Human monoclonal antibodies and engineered antibody domains as HIV-1 entry inhibitors

Purpose of review To summarize the in-vivo efficacy of neutralizing human monoclonal antibodies against HIV-1, to discuss the recent finding that an engineered human antibody V(H) domain, domain antibody (dAb), exhibits exceptionally potent and broadly cross-reactive neutralizing activity against HIV-1 primary isolates by targeting a hidden conserved epitope that is not accessible by larger antibodies and to suggest the possibility of developing a novel class of potent HIV-1 inhibitors based on human dAbs. Recent findings HIV-1 has evolved a number of strategies to evade humoral immunity, including protecting highly conserved and important structures from the access of antibodies generated by the immune system. We have recently demonstrated that a human dAb (size similar to 15 kDa), m36, targets a highly protected structure on the HIV-1 envelope glycoprotein (Env), gp120, and exhibits exceptionally potent neutralizing activity against HIV-1 primary isolates, with potency on average higher than those of the broadly cross-reactive neutralizing human monoclonal antibody, scFv m9, and the inhibitory peptide, C34. Summary The efficacy of the anti-HIV-1 therapy is significantly compromised by resistance to the currently used US Food and Drug Administration-approved antiretroviral drugs, which suggests an urgent need to develop novel classes of potent inhibitors. Several broadly cross-reactive neutralizing human monoclonal antibodies are highly effective against HIV-1 infection in vitro, but their administration to HIV-1-infected humans has only resulted in modest antiviral effects. Engineered human antibody fragments, dAbs, could be more potent because of their small size (about 10-fold smaller than that of an IgG), which allows targeting of highly conserved structures on the HIV-1 envelope glycoprotein that are not accessible by full-size antibodies and relatively efficient penetration into the densely packed lymphoid environment in which HIV-1 mostly replicates and spreads.