Early immunomonitoring studies in HCT patients indicated that control of reactivated hCMV infection correlates with the reconstitution of antiviral CD8+ T cells (94, 95), and subsequent adoptive cell transfer studies in the mouse model (see above) as well as in clinical trials (see above) confirmed a protective antiviral function of primed CD8+ effector and/or memory T cells. The gene discussed is CD8A; the disease is cytomegalovirus infection.