Ravulizumab in Thrombotic Microangiopathy After Hematopoietic Stem Cell Transplant

This study will evaluate the efficacy, safety, pharmacokinetics, and pharmacodynamics of ravulizumab in adult and adolescent participants with hematopoietic stem cell transplant-associated thrombotic microangiopathy (HSCT-TMA). In Stage 1, an open-label, single-arm period, the dosing regimen will be confirmed. In Stage 2, participants will be randomized to receive either blinded ravulizumab plus best supportive care or matching placebo plus best supportive care. The treatment period is 26 weeks (open-label for Stage 1, and randomized, double-blind, and placebo-controlled for Stage 2) followed by a 26-week follow-up period.

Inclusion Criteria: 1. 12 years of age or older at time of consent/assent. 2. Received HSCT within the past 12 months. 3. Diagnosis of TMA that persists for at least 72 hours after initial management of any triggering agent/condition. 4. A TMA diagnosis based on meeting the laboratory-based criteria during the Screening Period and/or ≤14 days prior to the Screening Period. 5. Body weight ≥ 30 kilograms at Screening or ≤7 days prior to the start of the Screening Period (date of consent). 6. Female participants of childbearing potential and male participants with female partners of childbearing potential must use highly effective contraception. 7. Participants must be vaccinated against meningococcal infections if clinically feasible. Participants who cannot receive meningococcal vaccine should receive antibiotic prophylaxis. Participants \