CXCR4 and CD4 expression during in vitro culture of CD34⁺ cells. Flow cytometric analysis of CXCR4 and CD4 expression on UCB CD34⁺ cells cultured for 0, 5, and 8 days, respectively. Cells were stained with anti-CD34 FITC, anti-CD4 PE, and anti-CXCR4 TC and analyzed for HIV-1 coreceptor expression on the subpopulation of cells that maintain the CD34 antigen during the culture. Quadrant regions were set using isotype matched-control antibodies. Similar results were obtained for uninfected and HIV-1–infected cells.