Mechanisms of antibody-mediated neutralization targeting viral glycoproteins

Thesis (Ph.D.)--University of Washington, 2018The antibody response against viral glycoproteins is important for preventing many viral infections but we lack a comprehensive understanding of the mechanisms by which antibodies act. Furthermore, the immense antigenic variability of glycoproteins complicates the design of immunogens that must elicit broadly neutralizing antibodies (bnAbs) capable of neutralizing a range of circulating isolates. The objective of this dissertation is to shed light on the mechanisms of antibody-mediated neutralization of enveloped viruses and the ability of nAbs to inhibit glycoprotein function by examining two significant human pathogens, influenza and HIV-1. Firstly, in Chapter 2, I investigate the effect of nAb binding and the role of IgG bivalency on inhibition of influenza’s hemagglutinin (HA) glycoprotein function for nAbs targeting distinct epitopes. I observe that the Ab-mediated inhibition of HA function occurs by multiple complementary mechanisms, and is largely dependent on the specific epitope that is targeted and on the bivalent nature of IgG molecules. My work reveals that the ability of nAbs to aggregate influenza virus particles enhances the inhibition of HA at an early stage of fusion peptide-induced membrane disruption through the occlusion of infectious virions. Epitopes further down the HA stem do not exhibit cross-linking across separate particles, but the findings here support a model of neutralization where bivalent binding to a sufficient amount of antigen is needed to disrupt the cooperative network of HA required for fusion. These results demonstrate that IgG bivalency enhances HA inhibition through functionally important modes not evident in pared-down Fab-soluble HA structures. In Chapter 3, I solve the cryo-EM structure of the first, and currently best described, infant-derived broadly neutralizing antibody against the HIV-1 envelope (Env) glycoprotein. We reveal that BF520.1 binds an epitope commonly targeted by adult-derived bnAbs, namely the V3-glycan region of HIV-1 Env. In addition, we highlight an important role in variable light chain development for BF520.1, which occurs early during lineage maturation and makes extensive contacts with the N332 glycan. Overall, the identification of a rapidly developed, infant bnAb is encouraging for vaccination strategies that aim to elicit bnAbs without the requirement for a long-term maturation pathway. Finally, Chapter 4 begins to explore BF520.1’s development through characterization of early antibody lineage intermediates. We propose that early light chain mutations help to establish the antibody’s epitope early in development, allowing focusing of heavy chain contacts. Overall, it is clear that future development of vaccination strategies will require in-depth knowledge of the critical interactions between antibody and virus, a comprehensive understanding of the mechanisms by which nAbs act, as well as familiarity with the developmental pathways bnAbs undergo in response to a rapidly evolving, antigenically diverse virus