AFFINITY DUCHENNE, a multi-centre, open-label trial of gene therapy RGX-202 for Duchenne muscular dystrophy has dosed its first patient, REGENXBIO has announced.

The company also revealed new, positive efficacy and safety data from the Phase I/II portion of the study, including the first functional data.

The positive functional results from the first five participants in the Phase I/II portion of the trial include 12-month data from three dose level 1 patients aged four to 10 and nine-month data from two dose level 2 (pivotal dose) patients aged eight and 12.

In all five participants, across both dose levels, RGX-202 demonstrated evidence of positively impacting disease trajectory, with patients demonstrating stable or improved function on the North Star Ambulatory Assessment (NSAA) and timed function tests.

Pivotal dose participants demonstrated improved performance on NSAA and timed function tests at nine months, exceeding external natural history controls. The NSAA mean score at this dose improved by 5.5 points.

All dose level 1 participants demonstrated improved performance and exceeded external natural history controls at 12 months.

Additionally, dose level 1 participants’ timed task velocity changes exceeded minimal clinically important difference (MCID) benchmarks at 12 months, a measure referenced by the FDA in the approval of the available gene therapy.

A differentiated microdystrophin construct

Curran Simpson, President and Chief Executive Officer of REGENXBIO, said: “The totality of our data demonstrates that RGX-202 provides evidence of improving outcomes for boys with Duchenne and altering the trajectory of this devastating disease, with consistent, robust expression of our novel microdystrophin translating into significant clinical benefit.

“Based on the strength of the Phase I/II data and our positive discussions and alignment with the FDA, we are quickly advancing RGX-202 toward a BLA filing in 2026 using the accelerated approval pathway. We continue to evaluate opportunities to expand the RGX-202 programme to benefit Duchenne patients worldwide.”

The Phase I/II AFFINITY DUCHENNE trial has been expanded into a Phase I/II/III trial of RGX-202. The pivotal trial is expected to support a Biologics License Application (BLA) submission using the accelerated approval pathway in 2026.

RGX-202 is the only gene therapy approved or in late-stage development for Duchenne with a differentiated microdystrophin construct that encodes key regions of naturally occurring dystrophin, including the C-Terminal (CT) domain. In preclinical studies, the CT domain has been shown to protect the muscle from contraction-induced stress and improve its ability to repair itself.

Diana Spencer, Senior Digital Content Editor, DDW