Less attention is given to this since either only a small subset among the total memory pool has this phenotype (e.g., upon infection with EBV or HIV) or the frequencies of the late-stage differentiated CD8 T cells are generally lower compared to those in CMV infection (e.g., infection with herpes simplex virus-1 (HSV-1) [71] and parvoviruses B19 and PARV4 [72]. This evidence concerns the gene CD8A and infection.