terms of the PSCA CRA, the Company made an upfront payment of $33,000 and will contribute an additional $125,000 per patient in connection with the on-going investigator-initiated study. Further, the Company agreed to fund approximately $200,000 annually pertaining to the clinical development of the PSCA-directed CAR T therapy. Manufacturing License On January 3, 2018, the Company entered into a non-exclusive license agreement with COH to acquire patent and licensed know-how rights related to developing, manufacturing, and commercializing licensed products. The Company paid $75,000 in consideration for the licenses to the patent rights and the licensed know-how in addition to an annual maintenance fee. Royalty payments in the low-single digits are due on net sales of licensed products. Sponsored Research Agreement - Manufacturing On January 3, 2018, the Company entered into an SRA with COH to optimize and develop CAR T cell processing procedures. Pursuant to the SRA, the Company funded continued research in the amount of $0.9 million for the program, with an initial term of two (2) years. The SRA expired in January 2020. University of California License On March 17, 2017, the Company entered into an exclusive license agreement with the Regents of UCLA (the “UCLA License”) to acquire intellectual property rights in patent applications related to the engineered anti-prostate stem cell antigen antibodies for cancer targeting and detection. Pursuant to the UCLA License, the Company paid UCLA the upfront fee of $0.2 million and owes an annual maintenance fee of $15,000 for the first two years, $25,000 for years three and four, and $50,000 per year thereafter. In addition, UCLA is eligible to receive milestone payments totaling up to $14.3 million, upon and subject to the achievement of certain milestones. Royalty payments in the mid-single digits are due on net sales of licensed products. Fred Hutchinson Cancer Center CD20 Technology License Effective July 3, 2017, Mustang entered into an exclusive, worldwide licensing agreement with Fred Hutch for the use of a CAR T therapy related to autologous T cells engineered to express a CD20-specific CAR (the “CD20 Technology License”). Pursuant to the CD20 Technology License, the Company paid Fred Hutch an upfront fee of $0.3 million and owes an annual maintenance fee of $50,000 on each 20 ​ Table of Contents anniversary of the license until the achievement by the Company of regulatory approval of a licensed product using the CD20 Technology. Additional payments are due for the achievement of eleven development milestones totaling $39.1 million. Royalty payments in the mid-single digits are due on net sales of licensed products. CD20 CTA (NHL and CLL) Also, on July 3, 2017, in conjunction with the CD20 Technology License from Fred Hutch, Mustang entered into 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 (“NHLs”). 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 for the treatment of five patients with chronic lymphocytic leukemia (“CLL”) and other research costs. In January 2022, the CTA was amended to increase funding by approximately $2.2 million for the treatment of additional patients. Sponsored Research Agreement On March 17, 2018, the Company entered into an SRA with Fred Hutch related to developing and optimizing processes and systems associated with CD20 cell processing. Pursuant to the SRA, the Company funded continued research in the amount of $0.6 million during the term of the SRA, which expired in March 2019. Nationwide Children’s Hospital License On February 20, 2019, the Company entered into an exclusive worldwide license agreement with Nationwide for the development of an oncolytic virus (referred to by Nationwide as C134; now referred to by the Company as MB-108) for the treatment of glioblastoma multiforme. The Company paid $0.2 million in consideration for the exclusive license. Nationwide is eligible to receive additional payments totaling $77.5 million upon the achievement of ten development and commercialization milestones. Royalty payments in the low-single digits are due on net sales of licensed products. CSL Behring (Calimmune) License On August 23, 2019, the Company entered into a non-exclusive license agreement with CSL Behring (Calimmune) for the Cytegrity TM stable producer cell line for the production of lentiviral gene therapy for the XSCID gene therapy program. The Cytegrit TM stable producer cell line will be used to produce the viral vector for Mustang’s MB-107 and MB-207 lentiviral gene therapies for the treatment of XSCID. The Company paid $0.2 million in consideration for the license. CSL Behring (Calimmune) is eligible to receive additional payments totaling $1.2 million upon the achievement of three development and commercialization milestones. Royalty payments in the low-single digits are due on net sales of licensed products. SIRION Biotech License On October 6, 2020, the Company announced a licensing agreement under which we acquired technology rights from SIRION Biotech GmbH (“SIRION”) for LentiBOOST™ technology for the development of MB-207, Mustang’s lentiviral gene therapy for the treatment of patients with XSCID, who have been previously treated with a hematopoietic stem cell transplantation (“HSCT”) and for whom re-treatment is indicated. LentiBOOST™ is SIRION’s proprietary non-cytotoxic transduction enhancer for lentiviral vectors. Pursuant to the agreement, the Company paid SIRION a one-time upfront fee of $0.1 million. In addition, SIRION is eligible to receive additional payments totaling up to approximately $9.1 million upon the achievement of certain development and commercialization milestones. Royalty payments in the low- to mid-single digits are due on aggregate cumulative worldwide net sales of licensed products. In December 2021 this licensing agreement was amended to include CD20-directed CAR Ts. SIRION is eligible to receive additional payments totaling up to approximately $9.1 million upon the achievement of certain development and commercialization milestones for the additional product. 