Potent Neutralization of Omicron and other SARS-CoV-2 Variants of Concern by Biparatopic Human VH Domains

The emergence of SARS-CoV-2 variants of concern (VOCs) requires the development of next-generation biologics that are effective against a variety of strains of the virus. Herein, we characterize a human VH domain, F6, which we generated by sequentially panning large phage displayed VH libraries against receptor binding domains (RBDs) containing VOC mutations. Cryo-EM analyses reveal that F6 has a unique binding mode that spans a broad surface of the RBD and involves the antibody framework region. Attachment of an Fc region to a fusion of F6 and ab8, a previously characterized VH domain, resulted in a construct (F6-ab8-Fc) that neutralized Omicron pseudoviruses with a half-maximal neutralizing concentration (IC50) of 4.8 nM in vitro. Additionally, prophylactic treatment using F6-ab8-Fc reduced live Beta (B.1.351) variant viral titers in the lungs of a mouse model. Our results provide a new potential therapeutic against SARS-CoV-2 VOCs - including the recently emerged Omicron variant - and highlight a vulnerable epitope within the spike protein RBD that may be exploited to achieve broad protection against circulating variants.

Emerging SARS-CoV-2 Variants of Concern: Spike Protein Mutational Analysis and Epitope for Broad Neutralization

Mutations in the spike glycoproteins of SARS-CoV-2 variants of concern have independently been shown to enhance aspects of spike protein fitness. Here, we report the discovery of a novel antibody fragment (VH ab6) that neutralizes all major variants, with a unique mode of binding revealed by cryo-EM studies. Further, we provide a comparative analysis of the mutational effects within variant spikes and identify the structural role of mutations within the NTD and RBD in evading antibody neutralization. Our analysis shows that the highly mutated Gamma N-terminal domain exhibits considerable structural rearrangements, partially explaining its decreased neutralization by convalescent sera. Our results provide mechanistic insights into the structural, functional, and antigenic consequences of SARS-CoV-2 spike mutations and highlight a spike protein vulnerability that may be exploited to achieve broad protection against circulating variants.