ABSTRACT: Obesity is a leading risk factor for progression and metastasis of many cancers1,2, yet can also promote improved survival for some cancers3-5 and enhance responses to some immune checkpoint blockade therapies6-8. 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 described9-12, 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 and that MTORC1 pathway signaling is essential for PD1 expression. PD-1+ TAMs had increased mitochondrial respiration, fatty acid metabolism and cell cylewhile PD-1- TAMs had increased inflammatory signature , phagocytosis and antigen presentation to T cells. These patterns were directly regulated by PD-1, as recombinant PD-L1 reduced macrophage glycolysis, phagocytic capacity and antigen presentation, and this was reversed with blocking PD-1 antibody. Further, inhibition of glycolysis with 2-deoxyglucose prevented the increase in CD86, MHC-I and MHC-II that would otherwise occur with anti-PD-1 treatment. 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 and type 1 inflammatory cues in obesity induces PD-1-mediated suppression of TAM function and reveal a unique macrophage-specific and glycolysis-dependent 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.
