In this study, researchers will learn more about the use of felzartamab in participants with immunoglobulin A nephropathy (IgAN). IgAN is a kidney disease caused by the buildup of an antibody called IgA in the kidneys over time. In people with IgAN, abnormal IgA and other antibodies form clusters that build up in the small filters of the kidneys, which leads to inflammation and damage. Felzartamab is designed to target certain immune cells that produce these abnormal antibodies. This study will focus on participants who have protein in their urine (proteinuria) as a result of damaged kidneys.
The main goal of the study is to learn about the effect felzartamab has on proteinuria. The main question that researchers want to answer is:
• How much does the amount of protein in the urine change from the start of the study to Week 36?
Researchers will learn about the effect felzartamab has on the kidneys' ability to filter blood. They will also learn more about the safety of felzartamab and how it is processed by the body.
The study will be done as follows:
* Participants will be screened to check if they can join the study. * Participants will be randomized to receive either felzartamab or a placebo. A placebo looks like the study drug but contains no real medicine. * Neither the researchers nor the participants will know what the participants will receive. * Participants will receive felzartamab or placebo as intravenous (IV) infusions. The treatment period will last 24 weeks. * Afterwards, participants will enter a follow-up period which will last 80 weeks. * In total, participants will have 17 study visits. Participants will stay in the study for about 2 years.
Biopsy-confirmed diagnosis of IgAN within the past 10 years prior to signature of the informed consent form (ICF). For participants with diabetes mellitus type 2, an IgAN diagnostic biopsy within the past 24 months prior to signing the ICF.
An eGFR ≥ 30 mL/min/1.73 m² at Screening as calculated using the 2021 chronic kidney disease epidemiology (CKD-EPI) creatinine formula. An eGFR of ≥ 20 and < 30 mL/min/1.73 m² is acceptable for the cohorts 3 and 4.
Proteinuria of ≥ 1.0 gram per day (g/day) or UPCR ≥0.8 gram per gram (g/g) as assessed by an adequate 24-hour urine collection.
Clinically stable on a maximally tolerated dose or maximally approved dose of angiotensin-converting enzyme inhibitors (ACEI) or angiotensin receptor blockers (ARB) for at least 12 weeks prior to Screening. Participants may also be using sodium-glucose cotransporter-2 inhibitors (SGLT2is); endothelin receptor antagonists (ERAs) or dual endothelin angiotensin receptor antagonist (DEARAs) approved for the treatment of IgAN; and/or mineralocorticoid receptor antagonists (MRAs) as long as the dose is stable for at least 12 weeks prior to Screening. Participants should remain on stable doses of these background medications for the duration of the study. Once the ICF is signed and thereafter, the doses cannot be changed during the study nor the drugs discontinued except if deemed related to an AE. Participants using a DEARA (e.g., sparsentan) will not be permitted to use simultaneous ACEI or ARB medication.
Any history of secondary forms of IgAN, indicated by the presence of any other systemic disease potentially leading to IgA deposits as determined by the Investigator.
History of rapidly progressive variant of IgAN, defined as eGFR loss by > 50% per 3 months and not explained by changes in renin-angiotensin system (RAS) blockade or other factors.
IgAN-(MCD) variant.
Concomitant other progressive glomerulonephritis or non-immunologic glomerular disease such as diabetic nephropathy.