Both experimental [74,75,76] as well as clinical [77] CD8-AT revealed that remarkably few virus-specific memory CD8 T cells can control virus infection in almost all susceptible organs, provided that CD8-AT is performed as a so-called “pre-emptive therapy” shortly after experimental infection in the mouse model or shortly after virus reactivation detected by routine follow-up PCR-monitoring of hCMV DNA in clinical HCT. This evidence concerns the gene CD8A and infection.