Abstract 1369: PD-1 directly suppresses macrophage metabolism to restrict anti-tumor immunity in an obesity-cancer connection
Authors: Bader Jackie , Rathmell Jeffrey 
Published: March 2024

Abstract
Obesity has been established as a leading risk factor for many cancers and can drive tumor progression and metastasis. Paradoxically, obesity has in some cases been associated with better survival and improved response to immune checkpoint blockade therapies. The role of the immune system in the obesity-cancer connection and how obesity affects immunotherapy responses, however, have been unclear. Here we show that obesity enhanced PD-1 expression on macrophages to reduce phagocytosis and antigen presentation to T cells that correlated with reduced T cell expansion and function. This obesity associated immune dysfunction, however, primed for enhanced anti-tumor response to PD-1 blockade. Single cell RNAseq showed obesity remodels myeloid and T cell populations but does not impact non-immune cell populations such as fibroblasts and epithelial cells. Specifically, obesity increased the overall number of tumor-associated macrophages (TAM) while effector T cells were decreased in abundance. Interestingly, the frequency of macrophages expressing PD-1 increased, while the remaining T cells maintained similar or reduced PD-1 expression and appeared less activated. Further, T cell depletion from the tumor microenvironment, enhanced macrophage PD-1 expression and worsened PD1-associated TAM dysfunction in an obesity enhanced manor. Obesity associated cytokines and adipokines including IFN-ã, leptin and insulin induced PD-1 expression on macrophages. This expression is associated with mTOR and c-myc activation signaling pathways; as such inhibiting these signaling pathways blocked PD1 expression. Bulk RNA sequencing analysis revealed PD-1+ TAMs had an altered gene profile compared to PD-1− TAMs. PD1 expressing macrophages exhibited increased mitochondrial respiration and expression of oxidative phosphorylation, increased lipid uptake and increased cell cycling related genes. Conversely PD1- TAMs exhibited increased phagocytosis and antigen presentation. PD-1/PDL1 interaction directly regulated TAMs, as recombinant PDL-1 reduced glycolysis and phagocytosis in purified macrophages, and these effects could be reversed with blocking PD-1 antibody. Conversely, PD-1−/− TAMs had reduced lipid uptake but high rates of glycolysis, phagocytosis, and expression of MHC-II. Myeloid-specific PD-1 deficiency correlated with slower tumor growth and decreased LAG3 and increased CD69 on CD8 T cells. In addition, myeloid specific PD1 deficiency enhanced TAM antigen presentation through OVA specific CD8 T cell activation. These findings identify PD-1 as a metabolic regulator in TAM dysfunction and reveal a unique PD-1 mediated and macrophage-specific mechanism for immune tumor surveillance and checkpoint blockade. This may contribute to improved immunotherapy response in TAM-enriched tumors and obesity.
Citation Format: Jackie Bader, Jeffrey Rathmell. PD-1 directly suppresses macrophage metabolism to restrict anti-tumor immunity in an obesity-cancer connection [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1369.