The purpose of this study is to evaluate the efficacy of povetacicept in adult participants compared with placebo in reducing proteinuria and preserving renal function.

Key Inclusion Criteria:

• Diagnosed IgAN, with biopsy confirmation
• 24-hr proteinuria excretion ≥1.0 g/day or 24-hour uPCR ≥0.75 g/g
• Estimated glomerular filtration rate (eGFR) ≥ 30 mL/min/1.73m^2
• Stable angiotensin converting enzyme inhibitor (ACEi) or angiotensin II receptor blocker (ARBs) as per protocol specification

Key Exclusion Criteria:

• Have received any immunosuppressive treatment or procedures (including corticosteroids, oral immunosuppressive agents, B cell or plasma cell targeted therapies, complement targeted therapies, herbal medicines per protocol, and tonsillectomy) within a wash-out period per protocol
• Rapidly progressive glomerulonephritis with eGFR reduction >50% within 12 weeks of the start of screening

Other protocol defined Inclusion/Exclusion criteria may apply.

Details on Vertex data sharing criteria and process for requesting access can be found at: https://www.vrtx.com/our-science/clinical-trials-data-sharing/