Mustang Bio Announces Updated Interim Data for Treatment of X-Linked Severe Combined Immunodeficiency with Support of Lentiviral Vector Gene Therapy Upcoming Pivotal Multicenter Phase 2 Trial for MB-107

The 23 patients treated are all alive after a median follow-up of 2.6 years, with no signs of malignant transformation

Data representing the largest cohort of infants with XSCID treated with gene therapy presented at the 25and American Society of Gene & Cell Therapy Annual Meeting

WORCESTER, Mass., May 19, 2022 (GLOBE NEWSWIRE) — Mustang Bio, Inc. (“Mustang”) (NASDAQ: MBIO), a clinical-stage biopharmaceutical company focused on translating current medical breakthroughs in cell therapies and genes with curative potential for blood cancers, solid tumors and rare genetic diseases, today announced that interim Phase 1/2 data on treatment with the same lentiviral vector used in MB-107, lentiviral gene therapy of Mustang for X-linked severe combined immunodeficiency (“XSCID”), also known as bubble boy disease, in newly diagnosed infants under two years of age, supports plans to initiate trial multi-center Phase 2 pivot for MB-107 in the Company’s Investigational New Drug (“IND”) application in the second half of this year.

Representing the largest cohort of infants with XSCID treated with gene therapy, the data include 23 infants with XSCID treated with the lentiviral vector at a median age of 3 months (range: 2-14 months) with a median follow-up of 2, 6 years (range: 4 months to 5.6 years). Transduced autologous CD34+ bone marrow 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 9.61×106/kg (range 4.40-22.45). Prior to cell infusion, patients received busulfan targeted to a cumulative area under the curve (AUCc) of 22 mg*h/L. The treatment was well tolerated and all patients experienced complete hematopoietic recovery. Serious adverse events occurred in three patients (two patients with pancytopenia and haemolytic anemia and one patient with delayed neutrophil engraftment) and all resolved. Seventeen patients had active infections before treatment, and in all cases these infections resolved. In addition, 15 patients have so far been able to discontinue intravenous immunoglobulin and, to date, 14 patients have been successfully immunized. All patients are currently alive with stable vector staining in all cell lines and with no evidence of malignant transformation.

“We are encouraged by the interim results of this ongoing trial, and our post-treatment follow-up shows that patients continue to do very well,” said Ewelina Mamcarz, MD, Department of Bone Marrow Transplantation and Cell Therapy, St. Jude Children’s Research Hospital (“St. Jude”). “The therapy appears to be safe and effective, and patients in the trial to date have developed a functioning immune system with no evidence of abnormal cell division. We plan to continue monitoring these patients for continued safety and lasting results, being given the limited number of studies where patients received gene therapy at such a young age.

The data, presented orally at the Clinical Trials Spotlight Symposium on 25and Annual Meeting of the American Society of Gene & Cell Therapy (“ASGCT”), are from an ongoing multicenter Phase 1/2 clinical trial at St. Jude, UCSF Benioff Children’s Hospital in San Francisco and at Seattle Children’s Hospital. Lentiviral gene therapy is also being evaluated in a Phase 1/2 clinical trial at the National Institute of Allergy and Infectious Diseases, part of the National Institutes of Health, for XSCID patients who have already been treated with hematopoietic stem cell transplantation (“HSCT”) and for whom retreatment is indicated.

“The data presented by Dr. Ewelina Mamcarz of St. Jude at ASGCT underscores the continued success and potential safety of lentiviral gene therapy treatment for infants with XSCID in the trial conducted to date. In this trial , the treatment created a stable and functioning immune system for these patients with no evidence of leukemogenesis.These data further validate our plan to initiate a pivotal multicenter Phase 2 trial for MB-107 in the Mustang IND in the second half of this year,” said Manuel Litchman, MD, Mustang President and CEO. “We remain hopeful that MB-107 can address the significant unmet need for a safe and sustainable for children with bubble boy disease.”

About X-Linked Severe Combined Immunodeficiency (“XSCID”)
X-linked severe combined immunodeficiency is characterized by the absence or lack of function of key immune cells, leading to a severely weakened immune system and death by age 1 if left untreated. Patients with XSCID do not have T cells or natural killer (NK) cells. Although their B cells are in normal numbers, they are not functional. As a result, patients with XSCID are usually affected by severe bacterial, viral, or fungal infections early in life and often present with interstitial lung disease, chronic diarrhea, and growth failure. Among patients who receive allogeneic HSCT, many are unable to establish adequate T-cell immunity or lose T-cell immunity over time. In addition, approximately two-thirds of patients who receive HSCT do not have sufficient B-cell immunity and require lifelong immunoglobulin replacement therapy. XSCID is a rare genetic disorder that occurs in approximately 1 in 225,000 births. There are approximately 2,800 patients with XSCID worldwide who have previously been treated with HSCT and therefore may be eligible for gene therapy now or later. ‘coming.

The specific genetic disorder causing XSCID is a mutation in the gene encoding the common gamma chain (γvs), a protein shared by receptors for at least six interleukins. These interleukins and their receptors are essential for the development and differentiation of immune cells. The gene coding for γvs 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 current medical breakthroughs in cell and gene therapies into potential treatments for hematological cancers, solid tumors and rare genetic diseases. Mustang aims to acquire rights to such technologies by licensing or otherwise acquiring an equity interest, fund research and development, and license or bring the technologies to market. Mustang has partnered with leading medical institutions to advance the development of CAR T therapies for multiple cancers, as well as lentiviral gene therapies for severe combined immunodeficiency. Mustang is registered under the Securities Exchange Act of 1934, as amended, and files periodic reports with the United States Securities and Exchange Commission (“SEC”). Mustang was founded by Fortress Biotech, Inc. (NASDAQ: FBIO). For more information, visit

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Company details :
Jaclyn Jaffe and Bill Begien
Mustang Bio, Inc.
(781) 652-4500

[email protected]

Contact with Investor Relations:
Daniel Ferry
LifeSci Advisors, LLC
(617) 430-7576

[email protected]

Contact person for media relations:
Tony Plohoros
6 degrees
(908) 591-2839

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