Fig. 4. S and S + N DNA vaccines protect against SARS-CoV-2 Omicron BA.2 infection in K18-hACE2 mice.

a Experimental protocol: On days 0 and 21, K18-hACE2 mice were inoculated with S and/or N DNA vaccines or pVAX control (25 µg, IM), challenged at 2 weeks post-boost with SARS-CoV-2 Omicron BA.2 variant (10⁴ PFU, IN), and tissues were harvested 3 days later. Representation of the experiment timeline was Created with BioRender.com. b SARS-CoV-2 genomic and subgenomic RNA were quantified by RT-qPCR. Dashed lines, detection limit. c Histopathology of SARS-CoV-2-induced lung disease. c Five histopathological parameters (necrosis of bronchiolar epithelial cells [BEC], cellular debris in bronchioles, inducible bronchus-associated lymphoid tissue [iBALT] hyperplasia, perivascular lymphocytic cuffing, and bronchointerstitial pneumonia) were scored from 0 (least severe) to 5 (most severe). d Representative bronchointerstitial pneumonia images, H&E-stain. e Splenocytes were stimulated with the indicated SARS-CoV-2 S or N peptides, and polyfunctional (IFN-γ⁺TNF-α⁺ or IFN-γ⁺TNF-α⁺IL-2⁺) and cytotoxic (IFN-γ⁺CD107a⁺) CD4⁺ and CD8⁺ T cells within the population of CD3⁺ cells were quantified by ICS. f Experimental protocol for one-dose vaccination regimen: On day 0, K18-hACE2 mice were inoculated with S and/or N DNA vaccines or pVAX control (25 µg, IM), challenged on day 35 with SARS-CoV-2 Omicron BA.2 (10⁴ PFU, IN), and tissues were harvested 3 days later. Representation of the experiment timeline was Created with Biorender.com. g SARS-CoV-2 genomic and subgenomic RNA quantified by RT-qPCR; dashed lines, detection limit. b–d Data are from 2 independent experiments (n = 10–11 mice/group). f, g Data is from 1 experiment (n = 6 mice/group). Group means were compared by the non-parametric Kruskal-Wallis test. *P < 0.05, **P < 0.01, ***P < 0.001. Circles, individual mice.