Protective non-neutralizing SARS-CoV-2 monoclonal antibodies.

Recent studies show an important role for non-neutralizing anti-spike antibodies, including monoclonal antibodies (mAbs), in robustly protecting against SARS-CoV-2 infection. These mAbs use Fc-mediated functions such as complement activation, phagocytosis, and cellular cytotoxicity. There is an untapped potential for using non-neutralizing mAbs in durable antibody treatments; because of their available conserved epitopes, they may not be as sensitive to virus mutations as neutralizing mAbs. Here, we discuss evidence of non-neutralizing mAb-mediated protection against SARS-CoV-2 infection. We explore how non-neutralizing mAb Fc-mediated functions can be enhanced via novel antibody-engineering techniques. Important questions remain to be answered regarding the characteristics of protective non-neutralizing mAbs, including the models and assays used for study, the risks of ensuing detrimental inflammation, as well as the durability and mechanisms of protection.

Protective Non-neutralizing anti-N-terminal Domain mAb Maintains Fc-mediated Function against SARS-COV-2 Variants up to BA.2.86-JN.1 with Superfluous In Vivo Protection against JN.1 Due to Attenuated Virulence.

Substantial evidence supports that Fc-mediated effector functions of anti-spike Abs contribute to anti-SARS-Cov-2 protection. We have previously shown that two non-neutralizing but opsonic mAbs targeting the receptor-binding domain and N-terminal domain (NTD), Ab81 and Ab94, respectively, are protective against lethal Wuhan SARS-CoV-2 infection in K18-hACE2 mice. In this article, we investigated whether these protective non-neutralizing Abs maintain Fc-mediated function and Ag binding against mutated SARS-CoV-2 variants. Ab81 and Ab94 retained their nanomolar affinity and Fc-mediated function toward Omicron and its subvariants, such as BA.2, BA.4, BA.5, XBB, XBB1.5, and BQ1.1. However, when encountering the more heavily mutated BA.2.86, Ab81 lost its function, whereas the 10 new mutations in the NTD did not affect Ab94. In vivo experiments with Ab94 in K18-hACE2 mice inoculated with a stringent dose of 100,000 PFU of the JN.1 variant revealed unexpected results. Surprisingly, this variant exhibited low disease manifestation in this animal model with no weight loss or death in the control group. Still, assessment of mice using a clinical scoring system showed better protection for Ab94-treated mice, indicating that Fc-mediated functions are still beneficial. Our work shows that a protective anti-receptor-binding domain non-neutralizing mAb lost reactivity when BA.2.86 emerged, whereas the anti-NTD mAb was still functional. Finally, this work adds new insight into the evolution of the SARS-CoV-2 virus by reporting that JN.1 is substantially less virulent in vivo than previous strains.

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 nonneutralizing. 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.

The hinge-engineered IgG1-IgG3 hybrid subclass IgGh47 potently enhances Fc-mediated function of anti-streptococcal and SARS-CoV-2 antibodies.

Streptococcus pyogenes can cause invasive disease with high mortality despite adequate antibiotic treatments. To address this unmet need, we have previously generated an opsonic IgG1 monoclonal antibody, Ab25, targeting the bacterial M protein. Here, we engineer the IgG2-4 subclasses of Ab25. Despite having reduced binding, the IgG3 version promotes stronger phagocytosis of bacteria. Using atomic simulations, we show that IgG3's Fc tail has extensive movement in 3D space due to its extended hinge region, possibly facilitating interactions with immune cells. We replaced the hinge of IgG1 with four different IgG3-hinge segment subclasses, IgGhxx. Hinge-engineering does not diminish binding as with IgG3 but enhances opsonic function, where a 47 amino acid hinge is comparable to IgG3 in function. IgGh47 shows improved protection against S. pyogenes in a systemic infection mouse model, suggesting that IgGh47 has promise as a preclinical therapeutic candidate. Importantly, the enhanced opsonic function of IgGh47 is generalizable to diverse S. pyogenes strains from clinical isolates. We generated IgGh47 versions of anti-SARS-CoV-2 mAbs to broaden the biological applicability, and these also exhibit strongly enhanced opsonic function compared to the IgG1 subclass. The improved function of the IgGh47 subclass in two distant biological systems provides new insights into antibody function.