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

Abstract

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.

Protective non-neutralizing mAbs Ab94 and Ab81 retain high-affinity and potent Fc-mediated function against SARS-CoV-2 variants from Omicron to XBB1.5

“…Such potent Fc-mediated functions of Ab94 and Ab81 could explain why they show a protective effect in vivo while another nnAb did not show this protective effect 13 . Not all opsonic nnAbs are necessarily protective 13 , and of our panel of 8 nnAbs, Ab81 and Ab94 stood out as far more potent opsonizers 10 .…”

“…Of our mAbs tested previously 10 , Ab94 IgG3 stood out as the most potent, closely followed by Ab81 IgG3. The location of its binding site could explain Ab94’s potent Fc-mediated effector functions.…”

“…Although we do not have complete information on the epitope sites for our anti-RBD nnAbs (clones 11, 36, 66, 77, and 81), we wanted to use these as well to test the hypothesis of using nnAbs to target, theoretically, less mutationprone epitopes. In previous work, we used spike-coated microsphere beads to assess the reactivity of our mAbs against the Wuhan spike protein [9][10] . Here, using the same approach, we incubated spike-coated microsphere beads (coated with Wuhan, Omicron, BA.2, BA.4, and BA.5 spike protein) with our anti-spike antibodies.…”

“…We further analyzed the avidity of clones 81 and 94 against the newer variants BQ.1.1 and XBB. We focused on these two clones since they were both shown to be protective against a lethal Wuhan infection in a K18-hACE2 mouse model [9][10] . These SPR experiments showed that both clones retain a high affinity towards BQ1.1 and XBB (Fig.…”

“…Antibodies with potent Fc-mediated function have not been given the same level of attention as neutralizing antibodies. Recently, we have shown that two potent opsonizing antibodies, Ab81 and Ab94, targeting the RBD and N-terminal domain (NTD), respectively, strongly protect against the Wuhan strain in transgenic K-18 mice [9][10] . Notably, these antibodies are non-neutralizing (nnAbs), mediating their protective effect through Fc-mediated effector functions.…”