Regenxbio's DMD Gene Therapy Shows Promise, But Fails to Outperform Sarepta's Elevidys

Regenxbio has released interim results from its Phase I/II AFFINITY DUCHENNE trial for RGX-202, a gene therapy aimed at treating Duchenne muscular dystrophy (DMD). While the data demonstrates potential, analysts suggest it may not offer significant advantages over Sarepta Therapeutics' already-approved Elevidys.

Trial Results and Comparisons

The interim data, derived from five patients aged 6 to 12 years old, showed "consistent, robust microdystrophin expression" at 9 and 12 months post-treatment. Regenxbio reported improvements in the North Star Ambulatory Assessment and timed function tests, including time to stand, 10-meter walk-run, and time to climb, which exceeded external natural history controls.

However, BMO Capital Markets analysts noted that while certain functional improvements appear slightly higher than those seen with Elevidys, the high variability across patients and lack of a placebo arm make it difficult to conclude that RGX-202 offers materially different or superior clinical outcomes.

Safety Profile and Immunosuppression

RGX-202's primary endpoint is safety, and Regenxbio reported no serious adverse effects in the trial. Notably, patients receiving RGX-202 are given immunosuppressants to mitigate potential side effects, a practice not employed with Elevidys. While this approach may contribute to the therapy's safety profile, BMO analysts caution that "heavy" immunosuppression carries its own risks.

The safety of DMD gene therapies has come under scrutiny following a patient death due to acute liver injury while taking Elevidys in March. Although RGX-202's trial results appear positive from a safety standpoint, concerns remain about the viral vector used by Regenxbio, which has been associated with mortality issues in other contexts.

Regulatory Outlook and Market Competition

Regenxbio is planning to submit a biologics license application for RGX-202 in mid-2026 through the FDA's accelerated approval pathway, with the goal of securing approval in the first half of 2027. This timeline places RGX-202 several years behind Sarepta's Elevidys, which received FDA approval in June 2023.

The two companies have a history of competition in the DMD space, including a patent infringement lawsuit filed by Regenxbio against Sarepta in 2020. The suit, which concerned an adeno-associated virus (AAV) gene therapy cell culture technique, was resolved in Sarepta's favor in 2024 when a Delaware district court ruled that the technique was not patentable.

As Regenxbio continues to advance RGX-202 through clinical development, the company faces the challenge of differentiating its therapy in an increasingly competitive market for DMD treatments. The lukewarm reception of the latest data by analysts, reflected in a 16% drop in Regenxbio's stock price following the announcement, underscores the uphill battle the company faces in establishing RGX-202 as a preferred option for DMD patients and clinicians.