CD4 and HIV-1 infection: Interestingly, an anti-CD4 antibody which recognizes a CD4 D2 epitope in proximity of the D1 CD4 domain (ibalizumab) [44] was recently tested in phase II clinical trials, in the form of humanized (IgG4) derivative, and appeared to be a promising tool to block HIV-1 infection without inducing any immunologically relevant side-effect either in vitro or in vivo[20], [45].