FDA Extends Decision Date On Regenxbio's Gene Therapy Into Next Year

Core Viewpoint - The FDA has extended the review timeline for REGENXBIO Inc.'s biologics license application for RGX-121, a gene therapy for Mucopolysaccharidosis II (MPS II), from November 9, 2025, to February 8, 2026, following the submission of additional long-term clinical data [1][2]. Group 1: FDA Review and Data Submission - The extension of the PDUFA goal date is due to the company's submission of longer-term clinical data from the pivotal study involving 13 patients [2]. - The FDA completed a pre-license and bioresearch monitoring inspection for RGX-121 with no observations and has raised no safety-related concerns during the review [4]. Group 2: Clinical Data and Efficacy - Positive 12-month clinical data for RGX-121 are consistent with previously submitted biomarker and neurodevelopmental data and will be presented at the International Congress of Inborn Errors of Metabolism in September 2025 [3]. - MPS II patients treated with RGX-121 showed an 86% median reduction in cerebrospinal fluid levels of D2S6, a key biomarker of brain disease activity, approaching normal levels [7]. Group 3: Mechanism and Treatment Implications - RGX-121 is designed to deliver the iduronate-2-sulfatase (IDS) gene to the central nervous system, potentially providing a permanent source of the I2S protein beyond the blood-brain barrier [4][5]. - The treatment could lead to long-term cross-correction of cells throughout the CNS, addressing the underlying deficiency in MPS II patients [5][6]. Group 4: Market Reaction - Following the news, REGENXBIO's stock price decreased by 7.46%, trading at $8.06 [8].