This difference in distribution is likely related to the distinct functions of these T-cell subtypes: CD8+ Tem cells mostly reside in peripheral tissues and lymphoid tissues and play an effector role (26); CD4+ Tem cells travel to the infection site to exert killing functions (27), while Treg cells reside in tumor tissue and play an immunosuppressive role (28). The gene discussed is CD8A; the disease is neoplasm.