While these memory T cells are critical for our response against previously encountered pathogens and/or latent infections, chronic exposure to high antigenic load can induce the functional exhaustion of T cells, which is characterized by a gradual loss of T-cell effector function and expression of inhibitory receptors such as programmed cell death protein 1 (PD-1), cytotoxic T-lymphocyte-associated protein 4 (CTLA4), T-cell immunoglobulin domain and mucin domain protein 3 (TIM3), and lymphocyte activation gene 3 (LAG3) (10). The gene discussed is PDCD1; the disease is disease arising from reactivation of latent virus.