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 creatinineratio (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 EpidemiologyCollaboration (CKD-EPI) equation.

• On a stable prescribed regimen of RAASi for at least 12 weeks that is at the maximumlabeled 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 ofmesangial 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 3months of screening)

• Evidence of nephrotic syndrome within 6 months of screening (serum albumin <30g/L inassociation 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 ofactive TB determined by a positive Quantiferon test

• Participation in the Phase 2b (Parts A and B) study or any previous treatment withatacicept