CXCR4 and HIV infectious disease: Using a primary cell model of HIV infection, activated CD4 T cells were infected with the CXCR4 (X4)-tropic HIV-1 molecular clone NL4-3 at day 7 and treated with 1 to 6 μM DMS, 0.5 to 20 μM SKI II, 2.5 to 40 μM ABC294640, or 100 nM FTY720, which we utilized as a positive control based on our previous studies (14), for 72 h while crowding cells in 96-well plates to promote HIV-1 cell-to-cell transmission (Fig. 1A).