Business
REGENXBIO Announces Regulatory Update on RGX-121 BLA for MPS II
REGENXBIO Inc. (Nasdaq: RGNX) today announced that the U.S. Food and Drug Administration (FDA) has issued a Complete Response Letter (CRL) regarding its Biologics License Application (BLA) for RGX-121 (clemidsogene lanparvovec) for the treatment of Mucopolysaccharidosis II (MPS II), an ultra-rare neurodegenerative disease also known as Hunter syndrome.
About this update from Regenxbio Inc.
[{"type":"list","items":[{"val":[{"type":"text","content":"FDA issues Complete Response Letter for RGX-121 (clemidsogene lanparvovec) for treatment of Mucopolysaccharidosis II (MPS II) ","length":125,"tagName":"p"}]},{"val":[{"type":"text","content":"REGENXBIO plans to work with FDA on a path forward with the goal of resubmitting the BLA","length":88,"tagName":"p"}]}],"tagName":"ul","bulletedList":true,"length":213,"olType":false},{"type":"text","content":"ROCKVILLE, Md., Feb. 9, 2026 /PRNewswire/ -- REGENXBIO Inc. (Nasdaq: RGNX) today announced that the U.S. Food and Drug Administration (FDA) has issued a Complete Response Letter (CRL) regarding its Biologics License Application (BLA) for RGX-121 (clemidsogene lanparvovec) for the treatment of Mucopolysaccharidosis II (MPS II), an ultra-rare neurodegenerative disease also known as Hunter syndrome.","length":414,"tagName":"p"},{"type":"text","content":"In May 2025, the FDA accepted the RGX-121 BLA under the accelerated approval pathway. In the February 7, 2026 CRL, the FDA stated that it had agreed to the study protocol in principle and outlined several reasons for not approving the gene therapy, including uncertainty regarding the study eligibility criteria to adequately define a population with neuronopathic disease (vs. attenuated disease), the comparability of the natural history external control to the study population, and the appropriateness of CSF HS D2S6 as a surrogate endpoint reasonably likely to predict clinical benefit. The CRL lists several potential paths forward, including a new study, treating additional patients and conducting longer-term follow up, and using an untreated control arm, all of which would be challenging in an ultra-rare disease population, like MPS II.","length":848,"tagName":"p"},{"type":"text","content":""This decision is devastating for the families of boys living with this progressive, life-threatening disease," said Curran Simpson, President and CEO of REGENXBIO. "We are concerned about FDA's feedback regarding the overall development path and evaluation of the data in the context of the urgent need for this irreversible ultra-rare disease. We remain confident in the quality and volume of evidence demonstrating the long-term potential of RGX-121 to positively change the trajectory of Hunter syndrome. This program has been in developme...