PD-1 is induced on tumor-associated macrophages in obesity to directly restrain anti-tumor immunity

Obesity is a leading risk factor for progression and metastasis of many cancers, yet can also promote improved survival for some cancers and enhance responses to some immune checkpoint blockade therapies. The role of the immune system in the obesity-cancer connection and how obesity influences immunotherapy, however, remain unclear. While PD-1 expression by macrophages has been described, we found that obesity selectively induced PD-1 on macrophages and that PD-1 directly impaired macrophage function. Single cell RNA sequencing of murine colorectal carcinoma tumors showed obesity remodeled myeloid and T cell populations, with fewer clonally expanded effector T cells and increased abundance of PD-1+ tumor-associated macrophages (TAM). Cytokines and molecules associated with obesity, including IL-6, leptin, and insulin, and the unsaturated fatty acid palmitate, induced PD-1 expression on macrophages in a glycolysis-dependent manner. PD-1+ TAMs had increased mitochondrial respiration and expression of genes regulating oxidative phosphorylation, lipid uptake and cell cycle while PD-1- TAMs showed greater signatures of phagocytosis and antigen presentation to T cells. These patterns were directly regulated by PD-1, as recombinant PD-L1 reduced macrophage glycolysis and phagocytic capacity, and this was reversed with blocking PD-1 antibody. Conversely, PD-1-deficient Pdcd1-/- TAMs had high rates of glycolysis, phagocytosis, and expression of MHC-II. Myeloid-specific PD-1 deficiency correlated with slower tumor growth, enhanced TAM antigen presentation capability, and increased CD8 T cell activation together with reduced markers of exhaustion. These findings show metabolic signaling in obesity induces PD-1-mediated suppression of TAM function and reveal a unique macrophage-specific mechanism to modulate immune tumor surveillance and checkpoint blockade. This may contribute to increased cancer risk yet improved response to PD-1 blockade in TAM-enriched tumors and obesity. ### Competing Interest Statement J.C.R. has held stock equity in Sitryx and within the past two years has received unrelated research support, travel, and honoraria from Sitryx, Caribou, Nirogy, Kadmon, Calithera, Tempest, Merck, Mitobridge and Pfizer. Within the past two years, W.K.R. has received unrelated clinical research support from Bristol-Meyers Squib, Merck, Pfizer, Peloton, Calithera and Incyte. K.E.B. received funding to the institution for preclinical research from BMS-IASLC-LCFA, funding to the institution for clinical trials from Arrowhead, Aravive, Aveo, BMS, Exelexis, Merck, and consulting fees from Alpine Immune Sciences, Aravive, Astrazeneca, Aveo, BMS, Exelexis, Merck, Seagen, Sanofi. V.A.B. has patents on the PD-1 pathway licensed by Bristol-Myers Squibb, Roche, Merck, EMD-Serono, Boehringer Ingelheim, AstraZeneca, Novartis, and Dako.