{
  "abstract": "Background Pancreatic ductal adenocarcinoma (PDAC) has poor survival which can be attributed to the highly immunosuppressive tumor microenvironment (TME) in which heterogenous stromal and myeloid populations contribute immunosuppression. We previously reported that CD200 is overexpressed in the pancreatic TME and may be a potential driver of the immunosuppression limiting immunotherapy efficacy. High levels of soluble CD200 in the plasma of metastatic PDAC patients correlate with significantly worse survival outcomes and antibody-blockade of CD200 in preclinical models of PDAC reduces tumor burden. We hypothesize that CD200-CD200R signaling promotes pancreatic tumor growth by enhancing the immunosuppressive function of myeloid cells.Methods We designed a novel CD200R fl/fl mouse by inserting loxP sites upstream exon 2 and downstream exon 4 of the CD200R gene to generate CD200Rfl/fl LysMCre mice in which CD200R is conditionally knocked-out of myeloid cells (CD200R cKO). KPC (LSL-KrasG12D/+;LSL-Trp53R172H/+;Pdx-1-Cre)-derived SIY-antigen expressing PK5L pancreatic tumor cells were orthotopically injected into the pancreas of CD200R cKO and WT mice. Starting 5 days post-injection, mice were treated with 200 µg anti-PD-1 or an isotype control 3x/week. At the end-of-study, tumors were weighed, and tumor-infiltrating lymphocytes (TILs) were isolated and stained to investigate changes in intratumoral immune populations via high-dimensional flow cytometry. To investigate the signaling mechanism downstream CD200R, myeloid cells were stimulated with recombinant CD200 for 1 hr before performing a phospho-tyrosine microarray. The expression of immunosuppressive factors PPARγ and IDO1 were analyzed via RT-qPCR and flow cytometry following 48 hrs of CD200 stimulation.Results Flow analysis of TILs confirmed CD200R was knocked down in myeloid cells of cKO mice. Additionally, TILs from CD200R cKO mice had a significant increase in the number of SIY-antigen-specific CD8+ Effector/Memory T cells (n=7-14 mice/group; p<0.05). While there was no difference in tumor burden between the CD200R cKO mice relative to WT mice, CD200R KO on myeloid cells did improve the response to anti-PD-1 compared to controls. CD200 stimulation of myeloid cells significantly increased the phosphorylation of c-Met and its downstream target p38 MAPK (p<0.05). Additionally, CD200 stimulation significantly increased the expression of PPARγ and IDO1 (p<0.05).Conclusions CD200 signaling enhances the immunosuppressive function of myeloid cells by activating the c-Met/p38 MAPK pathway and inducing the expression of PPARγ and IDO1. Increased intratumoral antigen-specific T cells in the CD200R cKO mice suggests improved T cell responses and improved responses to immunotherapy. Ultimately, our data provides the rationale for targeting the CD200-signaling axis to improve immunotherapeutic responses in PDAC.",
  "authors": [
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Jessica Wedig"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Morgan Kaiser"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Priya Matreja"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Shrina Jasani"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Debasmita Mukherjee"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Ayushi Das"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Hannah Lathrop"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Maria Schmidt"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Timothy Pfau"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Liliana D’Alesio"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Abigail Guenther"
    },
    {
      "affiliations": [
        "University of Michigan, Ann Arbor, MI, USA"
      ],
      "name": "Jake McGue"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Gina Sizemore"
    },
    {
      "affiliations": [
        "Department of Internal Medicine, The Ohio State University Comprehensive Cancer Center, Columbus, OH, USA"
      ],
      "name": "Anne M Noonan"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Mary Dillhoff"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Bradley Blaser"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Timothy Frankel"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Stacey Culp"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Phil Hart"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Andrew J Gunderson"
    },
    {
      "affiliations": [
        "The Ohio State University, Columbus, OH, USA"
      ],
      "name": "Zobeida Cruz-Monserrate"
    },
    {
      "affiliations": [
        "The Ohio State University Division of Gastroenterology, Hepatology and Nutrition, Department of Medicine, Columbus, OH, USA"
      ],
      "name": "Thomas A Mace"
    }
  ],
  "title": "782 CD200-CD200R signaling promotes myeloid cell immunosuppressive function and reduces efficacy of immune checkpoint blockade in pancreatic cancer",
  "uid": "0f8ac993-d26f-5999-ac09-459b387c9762"
}