21 ​ Table of Contents Minaris Regenerative Medicine Agreement On November 23, 2020, we announced an agreement with Minaris Regenerative Medicine GmbH (“Minaris”) to enable technology transfer and GMP clinical manufacturing in Europe of our MB-107 lentiviral gene therapy program for the treatment of XSCID. Under the terms of the agreement, Minaris will perform technology transfer of the manufacturing and analytical processes, as well as their adoption to the European regulatory environment, for the GMP-compliant manufacturing of the drug product at its site in Ottobrunn, Germany, with the goal of supplying clinical trials in Europe. In 2022, the Company made the decision to delay the technology transfer and clinical manufacturing processes. Mayo Clinic CAR T Technology License On August 12, 2021, we announced that the Company has executed an exclusive license agreement with Mayo Clinic for a novel technology that may be able to transform the administration of CAR T therapies and potentially allow such therapies to be used as an off-the-shelf therapy. The technology, developed by Larry R. Pease, Ph.D., principal investigator and former director of the Center for Immunology and Immune Therapies at Mayo Clinic, is a new platform to administer CAR T therapy using a two-step approach. First, a peptide is administered to the patient to drive the proliferation of the patient’s resident T cells. This is followed by the administration of a viral CAR construct directly into the lymph nodes of the patient. In turn, the viral construct infects the activated T cells and effectively forms CAR T cells in vivo in the patient. Successful implementation may lead to an off-the-shelf product with no need to isolate and expand patient T cells ex vivo. Preclinical proof-of-concept has been established, and the ongoing development of this technology will take place at Mayo Clinic. Mustang plans to file an Investigational New Drug (“IND”) application for a multicenter Phase 1 clinical trial once a lead construct has been identified. Pursuant to this agreement, the Company paid an upfront fee of $0.8 million and will pay an annual maintenance fee of $25,000. Additional payments are due for each of two licensed products for the achievement of eleven development and commercial milestones totaling up to $92.6 million per product, and royalty payments in the mid-single digits as a percentage of revenue are due on net sales of licensed products. Sponsored Research Agreement In connection with the Mayo Clinic license agreement, the Company entered into an SRA under which the Company will fund research in the amount of $2.1 million over a period of two years. In October 2022, the SRA was amended to include additional funding of $0.1 million. The research performed pursuant to this agreement will support the technology the Company has licensed from Mayo Clinic. Leiden University Medical Centre RAG1-SCID Technology License On November 10, 2021, we announced an exclusive license agreement with Leiden University Medical Centre (“LUMC”) for a first-in-class ex vivo lentiviral gene therapy for the treatment of RAG1 severe combined immunodeficiency (“RAG1-SCID”). Pursuant to this agreement, the Company paid an upfront fee of $0.4 million. Additional payments are due for the achievement of five development and commercial milestones totaling up to $31.0 million, and royalty payments in the low to mid-single digits as a percentage of revenue are due on net sales of licensed products. Sponsored Research Agreement In connection with the RAG1-SCID license, the Company entered into an SRA with LUMC under which the Company will fund research in the amount of 2.3 million euros over a period of five years. The research performed pursuant to this agreement will support the technology the Company has licensed from LUMC. 22 ​ Table of Contents COMPETITION Competition in the pharmaceutical and biotechnology industries is intense. Our competitors include pharmaceutical companies and biotechnology companies, as well as universities and public and private research institutions. In addition, companies that are active in different but related fields represent substantial competition for us. Many of our competitors have significantly greater capital resources, larger research and development staffs and facilities and greater experience in drug development, regulation, manufacturing and marketing than we do. These organizations also compete with us to recruit qualified personnel, attract partners for joint ventures or other collaborations, and license technologies that are competitive with ours. To compete successfully in this industry, we must identify novel and unique drugs