A tetrazolium-based colorimetric MTT assay to quantitate human monocyte mediated cytotoxicity against leukemic cells from cell lines and patients with acute myeloid leukemia.

The MTT-colorimetric monocyte mediated cytotoxicity assay, based upon the ability of living cells to reduce 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide (MTT) into formazan, was evaluated using leukemic cells from five representative human leukemic cell lines and from 28 patients with acute myeloid leukemia (AML). An excellent linearity between absorbance and leukemic cell number was observed up to 5 x 10(4) cells/well and 50 x 10(4) cells/well for all cell lines and patients samples tested, respectively, in a 96-wells microtiter culture system. A huge variability in the susceptibility of leukemic cells to purified and IFN-gamma-activated human monocytes could be observed at effector-to-target cell (E:T) ratios of 1. The mean signal-to-noise ratio of the MTT assay for monocyte-leukemic cell mixtures from patients was 2.69 +/- 0.39 at E:T 1. In conclusion, the MTT based monocyte mediated cytotoxicity assay should be useful for studying the susceptibility of a variety of leukemic cells from cell lines and from patients with AML to monocytes in a rapid, sensitive and semi-automated manner.