FDA Grants Mustang Bio’s MB-207 Rare Pediatric Disease Designation for Treatment of X-linked Severe Combined Immunodeficiency in Previously Transplanted Patients

WORCESTER, Mass., Aug. 31, 2020 (GLOBE NEWSWIRE) — Mustang Bio, Inc. (“Mustang”) (NASDAQ: MBIO), 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, today announced that the U.S. Food and Drug Administration (“FDA”) has granted Rare Pediatric Disease Designation to MB-207, Mustang’s lentiviral gene therapy for the treatment of patients with X-linked severe combined immunodeficiency (“XSCID”), also known as bubble boy disease, who were previously treated with a hematopoietic stem cell transplantation (“HSCT”) and for whom re-treatment is indicated.

The FDA grants Rare Pediatric Disease Designation for serious and life-threatening diseases that primarily affect children ages 18 years or younger and fewer than 200,000 people in the United States. If Mustang’s Biologics License Application 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 or 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.

Manuel Litchman, M.D., President and Chief Executive Officer of Mustang, said, “XSCID is a life-threatening and rare genetic disorder with limited treatment options. We are pleased with our ongoing progress with the FDA to advance potential treatments for this devastating disease, including the recent Rare Pediatric Disease Designation for MB-107 in newly diagnosed XSCID patients and now for MB-207 for patients with XSCID who have previously received HSCT and require re-treatment. We look forward to continuing to work efficiently to expedite the development of critically needed treatment options for children with XSCID.”

MB-207 is currently being assessed in a Phase 1/2 clinical trial for XSCID in patients over the age of two, who have received prior HSCT, at the National Institutes of Health. Mustang expects to file an investigational new drug application (“IND”) with the FDA to initiate a multi-center Phase 2 clinical trial of MB-207 in this patient population in the fourth quarter of 2020.

Another Phase 1/2 clinical trial for XSCID in newly diagnosed infants under the age of two is underway at St. Jude Children’s Research Hospital (“St. Jude”), UCSF Benioff Children’s Hospital in San Francisco and Seattle Children’s Hospital. The product in this trial is designated MB-107. In May 2020, Mustang submitted an IND to the FDA to initiate a multi-center Phase 2 clinical trial of MB-107 in newly diagnosed infants with XSCID who are between two months to two years of age. The trial is expected to enroll 10 patients who, together with 15 patients enrolled in the current multi-center trial led by St. Jude, will be compared with 25 matched historical control patients who have undergone HSCT. The primary efficacy endpoint will be event-free survival. The initiation of this trial is expected early in the fourth quarter of 2020. Mustang is targeting topline data from this trial in the second half of 2022. The FDA previously granted a Rare Pediatric Disease Designation in August 2020 and Regenerative Medicine Advanced Therapy Designation in August 2019 to MB-107 for the treatment of XSCID in newly diagnosed infants. Additionally, the European Medicines Agency granted Advanced Therapy Medicinal Product Classification to MB-107 in April 2020.

About X-linked Severe Combined Immunodeficiency (XSCID)
X-linked severe combined immunodeficiency is a rare genetic disorder that occurs in approximately 1 per 225,000 births. It is characterized by the absence or lack of function of key immune cells, resulting in a severely compromised immune system and death by 1 year of age if untreated. Patients with XSCID have no T-cells or natural killer cells. Although their B-cells are normal in number, they are not functional. As a result, XSCID patients are usually affected by severe bacterial, viral or fungal infections early in life and often present with interstitial lung disease, chronic diarrhea and failure to thrive.  Among patients who receive HSCT, many are unable to establish adequate T-cell immunity or lose T-cell immunity over time. Further, approximately two-thirds of patients who receive HSCT lack sufficient B-cell immunity and need lifelong immunoglobulin replacement therapy.

The specific genetic disorder that causes XSCID is a mutation in the gene coding for the common gamma chain (γc), a protein that is shared by the receptors for at least six interleukins. These interleukins and their receptors are critical for the development and differentiation of immune cells. The gene coding for γc is known as IL-2 receptor gamma, or IL2RG. Because IL2RG is located on the X-chromosome, XSCID is inherited in an X-linked recessive pattern, resulting in almost all patients being male.

About Mustang Bio
Mustang Bio, Inc. 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. Mustang aims to acquire rights to these technologies by licensing or otherwise acquiring an ownership interest, to fund research and development, and to outlicense or bring the technologies to market. Mustang has partnered with top medical institutions to advance the development of CAR T therapies across multiple cancers, as well as a lentiviral gene therapy for XSCID. Mustang is registered under the Securities Exchange Act of 1934, as amended, and files periodic reports with the U.S. Securities and Exchange Commission (“SEC”). Mustang was founded by Fortress Biotech, Inc. (NASDAQ: FBIO). For more information, visit www.mustangbio.com.

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