REGENXBIO Inc. announced it completed a successful Pre-Biologics License Application (BLA) meeting for RGX-121 for the treatment Mucopolysaccharidosis Type II (MPS II), where it finalized details of its BLA with the U.S. Food and Drug Administration (FDA). The FDA continues to be aligned with REGENXBIO's plan to use cerebrospinal fluid (CSF) levels of heparan sulfate (HS) D2S6, a key biomarker of brain disease activity, as a surrogate endpoint reasonably likely to predict clinical benefit to support accelerated approval of RGX-121. Additionally, REGENXBIO and the FDA discussed manufacturing, non-clinical, device delivery system and other critical elements of the BLA, including a confirmatory study designed to verify and describe the predicted clinical benefit.

REGENXBIO completed its database lock for the pivotal program and expects to initiate submission of a rolling BLA in the third quarter of 2024. REGENXBIO expects an FDA inspection of its Manufacturing Innovation Center in the first half of 2025. Commercial bulk drug and clinical trial material, both manufactured using REGENXBIO's proprietary NAVXpress platform process, were confirmed to be comparable.

A confirmatory study of RGX-121 is expected to initiate enrollment in the second half of 2025, prior to potential FDA approval. 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. Topline results from the Phase I/II/III CAMPSIITE trial of RGX-121 presented earlier this year demonstrated that the pivotal phase of the trial met its primary endpoint with statistical significance.

Pivotal results were consistent with data from the dose-finding phase of CAMPSIITE, in which the majority of patients were shown to be exceeding expectations in neurodevelopmental function compared to natural history data up to four years. Long-term follow-up of patients treated with RGX-121 also showed there was a high rate of patients for whom trial investigators chose to discontinue standard-of-care intravenous enzyme replacement therapy (ERT) or were allowed to remain ERT-naïve. As of January 3, 2024, RGX-121 continues to be well tolerated in 25 patients dosed across all phases of the CAMPSIITE trial. REGENXBIO expects to share additional safety and efficacy data from the CAMPSIITE trial in the second half of 2024.