Recombinant OC43 SARS-CoV-2 Spike Replacement Virus: An Improved BSL-2 Proxy Virus for SARS-CoV-2 Neutralization Assays

We generated a replication-competent OC43 human seasonal coronavirus (CoV) expressing the SARS-CoV-2 spike in place of the native spike (rOC43-CoV2 S). This virus is highly attenuated relative to OC43 and SARS-CoV-2 in cultured cells and animals and is classified as a biosafety level 2 (BSL-2) agent by the National Institutes of Health (NIH) biosafety committee. Neutralization of rOC43-CoV2 S and SARS-CoV-2 by S-specific monoclonal antibodies (mAbs) and human sera is highly correlated, unlike recombinant VSV-CoV2 S (rVSV-CoV2 S). Single-dose immunization with rOC43-CoV2 S generates high levels of neutralizing antibodies against SARS-CoV-2 and fully protects human ACE2 (hACE2) transgenic mice from SARS-CoV-2 lethal challenge, despite non-detectable replication in respiratory and non-respiratory organs. rOC43-CoV2 S induces S-specific serum and airway mucosal immunoglobulin A (IgA) and IgG responses in rhesus macaques. rOC43-CoV2 S has enormous value as a BSL-2 agent to measure S specific-antibodies in the context of a bona fide CoV and is a candidate live attenuated SARS-CoV-2 mucosal vaccine that preferentially replicates in the upper airway