PDCD1 and neoplasm: Programmed death-ligand 1 (PD-L1): CAF-mediated cytokines such as IL-6 and IL-8 can upregulate the expression of PD-L1 on tumor cells, and interaction of PD-L1 and PD-1 on TILs leads to TIL exhaustion, characterized by reduced cytotoxic activity and diminished production of effector molecules [162,163].