REGENXBIO Inc. (NASDAQ:RGNX) announced positive topline and interim functional data from the pivotal Phase III portion of the Phase I/II/III AFFINITY DUCHENNE® trial of RGX-202, a potential best-in-class gene therapy for Duchenne Muscular Dystrophy. The trial met its primary endpoint with high statistical significance (p<0.0001), with 93% of participants reaching at least 10% microdystrophin expression at Week 12 (n=30). Additionally, RGX-202 demonstrated statistically significant correlation between microdystrophin expression and interim functional improvement.

"These topline results are exciting for the Duchenne community," said Pat Furlong, Founding President of Parent Project for Muscular Dystrophy. "For decades, our community has pushed for therapies that can change the trajectory of this disease, and today's news gives us renewed optimism. Our families cannot wait; regulatory flexibility for innovative medicines to treat rare disease remains an urgent priority. We applaud the dedication of the patients and families who participated in this research and look forward to continued progress toward delivering stronger futures for people with Duchenne."

"Duchenne muscular dystrophy is a rare, progressive neuromuscular disease characterized by worsening muscle weakness and loss of function, and there continues to be a critical unmet need for therapies that can reliably alter the course of the disease", said AFFINITY DUCHENNE principal investigator Aravindhan Veerapandiyan, M.D., Arkansas Children's Hospital. "It's encouraging to see robust microdystrophin expression, correlation with functional outcomes, and a manageable safety profile. These data give us hope and reinforce the potential of RGX-202 to positively impact disease progression in individuals with Duchenne."

"RGX-202 is the first gene therapy in development for Duchenne to demonstrate strong, statistically significant correlation between microdystrophin expression and functional improvement, a landmark distinction in the field," said Steve Pakola, M.D., Chief Medical Officer of REGENXBIO. "Today's topline results underscore how our novel construct and differentiated therapeutic approach support a favorable safety profile and potential clinical benefit, including in older patients where progressive decline is expected. These data support the potential of RGX-202 to become a best-in-class gene therapy for Duchenne patients."

AFFINITY DUCHENNE Topline Pivotal Interim Data

As of April 16, 2026

The pivotal portion of the Phase I/II/III AFFINITY DUCHENNE trial evaluated RGX-202 at 2x1014 GC/kg in 31 ambulatory boys aged 1 year of age and older. Key topline interim results include safety (n=31), biomarker (n=30), and functional data (n=9 aged >4 years, 12 months post-treatment).1

More than 20 additional participants have been enrolled in the confirmatory trial of RGX-202 (n=30), and the Company expects to have completed dosing in all 60 patients across the pivotal and confirmatory trials by mid-year.

Primary Endpoint and Biomarker Data

93% of participants achieved >10% RGX-202 microdystrophin expression at Week 12 (p<0.0001). Microdystrophin expression averaged 71.1% across all participants, and 41.6% in older boys, aged >8 years.  Additionally, 80% of participants achieved >40% microdystrophin expression.

RGX-202 was appropriately localized to the sarcolemma, demonstrating that the differentiated construct with the inclusion of the C-Terminal (CT) domain is appropriately targeting the muscle. Additionally, robust vector copies per nucleus and percent positive fibers observed support the potential for sustained microdystrophin expression.

Interim Safety and Tolerability Data

RGX-202 was well tolerated and demonstrated a favorable safety profile as of last data cut. A proactive, short-course immune suppression regimen in combination with a differentiated construct and industry-leading product purity levels of more than 80% full capsids may contribute to a favorable safety profile for RGX-202. Mean gamma-glutamyl transferase (GGT) and total bilirubin, recognized markers of liver inflammation in Duchenne, did not exceed the upper limit of normal up to one year post-treatment (n=9).

Two serious adverse events were reported; both were easily managed and resolved within weeks without sequelae. One case of subacute myocarditis was reported in an 8-year-old participant. The participant's most recent cardiac MRI confirmed no heart muscle fibrosis and no change in ejection fraction. One case of asymptomatic liver injury was reported in a 10-year-old participant. This patient's GGT peak elevation was 123 U/L, and his abdominal ultrasound and bilirubin levels were normal. Common drug-related adverse events included vomiting, fatigue, and nausea, all considered mild or moderate, and resolved without sequelae.  

Interim One Year Functional Data

In interim functional results from nine participants aged approximately 5 to 12 years at dosing, RGX-202 demonstrated functional improvement and evidence of positively impacting disease trajectory at one year post-treatment, as measured by North Star Ambulatory Assessment (NSAA) and timed function tests (Time to Stand, 10 Meter Walk-run, Time to Climb).

Participants demonstrated statistically significant improved performance across NSAA and all timed function tests when compared to external control using propensity score weighting, which is the primary analysis method specified in the SAP for the pivotal trial. [Figure 1]

RGX-202 microdystrophin expression at Week 12 demonstrated a statistically significant correlation with functional improvement at one year as measured by NSAA change from baseline (correlation= .094, p = 0.0002) and NSAA change from baseline compared to the cTAP predictive model (correlation= .092, p = 0.0005). [Figure 2]

Primary Endpoint and Interim Data Support Potential Accelerated Approval 

In recent discussions with FDA, the agency shared that the use of RGX-202 microdystrophin expression as a surrogate endpoint will be based on the correlation analysis with clinical outcomes, which has been clearly demonstrated in the interim data. While the FDA has recommended a randomized controlled trial, it has guided that externally controlled trials may be adequate for demonstrating substantial evidence of effectiveness, especially when the treatment effect is sufficiently large enough to overcome limitations of externally controlled trials. FDA offered to review the RGX-202 data and alternative proposals. REGENXBIO plans to discuss this data with the FDA at a future meeting. The Company is also finalizing the trial design for an ex-U.S. study to support global regulatory submissions. 

Given the positive topline pivotal data, continued favorable safety profile, and statistically significant correlation between microdystrophin and functional improvement, REGENXBIO plans to pursue accelerated approval for RGX-202 and is preparing for a potential commercial launch in 2027.