FDA Approves First Therapy for Rare Pediatric Immune Disorder

The US Food and Drug Administration has approved the regenerative tissue-based therapy Rethymic for patients with congenital athymia, a rare pediatric immune disorder where the thymus does not develop in utero. This is the first FDA-approved treatment for children born with this condition.

“This therapy is the result of more than 25 years of research aimed at increasing survival for patients who previously had very little hope,” said M. Louise Markert, MD, PhD, principal investigator for RETHYMIC clinical trials, in a statement by Enzyvant, the biotechnology company that commercialized the treatment. “Our research program was inspired each and every day by the possibilities that exist for children who have congenital athymia with an FDA-approved treatment for this devastating condition.”

Between 17 to 24 children are diagnosed with congenital athymia in the United States each year. Because these babies lack a functioning immune system, they are extremely vulnerable to infection. Typically, a child with congenital athymia lives between 2 to 3 years, and up until now only supportive care was available.

Along with the approval, announced October 8, the FDA granted Enzyvant a rare pediatric disease priority review voucher, which the company can use to fast-track government review of one of its future drugs. Enzyvant had previously sought FDA-approval for Rethymic, but the therapy was rejected by the agency in 2019 due to manufacturing issues.

Rethymic, made up of donor-derived thymus tissue, helps improve immune function in congenital athymia patients. After the tissue is surgically implanted, naïve T-cells begin to reconstitute within 6 to 12 months. These immune cells continue increasing through 2 years after treatment, according to Enzyvant.

The safety and efficacy of the treatment was determined in clinical studies of 105 patients with congenital athymia who received a one-time treatment of Rethymic from 1993-2020. After 1-year post-treatment, 77% of patients were alive, with a 76% survival rate after 2 years. Children who survived the first year after implantation were generally expected to survive long-term. Of the total 105 patients, 29 died, with 23 deaths occurring within the first year after implantation.

“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,” said Rachelle Jacques, Enzyvant’s chief executive officer, in a statement. “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.”

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