EGENXBIO Inc. (Nasdaq: RGNX) announced positive 12-month pivotal data from its Phase I/II/III CAMPSIITE® trial of RGX-121 (clemidsogene lanparvovec), an investigational one-time gene therapy for Mucopolysaccharidosis Type II (MPS II, Hunter syndrome). Results were presented at the International Congress of Inborn Errors of Metabolism (ICIEM) 2025 and submitted to the FDA as part of the ongoing Biologics License Application (BLA) review.
Science Significance
The trial showed an >80% reduction in cerebrospinal fluid (CSF) HS D2S6, a biomarker of MPS II brain disease, sustained for one year. Patients also demonstrated continued neurodevelopmental skill acquisition or stability, stratified by baseline function. Importantly, the data confirm HS D2S6 reduction as a surrogate biomarker reasonably likely to predict clinical benefit, supporting its role in accelerated approval pathways.
Regulatory Significance
The primary endpoint of CSF HS D2S6 reduction at week 16 was met with statistical significance. A strong correlation between biomarker reduction and neurocognitive outcomes at one year strengthens the case for regulatory acceptance of HS D2S6 as a surrogate endpoint. The FDA has completed inspections with no observations and is expected to decide on the BLA by February 8, 2026. RGX-121 holds multiple designations: Orphan Drug, Rare Pediatric Disease, Fast Track, and RMAT.
Business Significance
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If approved, RGX-121 would be the first and only commercially available one-time therapy targeting the genetic cause of Hunter syndrome. This represents a landmark opportunity in rare disease gene therapy, reinforcing REGENXBIO’s leading position in the AAV-based therapeutics space and strengthening its late-stage pipeline.
Patients’ Significance
Hunter syndrome is a devastating rare pediatric disorder with no therapies addressing neurodevelopmental decline. Clinicians note that a one-time treatment like RGX-121 could alter the disease trajectory, providing long-term benefits for children who otherwise face progressive deterioration.
Policy Significance
The CAMPSIITE program exemplifies how accelerated approval pathways—leveraging surrogate biomarkers like HS D2S6—can bring transformative therapies to patients faster. This trial also underscores the role of global regulatory designations (FDA RMAT, EMA ATMP) in expediting treatments for rare diseases.
Transaction Highlights
In the pivotal phase of CAMPSIITE (n=13), patients maintained an 82% median reduction in CSF HS D2S6 through one year, consistent with prior dose-finding data. Neurodevelopmental stability or improvement was observed across Bayley Scales assessments. New analyses confirmed that early biomarker reductions strongly correlated with one-year neurocognitive outcomes, supporting the FDA’s use of HS D2S6 as a surrogate endpoint under accelerated approval.
Source: REGENXBIO Inc. Press Release
