SARS-CoV-2 Neutralizing Antibody Responses towards Full-Length Spike Protein and the Receptor-Binding Domain
Rafael Bayarri‐Olmos, Manja Idorn, Anne Rosbjerg, Laura Pérez‐Alós, Cecilie Bo Hansen, Laust Bruun Johnsen, Charlotte Helgstrand, Franziska Zosel, Jais Rose Bjelke, Fredrik Öberg, Max Søgaard, Søren R. Paludan, Theresa Bak-Thomsen, Joseph G. Jardine, Mikkel‐Ole Skjoedt, Peter Garred
Abstract
Abstract Tools to monitor SARS-CoV-2 transmission and immune responses are needed. We present a neutralization ELISA to determine the levels of Ab-mediated virus neutralization and a preclinical model of focused immunization strategy. The ELISA is strongly correlated with the elaborate plaque reduction neutralization test (ρ = 0.9231, p < 0.0001). The neutralization potency of convalescent sera strongly correlates to IgG titers against SARS-CoV-2 receptor-binding domain (RBD) and spike (ρ = 0.8291 and 0.8297, respectively; p < 0.0001) and to a lesser extent with the IgG titers against protein N (ρ = 0.6471, p < 0.0001). The preclinical vaccine NMRI mice models using RBD and full-length spike Ag as immunogens show a profound Ab neutralization capacity (IC50 = 1.9 × 104 to 2.6 × 104 and 3.9 × 103 to 5.2 × 103, respectively). Using a panel of novel high-affinity murine mAbs, we also show that a majority of the RBD-raised mAbs have inhibitory properties, whereas only a few of the spike-raised mAbs do. The ELISA-based viral neutralization test offers a time- and cost-effective alternative to the plaque reduction neutralization test. The immunization results indicate that vaccine strategies focused only on the RBD region may have advantages compared with the full spike.