CVnCoV and CV2CoV protect human ACE2 transgenic mice from ancestral B BavPat1 and emerging B.1.351 SARS-CoV-2

Abstract

The ongoing SARS-CoV-2 pandemic necessitates the fast development of vaccines. Recently, viral mutants termed variants of concern (VOC) which may escape host immunity have emerged. The efficacy of spike encoding mRNA vaccines (CVnCoV and CV2CoV) against the ancestral strain and the VOC B.1.351 was tested in a K18-hACE2 transgenic mouse model. Naive mice and mice immunized with a formalin-inactivated SARS-CoV-2 preparation were used as controls. mRNA-immunized mice develop elevated SARS-CoV-2 RBD-specific antibody and neutralization titers which are readily detectable, but significantly reduced against VOC B.1.351. The mRNA vaccines fully protect from disease and mortality caused by either viral strain. SARS-CoV-2 remains undetected in swabs, lung, or brain in these groups. Despite lower neutralizing antibody titers compared to the ancestral strain BavPat1, CVnCoV and CV2CoV show complete disease protection against the novel VOC B.1.351 in our studies.

Fig. 1. CVnCoV and CV2CoV protect K18-hACE2 mice against SARS-CoV-2 variants BavPat1 and B1.351.

K18-hACE2 mice that were vaccinated with 8 µg CVnCoV (orange) or different concentrations of CV2CoV (0.5 µg (light green), 2 µg (green), or 8 µg (dark green)), received 10⁶ FI-Virus (blue) or NaCl (black) (sham) on days 0 and 28 followed by i.n. challenge with 10^5.9 TCID₅₀ of SARS-CoV-2 variant BavPat1 or 10^5.5 TCID₅₀ B1.351. a RBD ELISA with sera from K18-hACE2 mice on days 0, 28, and 55 of the respective groups: median and interquartile range are presented. Dashed line indicates threshold for positive anti-RBD antibody level. b Virus neutralization assay using day 55 sera from all the groups. Bars indicate mean with SD. c, d Survival curves (Kaplan–Meier) for K18-hACE2 mice from all the groups challenged either with BavPat1 (c) or B.1.351 (d) and followed up for 10 days post infection (DPI). a, b Each dot represents one individual mouse sample. Each sample was tested once (RBD ELISA) or in triplicates (VNT), and assays were repeated at least once. c, d Each line represents groups of mice as shown in a, b from a single experiment (n = 5 sham, n = 10 all other groups). p Values were determined by nonparametric one-way ANOVA and Dunn’s multiple comparisons test (a, b) or two-sided log-rank (Mantel–Cox) test (c, d). Differences were considered significant at p < 0.05 with exact p values displayed in the figure. Source data are provided as a Source data file.

Fig. 2. CVnCoV and CV2CoV prevent replication of SARS-CoV-2 variants BavPat1 and B.1.351 in K18-hACE2 mice.

RT-qPCR for genomic RNA of SARS-CoV-2 was performed with a oral swab samples at day 4 or from organ samples of b the upper respiratory tract, c, d the lower respiratory tract (caudal lung = circle; cranial lung = squares), and e, f the brain at day 10 or at the humane endpoint. Mice that were vaccinated with 8 µg CVnCoV (orange) or different concentrations of CV2CoV (0.5 µg (light green), 2 µg (green) or 8 µg (dark green)), received 10⁶ FI-Virus (blue) or NaCl (black) (sham) on days 0 and 28 followed by i.n. challenge with 10^5.9 TCID₅₀ of SARS-CoV-2 variant BavPat1 or 10^5.5 TCID₅₀ B1.351. Each dot represents one individual mouse. Each sample was tested once, and assays were repeated at least once. p Values were determined by nonparametric one-way ANOVA and Dunn’s multiple comparisons test. Scatter plots are labeled with median (height of the bar) and interquartile range. Differences were considered significant at p < 0.05, with exact p values displayed in the figure. Source data are provided as a Source data file.