The primary objective of this study is to evaluate the safety and tolerability of SPOT-03 administered by intravenous (IV) infusion to DMD patients. In addition, this study will preliminarily investigate the changes in dystrophin nucleic acid concentration, dystrophin protein expression and engraftment, anti-dystrophin antibodies and cytokine profiles, as well as fat tissue mas and lean tissue mass following SPOT-03 administrations.

This is a FIH, open-label, single-arm, and single-center exploratory clinical study of SPOT-03 administered via IV infusion for DMD patients. SPOT-03 is a muscle-targeted extracellular vesicles (EVs) loaded with full-length dystrophin nucleic acid. The targeting ability of SPOT-03 is conferred by molecular targeting peptides on the EVs membrane, enabling the delivery of dystrophin nucleic acid as a gene therapy product for DMD.

The study has two dose groups:

Group I: 4.0E+11 dystrophin nucleic acid copies/kg, administered 8 times Group II: 4.0E+11 dystrophin nucleic acid copies/kg, administered 32 times The study will have a Screening Period of 30 days, during which patients or their legal guardian written informed consent will be obtained before Screening assessments and eligibility will be determined. A total of 6 to 9 DMD patients aged 2 to less than 8 years will be enrolled in this study according to the inclusion criteria. Complete data from at least 3 subjects will be obtained for Group II. All subjects will begin oral tacrolimus (0.05-0.2 mg/kg/d, adjustable according to actual clinical conditions) 3 days before the initial administration of SPOT-03 (D-3) and, with the duration aligned to the treatment schedule: 4 weeks for Group I and 16 weeks for Group II. In group I, the first dose of SPOT-03 will be administered by intravenous infusion on D1, followed by twice a week administration (once every 4 days) for a total of 8 doses. In group II, the first dose of SPOT-03 will be administered by intravenous infusion on D1, followed by twice a week administration (once every 4 days) for a total of 32 doses.

After all subjects in the previous dose group have completed SPOT-03 administrations, the next dose group may proceed after the investigators and sponsors have discussed and determined that there are no serious adverse reactions related to the drug.

Safety tests and evaluations will be conducted for the patients during each administration and follow-up.

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. Boys aged ≥ 2 years to < 8 years and capable of walking independently 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.

Male patients only, as Duchenne muscular dystrophy (DMD) predominantly affects males

Individual participant data will not be shared as this is an early-phase pilot study