CD8A and cytomegalovirus infection: During CMV infection or reactivation, CD8+ T cells are thought to be key mediators of protective immunity, and successful viral antigenic clearance is achieved through priming of naive CD8+ T cells, via T-cell receptor (TCR)-peptide-major histocompatibility complex restriction, after which cells clonally expand and differentiate into different CMV-specific memory CD8+ T subsets.