This clinical trial is a prospective, multicenter, non-randomized controlled study designed to evaluate the efficacy and safety of Telitacicept, a novel biologic agent, in treating pediatric IgA Nephropathy (IgAN) and IgA Vasculitis Nephritis (IgAVN). The study plans to enroll 124 children aged 5-18, divided into a test group (standard therapy + Telitacicept) and a control group (standard therapy alone), with a 24-week treatment period. The primary endpoint is the change in 24-hour urine protein levels at week 24, while secondary outcomes include UPCR (urine protein-to-creatinine ratio), eGFR, and drug safety.

Inclusion Criteria:

• Diagnosed with IgA nephropathy (IgAN) or IgA vasculitis nephritis (IgAVN) Aged 5 to 18 years Weight ≥25 kg Moderate or heavy proteinuria At enrollment, estimated glomerular filtration rate (eGFR) ≥30 mL/min/1.73m² calculated using the Schwartz formula (36.5 × height [cm] / serum creatinine [μmol/L]).

Willing to sign the informed consent form

Exclusion Criteria:

• There is an ongoing infection that requires antiviral drugs or antibiotics for treatment.

The patient has received other B cell-targeting biologics within the three months prior to enrollment.

Patients with uncontrolled severe hypertension or diabetes. Individuals with other autoimmune diseases, primary immunodeficiencies, or tumors.

A history of organ transplantation. Patients with chronic active infections, such as Epstein-Barr virus, cytomegalovirus, or Mycobacterium tuberculosis, whose disease state may be exacerbated by the use of steroids and immunosuppressive agents.

Patients with severe liver failure, heart failure, or end-stage renal disease (ESRD).

Any other medical conditions that may place the patient at increased risk by participating in this study.

Individuals deemed by the investigator as unsuitable for participation in this study.