LAUSR

e16591 Background: Immune checkpoint inhibitors targeting PD-1/L1 and CTLA-4 pathway have shown modest activity in patients with advanced PC. Additional immunosuppressive mechanisms in the PC tumor microenvironment need to be investigated. Increased CD73 (encoded by NT5E) expression results in generation of immunosuppressive adenosine in the tumor microenvironment and has been associated with metastasis and poor survival in PC. Utilizing the TCGA dataset, we investigated the association of NT5E expression with the immune landscape of PC. Methods: RNA-seq data for 331 PC tumor samples and 51 normal adjacent tissue (NAT) samples was downloaded and log2 transformed. Patients were split into low, intermediate, and high expression groups based on NT5E expression (≤ -1, -1 to 1 and ≥1 standard deviation from the overall mean) in tumor and NAT. A tumor inflammation signature (TIS) reflecting an inflamed tumor phenotype was calculated based on the averaged tumor expression of 18 previously validated genes (Ayers et al, 2017). Abundance of infiltrating immune cell subsets was estimated based on expression of previously identified 782 immune metagenes (Charoentong et al, 2017). Immune cell abundance scores and TIS were compared between NT5E expression groups using the Mann-Whitney U test and the Bonferroni correction was used to control for false discovery rate. Results: NT5E expression in NAT was not associated with the TIS or expression of immune cell marker genes. In contrast, NT5E expression in tumor tissue correlated positively with TIS (P < 0.001). Compared to tumors with low NT5E expression, those in high NT5E expression group had higher expression of central memory CD4+, effector memory CD8+, type 1 helper, NK and regulatory T (Treg) cell markers. Conclusions: In our analysis, NT5E expression correlated with markers of inflamed tumor phenotype in PC. Although NT5E expression was associated with higher CD8+and CD4+ T cells, concurrent increase in Tregs could inhibit the infiltrating lymphocytes and promote tumor growth. Our findings indicate a possible role for the adenosine pathway as a mediator of immunosuppression in PC and a potential therapeutic target. AT and EL: Equal contribution