Tumor-reactive effector lymphocytes were generated using tumor-derived amplified RNA and cultured dendritic cells (DC). Tumor RNAs were extracted from gastric cancer cell line MKN45 or cancer cells of malignant effusions, and were processed with T7 amplification. DCs were induced from an adherent cell population of peripheral blood mononuclear cells (PBMCs) with GM-CSF and IL-4. Tumor-RNA was introduced into DCs using electroporation. Effector cells were generated by stimulating a non-adherent fraction of PBMCs with tumor RNA-introduced DCs. It was observed that milligram RNA could efficiently be amplified from microgram RNA. The effector cells, designated as tumor-RNA-introduced DC-activated killer (TRiDAK) cells, showed IFN-gamma spots in a tumor-specific manner when examined using ELISPOT analysis, and demonstrated cytotoxic activities against tumor cells from which RNA was extracted. TRiDAK cells produced more tumor-specific IFN-gamma spots when stimulated repeatedly. These results suggest that TRiDAK cells are practical and may be effective lymphocytes for adoptive cancer immunotherapy.