CD8A and cancer: Furthermore, a recent pan-cancer single-cell landscape study of tumor-infiltrating lymphocytes (TILs) revealed that tumor-infiltrating CD8+ T cells in tumors (including GC) were characterized by the emergence of exhausted T cells (Zheng et al. 2021),and one of the main reasons for the poor efficacy of immune checkpoint therapy for gastric cancer is the multiple inhibitory metabolites secreted by tumor cells outside the tumor microenvironment (Li et al. 2019).