CD4 and HIV-1 infection: To understand the disconnect between sCD4 neutralization and CD4 binding of the w16 and w20 viruses, we assessed sCD4-induced gp120 release from the surface of 293T cells transiently expressing their envelope glycoprotein trimers, as this had been shown to be a mechanism by which sCD4 neutralizes HIV-1 infection [77], [78], [79], [80], [81].