Immunoglobulin A Nephropathy (IgAN) is a kidney disease where a protein called IgA builds up and causes damage. This study is looking at how a new medicine called felzartamab affects people with IgAN who have protein in their urine. Proteinuria means having too much protein in urine due to kidney damage. The study aims to see if felzartamab can reduce protein levels in urine and improve kidney function.

Participants will receive either felzartamab or a placebo (a pretend treatment) through an intravenous (IV) infusion, which is a method of delivering medicine directly into the bloodstream. The treatment lasts for 24 weeks, followed by an 80-week follow-up, totaling about 2 years.

• The study involves 17 visits over about 2 years.
• Participants must have an IgAN diagnosis and stable kidney function.
• Researchers will evaluate the safety and processing of felzartamab in the body.

Joining this study involves regular check-ups and may help understand how well felzartamab works for IgAN, but it requires a long-term commitment and participation until the study ends.