CD8A and disease arising from reactivation of latent virus: In most cases, CMV infection is subclinical and well tolerated, even though latent infection is associated with an age-related deterioration of the immune system, in particular CD8+ T cell compartment, causing a distortion of T cell repertoire with expansions of CMV-specific CD8+ T cells that can represent up to 20% of total CD8+ T cell population [5]–[7].