Safety and Dystrophin Expression of SPOT-mRNA03 in Duchenne Muscular Dystrophy (DMD) Patients

Inclusion Criteria: 1. According to the requirements of the region/country and/or IRB/IEC, the patient and/or legal guardian have signed a written informed consent form and are aware of all relevant study content. 2. Ambulatory boys aged between 2 to 6 years of age, inclusive who can work without assistance for at least 10 meters. 3. The medical history includes clinical diagnosis of DMD and confirmed Duchenne mutations using validated genetic testing (MLPA and whole genome sequencing). 4. Able to tolerate muscle biopsy under anesthesia and have no contraindications to biopsy. 5. Heart, liver, lung, and kidney functions are sufficient: 1. The left ventricular ejection fraction (LVEF) should be ≥ 50%; 2. Forced vital capacity (FVC) \> 50% of the expected value, and do not require nighttime ventilation; 3. Patient's glomerular filtration rate (GFR)\>30 mL/min/1.73 m2 Exclusion Criteria: 1. Complications other than DMD that may cause muscle weakness and/or motor dysfunction. 2. There are severe intellectual disabilities (such as severe autism, severe cognitive impairment, and severe behavioral disorders) that, according to the investigator's judgment, can affect the study. 3. Hospitalization for respiratory failure within 8 weeks prior to screening. 4. Asthma or underlying lung diseases that are poorly controlled, such as bronchitis, bronchiectasis, emphysema, or recurrent infectious pneumonia that investigator believes may affect respiratory function. 5. Severe uncontrolled heart failure (NYHA III-IV), including any of the following conditions： 1. Intravenous administration of diuretics or positive inotropic drugs is required within 8 weeks prior to screening. 2. Hospitalization due to worsening heart failure or arrhythmia within 8 weeks prior to screening. 6. Abnormal laboratory values considered clinically significant: 1. GGT \> 3 × upper limit of normal 2. Bilirubin ≥ 3.0 mg/dL 3. Creatinine ≥ 1.8 mg/dL 4. Hemoglobin \< 8 or \> 18 g/dL 5. White blood cell count \> 18,500/μL 7. Arrhythmias that require anti-arrhythmic treatment. 8. Subjects who are undergoing immunosuppressive therapy. 9. Has used other gene therapy, investigational drugs, or any treatment aimed at increasing dystrophin expression. 10. Subjects with a history of major surgeries within 12 weeks prior to the initial infusion or planning to undergo major surgeries (such as scoliosis surgery) during this study. 11. Subjects who are allergic to investigational products or local aesthetic drugs or have a history of severe allergies or genetic allergic reactions. 12. Within 6 months prior to the initial infusion, the subjects are exposed to another investigational drug or have participated in an intervention clinical trial. 13. Subjects with positive hepatitis B core antibody or hepatitis C antibody or HIV antibody during screening. 14. Investigator believes that the presence of any other serious diseases, medical conditions, or chronic drug treatment needs can pose unnecessary risks to gene transfer.