French gene therapy research laboratory Genethon and Sweden-based biotechnology company Hansa Biopharma AB (STO: HNSA), announced on Friday that they have reached a clinical milestone in treating Crigler-Najjar syndrome.

A patient with natural immunity to the AAV8 vector was successfully treated with Genethon's AAV-based GNT0003 gene therapy after receiving imlifidase, an enzyme developed by Hansa Biopharma that temporarily inhibits the immune response. This marks the first successful administration of gene therapy in a patient with Crigler-Najjar syndrome who has antibodies against AAV8.

The treatment was conducted as part of the GNT-018-IDES clinical trial led by Genethon in collaboration with Hansa Biopharma. The companies claim that the study demonstrated feasibility and safety, with imlifidase effectively cleaving antibodies and enabling administration of GNT0003, and no severe side effects reported.

Initial efficacy data showed that GNT0003 significantly reduced bilirubin levels, allowing the patient to discontinue daily phototherapy sixteen weeks after treatment.

If confirmed in further trials, the approach could expand access to gene therapy for patients previously excluded due to natural immunity to AAV vectors.