Coreceptor tropism of HIV-2KR.X7/HIV-1 V3 chimeras and fusion inhibition by T1249. (A) TZM-bl reporter cells were incubated with 10 μM TAK-779 (CCR5 antagonist), 1.2 μM AMD3100 (CXCR4 antagonist), medium only (untreated), or a combination of both coreceptor inhibitors for 30 min prior to the addition of infectious virus stock. TZM-bl cells express high levels of surface CD4, CCR5, and CXCR4, rendering them susceptible to infection by both CCR5- and CXCR4-tropic viruses. Entry was assessed by luciferase production (RLU) measured 48 h after infection. Values are presented as percent infectivity compared to the untreated control. HIV-1NL4.3 is a CXCR4-tropic control virus, and HIV-1YU2 is a CCR5-tropic control virus. Data are presented as the mean and standard deviation of 4 to 12 determinations. (B) Serial dilutions of T1249 were combined with an equal volume of infectious virus stock, incubated at 37°C for 1 h, and transferred to TZM-bl reporter cells. Virus entry was measured by luciferase production 48 h later and normalized to luciferase expression in the absence of T1249. Inhibition curves for HIV-2KR.X4, HIV-2KR.X7 YU2 V3, and HIV-2KR.X7 Ccon V3 are shown. IC50 values are presented in Table 1. Data represented are the mean and standard deviation of three independent experiments.