Fig. 4: LNP-based DNA vaccine protects K18-hACE2 mice against SARS-CoV-2 variants Gamma lineage (P.1).

A Scheme of immunization: K18-hACE2 mice were immunized with controls and LNP-HPS and boosted with equivalent doses 3 weeks later. Immunized mice were challenged with lethal 6 × 10⁴ PFU of SARS-CoV-2 variants Gamma lineage (P.1) 15 days after boost. B, C The lethality and weight loss were monitored for 15 days after challenge (n = 7/group). D Scheme of immunization wherein the lungs were harvested 5 days post infection for all immunized groups. E, F The plaque-forming unit measures the viable Vero cells treated with serum of immunized mice 5 days post infection (n = 5/group). Dashed line denotes limit of detection. G SARS-CoV-2 genome copies detected in the lung of the immunized mice at 5 days post infection (Mock n = 3; PBS, LNP-C, pHPS, BNT-mRNA, and LNP-HPS n = 5). H Analysis of infection via spike protein in lung sections of immunized mice at 5 days post infection via immunofluorescence from at least 20 fields of 3 different sections (n = 5/group). I Representative fluorescence images of lungs marked with anti-Spike antibody. Samples were stained with anti-SARS-CoV-2 Spike protein (RBD) antibody (magenta) and DAPI (blue) and acquired using a ×20 objective (n = 5/group). Data are presented as mean ± SEM; ns not significant, *p < 0.05, **p < 0.01, ****p < 0.0001. B Log-rank (Mantel–Cox) test. C Two-tailed, unpaired Spearman correlation to test. E, H One-way ANOVA with Dunnet’s post hoc test. G Kruskal–Wallis followed by Dunn’s multiple comparisons test. Source data are provided as a Source Data file.