The FDA has rejected Regenxbio’s RGX-121 gene therapy for mucopolysaccharidosis type II (Hunter syndrome), citing concerns about the surrogate cerebrospinal fluid biomarker used to predict longer-term cognitive benefit and casting doubt on the accelerated-approval pathway.
The FDA rejected Regenxbio’s RGX-121 for Hunter syndrome, citing unresolved issues in the trial design (defining the patient population), use of a natural history control, and a biomarker surrogate endpoint, with a PDUFA date already pushed from 2025. Regenxbio plans to resubmit with longer-term data. The decision follows a broader context of safety concerns linked to Regenxbio’s RGX-111 and its brain-tumor event, but the FDA noted those issues were not cited as reasons for RGX-121’s rejection. Industry experts emphasize ongoing questions around biomarker-based approvals and vector-related safety, underscoring the urgent need for effective therapies in these ultra-rare MPS diseases.