By adding entry inhibitors, maraviroc (MVC) or enfuvirtide (ENF) at different times at the start of the infection cycle (Fig 6A), we calculated t1/2 for HIV-1 to bind CD4 and to be ready for CCR5 engagement (Fig 6B) and the t1/2 for HIV-1 to bind both CD4/CCR5 and initiate the cell-virus membrane fusion step (Fig 6C), respectively. This evidence concerns the gene CD4 and infection.