REGENXBIO Inc. announced that the Phase I/II AFFINITY DUCHENNE trial of RGX-202 for the treatment of Duchenne muscular dystrophy (Duchenne) is now active and recruiting patients. RGX-202 is designed to deliver a transgene for a novel microdystrophin protein that includes the functional elements of the C-Terminal (CT) domain found in naturally occurring dystrophin. RGX-202 uses REGENXBIO's proprietary NAV AAV8 vector.

AFFINITY DUCHENNE is a multicenter, open-label dose evaluation and dose expansion clinical trial to evaluate the safety, tolerability and clinical efficacy of a one-time intravenous (IV) dose of RGX-202 in patients with Duchenne. Additionally, REGENXBIO is recruiting patients in the AFFINITY BEYOND trial, an observational screening study. The primary objective is to evaluate the prevalence of AAV8 antibodies in patients with Duchenne up to 12 years of age.

Information collected in this study may be used to identify potential participants for the AFFINITY DUCHENNE trial and potential future trials of RGX-202. REGENXBIO has manufactured additional clinical supply of RGX-202 in its in-house Manufacturing Innovation Center using the NAVXpress process platform. Located in REGENXBIO's 132,000 square foot headquarters in Rockville, MD, the Manufacturing Innovation Center is designed to meet global clinical and commercial regulatory standards, and includes two independent bulk drug substance production suites, a final drug product suite and integrated quality control labs. REGENXBIO is one of only a few gene therapy companies worldwide with a cGMP facility capable of production at scales up to 2,000 liters.

AFFINITY DUCHENNE Trial Design: In the dose evaluation phase of the trial, six ambulatory, pediatric patients (ages 4 to 11 years old) with Duchenne are expected to enroll in two cohorts with doses of 1x1014 genome copies (GC)/kg body weight (n=3) and 2x1014 GC/kg body weight (n=3). After an independent safety data review for each cohort, a dose expansion phase of the trial may allow for up to six additional patients to be enrolled at each dose level (for a total of up to nine patients in each dose cohort). The trial design also consists of thorough safety measures 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. Initial trial sites are located in the U.S., with additional sites in Canada and Europe expected to follow. AFFINITY BEYOND™ Observational Study: AFFINITY BEYOND is an observational screening study.

The primary objective is to evaluate the prevalence of anti-adeno-associated serotype 8 (AAV8) antibodies in participants with Duchenne muscular dystrophy. AAV gene therapies are delivered via viral vectors that are not known to cause disease in humans. For AAV gene therapies delivered systemically, it's important to screen patients for antibodies to the vector.

This observational study is intended to help inform future clinical research in Duchenne.