Ex Vivo PD-L1/PD-1 Pathway Blockade Reverses Dysfunction of Circulating CEA-Specific T Cells in Pancreatic Cancer Patients

Carcinoembryonic antigen (CEA) is a candidate target for cellular immunotherapy of pancreatic cancer. In this study, we have characterized the antigen-specific function of autologous cytotoxic T lymphocytes (CTL) specific for the HLA-A2-restricted peptide, pCEA691-699, isolated from the peripheral T-cell repertoire of pancreatic cancer patients and sought to determine if PD-L1 and TIM-3 blockade could enhance CTL function. CD8 T-cell lines were generated from peripheral blood mononuclear cells of 18 HLA-A2 patients with pancreatic cancer and from 15 healthy controls. peptide-specific responses were evaluated by flow cytometry after staining for intracellular cytokine production and carboxy fluorescein succinimydyl ester cytotoxicity assays using pancreatic cancer cell lines as targets. Cytokine-secreting functional CEA691-specific CTL lines were successfully generated from 10 of 18 pancreatic cancer patients, with two CTL lines able to recognize and kill both CEA691 peptide-loaded T2 cells and CEA HLA-A2 pancreatic cancer cell lines. In the presence of PD-L1 blockade, functional CEA691-specific CD8 T-cell responses, including IFNγ secretion and proliferation, were enhanced, and this effect was more pronounced on Ag-specific T cells isolated from tumor draining lymph nodes. These data demonstrate that CEA691-specific CTL can be readily expanded from the self-restricted T-cell repertoire of pancreatic cancer patients and that their function can be enhanced by PD-L1 blockade. .