Regenxbio's DMD Gene Therapy Data Falls Short of Sarepta's Elevidys

Regenxbio has released interim results from its ongoing Phase I/II trial for RGX-202, a gene therapy aimed at treating Duchenne muscular dystrophy (DMD). The results, presented in the AFFINITY DUCHENNE trial, focus on data collected from five children between the ages of six and twelve. The trial is investigating the safety and efficacy of RGX-202, particularly looking at microdystrophin expression levels, which are key indicators of the therapy's potential effectiveness in altering the progression of DMD.

According to analysts at BMO Capital Markets, the new data align closely with the results from Sarepta's Elevidys, another DMD gene therapy that received its first approval in June 2023. Although the RGX-202 trial showed some functional improvements that appeared slightly higher than those seen with Elevidys, the analysts noted the variability among patients and the absence of a placebo control group, suggesting that the efficacy differences were not substantial enough to alter clinical outcomes materially.

RGX-202's interim results were reflected in Regenxbio's stock performance, with a noted decrease of about 16% following the publication. The primary endpoint of the AFFINITY DUCHENNE trial is safety, complemented by a biomarker endpoint focusing on microdystrophin expression levels. To date, Regenxbio has reported no serious adverse effects among trial participants. It's noteworthy that patients receiving RGX-202 have been administered immunosuppressants to mitigate potential side effects, a precaution not observed with Elevidys, which adds a layer of complexity to the comparison of the two treatments.

On the efficacy front, RGX-202 continues to indicate positive impacts on the disease course. Improvements have been observed in assessments like the North Star Ambulatory Assessment and various timed function tests, which measure capabilities such as standing, walking, and climbing. These improvements surpassed external natural history controls, reinforcing the potential of RGX-202 to alter disease trajectory favorably.

Looking ahead, Regenxbio is preparing to submit a biologics license application to the FDA by mid-2026, targeting approval through the accelerated pathway in the first half of 2027. This timeline underscores the competitive atmosphere in the DMD treatment space, where Regenxbio and Sarepta are prominent players.

The rivalry between Regenxbio and Sarepta gained legal attention in 2020, when Regenxbio filed a lawsuit against Sarepta regarding a patent on an adeno-associated virus (AAV) gene therapy cell culture technique. However, the legal proceedings concluded in 2024 with a Delaware district court ruling in favor of Sarepta, declaring that the cell culture technique was not eligible for patent protection.

Safety concerns surrounding DMD gene therapies have intensified recently, particularly following the death of a patient treated with Elevidys due to acute liver injury earlier this year. Regenxbio's trial has so far shown a positive safety profile, but the extensive use of immunosuppressants presents its own potential risks. Additionally, the viral vector utilized by Regenxbio has been associated with mortality concerns, adding another layer of scrutiny in the evaluation of RGX-202's safety.

As the development of RGX-202 progresses, Regenxbio remains focused on advancing its treatment to meet FDA standards and bring a new therapeutic option to the market for DMD, aiming to improve the lives of those affected by this challenging condition.