Regenxbio Reports Promising Hunter Syndrome Trial Results, Submits Application to FDA for RGX-121 Approval

Regenxbio has reported promising results from its Phase I/II/III CAMPSIITE trial for Hunter syndrome, with participants experiencing an 82% median reduction in cerebrospinal fluid levels of heparan sulfate D2S6 within one year. The findings suggest a strong connection between CSF HS D2S6 levels and neurocognitive outcomes, potentially serving as a valuable surrogate endpoint for accelerated approval. The results support Regenxbio's Biologics License Application for RGX-121.

Regenxbio Inc. (Nasdaq: RGNX) has reported encouraging 12-month pivotal data from its Phase I/II/III CAMPSIITE trial for the treatment of Hunter syndrome (MPS II). The data, presented at the International Congress of Inborn Errors of Metabolism (ICIEM) 2025, demonstrate a significant reduction in cerebrospinal fluid (CSF) levels of heparan sulfate (HS) D2S6, a key biomarker for MPS II brain disease.

Participants in the pivotal phase of the CAMPSIITE trial (n=13) sustained an 82% median reduction in CSF HS D2S6 levels over one year. This reduction is consistent with previously reported topline pivotal results from the CAMPSIITE trial, which met its primary endpoint of CSF HS D2S6 reduction at week 16 with statistical significance (p 0.0001). The new data also show a strong correlation between CSF HS D2S6 levels at week 16 and neurocognitive outcomes at one year, supporting the use of CSF HS D2S6 as a surrogate endpoint for accelerated approval.

The trial's primary endpoint was to measure CSF GAGs, with accurate and sensitive measurements of CSF HS D2S6 having the potential to predict clinical benefit under the accelerated approval pathway. The buildup of GAGs in the CSF of MPS II patients correlates with clinical manifestations, including neurodevelopmental deficits.

Regenxbio submitted these longer-term pivotal results to the U.S. Food and Drug Administration (FDA) in response to an information request in the ongoing Biologics License Application (BLA) review of RGX-121. The FDA completed a pre-license inspection and bioresearch monitoring information inspection for the RGX-121 BLA with no observations. No safety-related concerns have been raised by the FDA during the BLA review, and RGX-121 has been well tolerated in all 26 patients dosed across all phases of the CAMPSIITE trial as of August 20, 2024.

RGX-121 is a potential one-time AAV therapeutic for the treatment of boys with MPS II, designed to deliver the iduronate-2-sulfatase (IDS) gene to the central nervous system (CNS). Delivery of the IDS gene within cells in the CNS could provide a permanent source of secreted iduronate-2-sulfatase (I2S) protein beyond the blood-brain barrier, allowing for long-term cross correction of cells throughout the CNS. RGX-121 expressed protein is structurally identical to normal I2S.

The FDA is expected to make a decision on the RGX-121 BLA by February 8, 2026. About MPS II, or Hunter syndrome, is a rare, X-linked recessive disease caused by a deficiency in the lysosomal enzyme I2S leading to an accumulation of glycosaminoglycans (GAGs), including HS in tissues which ultimately results in cell, tissue, and organ dysfunction, including in the CNS.

Regenxbio is a biotechnology company on a mission to improve lives through the curative potential of gene therapy. The company is advancing a late-stage pipeline of one-time treatments for rare and retinal diseases.

References:
[1] https://regenxbio.gcs-web.com/news-releases/news-release-details/regenxbio-presents-positive-twelve-month-pivotal-data-phase