Regenxbio has announced that the US Food and Drug Administration (FDA) accepted its Biologics License Application (BLA) for clemidsogene lanparvovec, known as RGX-121.
The application seeks accelerated approval for treating Mucopolysaccharidosis II (MPS II), commonly referred to as Hunter syndrome.
The FDA has assigned a Priority Review to this application, with a Prescription Drug User Fee Act (PDUFA) target action date of 9 November 2025.
Regenxbio president and CEO Curran Simpson said: “Acceptance of the RGX-121 BLA marks an exciting milestone on our path to bring the MPS II patient community a one-time treatment with the potential to address both the neurodevelopmental and systemic effects of Hunter syndrome.
“Supported by positive biomarker data and long-term outcomes, RGX-121 has the potential to be a first-in-class gene therapy that could dramatically transform the MPS II treatment landscape and reduce the significant burden patients and families currently face with weekly enzyme replacement therapy.”
RGX-121 is designed as a one-time gene therapy for boys with MPS II. It aims to introduce the iduronate-2-sulfatase (IDS) gene into the central nervous system (CNS). This process is intended to establish a continuous source of the iduronate-2-sulfatase (I2S) protein, potentially achieving long-term cellular correction beyond the blood-brain barrier. The protein expressed by RGX-121 is identical in structure to the normal I2S protein.
The FDA has awarded RGX-121 several designations, including Orphan Drug Product, Rare Pediatric Disease, Fast Track, and Regenerative Medicine Advanced Therapy (RMAT). Additionally, the European Medicines Agency has classified it as an advanced therapy medicinal product (ATMP).
In January 2025, Regenxbio and NS Pharma, a subsidiary of Nippon Shinyaku, entered a strategic partnership.
Under this agreement, NS Pharma will handle the US commercialisation of RGX-121 following potential FDA approval. This approval could result in a Priority Review Voucher (PRV), with Regenxbio retaining all rights and proceeds from any potential sale of the PRV.
