REGENXBIO wins FDA backing for first MPS II gene therapy

REGENXBIO Inc. said Monday the U.S. Food and Drug Administration will reconsider approving its experimental gene therapy for Hunter syndrome, reversing a rejection four months ago and clearing a path to what would be the first one-time treatment for the rare brain disorder.

The FDA confirmed no additional studies are required and will review existing longer-term data from the CAMPSIITE study on an expedited basis for accelerated approval, the Rockville, Maryland-based company said in a statement. REGENXBIO expects to resubmit the Biologics License Application in the third quarter of 2026.

"This alignment with the FDA represents a significant milestone for patients and families affected by MPS II," a company spokesperson said. "We are committed to bringing the first gene therapy to this community as quickly as possible."

NAVSUNLI, also known as clemidsogene lanparvovec-sngl and RGX-121, is a one-time gene therapy for Mucopolysaccharidosis type II, an ultra-rare neurodegenerative disease that primarily affects boys. The condition, also called Hunter syndrome, is caused by a deficiency of the iduronate-2-sulfatase enzyme, leading to progressive cognitive decline and organ damage. While Takeda Pharmaceutical Co.'s enzyme-replacement therapy Elaprase exists, it cannot cross the blood-brain barrier, leaving the neurological form of the disease without effective treatment. The CAMPSIITE study evaluated NAVSUNLI's ability to halt cognitive decline by delivering a functional copy of the IDS gene directly to brain cells.

The FDA's reversal is the latest in a series of apparent turnarounds by the agency after leaders installed by the Trump administration resigned or were fired, according to STAT News. Last week, UniQure said it was cleared to submit an application for a Huntington's disease gene therapy that the agency had previously rejected. The pattern suggests a shift in regulatory posture toward gene therapies for rare neurological conditions, which have historically faced high hurdles for approval.

REGENXBIO's broader pipeline includes RGX-202 for Duchenne muscular dystrophy, which is in Phase 3 trials, and ABBV-RGX-314 for wet age-related macular degeneration, developed with AbbVie Inc. The wet AMD program could trigger a $100 million milestone payment by the fourth quarter of 2026, according to Seeking Alpha. The company's NAV AAV platform, which delivers therapeutic genes using adeno-associated virus vectors, underpins all three programs and represents the core technology driving the company's valuation.

Shares of REGENXBIO rose on the news, according to MarketWatch, extending gains from earlier reports of the FDA's shift. The stock had fallen after the initial rejection four months ago, which had cast doubt on the company's gene therapy strategy and its ability to navigate the FDA's evolving regulatory framework.

For investors, the FDA alignment removes a major regulatory overhang and accelerates the timeline to potential approval. If approved, NAVSUNLI would address a market with no approved gene therapy alternatives, representing a substantial commercial opportunity. REGENXBIO trades at a valuation that reflects the binary risk of its pipeline; a successful approval could re-rate the stock significantly, while a second rejection would raise questions about the viability of the company's gene therapy platform.

This article is for informational purposes only and does not constitute investment advice.