Validation of flow-cytometric determination of Ki67 expression as a measure of growth factor response in acute myelogenous leukemia

Despite its growing use as a marker of proliferation, the relationship between expression of the nuclear antigen Ki67 and other indices of proliferation in acute myelogenous leukemia (AML) has not been elucidated. In this study, short-term primary suspension cultures of human AML bone marrow cells were used to compare flow-cytometric methods of quantifying Ki67 expression and to test whether flow-cytometric determination of Ki67 expression correlates with incorporation of ³H-thymidine or bromodeoxyuridine (BrdU). BrdU incorporation was determined by staining of cells with anti-BrdU and propidium iodide (PI) followed by flow cytometry. When samples were double-labeled with Ki67 and PI, Ki67 was underestimated compared to single-color quantification of the nuclear antigen. Ki67⁺ cell number correlated well with incorporation of ³H-thymidine (r=0.89, p<0.001). Cells from 17 cases of AML were cultured for 3 days in the presence and absence of a variety of growth factors and growth factor combinations before comparison of Ki67 expression and BrdU incorporation. Ki67 expression correlated strongly with BrdU incorporation (r=0.82, p<0.001). Unlike the double-label with PI, costaining with a phycoerythrin (PE)-labeled antibody directed against a cell surface antigen did not significantly affect Ki67 quantification. Flow cytometric determination of Ki67 is a simple and valid measurement of proliferation in AML bone marrow cells.