CD4 and HIV-1 infection: The mAB binds to the CD4 T cell extracellular domain 1 and 2 so preventing those conformational changes within the complex of the CD4 T cell and the HIV envelope gp120 that allow viral fusion and cell entry (81) Ibalizumab is approved for intravenous use as part of a combination antiretroviral regimen in heavily treatment-experienced patients with multidrug resistant (MDR) HIV-1 infection who did not respond to the current antiretroviral regimen (82).