Background: Tumor immune reactions not only provide host defense but also accelerate tumor immune escape and phenotype switching. Here, we examined the association of programmed cell death ligand 1 (PD-L1) expression with epithelial-mesenchymal transition (EMT)–associated markers in pancreatic ductal adenocarcinoma (PDA) within the context of the tumor microenvironment. Materials and methods: PDA samples from 36 patients were analyzed for PD-L1, vimentin, E-cadherin, and Snail expressions and for PDA cell and immune cell infiltration. PD-L1 expression and EMT in PDA cell lines under conditions of altering interferon gamma (IFN-γ) signals were also assessed. Results: Immunohistochemistry revealed a significant correlation between vimentin and PD-L1 expression, whereas double staining showed them to be simultaneously expressed by PDA cells. Positive vimentin expression was associated with the infiltration of a lower number of CD8 + T cells and a higher number of FoxP3 + cells and poor patient prognosis (P = 0.03). PDA tumor cells promoted PD-L1 expression and EMT under the presence of IFN-γ which was inhibited by the signal transducer and activator of transcription (STAT)1 small interfering RNA. Conclusions: Strong correlations were observed between PD-L1 expression, EMT, and the immunosuppressive tumor microenvironment. Targeting STAT1 combined with PD-1/PD-L1 immunotherapy may improve outcomes for patients with PDA.
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