IL-3 rescue assay. BaF3/ITD cells were incubated in quadruplicate wells of a 96-well plate in culture medium with increasing concentrations of the inhibitors in the absence (left) or presence (right) of 1 ng/mL IL-3. After 48 hours, the MTT reagent was added and OD values were obtained. The dose-response curves were prepared as percentage control (DMSO only), and regression analysis was used to obtain IC₅₀ values. The ratio of the IC₅₀ in the presence of IL-3 divided by the IC₅₀ in the absence of IL-3 is the IL-3 index, tabulated below the graphs.