PDCD1 and neoplasm: It has been reported that PD-1+ CD4+ tumor infiltrating lymphocytes (TILs) and CD8+ TILs had less proliferative capacity comparing to the PD-1- CD8+ or CD4+ TILs, suggesting that both CD8+ and CD4+ TILs are functionally anergic through activation of the PD-1/PD-L1 pathway (14).