or methods of treatment and then complete the development of those drugs as treatments in advance of our competitors. The drugs that we are attempting to develop will have to compete with existing therapies. In addition, a large number of companies are pursuing the development of pharmaceuticals that target the same conditions that we are targeting. Other companies have products or product candidates in various stages of pre-clinical or clinical development, or with marketing approvals, to treat conditions for which we are also seeking to discover and develop product candidates. Some of these potential competing drugs are further advanced in development than our product candidates and may be commercialized earlier. The field of CAR T therapy is extremely active. Companies and partnerships currently engaged in clinical trials with CAR T modalities include Bristol Myers Squibb, Novartis Pharmaceuticals/University of Pennsylvania, 2seventy bio, Allogene Therapeutics, Cellectis, Gilead Sciences, Bellicum Pharmaceuticals, MD Anderson/Ziopharm Oncology, Atara Biotherapeutics, Celyad, Autolus Therapeutics, Precigen Inc., Precision BioSciences, Adicet Bio, Cargo Therapeutics, and ImmPACT Bio. The gene therapy field is characterized by rapidly changing technologies, significant competition and a strong emphasis on intellectual property. We are aware of companies currently engaged in developing gene therapies in various indications, including Abeona Therapeutics, Adverum Biotechnologies, Astellas, AVROBIO, Axovant Sciences, Biogen, bluebird bio, BioMarin Pharmaceutical, Homology Medicines, Krystal Biotech, MeiraGTx, Novartis Pharmaceuticals, Orchard Therapeutics, Passage Bio, Prevail Therapeutics, REGENXBIO, Rocket Pharmaceuticals, Roche, Sangamo Therapeutics, Sarepta Therapeutics, Solid Biosciences, Ultragenyx Pharmaceuticals, uniQure and Voyager Therapeutics, as well as several companies addressing other methods for delivering or modifying genes and regulating gene expression. EMPLOYEES As of December 31, 2022, we had 113 full and part-time employees. None of our employees are represented by a labor union or covered under a collective bargaining agreement and we consider our employee relations to be good. Employees of Fortress also make valuable financial, legal, scientific and other strategic contributions to Mustang on a regular basis. SUPPLY AND MANUFACTURING As an early stage development company, we rely on our research partners to manufacture or have manufactured all lentiviral vectors used in the clinical development programs currently in progress at COH, Fred Hutch, St. Jude, the NIH, and LUMC under the IND applications filed by these institutions. In addition we rely on the NIH to produce oncolytic virus for UAB, the clinical trial site for the Phase 1 trial of Nationwide’s C134 oncolytic virus (MB-108). We will continue to rely on our research partners to manufacture lentiviral vectors and oncolytic virus for Mustang-IND trials until such time as material is available from our contract manufacturing organizations. Pursuant to the March 2015 Licensing Agreement with COH, we have the right to make and have made the cellular products, and we have negotiated Investigator-Initiated Clinical Research Support Agreements with COH and Fred Hutch which specify the cell processing costs and numbers of patients which will be supplied under filed protocols. Our research partners have extensive experience manufacturing clinical materials for development studies, but we are currently dependent on both their capacity limitations and continued operating success to manufacture viral vector and to process cells for all CAR T clinical trials for which these partners hold the INDs, as well as to have manufactured oncolytic virus for the MB-108 investigator-IND clinical trial being conducted at UAB. We have limited experience in processing cells for clinical or commercial purposes. In 2018 we opened our own cell processing facility in Worcester, Massachusetts, in order to manufacture and supply cellular product candidates for all clinical trials that will be conducted under IND applications to be filed by us. In August 2019, the FDA approved our IND application to initiate a multi-center Phase 1/2 clinical trial of MB-102 (CD123 CAR T) and in January 2021, the FDA approved our IND application to initiate a multi-center Phase 2 clinical trial of MB-107 (XSCID). In May 2021, the FDA approved our IND application to initiate a multi-center Phase 1/2 clinical trial of MB-106 (CD- 23 ​ Table of Contents 20). As with any supply program, obtaining raw materials of the correct quality cannot be guaranteed, and we cannot ensure that we will be successful in this endeavor. We expect to rely on contract manufacturing relationships for lentiviral vectors and for the MB-108 oncolytic virus, as well as for any non-CAR T products that we may in-license or acquire in the future for co-administration with our CAR T products. However, there can be no assurance that we will be able to successfully contract with such manufacturers on terms acceptable to us, or at all. Contract manufacturers for these current and potential future non-CAR T products would be subject to ongoing periodic and unannounced inspections by the FDA, the U.S. Drug Enforcement Administration (“DEA”) and corresponding state agencies to ensure strict compliance with the Current