Correlation between the CFSE-based cytotoxicity assay and the conventional ⁵¹Cr release assay. (A) Dot plots of AML-193 cells labeled with CFSE and incubated for 4 hours in the absence of T cells (target control) or in the presence of 2 specific CTL clones (E/T ratio, 1:1). Population 1 contained the fluorescent microspheres which could be discriminated on the basis of their scattering pattern and their fluorescence. Population 2 contained the CFSE and CD33⁺ AML-193 cells. The effector T cells added could be discriminated as a population of CFSE-negative CD33^- cells (population 3). (B) The percentages of surviving AML-193 cells (± SD) as measured by the CFSE-based cytotoxicity assay (▦) and the percentages of lysed AML-193 cells as measured by the ⁵¹Cr release assay (▪) after 4 hours of incubation in the absence of CTLs (control) or after incubation with CTL clone G or CTL clone H (n = 3).