Atacicept in Subjects with IgA Nephropathy

Key Inclusion Criteria:

* Must have the ability to understand and sign a written informed consent form
* Male or female of ≥18 years of age
* Total urine protein excretion ≥1.0 g per 24-hour or urine protein to creatinine ratio (UPCR) ≥1.0 mg/mg based on a 24-hour urine sample during the Screening Period
* Diagnosis of IgAN as demonstrated by renal biopsy conducted within 10 years
* eGFR ≥ 30 mL/min/1.73 m2, as per the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation.
* On a stable prescribed regimen of RAASi for at least 12 weeks that is at the maximum labeled or tolerated dose at Screening
* Systolic blood pressure ≤150 mmHg and diastolic blood pressure ≤90 mmHg

Key Exclusion Criteria:

* IgAN secondary to another condition (e.g., liver cirrhosis), or other causes of mesangial IgA deposition including IgA vasculitis (i.e., Henoch-Schonlein purpura), systemic lupus erythematosus (SLE), dermatitis herpetiformis, ankylosing spondylitis
* Total urine protein excretion ≥ 5g per 24-hour or urine protein to creatinine ratio (UPCR) ≥ 5 mg/mg based on a 24-hour urine sample during the Screening Period
* Evidence of rapidly progressive glomerulonephritis (loss of ≥ 50% of eGFR within 3 months of screening)
* Evidence of nephrotic syndrome within 6 months of screening (serum albumin \<30g/L in association with UPCR \>3.5 mg/mg
* Renal or other organ transplantation prior to, or expected during the study
* Concomitant chronic renal disease in addition to IgAN
* Uncontrolled diabetes, defined as hemoglobin-A1c (HbA1c) \>7.5% at screening
* History of tuberculosis (TB), untreated latent TB infection (LTBI), or evidence of active TB determined by a positive Quantiferon test
* Participation in the Phase 2b (Parts A and B) study or any previous treatment with atacicept