An Open-label Study of Povetacicept in Autoantibody-Associated Glomerular Diseases

Key Inclusion Criteria Summary: Part A: * Biopsy-confirmed autoantibody-associated glomerular disease: immunoglobulin A nephropathy (IgAN), primary membranous nephropathy (pMN), or lupus nephritis (LN) * On maximal dose or the maximally tolerated dose ACEis/ARBs for ≥12 weeks prior to study Day 1 * Indication-specific criteria: 1. IgAN * Biopsy-confirmed diagnosis less than or equal to (≤)10 years prior to the start of screening AND Screening UPCR greater than or equal to (≥)0.5 g/g. * No background immunosuppression therapies. 2. pMN * A historical biopsy-confirmed diagnosis with positive anti-PLA2R1 antibodies or anti-THSD7A antibodies at screening AND Screening UPCR ≥1 g/g * Inadequate reduction of proteinuria determined by the Principal Investigator (PI) despite optimal supportive care for at least 12 weeks. * No background immunosuppression therapies except for optional calcineurin inhibitors. 3. LN * A Biopsy-confirmed diagnosis of active, proliferative Class III, IV, (with or without Class V) LN ≤6 months prior to the start of screening AND Screening UPCR ≥1 g/g, * Anti-dsDNA at screening. Anti-dsDNA testing is required but the result need not be positive. * On stable background immunosuppression ≥ 8 weeks prior to Day 1 4. AAV * Past diagnosis of renal AAV, defined as either of the following: * History of renal biopsy consistent with renal AAV. * History of clinically diagnosed renal AAV. * Myeloperoxidase (MPO)-ANCA or proteinase 3 (PR3)-ANCA positive by enzyme-linked immunosorbent assay at screening. * At least 4 weeks since initiation of AAV induction therapy, if applicable. Part B: * Participants meet at least 1 of the following criteria: * Completed investigational product (IP) treatment and 24 weeks of follow-up in Part A, or * Had IP interruption(s) in Part A, but did not permanently discontinue IP, and completed study visits up to the last scheduled visit of the follow-up period of Part A. Key Exclusion Criteria Summary: Part A: * Prior diagnosis of, or fulfills diagnostic criteria for, another renal disease * eGFR \<30 milliliter per minute per square meter (mL/min/1.73m\^2) or rapidly progressive glomerulonephritis * Recent serious or ongoing infection; risk or history of serious infection * Receipt of B cell depleting therapies or anti-BAFF and/or APRIL therapies within protocol specified timeframes Part B: * History of poor compliance with IP and/or procedures in Part A, as deemed by the investigator or Sponsor * History of any AEs or clinical conditions during Part A or emerging thereafter that may pose a safety concern for participation in Part B as deemed by investigator or Sponsor. Other protocol defined Inclusion/Exclusion criteria will apply