Characterization of functional human antibodies targeting henipavirus and flavivirus glycoproteins
Doyle, Michael Patrick
The henipaviruses Hendra (HeV) and Nipah (NiV), and the flavivirus yellow fever (YFV), pose massive global public health threats. No small molecule or antibody-based countermeasures are available to treat humans infected by HeV, NiV, or YFV, and major gaps in knowledge regarding the humoral immune response to these viruses exist. To this end, I isolated panels of fully human monoclonal antibodies (mAbs) that target henipavirus (chapters II-IV) or flavivirus (chapter V) glycoproteins from immune human subjects. I characterized these mAbs for their binding, neutralization, competition, and mechanistic profiles. Using these data, I down-selected candidate mAbs for in vivo studies, and showed that antibodies with diverse functions against henipaviruses or flaviviruses are efficacious in small animal models of infection. The most promising henipavirus-targeting mAbs, HENV-103 and HENV-117, displayed orthogonal phenotypes when assayed for receptor blocking. HENV-117 was blocked by receptor binding, while HENV-103 was enhanced by receptor binding. I then showed these antibodies cooperated for binding to the HeV receptor binding protein (RBP), and synergistically neutralize virus in vitro. When administered as a cocktail, these two mAbs show superior efficacy in a hamster model of NiVB when compared to monotherapy. YFV-136, which potently neutralized the YFV vaccine strain YFV-17D in vitro, was functional primarily at a pre-attachment step, suggesting the mechanism of action of YFV-136 is blocking attachment of virus to host cells. I generated YFV-136 escape mutant viruses, which showed a single amino acid substitution at position 67 in DII of YFV-E abrogated the neutralization activity of YFV-136. Despite the ability of YFV-17D to escape YFV-136 in vitro, YFV-136 showed therapeutic protection in a hamster model of authentic YFV Jimenez. In sum, the studies presented herein address important gaps in knowledge regarding the human immune response to henipavirus and flavivirus infection, and provide candidate therapeutic mAbs for treatment of human infections by these pandemic-potential viruses.