RGX-121 Gene Therapy Meets Primary MPS II Trial Goal

In a significant breakthrough for the medical community, REGENXBIO Inc. has reported positive outcomes from its Phase I/II/III CAMPSIITE® trial of RGX-121, a gene therapy for treating Mucopolysaccharidosis Type II (MPS II), commonly referred to as Hunter syndrome. The trial results indicate that the treatment has not only met its primary endpoint with high statistical significance but also has the potential to alter the disease's progression by replenishing the missing gene in affected boys.

The pivotal phase demonstrated that patients who received RGX-121 experienced a substantial decrease in cerebrospinal fluid (CSF) levels of D2S6, a critical biomarker for brain disease activity. This reduction was observed within 16 weeks, with a median 86% decrease reported, which is close to reaching normal levels. The data aligns with findings from the dose-finding phase of the trial, where patients showed notable improvements in neurodevelopmental functions over a span of four years.

Importantly, the RGX-121 treatment has been well-tolerated, and a significant portion of the patients have been able to forego or not initiate enzyme replacement therapy (ERT), which is the standard of care for MPS II. The treatment involves a one-time delivery of the iduronate-2-sulfatase gene (IDS) directly to the central nervous system (CNS) using the NAV® AAV9 vector, aiming to provide a long-term solution beyond the blood-brain barrier.

REGENXBIO's President and CEO, Kenneth T. Mills, expressed excitement about the results and the company's plans to submit a Biologics License Application (BLA) in 2024 under an accelerated approval pathway. The FDA has shown openness to this accelerated approval, contingent upon a comprehensive review of the data.

Dr. Paul Harmatz, a principal investigator of the trial, highlighted the absence of treatments for the fatal neuronopathic CNS disease associated with MPS II and emphasized the importance of RGX-121 as a potential breakthrough. MPS II is a rare genetic disorder that leads to the accumulation of glycosaminoglycans (GAGs) due to a deficiency in the I2S enzyme, causing severe health complications.

REGENXBIO, a clinical-stage biotechnology company, is dedicated to advancing gene therapy to cure diseases. The company's NAV Technology Platform utilizes over 100 novel adeno-associated virus (AAV) vectors for gene delivery, with RGX-121 being a key candidate in its pipeline. The platform's goal is to advance five AAV therapeutics into pivotal-stage or commercial products by 2025.

The positive results from the RGX-121 trial are a testament to REGENXBIO's commitment to gene therapy and its potential to transform the lives of those suffering from rare genetic disorders like MPS II. The company's focus on innovative treatments and its strategic approach to drug development underscore its leadership in the field of biotechnology.