The SARS-CoV-2 receptor-binding domain elicits a potent neutralizing response without antibody-dependent enhancement

Brian D Quinlan; Huihui Mou; Lizhou Zhang; Yan Gao; Wenhui He; Amrita Ojha; Mark S Parcells; Guangxiang Luo; Wenhui Li; Guocai Zhong; Hyeryun Choe; Michael Farzan

. CC-BY-NC-ND 4.0 International license author/funder. It is made available under a The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.04.10.036418 doi: bioRxiv preprint Four female Sprague Dawley rats (R15, R16, R17, R18) were immunized with two sets of escalating doses of RBD conjugated to keyhole limpet hemocyanin. (A) The indicated dilutions of preimmune sera (day 0, gray) were compared to dilutions of sera harvested from immunized rats at day 40, and to the same dilutions of preimmune sera mixed to achieve the indicated ACE2-Ig concentrations before dilution. Each serum and serum-ACE2-Ig mixture was compared for its ability to neutralize S-protein-pseudotyped retroviruses (SARS2-PV), by measuring the activity of a firefly-luciferease reporter expressed by these pseudoviruses. Figure shows entry of SARS2-PV as a percentage of that observed without added rat serum. Error bars indicate the range of two neutralization studies. (B) The data from each rat of panel A are averaged for clarity. Error bars indicate s.e.m., with each rat considered a different experiment. Differences between day-0 and day-40 serum are significant at all dilutions (P < 0.001; two-way ANOVA). (C) Sera from each rat was pooled before characterization, and SARS2-PV entry was measured at the indicated dilutions. Day-0 preimmune sera, day-15 sera, and day-40 sera were compared to day-0 sera mixed with ACE2-Ig to achieve the indicated concentrations before dilution, and characterized for their ability to neutralize SARS2-PV. Day 40 sera was also tested for its ability to neutralize SARS-CoV-1 pseudoviruses (SARS1-PV) as indicated. Values shown indicate percentage of pseudovirus entry observed with the same dilution of day-0 preimmune sears. Significant differences compared . CC-BY-NC-ND 4.0 International license author/funder. It is made available under a The copyright holder for this preprint (which was not peer-reviewed) is the . https://doi.org/10.1101/2020.04.10.036418 doi: bioRxiv preprint to day-0 serum at each dilution are indicated above the bar (* indicates P < 0.05; ** indicates P < 0.01; *** indicates P < 0.005; **** indicates P < 0.001; ns indicates P > 0.05; two-way ANOVA).