Analysis of the specific cytotoxicity induced by a T-cell clone in different cell types within a heterogeneous target cell population. The MNC fraction isolated from a female patient with AML positive for HLA-A2 was stained with CFSE. (A) Malignant progeny were induced by culturing the target population in the presence of GM-CSF, IL-3, G-CSF, and SCF for 3 days (target control). The effect of 24 hours of incubation of the induced malignant progeny with an HA-1-specific T-cell clone in a 1:1 E/T ratio is demonstrated. (B) The capacity of leukemic cells to produce malignant progeny after the simultaneous addition of cytokines and the cytotoxic T-cell clone (E/T ratio, 1:1) is demonstrated. Demonstrated are the target control after 5 days of culture and the surviving cells after 5 days of exposure to cytokines and CTLs. Plotted are the PI-negative events in the life gate counterstained with CD3-PE. Population 1 represented the population of fluorescent microspheres. Population 2 represented the leukemic cells. Populations 3 and 4 contained the healthy patient T cells present and the added CFSE-negative effector T cells, respectively. The absolute numbers are listed for populations 2 and 3.