Regenxbio's DMD Gene Therapy Fails to Outperform Sarepta's Elevidys in Latest Trial Data

Regenxbio's efforts to introduce a new Duchenne muscular dystrophy (DMD) treatment hit a snag as interim Phase I/II data for its gene therapy RGX-202 failed to demonstrate significant advantages over Sarepta Therapeutics' Elevidys. The results, presented on Thursday, have sparked discussions about the future of gene therapies in the DMD treatment landscape.

Trial Results and Market Implications

The AFFINITY DUCHENNE trial, which included five patients aged 6 to 12 years, showed "consistent, robust microdystrophin expression" at 9 and 12 months post-treatment. However, BMO Capital Markets analysts noted that the efficacy improvements, while slightly higher than Elevidys in some aspects, did not represent a material difference that could "drive or prove differentiated clinical outcomes."

This assessment led to a significant market reaction, with Regenxbio's stock dropping approximately 16% following the announcement. The company's plans for a biologics license application in mid-2026, targeting approval in the first half of 2027 through the FDA's accelerated approval pathway, now face increased scrutiny.

Safety Considerations and Competitive Landscape

While Regenxbio reported no serious adverse effects in the trial, the use of immunosuppressants to mitigate potential side effects has raised questions. BMO analysts pointed out that this approach, not employed with Elevidys, carries its own risks. Additionally, concerns have been voiced about the viral vector used by Regenxbio, which has been associated with mortality issues in the past.

The safety profile of DMD gene therapies has come under intense scrutiny following a patient death due to acute liver injury while taking Elevidys in March. This incident has heightened the focus on safety across all gene therapy approaches for DMD.

Industry Competition and Legal Battles

The rivalry between Regenxbio and Sarepta in the DMD space extends beyond clinical trials. In 2020, Regenxbio sued Sarepta for patent infringement related to an adeno-associated virus (AAV) gene therapy cell culture technique. However, in 2024, a Delaware district court ruled in favor of Sarepta, determining that the cell culture technique was not patentable.

As the race to dominate the DMD treatment market continues, both companies face challenges in differentiating their products and ensuring patient safety. The coming years will likely see further developments as Regenxbio pursues its regulatory strategy and Sarepta works to maintain its market position with Elevidys.