PDCD1 and neoplasm: Through these complex mechanisms, tumor cells that bear surface PD-L1 effectively halt cytotoxic immune responses by CD8 cells and therefore facilitates “immune escape.” Multiple studies show TRM expression of PD-1 (10, 11, 74, 75) which indicates the cytotoxic potential of this cell type can be unleashed with anti-PD-1 antibodies such as nivolumab or pembrolizumab.