The spread of
COVID-19 has been exacerbated by the emergence of variants of concern (VoC). Many VoC contain mutations in the spike
protein (S-
protein) and are implicated in
infection and response to
therapeutics. Bivalent
neutralizing antibodies (nAbs) targeting the S-
protein receptor-binding domain (RBD) are promising
therapeutics for
COVID-19, but they are limited by low potency and vulnerability to RBD mutations in VoC. To address these issues, we used naïve phage-displayed
peptide libraries to isolate and optimize 16-residue
peptides that bind to the RBD or the N-terminal domain (NTD) of the S-
protein. We fused these
peptides to the N-terminus of a moderate-affinity nAb to generate tetravalent
peptide-
IgG fusions, and we showed that both classes of
peptides were able to improve affinities for the S-
protein trimer by >100-fold (apparent KD < 1 pM). Critically, cell-based
infection assays with a panel of six SARS-CoV-2 variants demonstrated that an RBD-binding
peptide was able to enhance the neutralization potency of a high-affinity nAb >100-fold. Moreover, this
peptide-
IgG was able to neutralize variants that were resistant to the same nAb in the bivalent
IgG format, including the dominant B.1.1.529 (Omicron) variant that is resistant to most clinically approved therapeutic nAbs. To show that this approach is general, we fused the same
peptide to a clinically approved nAb drug and showed that it enabled the neutralization of a resistant variant. Taken together, these results establish minimal
peptide fusions as a modular means to greatly enhance affinities, potencies, and breadth of coverage of nAbs as
therapeutics for SARS-CoV-2.