AIM: To assess if a specific cytotoxic T cell response can be induced in patients with malignant liver tumors treated with radio-frequency ablation (RFA).METHODS: Six Patients with liver metastases of colorectal cancer and 6 with hepatocellular carcinoma (HCC)underwent RFA. Blood was sampled before, 4 and 8 wk after RFA. Test antigens were autologous liver and tumor lysate obtained from each patient by biopsy. Peripheral T cell activation was assessed by an interferon gamma (IFNγ) secretion assay and flow cytometry. T cells were double-stained for CD4/CD8 and IFNγ to detect cytotoxic T cells. The ratio of IFNγ positive and IFNγ negative T cells was determined as the stimulation index (SI). To assess cytolytic activity, T cells were co-incubated with human CaCo colorectal cancer and HepG2 HCC cells and release of cytosolic adenylate kinase was measured by a luciferase assay.RESULTS: Before RFA SI was 0.021 (±0.006) for CD4+and 0.022 (±0.004) for CD8+T cells against nonmalignant liver tissue and 0.018 (±0.005) for CD4+ and 0.021(±0.004) for CD8+ cells against autologous tumor tissue.Four weeks after RFA SI against tumor tissue increased to 0.109 (±0.005) for CD4+ and 0.11 (±0.012) for CD8+T cells against HCC, and to 0.115 (±0.031) for CD4+ and 0.15 (±0.02) for CD8+ cells for colorectal metastases (P ＜0.0001). No increased SI was observed with nonmalignant tumor tissue at all time points. Before RFA cytolytic activity against the respective cancer cells was low with 2.62 (±0.37) relative luminescence units (RLU), but rose more than 100 fold 4 and 8 wk after RFA. Spontaneous release was ＜2% of maximum release in all experiments.CONCLUSION: Patients with primary and secondary tumors of the liver show a significant tumor-specific cytotoxic T-cell stimulation with a dramatically increased tumor specific cytolytic activity of CD8+ T cells after RFA.