Potent neutralization of primary human immunodeficiency virus clade C isolates with a synergistic combination of human monoclonal antibodies raised against clade B

OBJECTIVES: We investigated the ability of several human neutralizing monoclonal antibodies (mAbs), originally raised against human immunodeficiency virus (HIV) clade B isolates, to neutralize primary clade C isolates as single agents and in combination. STUDY DESIGN/METHODS: HIV clade C isolates from five different countries were tested for susceptibility to neutralization by anti-clade B mAbs in human peripheral blood mononuclear cells. Monoclonal antibody combinations were evaluated for possible synergy. RESULTS: All 20 primary HIV clade C isolates could be neutralized 97.5% to 100% by a quadruple combination of mAbs IgG1b12, 2G12, 2F5, and 4E10. These mAbs recognized conserved epitopes and were highly synergistic, resulting in strong cross-clade neutralization. CONCLUSIONS: In our previous experiment, a synergistic combination of human neutralizing mAbs protected all macaque neonates against oral challenge with a simian-human immunodeficiency virus encoding HIV env. Together, our data suggest that passive immunization with currently available anti-clade B mAbs could play a role in preventing HIV clade C transmission through breastfeeding.