FDA puts hold on Regenxbio gene therapies following brain tumor

The U.S. FDA has placed two of Regenxbio's gene therapies on hold after a brain tumor was found in a 5-year-old trial participant.

The tumor was discovered during a routine brain scan of a child who had received RGX-111 about four years earlier. RGX-111 is being developed as a treatment for Hurler syndrome, a rare autosomal recessive lysosomal storage disorder.

A second therapy, RGX-121, being developed as a one-time treatment of MPS II or Hunter Syndrome, was also put on hold, with the FDA citing similarities between the two programs. The hold on RGX-121comes just weeks before the therapy’s PDUFA date. The FDA had accepted Regenxbio’s BLA for RGX-121 in May 2025, granting it priority review with a PDUFA target action date of November 9, 2025. Then, in August, the agency extended its review timeline of the BLA to February 8, 2026, following the company's submission of longer-term clinical data for all patients in the pivotal study.

Regenxbio said no other tumors have been reported among the nine other patients treated with RGX-111, or among 32 patients treated with RGX-121.

RGX-121 and RGX-111 are being developed and potentially commercialized in partnership with Nippon Shinyaku, per a deal signed in January 2025. The deal gives the Japan-based drugmaker the rights to commercialize both Regenxbio products in the U.S. and Asia for mucopolysaccharidosis I (MPS I), also known as Hurler syndrome. Per the deal, Nippon Shinyaku paid Regenxbio $110 million upfront and will pay up to an additional $700 million if certain milestones are achieved.