FDA Grants Mustang Bio Rare Pediatric Disease Designation for XSCID Therapy

Rare Daily Staff

The U.S. Food and Drug Administration granted Rare Pediatric Disease designation to Mustang Bio’s MB-107 lentiviral gene therapy for the treatment of X-linked severe combined immunodeficiency in patients who were previously treated with a hematopoietic stem cell transplantation and for whom re-treatment is indicated.

The agency had granted the Rare Pediatric Disease designation, two weeks previously, to the lentiviral gene therapy for the treatment of infants newly diagnosed with the rare disorder.

X-linked severe combined immunodeficiency (XSCID) is also known as bubble boy disease. It is a rare X-linked genetic disorder that results in the absence or lack of function of key immune cells, resulting in a severely compromised immune system and death by one year of age if untreated. XSCID is the most common form of severe combined immunodeficiency, affecting approximately one in 50,000 to 100,000 newborns worldwide, and almost all patients are male.

Among patients who receive a hematopoietic stem cell transplantation (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.

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 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.

MB-107 is also currently being assessed in a phase 1/2 clinical trial for XSCID in newly diagnosed infants under the age of two. In May 2020, Mustang submitted an investigational new drug application 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, will be compared with 25 matched historical control patients who have undergone hematopoietic stem cell transplantation (HSCT). The primary efficacy endpoint will be event-free survival. The initiation of this trial is expected early in the fourth quarter of 2020 with topline data reported in the second half of 2022.

“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,” said Manuel Litchman, president and CEO of Mustang.

The FDA grants Rare Pediatric Disease designation for serious or life-threatening diseases with manifestations in individuals aged from birth to 18 years, including access to the FDA’s expedited review and approval process. The designation makes MB-107 eligible for a Rare Pediatric Disease Priority Review voucher upon approval of the therapy by the FDA. There are no approved therapies for the condition.

The vouchers can be used to reduce the time of an FDA new drug approval review to six months from ten months. The vouchers are potentially lucrative because they are transferable. Most recently, Sarepta sold its priority review voucher to Vifor Pharma $111 million in February 2020.

The FDA previously granted Regenerative Medicine Advanced Therapy designation to MB-107 for the treatment of X-SCID in newly diagnosed infants in August 2019. The European Medicines Agency granted Advanced Therapy Medicinal Product classification to MB-107 in April 2020.

Manuel Litchman, president and CEO of Mustang

Editor’s note: This story was updated to correct the most recent sales of a priority review voucher.