ABSTRACT
Neutralizing antibody responses to coronaviruses mainly target the receptor-binding domain (RBD) of the trimeric spike. Here, we characterized polyclonal immunoglobulin Gs (IgGs) and Fabs from COVID-19 convalescent individuals for recognition of coronavirus spikes. Plasma IgGs differed in their focus on RBD epitopes, recognition of alpha- and beta-coronaviruses, and contributions of avidity to increased binding/neutralization of IgGs over Fabs. Using electron microscopy, we examined specificities of polyclonal plasma Fabs, revealing recognition of both S1A and RBD epitopes on SARS-CoV-2 spike. Moreover, a 3.4 Å cryo-electron microscopy (cryo-EM) structure of a neutralizing monoclonal Fab-spike complex revealed an epitope that blocks ACE2 receptor binding. Modeling based on these structures suggested different potentials for inter-spike crosslinking by IgGs on viruses, and characterized IgGs would not be affected by identified SARS-CoV-2 spike mutations. Overall, our studies structurally define a recurrent anti-SARS-CoV-2 antibody class derived from VH3-53/VH3-66 and similarity to a SARS-CoV VH3-30 antibody, providing criteria for evaluating vaccine-elicited antibodies.
Subject(s)
Antibodies, Neutralizing/chemistry , Betacoronavirus/chemistry , Coronavirus Infections/immunology , Immunoglobulin Fab Fragments/chemistry , Immunoglobulin G/chemistry , Pneumonia, Viral/immunology , Spike Glycoprotein, Coronavirus/chemistry , Antibodies, Neutralizing/blood , Antibodies, Neutralizing/isolation & purification , Antibodies, Viral/immunology , Antibodies, Viral/isolation & purification , Betacoronavirus/immunology , COVID-19 , Coronavirus Infections/blood , Coronavirus Infections/therapy , Cross Reactions , Cryoelectron Microscopy , Epitope Mapping , Epitopes , Humans , Immunization, Passive , Immunoglobulin Fab Fragments/blood , Immunoglobulin Fab Fragments/isolation & purification , Immunoglobulin Fab Fragments/ultrastructure , Immunoglobulin G/blood , Immunoglobulin G/isolation & purification , Immunoglobulin G/ultrastructure , Middle East Respiratory Syndrome Coronavirus/chemistry , Middle East Respiratory Syndrome Coronavirus/immunology , Models, Molecular , Pandemics , Pneumonia, Viral/blood , Severe acute respiratory syndrome-related coronavirus/chemistry , Severe acute respiratory syndrome-related coronavirus/immunology , SARS-CoV-2 , Spike Glycoprotein, Coronavirus/immunology , COVID-19 SerotherapyABSTRACT
The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic continues, with devasting consequences for human lives and the global economy1,2. The discovery and development of virus-neutralizing monoclonal antibodies could be one approach to treat or prevent infection by this coronavirus. Here we report the isolation of sixty-one SARS-CoV-2-neutralizing monoclonal antibodies from five patients infected with SARS-CoV-2 and admitted to hospital with severe coronavirus disease 2019 (COVID-19). Among these are nineteen antibodies that potently neutralized authentic SARS-CoV-2 in vitro, nine of which exhibited very high potency, with 50% virus-inhibitory concentrations of 0.7 to 9 ng ml-1. Epitope mapping showed that this collection of nineteen antibodies was about equally divided between those directed against the receptor-binding domain (RBD) and those directed against the N-terminal domain (NTD), indicating that both of these regions at the top of the viral spike are immunogenic. In addition, two other powerful neutralizing antibodies recognized quaternary epitopes that overlap with the domains at the top of the spike. Cryo-electron microscopy reconstructions of one antibody that targets the RBD, a second that targets the NTD, and a third that bridges two separate RBDs showed that the antibodies recognize the closed, 'all RBD-down' conformation of the spike. Several of these monoclonal antibodies are promising candidates for clinical development as potential therapeutic and/or prophylactic agents against SARS-CoV-2.