Cell surface CXCR4 expression on lentiviral-transduced CD34⁺ ,cells. Following mock or lentiviral infection, CB and MPB CD34⁺ cells were analyzed by flow cytometry for either GFP expression alone or GFP together with CXCR4 expression using an anti-hCXCR4–PE antibody. Quadrants were set according to isotype-matched negative controls and mock-infected cells. (A) Data show a representative FACS analysis from CB CD34⁺ cells. Numbers indicate percent of total CD34⁺ cells. (B) Results indicate percentage of CB and MPB CD34⁺ cells expressing CXCR4 and represent mean ± SE of 7 independent experiments. ^*P < .01 compared to control GFP-infected cells. (C) Immunofluorescence detection of cell surface (top panel) and intracellular (bottom panel) CXCR4 expression of GFP-transduced (gray line), CXCR4-transduced (black line), or isotype control (dotted line) cells.