Mustang Bio has licensed a gene therapy from St. Jude Children’s Research Hospital for X-linked severe combined immunodeficiency (X-SCID), also called "bubble boy" syndrome. The deal adds a rare disease gene therapy to Mustang’s pipeline, which is focused on fighting various cancers using CAR-T treatments. 

SCID refers to a group of rare diseases caused by mutations in genes that play a role in the development and function of immune cells. Unless patients receive immune-restoring treatments—such as transplants of blood-forming stem cells, enzyme therapy, or gene therapy—the condition is fatal, usually in the first year or two of life, according to the National Institute of Allergy and Infectious Diseases. 

St. Jude’s treatment entails administering a low dose of the cancer drug busulfan before reinfusing a patients with their own stem cells that have been gene-modified. It’s currently in a pair of phase 1/2 trials in infants under age 2 and in children over the age of 2. Eight patients under 2 have been treated so far, with six of them "[achieving] reconstituted immune systems within three to four months following treatment," according to the company.

"Our therapy has been well tolerated thus far, and none of the infants required any blood product support after low dose of busulfan," said Ewelina Mamcarz, M.D., an assistant member at St. Jude who led the study, in a release. "Most importantly, we observe recovery of all cells of the immune system, which is truly an achievement over prior gene therapy trials, where B cell reconstitution did not occur, and patients required intravenous immunoglobulin for life." 

Mustang and St. Jude did not disclose financial terms of their agreement. The pair think there may be as many as 1,500 patients in the U.S. and a similar number in Europe with X-linked SCID for whom allogeneic stem cell transplants aren’t enough. These patients could be eligible for their lentiviral gene therapy. 

"We are thrilled to announce the expansion of our pipeline into gene therapy for patients with X-SCID, a natural fit for our Worcester, Massachusetts, cell processing facility," said Mustang CEO Manny Litchman, M.D., in a statement. "We look forward to working with St. Jude to advance this program through ongoing phase 1/2 trials, with the goal of providing a novel, long-term treatment to the more than 80% of infants who lack fully matched bone marrow transplant donors and those patients who continue to have significant impairment of immunity."

U.K.-based Orchard Therapeutics is working on its own gene therapies for primary immunodeficiencies, including ADA-SCID, a version of SCID caused by adenosine deaminase deficiency. In April, the company picked up GlaxoSmithKline’s rare disease gene therapies, including EMA-approved ADA-SCID treatment Strimvelis, in exchange for a 19.9% stake.

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