PDCD1 and neoplasm: Considering that cancer vaccines containing neoantigen-derived peptides lead to an accumulation of the number of cancer antigen-specific CTLs in GBM tumor microenvironment [48], PD-1 inhibition may be effective in tumor types with few tumor-infiltrating T cells by combined with agents that strongly induce antitumor T cell immunity, such as DSP-7888 Emulsion.