Good Manufacturing Practice regulations (“cGMP”) and other state and federal regulations. Our contractors, if any, in Europe would face similar challenges from the numerous EU and member state regulatory agencies and authorized bodies. We do not have control over third-party manufacturers’ compliance with these regulations and standards, other than through contractual obligations. If they are deemed out of compliance with cGMPs, product recalls could result, inventory could be destroyed, production could be stopped, and supplies could be delayed or otherwise disrupted. If we need to change manufacturers for these current and potential future non-CAR T products after commercialization, the FDA and corresponding foreign regulatory agencies must approve these new manufacturers in advance, which will involve testing and additional inspections to ensure compliance with FDA regulations and standards and may require significant lead times and delay. Furthermore, switching manufacturers may be difficult because the number of potential manufacturers is limited. It may be difficult or impossible for us to find a replacement manufacturer quickly or on terms acceptable to us, or at all. GOVERNMENT AND INDUSTRY REGULATIONS Numerous governmental authorities, principally the FDA and corresponding state and foreign regulatory agencies, impose substantial regulations upon the clinical development, manufacture and marketing of our product candidates, as well as our ongoing research and development activities. None of our product candidates has been approved for sale in any market. Before marketing in the U.S., any drug that we develop must undergo rigorous pre-clinical testing and clinical trials and an extensive regulatory approval process implemented by the FDA under the FDCA. The FDA regulates, among other things, the pre-clinical and clinical testing, safety, efficacy, approval, manufacturing, record keeping, adverse event reporting, packaging, labeling, storage, advertising, promotion, export, and the sale and distribution of biopharmaceutical products. The regulatory review and approval process is lengthy, expensive and uncertain. We are required to submit extensive preclinical and clinical data and supporting information to the FDA for each indication or use to establish a product candidate’s safety and efficacy before we can secure FDA approval to market or sell a product in the U.S. The approval process takes many years, requires the expenditure of substantial resources and may involve ongoing requirements for post-marketing studies or surveillance. Before commencing clinical trials in humans, we must submit an IND to the FDA containing, among other things, preclinical data, chemistry, manufacturing and control information, and an investigative plan. Our submission of an IND may not result in FDA authorization to commence a clinical trial. The FDA may permit expedited development, evaluation, and marketing of new therapies intended to treat persons with serious or life-threatening conditions for which there is an unmet medical need under its fast track drug development program. A sponsor can apply for fast track designation initially at the time of submission of an IND, or at any time prior to receiving a marketing approval of the new drug application (“NDA”) or biologics license application (“BLA”). To receive fast track designation, an applicant must demonstrate: ● that the therapy is intended to treat a serious or life-threatening condition; ​ ● that the therapy is intended to treat a serious aspect of the condition; and ​ ● that the therapy has the potential to address unmet medical needs, and this potential is being evaluated in the planned drug development program. ​ The FDA must respond to a request for fast track designation within 60 calendar days of receipt of the request. Over the course of development, a product in a fast track development program must continue to meet the criteria for fast track designation. Sponsors of products in fast track drug development programs must be in regular contact with the reviewing division of the FDA to ensure that the evidence necessary to support marketing approval will be developed and presented in a format conducive to an efficient review. Sponsors of products in fast track drug development programs ordinarily are eligible for priority review of a completed application in six months or less and also may be permitted to submit portions of an NDA or BLA to the FDA for review on a rolling basis before the complete application is submitted. 24 ​ Table of Contents In accordance with the FDCA, sponsors of drugs for serious or life-threatening diseases that fill an unmet medical need may seek approval under the FDA’s accelerated approval regulations. Under this authority, the FDA may grant marketing approval for a new drug product on the basis of adequate and well-controlled clinical trials establishing that the drug product has an effect on a surrogate endpoint that is reasonably likely, based on epidemiologic, therapeutic, pathophysiologic, or other evidence, to predict clinical benefit or on the basis of an effect on a clinical endpoint other than survival or irreversible morbidity. Approval will be subject to the requirement that the applicant study the drug further to verify and describe its clinical benefit where there is uncertainty as to the relation of the surrogate