Regenxbio says CAMPSIITE trial of RGX-121 achieves primary endpoint

REGENXBIO announced topline results from the Phase I/II/III CAMPSIITE trial of RGX-121 for the treatment of patients up to 5 years old diagnosed with Mucopolysaccharidosis Type II, also known as Hunter syndrome, demonstrating that the pivotal phase of the trial met its primary endpoint with statistical significance. The results were presented at the 20th Annual WORLDSymposium by Paul Harmatz, M.D., UCSF Benioff Children’s Hospital and trial investigator. In the pivotal phase, MPS II patients treated with RGX-121 achieved decreased cerebrospinal fluid levels of D2S6, a key biomarker of brain disease activity, below maximum attenuated disease levels at 16 weeks. Patients receiving RGX-121 demonstrated an 86% median reduction in D2S6, approaching normal levels. Pivotal results were consistent with data from the dose-finding phase of CAMPSIITE. In the dose-finding phase, the majority of patients are exceeding expectations in neurodevelopmental function compared to natural history data up to four years. New long-term follow-up of patients treated with RGX-121 in the dose-finding phase also showed there was a high rate of patients for whom trial investigators chose to discontinue standard-of-care intravenous enzyme replacement therapy or were allowed to remain ERT-naive. At the pivotal dose level, 80% of patients were ERT-free at last time point. As of January 3, 2024, RGX-121 continues to be well tolerated in 25 patients dosed across all phases of the CAMPSIITE trial. Following an RMAT meeting held with FDA at the end of 2023, REGENXBIO continues with plans to use CSF levels of D2S6 as a surrogate endpoint for accelerated approval and is completing remaining activities in order to file a BLA in the second half of 2024. Based on an expected priority review, potential approval of the planned BLA could result in receipt of a Rare Pediatric Disease Priority Review Voucher in 2025.