PURPOSE: Activated bone marrow-derived dendritic cells (DCs) express high level of MHC class I and II molecules as well as intercellular adhesion molecule and B7, required for T cell activation. This study was designed to examine whether DCs pulsed with tumor lysates were capable of inducing tumor specific CTLs. METHODS: To generate mature DCs, bone marrow cells of female BALB/c mice were cultured in the presence of GM-CSF and IL-4. Mature DCs were idenfied by surface expression of MHC class II molecules and costimulatory molecules. By FACS analysis, it was found that most DCs highly expressed B7-1, B-7-2 and CD40 as well as MHC class II molecules. BAlB/c were immunized subcutaneously. Cytolytic activity was determined by chromium release assay using splenocytes harvested from immunized mice 7 days after the immunization, Cytolytic activity was measured against CT-26 and RAG tumor cells. In vivo protection experiment was performed. Mice were immunized subcutaneously wity DCs pulsed with CT-26 lysates (1x10(6) per mouse) and were challenged intrahepatically with wild type CT-26 (5x10(4) per mouse) two weeks following immunization. Three weeks after the challenge, animals were euthanized for identification of hepatic tumors. RESULTS: Lysis of CT-26 cells were significantly greater with the splenocytes from the immunized mice. Incidence and mean volume of hepatic cancer in the immunized group were 50% (5/10) and 78+/-22 mm3. These results were significantly different from those from control groups:100% (10/10) and 1014.5+/-667.8 mm3 in media treated group, 90% (9/10) and 855.5+/-270.6 mm3 in mice treated with irradiated CT-26, 100% (10/10) and 994 255 mm3 in the animals treated with DC alone. CONCLUSIONS: DCs pulsed with CT-26 lysates could successfully induce antitumor immunity in the BLAB/c against syngeneic CT-26 carcinoma cells. Pulsing method was so simple that neither genetic engineerings nor cellular fusion were not necessary. Even though the present study did not conduct survival experiments, it was thought that clinical application of DC-based immunotherapy could be expedited by pulsing of tumor lysate into the DCs.