PDCD1 and neoplasm: Stem-like CD8+ T cells have been found to differentiate into two major classes: CD8+ precursor exhausted T cells (Tpex), which maintain the immune function of specific CD8+ T cells in a chronic antigen-stimulated environment and are considered to be important target cells for PD-1/PD-L1 blockade therapy [53]; and tumor-specific Tmem, which are usually generated in TDLNs and act as key responders of anti-tumor immunity in ICIs therapy [54].