Trial of Sibeprenlimab in the Treatment of A Nephropathy (IgAN)

Inclusion Criteria: * Male and female patients ≥ 18 years of age . * Biopsy-confirmed IgAN. (Patients with an eGFR of 30 to 45 mL/min/1.73m2 must have had a kidney biopsy performed within 36 months of the screening visit). * Stable and maximally tolerated dose of ACEI and/or ARB for at least 3 months prior to screening. Patients who are on a stable dose of SGLT2i may participate if treatment was initiated ≥3 months prior to screening. Patients who are unable to take an ACEI or ARB may participate if their overall management conforms with standards of care and other protocol requirements. * Screening urine protein/creatinine ratio (uPCR) ≥ 0.75 g/g or urine protein ≥ 1.0 g/day * eGFR ≥ 30 mL/min/1.73 m2, (for the exploratory cohort only: eGFR 20- \<30 mL/min/1.73 m2), calculated using the 2021 CKD-EPI equation Exclusion Criteria: * Secondary forms of IgAN or IgA vasculitis. * Coexisting chronic kidney disease other than IgAN. * Kidney biopsy findings in addition to IgAN including those of diabetic nephropathy, membranous nephropathy, or lupus nephritis. Hypertensive vascular changes are acceptable. * Kidney biopsy MEST or MEST-C score of T2 or C2 (Oxford IgAN classification). If MEST-scoring was not performed, the presence of \> 50% tubulo-interstitial fibrosis, or crescents in \> 25% of glomeruli is exclusionary. This does not apply to the exploratory cohort. * Nephrotic syndrome * Serum IgG \< 600 mg/dL at screening. * Chronic systemic immunosuppression, including glucocorticoids, within 16 weeks of randomization * Participation in another interventional clinical trial and receipt of another investigational drug within 30 days prior to the administration of IMP or 5 half-lives from last investigational drug administration, whichever is longer. * Chronic infectious disease, or acute infectious disease at time of screening. * Type 1 diabetes, or poorly controlled Type 2 diabetes * Uncontrolled hypertension The protocol provides additional information about these and other inclusion and exclusion criteria.