Tumor specific T cell cytotoxicity. P phase and R phase CTVT cells (8 × 106 cells/ml) were incubated with mitomycin C and R phase peripheral blood mononuclear cells (PBMC; 3.2 × 106 cells/ml) for 6 days. Freshly prepared target (T) cells (CTVT; 4 × 103/well) were incubated at 37°C overnight with the effector (E) cells (R phase PBMC) at various E:T ratios (100:1, 50:1, 25:1, 12.5:1, 6.25:1). The supernatants were collected and the CTL cytotoxic activity was measured by the CytoTox 96® Non-Radioactive Cytotoxicity Assay (Promega, USA)