This is a multi-part study comprising of the original Phase 2b study (Parts A/B) and the addition of a separate Phase 3 study (Parts C/D).~Part A/B (Dose Ranging Study):~This portion of the study will assess multiple doses of atacicept vs. placebo on impact of renal function as measured by proteinuria. Safety, eGFR, serum immunoglobulins and Gd-IgA1 will also be clinically assessed. The clinical study is comprised of a 36wk double-blind treatment period, followed by a 60wk open-label treatment period and a 26wk safety follow-up period. (No longer recruiting)~Part C/D (Pivotal Study):~This portion of the study will evaluate the efficacy and safety of atacicept compared to placebo in reducing proteinuria in subjects with IgAN and persistent proteinuria despite being on a maximally tolerated dose (MTD) of a RASi. Safety, eGFR, serum immunoglobulins and Gd-IgA1 will also be clinically assessed. The clinical study is comprised of a 104wk double-blind treatment period, followed by a 52wk open-label treatment period and a 26wk safety follow-up period.
Primary Objectives:~Part A/B (Dose Ranging Study):~Evaluate the effect of atacicept compared to placebo on change in proteinuria in adult subjects with IgAN at 24 weeks.~Part C/D (Pivotal Study):~Evaluate the effect of atacicept compared to placebo on change in proteinuria in adult subjects with IgAN at 36 weeks.~Secondary Objectives:~Part A/B:~Evaluate the effect of atacicept compared to placebo on change in proteinuria in adult subjects with IgAN at 36 weeks.~Part C/D:~Evaluate the effect of atacicept on annualized rate of change in estimated glomerular filtration rate (eGFR) at 104 weeks.