CD4 and infection: To examine this, we developed a coculture infection model in which target cells were pretreated for 48 h with 100 nM FTY720, 3 μM DMS, 10 μM SKI II, or 20 μM ABC294640 (days 10 to 12) and then labeled with Cell Trace Yellow in fresh medium with treatment removed and cocultured with primary CD4 cells infected with a panel of HIV-1 primary isolates and molecular clones representing a range of HIV-1 subtypes as described above (coculture model, Fig. 3A; viruses, Fig. 2A).