PVR and neoplasm: Since PD-1 reportedly inhibits TCR signaling pathways, PD-1 blockade activates these pathways.32 Altogether, TCR signaling pathways, which can be activated by PD-1 blockade, increase TIGIT expression in effector T cells, and TIGIT+ effector T cells are suppressed by CD155 expressed in tumor cells, resulting in the survival of CD155-expressing tumor cells and acquired resistance.