Encoded Therapeutics Reports Initial Results from Gene Therapy Trial for Dravet Syndrome

A medicine increasingly used to mitigate the risk of deadly gene therapy side effects could also blunt the therapy’s effectiveness, a new study finds. The trial, from the startup Encoded Therapeutics, tested a gene therapy for Dravet syndrome, a severe form of genetic epilepsy.

Most of the 21 children in the trial were assigned to receive steroids, the most commonly used immune suppressant in gene therapy trials.

A subset of patients — including most of the patients on the highest dose level — were assigned to also receive sirolimus, also known as rapamycin. Sirolimus is a drug historically given to prevent rejection in transplant recipients. A key concern in gene therapy trials is that patients could mount an immune response against the engineered viruses used to deliver new genes into the brain.

The article detailing the Encoded Therapeutics trial was written by Jason Mast and published on May 13, 2026. The article is based in Boston, Stat reported.

Stat reported that the trial involved 21 children. A subset of patients in the Encoded Therapeutics trial were assigned to also receive sirolimus in addition to steroids.

Most of the patients on the highest dose level received this combination. The new study was conducted by Encoded Therapeutics testing a gene therapy for Dravet syndrome. Steroids remain the most commonly used immune suppressant despite the findings on sirolimus.