PDCD1 and melanoma: Additionally, the simultaneous upregulation of FAS (Fas cell surface death receptor)/PD-1 (Programmed cell death protein 1) on T cells and FASL (Fas ligand)/PD-L2 (Programmed cell death ligand 2) on CAFs impairs the function and survival of tumor antigen-specific T cells, ultimately facilitating melanoma survival and progression [215].