Manipulation of the proliferative status of primary leukemic cells by cytokines. Leukemic cells within the mononuclear cell (MNC) fraction isolated from the peripheral blood of a patient with AML are visualized by CD33 staining. Plotted are the propidium iodide (PI)-negative events in the life gate. Population F represents the fluorescent microspheres added for quantification. Population T represents a population of healthy patient T cells. The CFSE histograms are shown of the viable CD33⁺ leukemic cells (population L) cultured for 3 days either in the absence of cytokines (A) or in the presence of GM-CSF, G-CSF, IL-3, and SCF (B). The number of cell divisions is marked as well as the percentages of cells in every fraction.