Regenxbio Gets FDA Agreement to Refile Gene Therapy BLA

Regenxbio has reached agreement with FDA on a path toward a potential accelerated approval of Navsunli (clemidsogene lanparvovec-sngl), the first gene therapy for treating Hunter syndrome, or mucopolysaccharidosis type II (MPS II). The company says FDA has concluded that existing clinical data for the gene therapy are sufficient to support consideration under the accelerated approval pathway and that no additional studies or patient enrollment will be required for a BLA resubmission.

The update follows a February Complete Response Letter (CRL) in which FDA requested additional evidence to support approval of the investigational therapy. According to Regenxbio, the agency's latest position emerged through discussions conducted as part of the company's formal appeal of that decision.

In the CRL, FDA cited several concerns, including uncertainty in defining the neuronopathic patient population, questions about the comparability of natural history external controls, and whether the proposed CSF HS D2S6 biomarker is a reliable surrogate endpoint to predict clinical benefit, according to the company. At the time, the agency suggested multiple potential paths forward, including additional studies, longer-term follow-up, and inclusion of untreated control arms — options that are particularly challenging in an ultra-rare disease population like MPS II, it says.

Under the revised regulatory pathway, FDA has asked Regenxbio to request a Type A meeting to review longer-term biomarker and clinical data generated from the ongoing CAMPSIITE study. Following that meeting, the company plans to rapidly resubmit its BLA during the third quarter of 2026.

Importantly, Regenxbio says the agency indicated that the resubmission would receive an expedited review and that labeling discussions would begin shortly after the application is refiled.

Navsunli is designed as a one-time gene therapy that delivers a functional copy of the iduronate-2-sulfatase (IDS) gene directly to the central nervous system, according to the company. The treatment aims to provide sustained production of the deficient enzyme responsible for Hunter syndrome, including within the brain, where currently available enzyme replacement therapies have limited impact.

Hunter syndrome is a rare inherited lysosomal storage disorder caused by deficiency of the IDS enzyme. The disease leads to progressive accumulation of glycosaminoglycans throughout the body, resulting in neurological decline, organ dysfunction, and reduced life expectancy. About 2,000 patients worldwide are diagnosed with the condition.

The regulatory development represents a significant reversal from FDA's earlier position and could provide an important test case for how the agency's current leadership approaches accelerated approval decisions in ultra-rare diseases, particularly where randomized controlled studies are difficult to conduct.