A First-in-Human Safety and Efficacy Study of ALN-CFB, a Small Interfering RNA (siRNA) Targeting Complement Factor B, in Adult Participants With Paroxysmal Nocturnal Hemoglobinuria With Persistent Anemia on a C5 Inhibitor

Key Inclusion Criteria: 1. Has been diagnosed with PNH confirmed by a history of high flow cytometry from prior testing 2. Treated with a stable dose of C5 inhibitor (eculizumab or approved eculizumab biosimilar, ravulizumab, or crovalimab) for at least 24 weeks prior to screening visit, as described in the protocol 3. Has hemoglobin ≤10.5 g/dL at screening visit 1, with evidence of anemia prior to this visit, as described in the protocol 4. Has peripheral blood reticulocyte count of ≥100 x 10\^9/L at screening visit 1 Key Exclusion Criteria: 1. Has history of bone marrow transplantation or receipt of an organ transplant 2. Has history of meningococcal infection or similar recurrent infections by other encapsulated bacterial organisms 3. Has any active, ongoing infection or a recent infection requiring ongoing systemic treatment with antibiotics, antivirals, or antifungals within 2 weeks of screening or during the screening period 4. Has laboratory evidence of bone marrow failure, as described in the protocol 5. Have recent, unstable medical conditions, not related to PNH or PNH-related complications, as described in the protocol NOTE: Other Protocol Defined Inclusion / Exclusion Criteria Apply