CD4 and HIV-1 infection: For example, the CCR5 targeting humanized IgG4 mAb Pro 140 has been tested in clinical trials and the antibody exhibited potent, long-lived antiviral activity and was generally well tolerated.79, 98, 99 Ibalizumab (iMab), a humanized mAb that binds to a conformational epitope on CD4 and blocks entry of HIV-1, is also being tested in clinical trials.100 In another approach, bispecific Abs that combine the HIV-1 inhibitory activity of ibalizumab with that of anti-gp120 bNAbs were constructed for passive immunization to prevent HIV-1 infection.101, 102