A Study to Assess the Effects of Zigakibart on IgA Nephropathy.

Inclusion Criteria: * Primary IgAN, confirmed by kidney biopsy, within 5 years prior to Screening * eGFR ≥45 mL/min/1.73 m2, based on the 2021 CKD-EPI equation, at Screening * Persistent proteinuria, defined as either * Total Urine Protein ≥0.5 g/day or UPCR ≥0.5 g/g in a 24-hour urine collection, at Screening, despite maximally tolerated dose or poorly tolerated supportive therapy or * IgAN diagnosis \<6 months prior to Screening with Total Urine Protein \>1.5 g/day or UPCR \>1.5 g/g in a 24-hour urine collection, at the time of clinical presentation or diagnosis * Body weight ≥45 kg and body mass index (BMI) ≤35.0 kg/m2, at Screening Exclusion Criteria: * Secondary forms of IgAN, as determined by the Investigator, diagnosis of IgA vasculitis, or any other nephropathy or chronic urinary tract disorder * Total IgG \<6.0 g/L at screening * Any chronic urinary tract disorder, including but not limited to retention, incontinence, and/or recurrent urinary tract infections * Untreated hypertension or uncontrolled hypertension despite treatment (i.e., resistant hypertension) * Treatment with complement pathway inhibitors, mycophenolic acids, systemic calcineurin inhibitors or corticosteroids, immunosuppressive or immunomodulatory agents within 12 months prior to screening * Acute kidney injury (AKI), defined by AKI network criteria, within 4 weeks prior to screening * Current treatment with anti-APRIL monoclonal antibodies or dual APRIL/BAFF inhibitors or past treatment of …