A Study to Evaluate the Safety and Tolerability of GEN6050X in Duchenne Muscular Dystrophy.

GEN6050X is an intravenously administered human DMD exon 50 skipping base editing drug containing dual single-stranded adeno-associated virus serotype 9 (ss.AAV9) vectors.

The study is a first-in-human, single-arm, open-label, single-center clinical trial to evaluate safety and tolerability of a single intravenous infusion of GEN6050X in ambulatory boys with DMD. Other objectives include pharmacokinetics, pharmacodynamics, and the preliminary clinical efficacy of GEN6050X over 52 weeks. A total of three ambulatory pediatric participants (aged 4 to 9 years old) are expected to enroll, each receiving a dose of 5×10^13 vg/kg. These participants will be dosed in a staggered fashion.

Safety assessments will include monitoring of adverse events (AEs), laboratory tests, electrocardiograms (ECGs), vital signs, and physical examinations throughout the study duration. In addition, a comprehensive short-term prophylactic immunosuppression regimen(including rituximab and sirolimus) will be administered prior to treatment in order to mitigate potential immune response.

Inclusion criteria

• Subject age: 4-10 years old (including 10 years old)
• Gender: Male
• Patients with DMD gene exon deletion types confirmed by molecular diagnosis: 8-49, 20-49, 22-49, 51, 51-53, 51-55, 51-57, 51-59, 51-60, 51-67, 51-69, 51-75 or 51-78 and other mutations amenable to exon 50 skipping.
• The participant is able to walk independently and completes the 10-meter walk test without assistance.
• Participant is able to complete time to stand from supine independently in less than 30s.
• The participant is able to cooperate with motor assessment testing.
• Receipt of glucocorticoids for 6 months and a stable daily dose for at least 12 weeks prior to study entry
• Ability to tolerate muscle biopsies under anesthesia with no contraindications to these procedures.

Exclusion criteria

• Participants are in the active period of viral infection, including infections such as TORCH virus, Epstein-Barr(EB) virus, and severe acute respiratory syndrome coronavirus 2 (SARS-COV-2).
• Received a live attenuated vaccine within 3 months prior to receiving GEN6050X, or was exposed to an influenza (or other inactivated) vaccine within 30 days prior to receiving GEN6050X, or received systemic antiviral, anti-infective, and/or interferon therapy.
• Serological tests found HIV, Hepatitis B Virus(HBV), hepatitis C virus(HCV), and syphilis infection.
• Severe infection (e.g., pneumonia, pyelonephritis, or meningitis) within 4 weeks prior to receiving gene therapy.
• With clear symptoms of cardiomyopathy, echocardiography shows that the left ventricular ejection fraction is less than 40%.
• Need for continuous or intermittent assisted support from a ventilator.
• Diagnosed with autoimmune disease or receiving related treatment for autoimmune disease.
• The following indicators are abnormal in laboratory biochemical testing:

γ-glutamyl transpeptidase (GGT) above the 2-fold upper limit and total bilirubin above 1.5 times the upper limit, cystatin C (cystatin C) > 1.27 mg/L, hemoglobin (Hgb) < 100 or >200 g/L; Leukocytes (WBC) > 18.5×10^9/L or platelet ≤ 125×10^9/L.

• The titer of AAV9 neutralizing antibody determined by cell suppression assay > 1:50.
• Patients have received any gene therapy (e.g., adeno associated virus(AAV) gene therapy), cell therapy (e.g., stem cell transplantation), in vivo editing, or ex vivo editing therapy (e.g., CRISPR-Cas9, TALEN) in the past.
• Participant has any contraindication to immunosuppressive therapy.
• Has a medical condition or extenuating circumstance that, in the opinion of the principal investigator, is unsuitable for participation in the clinical trial.
• The family does not wish to disclose the patient's study participation to the attending physician and other medical providers.