Regenxbio touts one-year data for MPS II gene therapy

Regenxbio announced new, positive data from the phase 1/2/3 CAMPSIITE trial of its gene therapy, RGX-121, for the treatment of patients with mucopolysaccharidosis type II (MPS II), also known as Hunter syndrome.

The 12-month pivotal data further demonstrate the ability of one-time RGX-121 treatment to improve outcomes for patients with MPS II. In the 13-person pivotal phase of the CAMPSIITE trial, participants through one year sustained an 82% median reduction of cerebrospinal fluid levels of heparan sulfate D2S6, a key biomarker of MPS II brain disease that is reasonably likely to predict clinical benefit. These longer-term data are consistent with previously reported topline pivotal results from the CAMPSIITE trial.

Regenxbio says it has submitted these longer-term pivotal results to the FDA in response to an information request in the ongoing BLA review of RGX-121. The FDA had accepted Regenxbio’s BLA 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.

MPS II is a rare disease where the body can't break down sugar molecules. It is caused by a variation in the IDS gene, which contains the instructions for the production of a specific enzyme, I2S. RGX-121, an AAV therapeutic designed to deliver a functional copy of the I2S gene directly to the central nervous system, is on track to be the first gene therapy and one-time treatment for the disease.

The treatment is being developed and potentially commercialized in partnership with Nippon Shinyaku, per a deal signed back in January. The deal gives the Japan-based drugmaker the rights to commercialize two Regenxbio products in the U.S. and Asia — RGX-121 and RGX-111 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.