Anti-tumor effector cells were generated by stimulating peripheral blood lymphocytes with cultured dendritic cells (DCs) and mRNA extracted from the gastric cancer cell line MKN45 or ascites tumor cells of gastric cancer patients. DCs were generated from an adherent fraction of peripheral blood mononuclear cells (PBMCs) in the presence of GM-CSF and IL-4. mRNA was extracted from tumor cells and subjected to T7-amplification. The DCs were electroporated (150 V/150 microF) with amplified mRNA and used after maturation with TNF-alpha to stimulate PBMCs to generate tumor RNA-introduced DC-activated killer (TRiDAK) cells. It was found that tumor RNA could efficiently be introduced into cultured DCs by electroporation (55% efficiency, 78% viability), and tumor RNA-introduced DCs could reproducibly stimulate lymphocytes to be tumor-reactive TRiDAK cells. The TRiDAK cells expressed an IFN-gamma response specific for tumor cells, but not for normal cells. Mock DCs or normal cell RNA-introduced DCs did not induce any killer cells. RNA-specific recognition of the effector cells generated was demonstrated using an amplified EGFP-mRNA system. The tumor killing activity of TRiDAK cells was inhibited not only with the anti-HLA class I antibody but also with the anti-HLA class II antibody as well as the anti-TCR antibody. TRiDAK cells reactive with autologous tumor cells could be generated in a CEA-positive gastric cancer patient with malignant ascites, in whom effector cell generation using DCs and CEA peptides had failed. These results suggest that TRiDAK cell generation is safe, feasible, and active in gastric cancer patients with malignant ascites, and is superior to other effector cell generation systems using DCs and epitope peptides. The adoptive immunotherapy of cancer using TRiDAK cells may be warranted in a clinical setting. This is the first study investigating anti-tumor effector cell generation using cultured DCs and tumor mRNA from gastric cancer cells.