Gene Therapy RGX-202 Shows Positive Interim Results in Duchenne Muscular Dystrophy Trial

Carolina Tesi-Rocha, MD

(Credit: Stanford Children's Hospital)

New, positive interim data from the phase 1/2 AFFINITY DUCHENNE trial (NCT05693142) of RGX-202 (REGENXBIO), an investigational gene therapy for Duchenne muscular dystrophy (DMD), were recently presented at the 2025 Muscular Dystrophy Association (MDA) Clinical & Scientific Conference, held March 16-19 in Dallas, Texas. The new findings, which include biomarker data from 2 additional patients, may further support the therapy’s potential across a wide range of age groups.¹

The new biomarker data presented at the 2024 MDA conference highlighted robust and consistent microdystrophin expression in patients receiving the pivotal dose of RGX-202. In a 3-year-old patient, microdystrophin expression was measured at 122.3% compared with the control. In a 7-year-old patient, microdystrophin expression reached 31.5% compared to control. Across all patients, RGX-202 was appropriately localized to the sarcolemma, reinforcing its targeted muscle delivery.

"Patients with Duchenne continue to be in need of treatment options that could meaningfully impact the course of disease," lead author Carolina Tesi-Rocha, MD, clinical professor of neuromuscular medicine at Stanford Children's Hospital, said in a statement.¹ "The microdystrophin expression and biomarker data presented represent key indicators of potential therapeutic effect. Combined with the safety and functional data to date, I am highly encouraged by the profile of RGX-202."

The pivotal phase of the AFFINITY DUCHENNE trial is designed to support a biologics license application (BLA) submission via the accelerated approval pathway. The primary end point is the proportion of participants with microdystrophin expression at least 10% at Week 12. Additionally in the trial, RGX-202 has demonstrated the highest vector genome copies (4.9-55.4) measured by qPCR among approved or investigational gene therapies, further supporting its efficacy.

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According to REGENXBIO, the company is the only gene therapy sponsor currently recruiting patients under the age of 4 in the United States. Notably, microdystrophin expression levels in ambulatory patients aged 8 and older were the highest reported across approved or investigational gene therapies.

As of February 21, 2025, RGX-202 was well tolerated, with no serious adverse events (AEs) or AEs of special interest reported. The most common drug-related AEs—nausea, vomiting, and fatigue—were mild, resolved over time, and consistent with typical gene therapy administration. A combination of a short-course immune modulation regimen and high product purity, more than 80% full capsids, may be contributing to RGX-202’s strong safety profile.

Looking ahead, REGENXBIO plans to share additional phase 1/2 functional data in the first half of 2025 and complete pivotal trial enrollment by the end of the year, with a BLA submission expected by mid-2026. With these promising interim results, RGX-202 continues to advance as a potential transformative therapy for DMD, potentially offering hope to a broader range of patients.

"RGX-202 is the only next generation gene therapy for Duchenne in a pivotal phase trial. The new data from the age 1-3 cohort builds on the favorable safety and efficacy profile seen in ages 4 and older and reinforces the potential of RGX-202 to serve a wide age range of patients," Steve Pakola, MD, chief medical officer at REGENXBIO, said in a statement.¹ "The consistent, robust microdystrophin levels seen across the age range as well as the functional improvements previously reported support RGX-202's potential to alter the course of this devastating disease."

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REFERENCES
1. Rocha CT, Harper A, Iannaccone S, et al. RGX-202, an investigational gene therapy for the treatment of Duchenne Muscular Dystrophy: Interim clinical data. Presented at: 2025 MDA Clinical & Scientific Conference; March 16-19. Dallas, TX. Abstract O75
2. REGENXBIO Reports Positive Biomarker Data From AFFINITY DUCHENNE® Trial of RGX-202 Gene Therapy. News Release. REGENXBIO. Published March 19, 2025. Accessed March 20, 2025. https://regenxbio.gcs-web.com/news-releases/news-release-details/regenxbio-reports-positive-biomarker-data-affinity-duchenner