Intertumoral CD4+ T-cells instruct monocyte differentiation in pancreatic ductal adenocarcinoma

Abstract

Abstract Pancreatic ductal adenocarcinoma (PDA) is a lethal malignancy that is currently the third leading cause of cancer related deaths. PDA creates a suppressive fibroinflammatory tumor microenvironment (TME) composed of stromal and immune cells that inhibit anti-tumor immune responses. Tumor associated macrophages (TAMs) account for a large percentage of the TME and have remarkably heterogeneous functions, with some subsets promoting anti-tumor responses while others suppress tumor specific T-cells. While many studies have highlighted macrophage heterogeneity in PDA, it remains unclear mechanisms regulating monocyte differentiation into pro vs anti-tumor populations. To understand monocyte differentiation in PDA, we performed trajectory analysis on scRNA-seq data from mouse and human tumors and identified predicted monocyte differentiation pathways toward either MHCII-hi anti-tumor TAMs or Trem2-hi pro-tumor TAMs. Using a newly designed monocyte tracking mouse (CCR2CreER x R26tdTomato) implanted with orthotopic tumors that express the click beetle luciferase (CB) neoantigen, we temporally tracked monocyte differentiation within tumors into TAM populations. Furthermore, using antibody depletion, we found that CD4 depletion led to increased monocyte differentiation into pro-tumor macrophages and a dramatic downregulation of PDL1 on monocyte derived TAMs. Finally, using Ifngr1−/− mice implanted with CB+ tumors, we identify that polarization toward anti-tumor macrophages was driven by IFNy, but TAM PDL1 expression was IFNy independent. Together these data are the first to address monocyte differentiation within PDA and identify previously unexpected role for CD4 T cells governing TAM differentiation program.