CXCR-4 expression is heterogeneous on PB and BM CD34⁺ cells and is up-regulated on PB Inc⁺CD34⁺ cells.

BM and PB CD34⁺ cells were purified immediately after density gradient separation (Inc−, plots a and c) or after incubation on a plastic support (Inc⁺, plots b and d). Cells were stained with CD34-PerCP, CD38-FITC, and CXCR-4-biotin-APC antibodies and analyzed by 3-color cytometry. An R1 region was first drawn by selecting the lymphomononuclear cells and excluding dead cells on an FSC/SSC dot plot (plot 1). A second region R2 corresponding to CD34⁺ cells was drawn on a second CD34-PerCP/CD38-FITC dot plot gated on R1 (plot 2). Expression of CXCR-4-APC versus CD34-PerCP (plots 3) and of CXCR-4-APC versus CD38-FITC (plot 4) was then assessed on the additive R1 plus R2 gates. The arbitrary quadrants were drawn on the basis of isotype-matched negative control profiles (top dot plot). The results shown are for 1 experiment representative of the 5 to 8 performed.