PDCD1 and cancer: Increasing ketogenesis markedly decreased KLF5-dependent synthesis of C-X-C Motif Chemokine Ligand 12 (CXCL12) in cancer-associated fibroblasts, ultimately increasing the infiltration of immune effector cells in tumors and enhancing sensitivity to immune checkpoint inhibitors specific for programmed cell death 1 (PD-1) [181].