Rare, convergent antibodies targeting the stem helix broadly neutralize diverse betacoronaviruses.

Humanity has faced three recent outbreaks of novel betacoronaviruses, emphasizing the need to develop approaches that broadly target coronaviruses. Here, we identify 55 monoclonal antibodies from COVID-19 convalescent donors that bind diverse betacoronavirus spike proteins. Most antibodies targeted an S2 epitope that included the K814 residue and were non-neutralizing. However, 11 antibodies targeting the stem helix neutralized betacoronaviruses from different lineages. Eight antibodies in this group, including the six broadest and most potent neutralizers, were encoded by IGHV1-46 and IGKV3-20. Crystal structures of three antibodies of this class at 1.5–1.75-Å resolution revealed a conserved mode of binding. COV89-22 neutralized SARS-CoV-2 variants of concern including Omicron BA.4/5 and limited disease in Syrian hamsters. Collectively, these findings identify a class of IGHV1-46/IGKV3-20 antibodies that broadly neutralize betacoronaviruses by targeting the stem helix but indicate these antibodies constitute a small fraction of the broadly reactive antibody response to betacoronaviruses after SARS-CoV-2 infection. [Display omitted] • Isolation of 55 broadly reactive monoclonal antibodies to betacoronaviruses • Only a minority are broadly neutralizing and target the stem helix • Identification of an IGHV1-46/IGKV3-20 gene signature of the broad neutralizers • Structures of IGHV1-46/IGKV3-20 antibodies reveal a conserved mode of binding The characteristics of antibodies that broadly neutralize coronaviruses are poorly understood. Here, Dacon et al. identify a class of stem helix-specific monoclonal antibodies from COVID-19 convalescent donors that neutralize diverse betacoronaviruses, use an IGHV1-46/IGKV3-20 gene signature, and bind in a conserved manner to the spike protein. [ABSTRACT FROM AUTHOR]