The U.S. Food and Drug Administration last week approved the first treatment for a rare immune disorder called congenital athymia that causes children to be born without a thymus gland, the small organ under the breastbone that produces white blood cells to protect the body against infections. Without it, children typically die in the first two years of their lives.

The new therapy, called Rethymic, is a one-time surgical treatment that involves processing and culturing thymus tissue from donors, then implanting it in patients, who then develop sufficient immune support in 6 to 12 months.

Approval came after a clinical trial that ran from 1993 to 2020 in which 105 patients ranging from one month to 16 years old received the treatment. Children who received the therapy and survived past the first year generally went on to survive long-term. It also reduced the number and severity of infections they developed over time.

“For too long, families have faced a reality that the brutal journey for pediatric congenital athymia patients receiving supportive care only would end tragically. The FDA approval of Rethymic will help patients access this desperately needed therapy beyond clinical study,” said Rachelle Jacques, CEO of Enzyvant Therapeutics, Inc., which developed Rethymic. “We are deeply grateful to the 105 patients who participated in clinical trials, their families, and all of the stakeholders who contributed to this pioneering regenerative medicine research program.”

An efficacy analysis estimated that more than three-quarters of the patients who receive the therapy survive beyond one year—and of those, 94 percent go on to survive long-term. Among the side effects that Enzyvant lists in the prescribing information for Rethymic, the company notes that 19 percent of patients experience high blood pressure, 15 percent have rashes, and 12 percent have decreased kidney function.

Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research, hailed the new therapy’s approval as a milestone for children afflicted with the disease, adding, “We remain committed to helping advance the development of safe and effective medical products for patients affected by rare diseases—an area of such critical need.”