Viral infections are a significant cause of morbidity and mortality, particularly in pediatric allogeneic haematopoietic stem cell transplant recipients. Effective therapies are limited and often associated with significant side effects. Adoptive transfer of virus-reactive T cells offers a means of reconstituting antiviral immunity and this approach has been successfully used to prevent and treat cytomegalovirus, Epstein-Barr virus, and adenovirus infections in vivo. This review outlines the clinical trials that have been performed to date, and will describe future initiatives to (a) develop strategies that can increase the breadth of the viruses that can be targeted, and (b) simplify the process to extend this technology to more centers so that cellular therapy to reconstitute immunity can be more widely applied.