REGENXBIO's RGX-121 Secures FDA Acceptance for MPS II Treatment Review

REGENXBIO Secures FDA Acceptance for RGX-121

On May 13, 2025, REGENXBIO Inc. (Nasdaq: RGNX) made a crucial announcement regarding its investigational gene therapy RGX-121. The U.S. Food and Drug Administration (FDA) has formally accepted the Biologics License Application (BLA) for RGX-121 aimed at treating Mucopolysaccharidosis II (MPS II), also recognized as Hunter syndrome. The FDA's action signifies a pivotal moment for the company and the affected patient community, as it granted the application a Priority Review designation, with a target action date set for November 9, 2025.

A Groundbreaking Potential

RGX-121 represents an innovative approach to treating MPS II by delivering the iduronate-2-sulfatase (IDS) gene directly to the central nervous system (CNS). This gene therapy has the potential to provide a one-time treatment option that could address both the systemic and neurodevelopmental impacts of Hunter syndrome. Current treatment options primarily consist of weekly enzyme replacement therapies, which often fail to provide adequate relief and can impose a significant burden on patients and their families.

“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,” Curran M. Simpson, President and CEO of REGENXBIO stated. This reflects a strong commitment to innovate within the field of gene therapy to transform the trajectory of MPS II treatment.

Aside from its FDA acceptance, RGX-121 has also received Orphan Drug Product, Rare Pediatric Disease, Fast Track, and Regenerative Medicine Advanced Therapy (RMAT) designations from the FDA, underscoring its potential significance.

Collaboration for Commercialization

Following potential FDA approval, NS Pharma, Inc., a wholly-owned subsidiary of Nippon Shinyaku, is set to take charge of the commercialization of RGX-121 in the U.S. This strategic partnership is imperative, as it enables REGENXBIO to focus on manufacturing and ensuring a robust supply chain for the therapy while leveraging NS Pharma’s market expertise.

Moreover, REGENXBIO retains full rights concerning the priority review voucher that could accompany RGX-121’s approval, which may have substantial financial implications for the company.

Understanding MPS II

MPS II, a rare X-linked recessive disorder, arises due to a deficiency in the enzyme iduronate-2-sulfatase (I2S), leading to the accumulation of glycosaminoglycans (GAGs) in the body, particularly in the CNS. Patients present a variety of symptoms resulting from this dysfunction, including developmental delays and neurological symptoms that necessitate aggressive management and treatment. Currently, there is a dire need for effective therapies targeting the neurological aspects of the condition, as traditional enzyme replacement therapies do not adequately address these symptoms.

The biomarker heparan sulfate (HS) serves as a key indicator of I2S activity and correlates with cognitive manifestations in affected individuals, highlighting the importance of effective management across various symptoms of the disease.

The Road Ahead

REGENXBIO aims to lead the transformation in treatment paradigms for MPS II through its pioneering gene therapy. With thousands of patients benefiting from REGENXBIO's AAV gene therapy platform, including notable products like Novartis' ZOLGENSMA®, the potential impact of RGX-121 cannot be overstated.

The company's commitment to gene therapy demonstrates a clear vision: to dramatically enhance healthcare delivery for myriad patients grappling with rare diseases. For more updates and insights, visit www.REGENXBIO.com.