FDA Grants Mustang Bio Rare Pediatric Disease Designation for XSCID Treatment

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 newly diagnosed infants.  

X-linked severe combined immunodeficiency (X-SCID) 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. X-SCID is the most common form of severe combined immunodeficiency, affecting approximately one in 50,000 to 100,000 newborns worldwide.

MB-107 is currently being assessed in a phase 1/2 clinical trial for X-SCID 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 X-SCID 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.

Another phase 1/2 clinical trial for X-SCID in patients over the age of two years, who have received prior HSCT, is underway at the National Institutes of Health, and Mustang expects to file an IND to the FDA to initiate a multi-center phase 2 clinical trial in this population before the end of the year. The product in this second trial will be designated MB-207.

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.

“We are very pleased that the FDA has granted Rare Pediatric Disease designation to MB-107 for XSCID, a life-threatening and rare genetic disorder with limited treatment options, in newly-diagnosed infants,” said Manuel Litchman, president and CEO of Mustang. “We anticipate that our pivotal clinical program will begin shortly, and we look forward to continuing to work efficiently with the FDA, in order to bring MB-107 to children suffering from this devastating disease as quickly and safely as possible.”

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.

Photo: 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.