During the period of immune recovery after allogeneic hematopoietic cell transplant (allo-HCT), viral infections and reactivations, including those with AdV, are an important cause of morbidity and mortality. Progression to AdV disease is associated with significant morbidity and mortality rates. This Phase 3, multicenter, randomized, double-blind, placebo-controlled study will assess the safety and efficacy of Posoleucel for the treatment of AdV infection in pediatric and adult allo-HCT recipients receiving SoC.