The purpose of the study is to evaluate the safety, tolerability, and efficacy of BBM-D101 to treat participants with Duchenne Muscular Dystrophy.

This is a single-arm, open-label study to evaluate the safety, tolerability, efficacy, pharmacokinetic, pharmacodynamic, and immune response of BBM-D101 within 52 weeks after a single intravenous infusion in DMD boys, as well as the long-term safety and efficacy of BBM-D101 for up to 5 years post infusion.

BBM-D101 is a gene addition therapy based on engineered AAV delivery therapeutic protein gene cassette into muscle for treating DMD. Therapeutic protein could mediate the dystrophin-associated protein complex to prevent muscular dystrophy and to rescue the function of muscle.

Inclusion Criteria:

1. The Participants and/or his legal guardian must fully understand the purpose, nature, methods, and potential risks of the study, and sign a written informed consent form.
2. Ambulatory male subjects aged 4 years and above but under 9 years (4 years ≤ age < 9 years).
3. Any mutation in the DMD gene confirmed by genetic testing
4. Serum creatine kinase (CK) during the screening period meets the study requirements.
5. Receiving stable, standard-dose glucocorticoids before screening.
6. The subject's AAV capsid antibodies meet the clinical trial requirements.
7. Able to cooperate with motor function assessment, MRI, and muscle biopsy as required by the study.
8. Laboratory test results during the screening period and at baseline meet the standards.
9. The subject and/or his legal guardian must fully understand the study procedures, be willing to actively cooperate, commit to high compliance with the protocol, and ensure that the subject attends all scheduled visits.

Exclusion Criteria:

1. Positive for hepatitis B surface antigen (HBsAg), hepatitis B virus deoxyribonucleic acid (HBV-DNA) ≥ 1000 U/mL, hepatitis C virus ribonucleic acid (HCV-RNA) positive, human immunodeficiency virus (HIV) positive, or positive for Treponema pallidum antibodies.
2. Currently receiving antiviral therapy for hepatitis B, hepatitis C, HIV, etc.
3. The investigator deems the subject has severe behavioral or cognitive disorders that may hinder participation in this study.
4. Poorly controlled asthma, or Duchenne Muscular Dystrophy (DMD) leading to significant decline in lung function, or recurrent infectious pneumonia that the investigator considers may affect respiratory function.
5. Left ventricular ejection fraction (LVEF) < 50% or New York Heart Association (NYHA) cardiac function class ≥ III.
6. Severe or persistent arrhythmias (such as atrial fibrillation, frequent ventricular premature beats, ventricular bigeminy, ventricular trigeminy, severe bundle branch block, etc.), and congenital heart disease that is evaluated by the investigator as unsuitable for participation in this study.
7. Any changes in preventive/cardiomyopathy treatment (initiation of treatment, drug changes, dosing regimen changes, treatment interruption, termination, or restart) within 1 month before the infusion of the study drug.
8. History of liver diseases such as portal hypertension, splenomegaly, hepatic encephalopathy, liver fibrosis ≥ stage 3, or hepatic nodules/cysts found by ultrasound during screening, or elevated alpha-fetoprotein with clinical significance as determined by the investigator.
9. Severe infection (such as pneumonia, pyelonephritis, or meningitis) within 4 weeks before the treatment visit (enrollment may be postponed).
10. History of gene therapy or cell therapy (such as stem cell transplantation).
11. History of or current presence of autoimmune diseases, severe renal, gastrointestinal, neurological, or coagulation disorders, malignant tumors, or other diseases.
12. Other diseases that the investigator deems unsuitable for participation in this study.