Pancreatic cancer is characterized by aggressive growth and treatment resistance. New approaches include immunotherapeutic strategies but the type and extent of spontaneous immune responses against tumor antigens remains unclear. A dominance of TH2 cytokines in patients' sera reported previously suggests systemic tumor-induced immunosuppression, potentially inhibiting the induction of tumor-reactive T cells. We characterized the localization, frequencies, and functional potential of spontaneously induced memory T cells specific for individual tumor antigens or the tumor-associated antigen mucin-1 in the peripheral blood and bone marrow of 41 pancreatic cancer patients. We found high numbers of tumor-reactive T cells in all bone marrow samples and in 50% of the blood samples. These cells secreted the TH1 cytokine IFN-; rather than TH2 cytokines upon stimulation with tumor antigens. Although consistently induced during pancreatic cancer, T cells specific for pancreatic antigens were not detected during chronic pancreatitis, suggesting that their evaluation may be of diagnostic use in both diseases. Freshly isolated T cells from cancer patients recognized autologous tumor cells and rejected them in vitro and in a xenotransplant model in vivo, suggesting their therapeutic potential. Thus, tumor antigen-specific T cell responses occur regularly during pancreatic cancer disease and lead to enrichment of tumor cell-reactive memory T cells in the bone marrow. The bone marrow can therefore be considered an important organ for antitumor immune responses in pancreatic cancer. (Cancer Res 2005; 65(21): 10079-87)

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