Study of ARO-CFB in Adult Healthy Volunteers and Patients With Complement-Mediated Kidney Disease

Inclusion Criteria (All Participants): * Willing to provide written informed consent and to comply with study requirements * Female participants must be non-pregnant/non-lactating * Healthy volunteers must be willing to be vaccinated with a meningococcal and pneumococcal vaccine. IgAN participants must have been vaccinated or willing to undergo vaccination * All participants must be willing to be vaccinated or have a history of vaccination for Haemophilus influenzae type B * Body Mass Index (BMI) between 18.0 and 35.0 kg/m2 * Participants of childbearing potential must agree to use highly effective contraception in addition to a condom during the study and for at least 90 days following the end of the study or the last dose of study drug, whichever is later. Participants must not donate sperm or eggs during the study and for at least 90 days following the end of the study or last dose of study drug, whichever is later. * No abnormal finding of clinical relevance at the Screening evaluation that, in the opinion of the Investigator, could adversely impact participant safety or adversely impact study results. Inclusion Criteria (IgAN Participants): * Diagnosis of IgA Nephropathy based on renal biopsy within 5 years * Clinical evidence of ongoing disease based on significant proteinuria * Estimated glomerular filtration rate ≥30 mL/min/1.73m2 at Screening and currently not on dialysis * Must have stable or worsening renal disease, on stable and optimized treatment for at least 30 days prior to Screening and willing to stay on a stable standard of care regimen for the duration of the study * Must be on a maximally recommended or tolerated dose of an angiotensin-converting enzyme inhibitor (ACEI) or angiotensin receptor blocker (ARB) Exclusion Criteria (All Cohorts): * History of recurrent or chronic infections including infections caused by encapsulated bacterial organisms or viruses * History of active bacterial, viral, or fungal infection within 14 days prior to treatment administrations * Seropositive for Human immunodeficiency virus (HIV), hepatitis B virus (HBV) or hepatitis C virus (HCV) * History of meningococcal infection * History of asplenia * History of severe aplastic anemia or concurrent severe aplastic anemia * Known or suspected hereditary complement deficiency or other primary immunodeficiency syndrome * History of diabetes mellitus (Type 1 or Type 2) * Uncontrolled hypertension Exclusion Criteria (IgAN Participants): * Nephrotic syndrome or rapidly progressive glomerulonephritis * Suspicion for secondary etiologies of IgAN * Evidence of non-IgAN kidney disease on renal biopsy * Renal biopsy showing interstitial fibrosis/tubular atrophy of more than 50% * Use of complement inhibitors or monoclonal antibody therapies for treatment of IgAN Note: Additional Inclusion/Exclusion criteria may apply per protocol