The SARS-CoV-2 Neutralizing Antibody Response to SD1 and Its Evasion by BA.2.86

Under pressure from neutralising antibodies induced by vaccination or infection the SARS-CoV-2 spike gene has become a hotspot for evolutionary change, leading to the failure of all mAbs developed for clinical use. Most potent antibodies bind to the receptor binding domain which has become heavily mutated. Here we study responses to a conserved epitope in sub-domain-1 (SD1) of spike which have become more prominent because of mutational escape from antibodies directed to the receptor binding domain. Some SD1 reactive mAbs show potent and broad neutralization of SARS-CoV-2 variants. We structurally map the dominant SD1 epitope and provide a mechanism of action by blocking interaction with ACE2. Mutations in SD1 have not been sustained to date, but one, E554K, leads to escape from mAbs. This mutation has now emerged in several sublineages including BA.2.86, reflecting selection pressure on the virus exerted by the increasing prominence of the anti-SD1 response. Due to the focus of vaccination on the SARS CoV-2 spike protein, spike has been associated with high levels of viral mutation and subsequent immune escape. Here the authors study a conserved epitope in SARS CoV-2 sub-domain-1 and characterise the neutralising antibody response and evasion in contemporary SARS COV-2 viral strains.