REGENXBIO Inc. announced it initiated enrollment in a new cohort of patients ages 1-3 in its Phase I/II AFFINITY DUCHENNE® trial to evaluate the safety and efficacy of RGX-202 in boys with Duchenne muscular dystrophy (Duchenne). RGX-202 is an investigational one-time AAV Therapeutic targeted to deliver a novel microdystrophin, representing the next wave of innovative design in Duchenne gene therapy. The new cohort is expected to enroll up to five patients aged 1-3 to receive RGX-202 at the pivotal dose level (2x1014 genome copies (GC)/kg body weight).

Additionally, REGENXBIO has confirmed an end-of-Phase II (EOP2) meeting is scheduled with the FDA at the end of July. This meeting is expected to finalize the AFFINITY DUCHENNE pivotal trial design, with the goal of continuing to expedite the development of RGX-202. The Company anticipates that all patients enrolled at dose level 2 (n=12) will be included in its pivotal trial data set.

The Company plans to use RGX-202 microdystrophin expression as a surrogate endpoint to support a Biologics License Application (BLA) submission using the accelerated approval pathway with the potential to receive a broad label. REGENXBIO has recently confirmed with the FDA that the pathway can be used given the ongoing high unmet need for differentiated treatment options in the Duchenne community. RGX-202 is the most advanced gene therapy enrolling in active clinical trials and is anticipated to be the next gene therapy in a BLA filing for Duchenne.

Clinical Program Updates: The Company continues to rapidly enroll the remaining patients in the ages 4-11 cohort (dose level 2 expansion cohort) and expects to imminently complete the enrollment of up to seven patients at dose level 2 early third quarter of 2024. REGENXBIO expects to share initial strength and functional assessment data for both dose levels of the AFFINITY DUCHENNE trial in the second half of 2024. Initiation of the pivotal trial is on track for late third quarter to early fourth quarter of 2024.

RGX-202 in the AFFINITY DUCHENNE trial is manufactured using REGENXBIO's proprietary, high-yielding NAVXpress? platform process. This suspension-based manufacturing process has demonstrated robust scalability with consistent yield and product purity and is ready for product commercialization.

AFFINITY DUCHENNE Trial Design: The Phase I/II AFFINITY DUCHENNE trial is a multicenter, open-label dose escalation and dose expansion clinical study to evaluate the safety, tolerability and clinical efficacy of a one-time intravenous (IV) dose of RGX-202 in patients with Duchenne aged 1-11. The trial design was informed by the Duchenne community and engagement with key opinion leaders, including a comprehensive, short-term, prophylactic immunosuppression regimen to proactively mitigate potential complement-mediated immunologic responses, and inclusion criteria based on dystrophin gene mutation status, including DMD gene mutations in exons 18 and above. Trial endpoints include safety, immunogenicity assessments, pharmacodynamic and pharmacokinetic measures of RGX-202, including microdystrophin protein levels in muscle, and strength and functional assessments, including the North Star Ambulatory Assessment (NSAA) and timed function tests.