A Study of Anti-CD38 Monoclonal Antibody (SG301) Subcutaneous Injection in Children With Nephrotic Syndrome With Frequent Relapses or Steroid Dependence

Inclusion Criteria: 1. Aged 6 - 18 years. 2. Steroid-sensitive nephrotic syndrome with frequent relapses (FRNS) or steroid dependence (SDNS). 3. Normal renal function: eGFR≥90 ml/min/1.73m². 4. After steroid treatment, morning urine protein\<1 + or urine protein/creatinine\<0.2 g/g (\<20 mg/mmol) for ≥3 consecutive days. 5. Within 7 days before enrollment, blood tests (without growth factors or transfusions) must meet: hemoglobin\>80 g/L; platelets\>75×10⁹/L; neutrophils\>1.5×10⁹/L. 6. Prothrombin time/INR≤1.5×ULN, unless due to anticoagulation. 7. No Tacrolimus, cyclosporine A, mycophenolate mofetil, belimumab, levamisole, azathioprine, or cyclophosphamide in prior 2 months; no rituximab or obinutuzumab in prior 6 months. Exclusion Criteria: 1. Family history of nephrotic syndrome, chronic glomerulonephritis, or uremia. 2. Alanine aminotransferase \>2×ULN or total bilirubin\>2×ULN with a sustained increase for 2 weeks. 3. HBsAg or HBcAb positive with Hepatitis B virus DNA above the lower limit of normal; Hepatitis C virus antibody - positive with Hepatitis C virus RNA positive; HIV antibody - positive. 4. Chronic active infections (e.g., Epstein-Barr Virus, Cytomegalovirus, tuberculosis) that may worsen with steroids/ immunosuppressants. 5. Acute active infection (excluding onychomycosis) requiring systemic antibiotics/antivirals. 6. Secondary nephrotic syndrome (e.g.,immunoglobulin A - associated, lupus nephritis); steroid - resistant nephrotic syndrome (SRNS). 7. Other autoimmune diseases, primary immunodeficiency, or malignancy. 8. Prior anti - cluster of differentiation 38 (CD38) treatment. 9. Live/attenuated vaccine receipt or major surgery (non - diagnostic) within 4 weeks before first dose.