Keywords: Cox-2, cytotoxicity, gammadelta T lymphocytes, human, pancreatic ductal adenocarcinoma, PGE2Abbreviations: BrHPP, bromohydrin-pyrophosphate; Cox, cyclooxygenase; n-BP, nitrogen-containing bisphosphonates; PAg, phosphorylated antigen; PDAC, pancreatic ductal adenocarcinoma; PG, prostaglandins; RTCA, Real Time Cell Analyzer; TCR, T cell receptor.The prostaglandin (PG) synthetase cyclooxygenase 2 (Cox-2) promotes tumorigenesis, tumor progression, and metastasis in a variety of human cancer entities including pancreatic ductal adenocarcinoma (PDAC). In this study, we demonstrate that in PDAC cells such as Colo357 cells, enhanced Cox-2 expression and increased release of the Cox-2 metabolite prostaglandin E2 (PGE2) promotes resistance against gd T cell-mediated lysis. Co-culture with activated gd T cells induced an upregulation of Cox-2 expression in Colo357 cells, and thereby an enhanced PGE2 release, in response to tumor necrosis factor a .TNFa/ secretion from gd T cells. The PGE2-mediated inhibition of gd T cell cytotoxicity against Cox-2-expressing PDAC cells can be partially overcome by Cox-2 inhibitors. Our results show that differences between PDAC cells in regards to sensitivity to gd T-cell cytotoxicity can be due to distinct levels of Cox-2 expression associated with varying amounts of PGE2 release. While gd T cell cytotoxicity against PDAC cells expressing low levels of Cox-2 can be effectively enhanced by tribody [(Her2) 2 £Vg9] with specificity for Vg9 T cell receptor and HER-2/neu on PDAC cells, a combination of tribody [(Her2) 2 £Vg9] and Cox-2 inhibitor is necessary to induce complete lysis of Cox-2 high expressing Colo357. In conclusion, our results suggest that the application of tribody [(Her2) 2 £Vg9] that enhances gd T-cell cytotoxicity and Cox-2 inhibitors that overcome PGE2-mediated resistance of PDAC cells to the cytotoxic activity of gd T cells might offer a promising combined immunotherapy for pancreatic cancer.