CD8A and infection: Humanized mice generated by transplantation of human HSCs have demonstrated long-term reconstitution and some degree of maturation of human T cells, evidenced by the presence of CD4/CD8 single-positive T cells in the spleen and peripheral blood [13, 15, 42], CD8+ T cells with effective cytotoxic activity against infection with Epstein-Barr virus (EBV) [24], and development of human B cells that produce antigen-specific IgM upon immunization with exogenous antigens [43, 44].