CD200 promotes immunosuppression in the pancreatic tumor microenvironment

Abstract

BackgroundA significant challenge to overcome in pancreatic ductal adenocarcinoma (PDAC) is the profound systemic immunosuppression that renders this disease non-responsive to immunotherapy. Our supporting data provide evidence that CD200, a regulator of myeloid cell activity, is expressed in the PDAC microenvironment. Additionally, myeloid-derived suppressor cells (MDSC) isolated from patients with PDAC express elevated levels of the CD200 receptor (CD200R). Thus, we hypothesize that CD200 expression in the PDAC microenvironment limits responses to immunotherapy by promoting expansion and activity of MDSC.MethodsImmunofluorescent staining was used to determine expression of CD200 in murine and human PDAC tissue. Flow cytometry was utilized to test for CD200R expression by immune populations in patient blood samples. In vivo antibody blocking of CD200 was conducted in subcutaneous MT-5 tumor-bearing mice and in a genetically engineered PDAC model (KPC-Brca2 mice). Peripheral blood mononuclear cells (PBMC) from patients with PDAC were analyzed by single-cell RNA sequencing. MDSC expansion assays were completed using healthy donor PBMC stimulated with IL-6/GM-CSF in the presence of recombinant CD200 protein.ResultsWe found expression of CD200 by human pancreatic cell lines (BxPC3, MiaPaca2, and PANC-1) as well as on primary epithelial pancreatic tumor cells and smooth muscle actin+ stromal cells. CD200R expression was found to be elevated on CD11b+CD33+HLA-DRlo/− MDSC immune populations from patients with PDAC (p=0.0106). Higher expression levels of CD200R were observed in CD15+ MDSC compared with CD14+ MDSC (p<0.001). In vivo studies demonstrated that CD200 antibody blockade limited tumor progression in MT-5 subcutaneous tumor-bearing and in KPC-Brca2 mice (p<0.05). The percentage of intratumoral MDSC was significantly reduced in anti-CD200 treated mice compared with controls. Additionally, in vivo blockade of CD200 can also significantly enhance the efficacy of PD-1 checkpoint antibodies compared with single antibody therapies (p<0.05). Single-cell RNA sequencing of PBMC from patients revealed that CD200R+ MDSC expressed genes involved in cytokine signaling and MDSC expansion. Further, in vitro cytokine-driven expansion and the suppressive activity of human MDSC was enhanced when cocultured with recombinant CD200 protein.ConclusionsThese results indicate that CD200 expression in the PDAC microenvironment may regulate MDSC expansion and that targeting CD200 may enhance activity of checkpoint immunotherapy.

Quantitative Assessment of CD200 and CD200R Expression in Lung Cancer

“…While stromal cells express both CD200 and CD200R, future work is underway to more specifically define the immune cell populations that express each protein. CD200R is principally expressed on immune cells of monocyte-macrophage lineage, with an emphasis on myeloid-derived suppressor cells (MDSCs) [ 19 , 24 ]. Additionally, Gaiser et al found evidence of CD200R-expressing macrophages in Merkel cell carcinoma and suggested a role for the induction of an immunosuppressive M2 phenotype [ 25 ].…”

“…Recently published preclinical data illustrated that inhibition of the CD200/CD200R interaction can induce chemokine response, stimulate dendritic cell differentiation, enhance antigen-specific response and ultimately lead to downregulation of PD-1 receptors in glioblastoma multiforme cells [ 29 ]. Additionally, in vivo blockade of this pathway in pancreatic ductal adenocarcinoma animal models significantly reduced intratumoral infiltration and suppressive activity of MDSCs, limited tumor growth, and enhanced the efficacy of PD-1/PD-L1 axis inhibitors [ 24 ]. To our knowledge, our study is the first to assess the correlation between CD200/CD200R and PD-1/PD-L1 pathways in human NSCLC.…”

The Immune Microenvironment in Pancreatic Cancer

“…Similarly, the yes-associated protein (Yap) has been described to contribute to an immunosuppressive tumor microenvironment by inducing the expression and secretion of cytokines and chemokines involved in the differentiation and accumulation of MDSCs [ 63 ]. Within tumor tissue, the expansion of MDSC numbers has been reported to be driven by elevated CD200 expression [ 64 ].…”

CD200:CD200R Interactions and Their Importance in Immunoregulation

“…CD200 blockade significantly inhibits tumor growth and diminishes the percentage and number of MDSCs that penetrate in tumor tissue. Similarly, sCD200 present in tumor microenvironment of many cancers extends its effects on MDSCs in the same manner [ 77 , 78 ].…”

“…CD200 is also broadly expressed in other solid tumors, such as pancreatic ductal adenocarcinoma, lung cancer, ovarian cancer, renal cell carcinoma, CNS malignancies and head and neck squamous carcinomas (HNSCC), where its interaction with CD200R(1) promotes immune suppression in tumor microenvironment. The immunosuppressive mechanism promoted by CD200:CD200R interaction relies, as mentioned above, on the inhibition of macrophages, induction of regulatory T cells, switching of cytokine profiles from Th1 to Th2, inhibition of tumor-specific T cell immunity and induction of MDSC (myeloid-derived suppressor cells) expansion [ 77 , 78 , 96 , 98 , 99 ].…”