PRF1 and cytomegalovirus infection: Evidence suggests that CMV infection and repeated reactivation leads to the inflation of the CD8+ effector memory cell compartment in peripheral blood, marked by the following: (1) loss of CD27, CD28, and CCR7 expression; (2) gain of CD57 and CX3CR1 expression; (3) enhanced cytolytic function with increased granzyme B and perforin expression; and (4) reduced overall proliferative potential (57–59).