#United States #Rockville #REGENXBIO #RGX-121 #MPS II

Encouraging 12-Month Results for RGX-121 in MPS II Treatment

REGENXBIO Inc. recently presented positive twelve-month data from the pivotal Phase I/II/III CAMPSIITE® trial of RGX-121 (clemidsogene lanparvovec) for Mucopolysaccharidosis Type II (MPS II), also known as Hunter syndrome. The impressive results were revealed during the International Congress of Inborn Errors of Metabolism (ICIEM) 2025, illustrating significant advancements in the treatment of this rare disorder that affects boys by impairing their neurodevelopment.

According to the latest findings, over 80% reduction in cerebrospinal fluid (CSF) levels of heparan sulfate (HS) D2S6—a pivotal biomarker of MPS II brain disease—was sustained throughout a year among pivotal trial participants. Data showcased sustained skill acquisition and stability across a range of neurodevelopmental functions when evaluating the subjects after one year, providing solid evidence of RGX-121's effectiveness.

Dr. Steve Pakola, Chief Medical Officer at REGENXBIO, stated, "These biomarker and functional data provide further assurance of RGX-121’s long-term potential to redefine the trajectory of Hunter syndrome for affected boys." He further mentioned the strong correlation between CSF HS D2S6 levels and neurodevelopmental outcomes after one year, illustrating its reliability as a surrogate biomarker that could predict clinical benefits.

Details from the CAMPSIITE Trial

The CAMPSIITE trial consisted of 13 participants and achieved remarkable results. A median reduction of 82% in CSF levels of HS D2S6 was observed, consistent with prior findings. The primary endpoint of the trial was to measure HS D2S6 levels, which met statistical significance within just 16 weeks (p < 0.0001). Previous iterations of the trial had recorded 85% reductions sustained over two years. This improvement showcases RGX-121’s potential as a transformative one-time therapy to address the underlying genetic defect responsible for Hunter syndrome.

Notably, neurodevelopmental assessments using the Bayley Scales of Infant and Toddler Development, 3rd Edition (BSID-III), revealed skill acquisition or stability in participants across all sub-scales. This is particularly meaningful since most patients suffering from Hunter syndrome currently lack effective treatment options to mitigate neurodevelopmental regression.

Dr. Roberto Giugliani, Professor at UFRGS, expressed optimism about the data, emphasizing the urgency for new treatments in Hunter syndrome as current therapies fall short of addressing patients' developmental decline.

Regulatory Path Forward

REGENXBIO has submitted these positive long-term results to the U.S. Food and Drug Administration (FDA) in connection with the ongoing Biologics License Application (BLA) review process for RGX-121, signaling hope for accelerated approval by early next year. In August 2025, the FDA conducted inspections for the RGX-121 BLA and found no safety concerns, a pivotal factor as REGENXBIO prepares for a significant regulatory decision anticipated by February 8, 2026.

Overview of RGX-121

RGX-121 is designed to deliver the iduronate-2-sulfatase (IDS) gene directly to the central nervous system (CNS), potentially providing lasting benefits by correcting the genetic deficiency that leads to MPS II. The therapy has received multiple designations from the FDA, including Orphan Drug Product, Rare Pediatric Disease, Fast Track, and Regenerative Medicine Advanced Therapy (RMAT) classifications.

With a focus on leveraging innovative gene therapies to enhance patient care, REGENXBIO’s RGX-121 stands as a beacon of hope for many families impacted by Hunter syndrome. As clinical trials continue to yield promising results, healthcare providers and patients alike remain optimistic about a new era of treatment for this challenging condition.

In conclusion, the 12-month pivotal data shared by REGENXBIO shine a light on the potential RGX-121 holds for altering the landscape of treatment for MPS II, reaffirming the need for continued research and support for those affected by rare diseases.