Subclass-switched anti-spike IgG3 oligoclonal cocktails strongly enhance Fc-mediated opsonization

Antibodies play a central role in the immune defense against SARS-CoV-2. Emerging evidence has shown that nonneutralizing antibodies are important for immune defense through Fc-mediated effector functions. Antibody subclass is known to affect downstream Fc function. However, whether the antibody subclass plays a role in anti-SARS-CoV-2 immunity remains unclear. Here, we subclass-switched eight human IgG1 anti-spike monoclonal antibodies (mAbs) to the IgG3 subclass by exchanging their constant domains. The IgG3 mAbs exhibited altered avidities to the spike protein and more potent Fc-mediated phagocytosis and complement activation than their IgG1 counterparts. Moreover, combining mAbs into oligoclonal cocktails led to enhanced Fc-and complement receptor-mediated phagocytosis, superior to even the most potent single IgG3 mAb when compared at equivalent concentrations. Finally, in an in vivo model, we show that opsonic mAbs of both subclasses can be protective against a SARS-CoV-2 infection, despite the antibodies being nonneutral-izing. Our results suggest that opsonic IgG3 oligoclonal cocktails are a promising idea to explore for therapy against SARS-CoV-2, its emerging variants, and potentially other viruses.SignificanceMonoclonal antibodies have been widely used as a therapy for COVID-19. The focus thus far has been on neutralizing antibodies that block viral entry into host cells. However, a typical immune response mostly leads to antibodies that cannot neutralize but help clear the infection by promoting immune cell function through opsonization. The constant antibody domain determines its class and subclass and can directly influence immune effects. Here, we show that switching subclass can modulate the immune response against the SARS-CoV-2 virus. Further, we enhance antibody-mediated immune function by combining antibodies into cocktails. This study highlights how antibody subclass engineering and incorporating antibodies into cocktails can modulate the efficacy of antibodies as potential therapeutics against viral infections.