FDA Reverses Decision on Regenxbio’s Gene Therapy for Hunter’s Syndrome, Supporting BLA Resubmission for Accelerated Approval
REGENXBIO said the FDA will consider existing longer-term data for NAVSUNLI under the accelerated approval pathway without requiring new studies, allowing the company to target a BLA resubmission in Q3 2026.
Key Points
- REGENXBIO said the FDA will consider existing longer-term data for NAVSUNLI under the accelerated approval pathway and will not require additional studies or new patient enrollment before a BLA resubmission.
- The company expects a Type A meeting with the FDA in July and plans to resubmit the BLA in Q3 2026.
- NAVSUNLI is an investigational one-time gene therapy for Mucopolysaccharidosis Type II, also known as Hunter syndrome, a rare neurodegenerative disease.
In February 2026, the FDA rejected REGENXBIO’s gene therapy for Hunter’s syndrome. However, today, it appears that the decision has been reversed, and Regenxbio is now aligned with the FDA on the next steps for a potential accelerated approval resubmission for NAVSUNLI (clemidsogene lanparvovec-sngl, RGX-121).
The company said the FDA confirmed that existing clinical data can be considered under the accelerated approval pathway and that REGENXBIO does not need to enroll additional patients or run additional studies, including the previously recommended untreated control arm.
According to the company, the FDA asked REGENXBIO to request a Type A meeting to review existing longer-term biomarker and clinical data from the CAMPSIITE study, then resubmit the Biologics License Application after that meeting. REGENXBIO said the FDA would review the resubmission on an expedited basis, with labeling discussions expected to begin shortly after the filing.
REGENXBIO expects the Type A meeting to take place in July and said it plans to resubmit the BLA in Q3 2026.
Company and Community Response
“We are encouraged by recent signals from the new FDA leadership reinforcing a commitment to address the unique nature of rare diseases and use the accelerated approval pathway to bring transformative therapies to patients with serious, unmet medical needs,” said Curran Simpson, President and CEO of REGENXBIO. “We will continue to work closely with the FDA and remain focused on bringing this important therapy to boys living with Hunter syndrome as quickly as possible.”
“Hunter syndrome is a devastating, progressive disease with significant unmet medical needs and we are thrilled to see this progress for NAVSUNLI,” said Scott Loiler, Ph.D., Chief Scientific Officer National MPS Society. “The MPS community urgently needs new treatment options, and we appreciate the FDA’s willingness to use the accelerated approval pathway for rare diseases and expedite the review of NAVSUNLI so that the Hunter syndrome community may soon have access to a potentially transformative one-time treatment.”
About the Disease and Therapy
Mucopolysaccharidosis Type II (MPS II), or Hunter syndrome, is a rare X-linked recessive disorder caused by deficiency of the lysosomal enzyme iduronate-2-sulfatase, or I2S. The disease leads to buildup of glycosaminoglycans, including heparan sulfate, in tissues and can cause dysfunction across multiple organs, including the central nervous system. REGENXBIO said about 2,000 patients worldwide have been diagnosed with MPS II, and more than 500 babies are born with the disease each year.
The company said most patients have severe disease. Early developmental milestones may be reached, but developmental delay often becomes apparent between 18 and 24 months. Cerebrospinal fluid heparan sulfate is a key biomarker in MPS II, and the company noted that the D2S6 disaccharide has been shown to correlate with neurocognitive manifestations.
NAVSUNLI is an investigational one-time gene therapy designed to deliver the IDS gene to the central nervous system. REGENXBIO says this approach could enable long-term production of I2S beyond the blood-brain barrier and support cross-correction of cells throughout the CNS. The therapy has received Orphan Drug, Rare Pediatric Disease, Fast Track, and RMAT designations from the FDA, along with ATMP classification in Europe.
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