 Viral infections are normally controlled by T-cell immunity and so are an important cause of morbidity and mortality during the period of immune recovery after hematopoietic stem cell transplantation HSCT.1 Risk for infection is impacted by the degree of tissue mismatch between donor and recipient and the immune status of the donor, including the degree and length of immunosuppression following transplantation. Reactivation of latent viruses such as cytomegalovirus CMV and Epstein-Barr virus EBV are common and often cause symptomatic disease. Respiratory viruses such as adenovirus also frequently cause infection. Antiviral pharmacologic agents are only effective against some of these viruses; their use is costly, and associated with significant toxicities and the outgrowth of drug-resistant mutants. As delay in recovery of virus-specific cellular immune response is clearly associated with viral reactivation and disease in these patients, cellular immunotherapy to restore viral-specific immunity is an attractive option that has already been successfully used to target some of these viruses. 