Fc-Dependent Antibody-Mediated Functions Against HIV-1

Abstract

Antibodies are important therapeutic agents that can be elicited by vaccination or directly infused. However, the mechanisms by which antibodies achieve protection against pathogens are not fully elucidated, in particular since antibodies mediate multiple functions, including direct neutralization as well as Fc-mediated effector functions. In this dissertation, I focused on one such Fc-mediated effector function, antibody-dependent phagocytosis, and examined it in the context of HIV-1. Firstly, with regard to the antibody Fv interaction with antigen, I used a novel HIV-1 virion phagocytosis assay to identify targets on the HIV-1 virion surface that can be targeted for antibody-mediated phagocytosis in the context of monoclonal and polyclonal antibodies from HIV-1 infection and vaccination settings, and demonstrated that these include both broadly neutralizing and non-neutralizing antibody epitopes. To examine whether antibody-mediated phagocytosis of HIV-infected cells can be an additional potential antiviral mechanism, I also developed an infected cell phagocytosis assay and demonstrated that in addition to virions, HIV-infected cells can also be targeted for antibody-mediated phagocytosis. Secondly, with regard to the antibody Fc interaction with FcR, I utilized recombinant subclass-switched antibodies and demonstrated that antibody isotypes and subclasses differ for antibody-dependent phagocytosis function, with IgG3 being the most potent. Furthermore, by examining the phagocytosis responses of humans and non-human primates, I demonstrated that there exists sufficient cross-reactivity between humans and rhesus macaques to examine human antibody subclass-specific phagocytosis activity in the rhesus macaque system despite evolutionary divergence in the Fc-FcR systems of the two species. Thirdly, I examined the downstream effects of antibody-mediated HIV-1 virion phagocytosis, and demonstrated that virions phagocytosed by antibody-dependent mechanisms likely do not cause enhanced infection, and also do not elicit additional inflammatory cytokines including IL-1β, IL-6, and TNFα. Thus, my work contributes to the understanding of antibody Fc-mediated phagocytosis function, with implications for HIV-1 vaccine and passive immunotherapy strategies, and broader relevance also for other infectious diseases as well as antibody-based cancer immunotherapy.