T cell immunity to cytomegalovirus infection.

T cell responses are critical for controlling cytomegalovirus (CMV) infection. However, CMV expresses immune evasion genes promoting escape from T cell immunity. Furthermore, CMV persistence in form of latency, coupled with viral reactivation events, provokes two unique features of CMV-specific CD8 T cell responses: their size and phenotype. CMV-specific T cells with certain specificities respond to the infection by an initial expansion and thereafter a secondary increase to reach high and stably maintained frequencies of functional and widely dispersed CMV-specific CD8 T cells - in a process termed 'memory inflation'. Additionally, many of these 'inflated' CD8 T cells exhibit a particular phenotype, characterized by the expression of effector-memory and natural killer-associated markers. Here, we review and discuss insights into T cell responses elicited by CMV infection combined with cellular and molecular mechanisms explaining the scale and the phenotype of inflationary cells and their function in CMV infection.