Equal amount of infectious unit from each chimeric virus bearing patient-derived Env V1-V5 region was used to infect TZM-bl cells. NL4-3 was used as control. Cell-free supernatant was collected and assayed for replication kinetics at indicated days post-infection. The level of viral replication was determined by infection TZM-bl cells by viruses harvested from day 2, 4, 6, 8, 10, 12 and 14. After 48 hrs post-infection, cells were lysed and luciferase activity was measured.