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. (Darwin Laganzon)

When babies are born they’re somewhat protected from infections through antibodies that were transferred to them in the womb. However, as time passes and immune systems develop their bodies start to learn how to combat infections on their own. For some children this process is seamless, but for others, it can be a sensitive time when parents learn about immune problems that haven’t resolved normally in the first months of life.

For starters, the immune system has many parts and symptoms of immune deficiency can depend on what part of the immune system is affected. These deficiencies can range from mild to aggressive and even life-threatening. One example of a life-threatening immune problem is severe combined immunodeficiency (SCID). Last year a CIRM-funded clinical trial run by St. Jude Children’s Research Hospital and UC San Francisco saved the life of a little boy named Ronnie who suffered from SCID. Based on the success of this approach a company named Mustang Bio just licensed a gene therapy from St. Jude Children’s Research Hospital for X-linked severe combined immunodeficiency (X-SCID), also called “bubble boy” syndrome. This agreement adds a rare disease gene therapy to Mustang’s pipeline, which is focused on fighting various cancers using CAR-T treatments.

Photo Credit: Pawash Priyank of Ronnie Priyank

In most cases, unless SCID 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 haven’t disclosed financial terms of their agreement. They believe 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 donor bone marrow or blood stem cell transplants simply aren’t enough. They feel 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.

Mustang and St. Jude will advance the program through ongoing phase 1/2 trials, with the goal of providing long-term treatment to the more than 80% of infants who lack fully matched bone marrow transplant donors. Through their partnership they hope to help the small number of patients who continue to have significant impairment of immunity.