Pancreatic Tumors and Immature Immunosuppressive Myeloid Cells in Blood and Spleen: Role of Inhibitory Co-Stimulatory Molecules PDL1 and CTLA4. An In Vivo and In Vitro Study

Abstract

BackgroundBlood and spleen expansion of immature myeloid cells (IMCs) might compromise the immune response to cancer. We studied in vivo circulating and splenic T lymphocyte and IMC subsets in patients with benign and malignant pancreatic diseases. We ascertained in vitro whether pancreatic adenocarcinoma (PDAC)-associated IMC subsets are induced by tumor-derived soluble factors and whether they are immunosuppressive focusing on the inhibitory co-stimulatory molecules PDL1 and CTLA4.Methodology and Principal Findings103 pancreatic and/or splenic surgical patients were enrolled including 52 PDAC, 10 borderline and 10 neuroendocrine tumors (NETs). Lymphocytes and IMCs were analysed by flow cytometry in blood, in spleen and in three PDAC cell conditioned (CM) or non conditioned PBMC. PDL1 and CTLA4 were studied in 30 splenic samples, in control and conditioned PBMC. IMCs were FACS sorted and co-coltured with allogenic T lymphocytes. In PDAC a reduction was found in circulating CD8+ lymphocytes (p = 0.004) and dendritic cells (p = 0.01), which were reduced in vitro by one PDAC CM (Capan1; p = 0.03). Blood myeloid derived suppressive cells (MDSCs) CD33+CD14−HLA-DR− were increased in PDAC (p = 0.022) and were induced in vitro by BxPC3 CM. Splenic dendritic cells had a higher PDL1 expression (p = 0.007), while CD33+CD14+HLA-DR− IMCs had a lower CTLA4 expression (p = 0.029) in PDAC patients. In vitro S100A8/A9 complex, one of the possible inflammatory mediators of immune suppression in PDAC, induced PDL1 (p = 0.018) and reduced CTLA4 expression (p = 0.028) among IMCs. IMCs not expressing CTLA4 were demonstrated to be immune suppressive.ConclusionIn PDAC circulating dendritic and cytotoxic T cells are reduced, while MDSCs are increased and this might favour tumoral growth and progression. The reduced CTLA4 expression found among splenic IMCs of PDAC patients was demonstrated to characterize an immune suppressive phenotype and to be consequent to the direct exposure of myeloid cells to pancreatic cancer derived products, S100A8/A9 complex in particular.

Overexpression of MERTK Receptor Tyrosine Kinase in Epithelial Cancer Cells Drives Efferocytosis in a Gain-of-Function Capacity

“…To begin addressing this issue, we examined the effect of MERTK on the expression of the immune checkpoint blockades, Programmed death-ligand 1 (PD-L1) and 2 (PD-L2). PD-L1 and PD-L2 are often overexpressed in poorly immunogenic tumors, and allow cancers to evade host immune responses and promote cancer invasiveness (55)(56)(57)(58). In our study, when Mertk was constitutively activated in 293T cells by means of Fc-Mertk transfection, mRNA transcripts and surface expression of PD-L1 and PD-L2 were increased (Fig.…”

Requirement for Interactions of Natural Killer T Cells and Myeloid-Derived Suppressor Cells for Transplantation Tolerance

“…The immunosuppressive molecules PDL1 and arginase-1 are expressed by activated MDSCs in tumor infiltrates or after immune stress, and contribute to their regulatory function (32, 33). In addition, signaling via the IL-4Rα and IL-13R has been reported to activate MDSCs to secrete TGFβ and to upregulate the IL-4Rα receptor expression (22, 34).…”

Pancreatic adenocarcinoma up-regulated factor (PAUF) enhances the accumulation and functional activity of myeloid-derived suppressor cells (MDSCs) in pancreatic cancer

“…Immune cells in the tumor stroma in particular are increasingly recognized for their role in shaping TME through crosstalk with tumor cells and other stromal components [44–46]. MDSCs are a major component of the pancreatic cancer-associated immunosuppressive microenvironment and their expansion and accumulation is well known to be associated with tumor immune evasion [11, 47, 48]. However, the molecular mechanisms underlying MDSC activation, expansion, and migration are not completely understood in pancreatic cancer.…”