Inclusion Criteria:
1. Age ≥ 18 years and ≤ 75 years, both male and female are included.
2. Clinically diagnosed as granulomatosis with polyangiitis (GPA) or microscopic polyangiitis (MPA) according to the definition of the 2012 Chapel Hill Consensus Conference (CHCC).
3. Positive serological detection of autoantibodies, defined as follows: positive anti-proteinase 3 (PR3-ANCA) or anti-myeloperoxidase (MPO-ANCA) (previous or screening test results).
4. Renal involvement at screening, defined as at least one of the following: (1) At least one renal item in the Birmingham Vasculitis Activity Score (BVAS) version 3.0; (2) According to the pathological classification criteria formulated by the European Vasculitis Society (EUVAS) in 2003, there is active, biopsy-confirmed ANCA-associated nephritis (biopsy must be performed within 1 year before the screening visit or during the screening period); (3) Microscopic examination of urine shows red blood cell casts.
5. Voluntarily participate in this clinical trial and sign the informed consent form.
Exclusion Criteria:
1. Life-threatening severe vasculitis (including diffuse alveolar hemorrhage, respiratory failure, intestinal perforation or massive bleeding, cerebral vasculitis, cardiac vasculitis, etc.).
2. Secondary vasculitis (such as systemic lupus erythematosus, Henoch-Schönlein purpura, drugs, tumors, infections, primary immunodeficiency, etc.).
3. Patients with primary kidney diseases (such as IgA nephropathy, membranous nephropathy and anti-glomerular basement membrane nephritis, etc.).
4. Major or uncontrolled diseases unrelated to AAV.
5. Rapidly progressive glomerulonephritis with rapid decline in renal function: estimated glomerular filtration rate (eGFR) ≤ 30 ml/min/1.73m² before the first administration, or already receiving continuous dialysis treatment.
6. Patients with central nervous system diseases (including epilepsy, psychosis, organic brain syndrome, cerebrovascular accident, encephalitis, central nervous system vasculitis).
7. Other multisystem autoimmune diseases including systemic lupus erythematosus, IgA, rheumatoid vasculitis, anti-glomerular basement membrane disease, cryoglobulinemic vasculitis, etc.
8. Active hepatitis or a history of severe liver disease or liver lesions (HBsAg positive, or HBcAb positive and HBV-DNA positive), active pulmonary tuberculosis.
9. Immunodeficiency, uncontrolled severe infection.
10. Abnormal laboratory indicators that need to exclude subjects include but are not limited to the following indicators: total bilirubin ≥ 3 times the upper limit of normal, alanine aminotransferase (ALT) ≥ 3 times the upper limit of normal, aspartate aminotransferase (AST) ≥ 3 times the upper limit of normal, white blood cell (WBC) \< 2.5×109/L, hemoglobin (Hb) \< 85 g/L, platelet count (PLT) \< 50×109/L.
11. Received any of the following treatments within 364 days before day 0: a) B-cell targeted therapy (e.g., rituximab, other anti-CD20 drugs, anti-CD22 \[epratuzumab\], anti-CD52 \[alemtuzumab\], BLyS receptor fusion protein \[BR3\], TACI-Fc); b) abatacept; c) experimental biological products.
12. Patients who have undergone kidney transplantation or other organ transplantation.
13. Received intravenous immunoglobulin or plasma exchange within 4 weeks before the first administration.
14. Pregnant women, lactating women and men or women with plans for childbearing during the trial.
15. Participated in other new drug clinical trials within 3 months before the first administration.
16. Psychiatric patients with depression or suicidal thoughts.
17. Have a history of major organ (such as heart, lung, kidney, liver) transplantation or hematopoietic stem cell/bone marrow transplantation or plan to receive transplantation.
18. Those with positive test results within 4 weeks before screening suggesting COVID-19 infection, or those with a severe history of COVID-19 requiring hospitalization within 12 months before screening.
19. Those allergic to Telitacicept.
20. Other diseases or conditions that the investigator deems inappropriate for participation in this trial.