endpoint to clinical benefit or uncertainty as to the relation of the observed clinical benefit to ultimate outcome. Post-marketing studies are usually underway at the time an applicant files the NDA or BLA. When required to be conducted, such post-marketing studies must also be adequate and well-controlled. The applicant must carry out any such post-marketing studies with due diligence. Many companies who have been granted the right to utilize an accelerated approval approach have failed to obtain approval. Moreover, negative or inconclusive results from the clinical trials we hope to conduct or adverse medical events could cause us to have to repeat or terminate the clinical trials. Accordingly, we may not be able to complete the clinical trials within an acceptable time frame, if at all, and, therefore, could not submit the NDA or BLA to the FDA or foreign regulatory authorities for marketing approval. Clinical testing must meet requirements for institutional review board oversight, informed consent and good clinical practices, and must be conducted pursuant to an IND, unless exempted. For purposes of NDA or BLA approval, clinical trials are typically conducted in the following sequential phases: ● Phase 1 : The drug is administered to a small group of humans, either healthy volunteers or patients, for the first time to test for safety, dosage tolerance, absorption, metabolism, excretion and clinical pharmacology. ​ ● Phase 2 : Studies are conducted on a larger number of patients to assess the efficacy of the product, to ascertain dose tolerance and the optimal dose range, and to gather additional data relating to safety and potential adverse events. ​ ● Phase 3 : Studies establish safety and efficacy in an expanded patient population. ​ ● Phase 4 : The FDA may request phase 4 post-marketing studies to find out more about the drug’s long-term risks, benefits, and optimal use, or to test the drug in different patient populations. ​ The length of time necessary to complete clinical trials varies significantly and may be difficult to predict. Clinical results are frequently susceptible to varying interpretations that may delay, limit or prevent regulatory approvals. Additional factors that can cause delay or termination of our clinical trials, or that may increase the costs of these trials, include: ● slow patient enrollment due to the nature of the clinical trial plan, the proximity of patients to clinical sites, the eligibility criteria for participation in the study or other factors; ​ ● inadequately trained or insufficient personnel at the study site to assist in overseeing and monitoring clinical trials or delays in approvals from a study site’s review board; ​ ● longer treatment time required to demonstrate efficacy or determine the appropriate product dose; ​ ● insufficient supply of the product candidates; ​ ● adverse medical events or side effects in treated patients; and ​ ● ineffectiveness of the product candidates. ​ In addition, the FDA, equivalent foreign regulatory authority, or a data safety monitoring committee for a clinical trial may place a clinical trial on hold or terminate it if it concludes that subjects are being exposed to an unacceptable health risk, or for futility. Any drug is likely to produce some toxicity or undesirable side effects in animals and in humans when administered at sufficiently high doses and/or for a sufficiently long period of time. Unacceptable toxicity or side effects may occur at any dose level at any time in the course of studies in animals designed to identify unacceptable effects of a product candidate, known as toxicological studies, or clinical trials of product candidates. The appearance of any unacceptable toxicity or side effect could cause us or regulatory authorities to interrupt, limit, delay or abort the development of any of our product candidates and could ultimately prevent approval by the FDA or foreign regulatory authorities for any or all targeted indications. 25 ​ Table of Contents Sponsors of drugs may apply for a special protocol assessment (“SPA”) from the FDA for studies intended to form the primary basis of an efficacy claim. The SPA process is a procedure by which the FDA provides official evaluation and written guidance on the design and size of proposed protocols that are intended to form the basis for an NDA or BLA. However, final marketing approval depends on the results of efficacy, the adverse event profile and an evaluation of the benefit/risk of treatment demonstrated in the pivotal clinical trial. Once approved, the SPA may only be changed through a written agreement between the sponsor and the FDA, or in rare cases if the FDA becomes aware of a substantial scientific issue essential to product safety or efficacy the SPA can be rescinded. Before receiving FDA approval to market a product, we must demonstrate that the product is safe and effective for its intended use by submitting to the FDA an NDA or BLA containing the preclinical and clinical data that have been accumulated, together with chemistry and manufacturing and controls specifications and information, and proposed labeling, among other things. The FDA may refuse to accept an NDA or BLA for filing if certain content criteria are not met and, even after accepting an NDA or BLA, the FDA may require additional information, including clinical data, before approval