Determination of the growth fraction in cell suspensions by flow cytometry using the monoclonal antibody Ki-67

A novel procedure for determining the growth fraction of cell suspensions by flow cytometry is described. This method identifies proliferating cells by binding the monoclonal antibody Ki-67 to a nuclear antigen present in all cells that are in the G1, S, G2, and M phase of the cell cycle, but not in the G0 phase. In a kinetic study of Na cell line U937 using concanavalin A for stimulation of peripheral blood mononuclear cells, a steady increase of Ki-67 positive cells evaluated by flow cytometry was observed. Simultaneously, the [3H]thymidine uptake of the ConA blasts was measured and compared to the expression of Ki-67. A linear correlation between the percentage of Ki-67 positive cells and the log transformed counts per minute was demonstrated, and staining with Ki-67 detected cell proliferation with the same sensitivity as 3H-TdR uptake. In addition, it was possible to stain Ki-67-labelled cells with a second cell marker if a second fluorescent dye coupled to an antibody was used. This provided the opportunity to define precisely the phenotype of proliferating cells. Conversely, the number of proliferating cells expressing certain preselected surface markers could be easily determined.