targeting coronaviruses through fc-dependent antibody activities

Antiviral vaccines and immunotherapies focus predominantly on neutralising antibodies (NtAbs), which prevent cell-free virus from entering cells. These are critical to prevent transmission between people. However, once a cell is infected, the virus becomes inaccessible to NtAbs. As a result, although such antibodies are effective when given prophylactically, they are less effective when given therapeutically. Instead, antibodies that recognise the infected cell are required. These bind to viral antigens on the infected cell surface, where the Fc domain activates effector cells such as NK cells to carry out antibody-dependent cellular cytotoxicity (ADCC), killing the infected cell and controlling the infection. Thus, NtAbs and ADCC promoting antibodies carry out complementary activities, with NtAbs targeting cell-free virus, and ADCC antibodies targeting cell-associated virus. The importance of Fc-dependent antibody activity is underscored by multiple observations: (i) it correlates with natural and vaccine-mediated control of multiple viruses; (ii) enhancing or abrogating these functions in monoclonal antibodies alters their ability to control viruses in animal models; (iii) it is responsible for the efficacy of numerous clinically approved anti-cancer antibodies; (iv) viruses dedicate genomic space to antagonising it. The viral entry glycoproteins that are targets for NtAbs are often found on the surface of infected cells, leading to the assumption that NtAbs (that bind virions) will also bind infected cells and induce ADCC. As a result, most studies use entry glycoproteins in the form of immobilised protein or transfected cells to assess ADCC. However, when we developed novel unbiased proteomics techniques to map the ability of all viral cell-surface antigens to promote ADCC in the context of live virus, we unexpectedly discovered that although cell-surface entry glycoproteins bind antibody, they are poor inducers of ADCC. Instead, non-entry glycoproteins dominate the ADCC response across multiple viruses. As a result, we found that current vaccine strategies fail to robustly engage a major arm of humoral immunity when tested against live virus. Our discovery that novel antigens promote enhanced ADCC now allows us to assess the role of these previously uncharacterised responses in viral control, the impact that superior targeting of cell-associated virus provides in vaccines and immunotherapies, and to dissect the underlying biology of effective ADCC. In our studies of SARS-CoV-2 we discovered that although the Spike protein in current vaccines induces potent neutralising antibodies, Nucleocapsid, Membrane, and ORF3a, are superior ADCC targets. When we tested antibodies against one of these in animal models, despite having no neutralising activity, it was capable of controlling SARS-CoV-2 in the lungs and preventing viral-mediated lung damage. This demonstrates the protective potential in these novel targets. In addition to expanding the breadth of immune mechanisms induced by vaccines and improving control of cell-associated virus, increasing the number of antigens and epitopes targeted also has the potential to enable maintenance of antiviral efficacy as novel virus variants evolve. We will therefore answer the following questions in order to understand the potential for greater ADCC activity to improve vaccine and immunotherapeutic efficacy: Which of our novel ADCC targets most efficiently induce ADCC in vitro and in vivo?. How is ADCC affected by the evolution of antigenically distinct virus variants? Is ADCC more resistant to antibody waning than neutralisation? Are superior systemic and/or mucosal ADCC responses are a correlate of protection in natural and experimental human challenge models?