Monitoring and functional characterization of the lymphocytic compartment in pancreatic ductal adenocarcinoma patients

Background/Objectives: Pancreatic ductal adenocarcinoma (PDAC) still has a poor prognosis and current treatments including immunotherapy often fail. This might be due to the pronounced immunosuppressive milieu impairing infiltration and function of immune effector cells. This study aimed at a comprehensive analysis of immune cells in PDAC patients by determining absolute and relative peripheral blood cell numbers of immune cell subsets along with their functional capacity. Methods: Whole blood cells or isolated peripheral blood mononuclear cells were characterized by flow cytometry. PDAC tissues were analyzed by immunohistochemistry. Anti-tumor activity of immune effector cells was determined by RTCA system. Results: Our data demonstrate that relative CD4(+) memory- and regulatory T cell numbers were enhanced, whereas determination of absolute cell numbers revealed generally lower immune cell numbers in PDAC patients compared to healthy controls. gamma delta T cells accumulated at higher numbers compared to alpha beta T cells in the malignant ductal epithelium of PDAC tissues indicating that gamma delta T cells infiltrate into the tumor. Cytotoxicity against tumor cells of even small numbers of T- and NK cells could be induced by a bispecific antibody targeting CD3(+) T cells to human epidermal growth factor receptor (HER)2 expressing PDAC cells or Trastuzumab. Importantly, a critical number of gamma delta T cells was required for significant tumor cell killing by a bispecific antibody engaging the gamma delta T cell receptor on gamma delta T cells and HER2 on tumor cells. Conclusion: Monitoring immune cells along with the determination of their functional capacity provides a comprehensive assessment as a prerequisite for a personalized immunotherapeutic PDAC treatment. (C) 2016 IAP and EPC. Published by Elsevier B.V. All rights reserved.