for marketing a product. Although uncommon, the FDA may request a Risk Evaluation and Mitigation Strategy, or REMS, as part of an NDA or BLA approval for products with serious safety concerns to help ensure that the benefits of the product outweigh the risks. The REMS plan contains post-marketing obligations of the sponsor to train prescribing physicians, monitor off-label drug use, and perhaps the conduct of Phase 4 follow-up studies and registries to ensure the continued safe use of the drug. ​ As part of the approval process, the FDA must inspect and approve each manufacturing facility. Among the conditions of approval is the requirement that a manufacturer’s quality control and manufacturing procedures conform to cGMP. Manufacturers must expend significant time, money and effort to ensure continued compliance, and the FDA conducts periodic inspections to certify compliance. It may be difficult for our manufacturers or for us to comply with the applicable cGMP, as interpreted by the FDA, and other FDA regulatory requirements. If we, or our contract manufacturers, fail to comply, then the FDA may not allow us to market products that have been affected by the failure. If the FDA grants approval, the approval will be limited to those conditions and patient populations for which the product is safe and effective, as demonstrated through clinical studies and as reflected in the approved labeling. Further, a product may be marketed only in those dosage forms and for those indications approved in the NDA or BLA. Certain changes to an approved NDA or BLA, including, with certain exceptions, any significant changes to labeling, may require prior approval of a supplemental application before the drug may be marketed as changed. Any products that we manufacture or distribute pursuant to FDA approvals are subject to continuing monitoring and regulation by the FDA, including compliance with cGMP and the reporting of adverse experiences with the drugs. The nature of marketing claims that the FDA will permit us to make in the labeling and advertising of our products will generally be limited to those specified in FDA approved labeling, and the advertising of our products will be subject to comprehensive monitoring and regulation by the FDA. Drugs whose review was accelerated may carry additional restrictions on marketing activities, including the requirement that all promotional materials are pre-submitted to the FDA. Claims exceeding those contained in the approved labeling will constitute a violation of the FDCA. Violations of the FDCA or regulatory requirements at any time during the product development process, approval process, or marketing and sale following approval may result in agency enforcement actions, including withdrawal of approval, recall, seizure of products, warning letters, injunctions, fines and/or civil or criminal penalties. Any agency enforcement action could have a material adverse effect on our business. Failure to comply with applicable federal, state and foreign laws and regulations would likely have a material adverse effect on our business. In addition, federal, state and foreign laws and regulations regarding the manufacture and sale of new drugs are subject to future changes. Other Healthcare Laws and Compliance Requirements In the U.S., our activities are potentially subject to regulation by various federal, state and local authorities in addition to the FDA, including the Centers for Medicare and Medicaid Services (formerly the Health Care Financing Administration), other divisions of the United States Department of Health and Human Services (e.g., the Office of Inspector General), the United States Department of Justice and individual United States Attorney offices within the Department of Justice, and state and local governments. Pharmaceutical Coverage, Pricing and Reimbursement In the U.S. and markets in other countries, sales of any products for which we receive regulatory approval for commercial sale will depend in part on the availability of reimbursement from third-party payors, including government health administrative authorities, managed care providers, private health insurers and other organizations. Third-party payors are increasingly examining the medical necessity and cost-effectiveness of medical products and services, in addition to their safety and efficacy, and, accordingly, significant uncertainty exists as to the reimbursement status of newly approved therapeutics. Adequate third-party reimbursement may not be available for our products to 26 ​ Table of Contents enable us to realize an appropriate return on our investment in research and product development. We are unable to predict the future course of federal or state health care legislation and regulations, including regulations that will be issued to implement provisions of the health care reform legislation enacted in 2010, known as the Affordable Care Act. The Affordable Care Act and further changes in the law or regulatory framework could have a material adverse effect on our business. International Regulation In addition to regulations in the U.S., there are a variety of foreign regulations governing clinical trials and commercial sales and distribution of our product candidates. The approval process varies from country to country, and the time may be longer or shorter than that required for FDA approval. ​