RGX-121 MPS II Gene Therapy Trial Meets Primary Endpoint

In a significant breakthrough for the treatment of Mucopolysaccharidosis Type II (MPS II), also known as Hunter syndrome, REGENXBIO Inc. has reported that its Phase I/II/III CAMPSIITE® trial of RGX-121 has achieved its primary endpoint with high statistical significance. The trial's results indicate that RGX-121, a one-time gene therapy, has the potential to substantially improve brain function in patients suffering from this rare genetic disorder.

The pivotal trial's data revealed that patients who received RGX-121 experienced a significant reduction in cerebrospinal fluid (CSF) levels of D2S6, a biomarker indicative of brain disease activity. The treatment led to an 86% median decrease in D2S6 levels, nearly reaching normal ranges, within 16 weeks of administration. This outcome was a remarkable achievement, given the lack of existing treatments addressing the severe neurological aspects of MPS II.

The study's findings were presented at the 20th Annual WORLDSymposium™ by Dr. Paul Harmatz, a trial investigator from UCSF Benioff Children's Hospital. Dr. Harmatz expressed optimism about the potential of RGX-121 to alter the natural progression of the disease, allowing affected boys to develop beyond the typical limitations imposed by MPS II.

REGENXBIO's President and CEO, Kenneth T. Mills, highlighted the significance of the data in supporting the Biologics License Application (BLA) submission for RGX-121, planned for 2024 through an accelerated approval pathway. The company has already shared the positive trial results with the FDA, which has shown openness to the accelerated approval based on a comprehensive review of the data.

Furthermore, the RGX-121 treatment has been well-tolerated in all 25 patients who participated in the trial across its various phases, as of January 3, 2024. The treatment's safety profile, coupled with its efficacy, positions it as a promising candidate for approval.

REGENXBIO's NAV Technology Platform, which includes the NAV® AAV9 vector used in RGX-121, has been instrumental in developing this groundbreaking therapy. The platform's proprietary adeno-associated virus (AAV) gene delivery system holds the potential to treat a wide range of diseases.

MPS II is a rare and severe X-linked recessive disorder characterized by a deficiency of the enzyme iduronate-2-sulfatase (I2S), leading to the accumulation of glycosaminoglycans (GAGs) and subsequent damage to cells, tissues, and organs, particularly in the central nervous system. RGX-121 is designed to deliver the IDS gene, which encodes the I2S enzyme, directly to the CNS, providing a long-term solution that bypasses the blood-brain barrier.

The success of the CAMPSIITE trial and the potential approval of RGX-121 underscore REGENXBIO's commitment to advancing gene therapy as a curative option for patients with rare and life-altering diseases. The company's "5x'25" strategy aims to progress five AAV Therapeutics into pivotal-stage or commercial products by 2025, marking a significant step forward in the field of gene therapy.