Regenxbio is pushing its Duchenne muscular dystrophy gene therapy into pivotal development, with a BLA planned for 2026—potentially posing a threat to Sarepta’s Elevidys.
Regenxbio on Monday announced that it has aligned with the FDA on a development track and accelerated approval path for its investigational gene therapy RGX-202, which the biotech is proposing as a one-time treatment for Duchenne muscular dystrophy.
As per its End of Phase II meeting with the regulator, Regenxbio is aiming to file a Biologics License Application for RGX-202 in 2026. The FDA has also signed off on expanding the current Phase I/II AFFINITY DUCHENNE trial into a multicenter, open-label, pivotal Phase I/I/III study, which will administer a 2×1014 GC/kg dose of the gene therapy to around 30 ambulatory patients aged 1 year and older.
Regenxbio dosed its first patient in this study on Monday.
RGX-202’s pivotal development follows encouraging early-stage data, which provide “evidence of improving outcomes for boys with Duchenne and altering the trajectory of this devastating disease,” CEO Curran Simpson said in a statement. For instance, 12-month data unveiled on Monday showed stable or improved function scores in all five treated patients, as measured by the North Star Ambulatory Assessment, a validated tool used to assess functional motor capacity in ambulant Duchenne patients.
Regenxbio compared its functional findings with those from natural history controls—matched for age and baseline performance—and touted better outcomes in patients treated with the pivotal RGX-202 dose.
As for safety, RGS-202 was well-tolerated and no serious adverse events were documented. Common side effects included nausea, vomiting and fatigue, all of which are typical of gene therapies and were successfully resolved.
According to Simpson, these data indicate that “consistent, robust expression of our novel microdystrophin translating into significant clinical benefit.”
After Pfizer’s gene therapy fordadistrogene movaparvovec failed the Phase III CIFFREO study in June 2024, Regenxbio is now the biggest threat to Sarepta Therapeutics and its FDA-approved Elevidys (delandistrogene moxeparvovec-rokl), which has become a dominant force in the Duchenne market. In its third-quarter earnings report, Sarepta reported $190.5 million in worldwide sales for Elevidys, representing a year-on-year growth of 49%.
However, experts appear to be underwhelmed by Sarepta’s data for Elevidys so far. At the World Muscle Society meeting last month, the biotech presented five-year findings for the first four patients treated with the gene therapy, a readout that many experts found wanting, especially as Sarepta’s came from “a small open-label trial” not powered to assess the effects of Elevidys on disease progression, Michael Kelly, chief scientific officer at CureDuchenne, told BioSpace at the time.
Still, analysts appear not be worried about Regenxbio’s challenge. Jefferies’ Andrew Tsai in a Monday note pointed out that Regenxbio remains years behind Sarepta and that its data come from a relatively small number of ambulatory patients.
BMO Capital Markets’ Kostas Biliouris similarly noted that while RGX-202’s results look “promising,” there is still a need for “richer datasets before drawing conclusions.” And even if Regenxbio’s gene therapy maintains its promising profile, “we believe its pivotal design may lead to a narrow label that could enable market share for RGX-202 but wouldn’t threaten Elevidys opportunity,” Biliouris added.
