A Study to Evaluate the Effectiveness and Safety of IONIS-FB-LRx, an Antisense Inhibitor of Complement Factor B, in Adult Participants With Primary IgA Nephropathy

Prior treatment

• Active infection 30 days prior to study
• Treatment with another investigational drug, biological agent, or device within 6 months of screening, or 5 half-lives of investigational agent, whichever is longer
• Administration of immunosuppressive/immunomodulatory medication 12 months prior to study drug administration, except for short-term treatments.

Other illness

• Clinically significant abnormalities in medical history (e.g., dementia, stroke, acute coronary syndrome, thrombocytopenia, or major surgery within 3 months of Screening)
• Presence of another renal disease including, but not limited to, diabetes and/or diabetic nephropathy, thin basement membrane disease, Alport's disease, IgA Nephritis (Henoch-Schonlein purpura), lupus nephritis, Minimal Change Disease, post-infectious glomerulonephritis or any other cause of proteinuria or secondary IgA nephropathy (including, but not limited to Celiac disease, Crohn's disease, human immunodeficiency virus (HIV), liver cirrhosis)
• History of renal transplant or another organ transplant

Lab values

• Diagnosis of primary or secondary immunodeficiencies of B-lymphocyte function, splenectomy, or history of recurrent meningococcal disease
• Estimated glomerular filtration rate (eGFR) ≤ 40 milliliters per minute per 1.73 square meters (mL/min/1.73m\^2) using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI)

Other

• Other protocol-specified inclusion/exclusion criteria may apply

• Females must be non-pregnant and non-lactating, and either surgically sterile or post-menopausal OR use a highly effective method of birth control
• Biopsy-proven primary immunoglobulin A (IgA) nephropathy
• Hematuria
• Proteinuria