Investigating The Tumor-Immune Microenvironment In An Autochthonous Murine Model Of Cholangiocarcinoma.

53 Background: Cholangiocarcinoma (CCA) is the most common liver malignancy within the biliary tree with increasing incidence and poor survival. Although surgical resection can be curative, prognosis remains abysmal with high rates of unresectability and recurrence, and new systemic therapies are needed. CCA tumors are characterized by an abundant inflammatory immune cell infiltrate, yet little is known about the immune dynamics underlying the disease. Here, we present a preclinical murine model of CCA for identifying potential targets susceptible to immune-based therapies. Methods: Mice with targeted activation of Kras G12D and loss of p53 (Kras-p53 -/- ) in the liver were exposed to 5-Diethoxycarbonyl-1.4-dihydrocollidine for 4 weeks to induce spontaneous CCA tumorigenesis. Immunohistochemistry staining was performed for mouse and human CCA. Immune compartments (bone marrow, spleen, peripheral blood, tumor draining and non-draining lymph nodes, and CCA tumor) of mice were processed for CyTOF analysis. In vitro assays of isolated myeloid leukocytes were performed to demonstrate function. Results: Tumor associated neutrophils (TANs) and tumor associated macrophages (TAMs) were present in high levels in human CCA tumors and the murine model. CyTOF analysis demonstrated mobilization of TANs, TAMs, and CCR2 + inflammatory monocytes into the tumor. The checkpoint marker PD-1 was upregulated on CD8 + and CD4 + T cells and associated with PD-L1 + TANs, TAMs, monocytes, and dendritic cells. The immunosuppressive tumor microenvironment was also characterized by TAMs expressing IL-10, TGFβ, and arginase 1; regulatory B cells expressing IL-10 and TGFβ; and Gata3 + T H 2 cells. Isolated myeloid leukocytes suppressed T cell proliferation and induced invasive migration. Conclusions: Kras-p53 -/- mice developed CCA tumors histologically similar to human disease: the data portray immunosuppressive cells in the tumor microenvironment, a possible obstacle for an effective anti-tumor response. Understanding the immune dynamics of immunosuppressive populations within the tumor microenvironment will be key to mount a potent therapeutic response for durable remission and improved survival.