Fluorescence intensity of human ML-1 cells (left panel) and purified human CD34⁺ marrow cells (right panel) labeled with MoAb against Flt3 receptor and stained with FITC-conjugated secondary antibody. (1) Unstained cells (dotted line), (2) cells stained with mouse isotype control antibody (thin solid line), (3) cells stained with a single MoAb against Flt3 receptor (MoAb 4A6.6.3; dashed line, shown only for ML-1 cells), (4) cells stained with a combination of three anti-Flt3 receptor MoAbs (MoAbs 4A6.6.3, 1E7.3.2, and 2G3.9.14; thick solid line). The mean fluorescence intensity (MFI) of each histogram is provided below the panels. The results shown are representative of two experiments.