Key Inclusion Criteria:  Patients ≥ 18 to ≤ 80 years (at date of signing the informed consent form [ICF]), but at least of legal age in the given country Biopsy confirmed diagnosis of IgAN within the past 8 years prior to signature of the ICF Proteinuria at screening visit ≥ 1.0 g/d. Treatment with an angiotensin-converting enzyme inhibitor (ACEi) and/or angiotensin receptor blocker (ARB) at maximum doses or maximally tolerated doses for ≥ 3 months prior to date of informed consent and adequate blood pressure (BP) control. A female of childbearing potential (FCBP), is only eligible to participate if she is not pregnant, not breast feeding, and agrees to follow the contraceptive guidance during the treatment period and for at least 3 months after the last dose of IMP  Key Exclusion Criteria:  Hemoglobin < 90 g/L Thrombocytopenia: Platelets < 100.0 x 10^9/L. Neutropenia: Neutrophils < 1.5 x 10^9/L. Leukopenia: Leukocytes < 3.0 x 10^9/L Diabetes mellitus type 1 Aspartate aminotransferase or alanine aminotransferase >1.5 x ULN, alkaline phosphatase >3.0 x ULN