CD4+ lymphocytes were stimulated with PHA for 3 days, transduced with either control or CCR5-expressing lentiviruses, and maintained in the presence of IL-2. Two days post-transduction, cells were pretreated for 1 hour with CXCR4 blocker AMD3100 and infected with HIV-1 luciferase pseudotypes in the continued presence of blocker. Infection was determined by luciferase activity in cell lysates four days later. The results are shown as the proportion of CD4+ lymphocyte infection mediated through CCR5 for R3A (A), DH12 (B) and 89.6 (C) on the Y-axis, plotted against the percentage of CD4+ lymphocytes that express CCR5 after transduction with a control or CCR5 expression vectors. Data are from three independent experiments using cells from different donors.