Protein expression of neurobiologic surface receptors dependent on the developmental stage of human CD34⁺ cells. Highly enriched CD34⁺ cells were subjected to 2-color immunofluorescence using a FITC-conjugated anti-CD38 antibody and surface receptor–specific antibodies, the binding of which was detected by a rhodamine (R)–conjugated secondary antibody. In each dot plot, cell populations are divided into a developmentally early CD38^dim subset and a CD38^bright subset representing more mature hematopoietic progenitors. Mean rhodamine fluorescence values, which reflect the surface receptor expression, are indicated for each subset. Displayed is 1 representative of 4 experiments.