Proliferation inhibition of AML cells by DT-GM-CSF measured in the ³H-TdR incorporation assay. Cells were examined for inhibition of proliferation in cytokine-free medium (p) and in conditions of stimulated growth by SCF, IL-3, and G-CSF (m). Specificity of DT-GM-CSF was tested by adding an excess of GM-CSF (2 μg/mL) simultaneously with DT-GM-CSF in cytokine free medium (n) or SCF, IL-3, and G-CSF containing medium (l).