Defining neutralization and allostery by antibodies against COVID-19 variants (preprint)

The changing landscape of mutations in the SARS-CoV-2 Spike protein is linked to the emergence of variants, immune-escape and reduced efficacy of the existing repertoire of anti-viral antibodies. A major factor that contributes to the functional activity of the neutralizing antibodies are the intrinsic quaternary changes that occur as a result of antibody-Spike trimer interactions. In this study, we reveal the conformational dynamics and allosteric perturbations linked to binding of human monoclonal antibodies and the viral Spike protein. We identify epitope hotspots of known and novel antibodies, and associated changes in Spike dynamics that define weak, moderate and strong neutralizing antibodies. We show the impact of mutations in Wuhan, Delta, and Omicron variants of concern (VoCs) and differences observed in the antibody-induced conformational changes and illustrate how these render certain antibodies ineffective. Our comparative analyses of the antibody-footprints on Spike variants reveal how antibodies with similar binding affinities may induce destabilizing and stabilizing allosteric effects. These differences have important implications for neutralization efficacy and for developing new antibodies targeting emerging variants. Our results provide mechanistic insights into the functional modes and synergistic behavior of human antibodies against COVID-19, and provide a rationale to design effective antiviral strategies.

Engineering SARS-CoV-2 cocktail antibodies into a bispecific format improves neutralizing potency and breadth (preprint)

One major limitation of neutralizing antibody-based COVID-19 therapy is the requirement of costly cocktails to reduce antibody resistance. We engineered two bispecific antibodies (bsAbs) using distinct designs and compared them with parental antibodies and their cocktail. Single molecules of both bsAbs block the two epitopes targeted by parental antibodies on the receptor-binding domain (RBD). However, bsAb with the IgG-(scFv)2 design (14-H-06) but not the CrossMAb design (14-crs-06) increases antigen-binding and virus-neutralizing activities and spectrum against multiple SARS-CoV-2 variants including the Omicron, than the cocktail. X-ray crystallography and computational simulations reveal distinct neutralizing mechanisms for individual cocktail antibodies and suggest higher inter-spike crosslinking potentials by 14-H-06 than 14-crs-06. In mouse models of infections by SARS-CoV-2 and the Beta, Gamma, and Delta variants, 14-H-06 exhibits higher or equivalent therapeutic efficacy than the cocktail. Rationally engineered bsAbs represent a cost-effective alternative to antibody cocktails and a promising strategy to improve potency and breadth.