Fig. 5.

Immunization of S1 protein co-delivery of IL-15 with TLR-Ls provides the best humoral protection against live SARS-CoV-2 virus and variants of concern. B6 (WT) mice were immunized with S1 protein alone (black) or co-delivered with Alum (green), IL-12 and GM-CSF (red), or IL-15 and TLR-Ls (blue) in DOTAP. Serum samples from day 60 post-immunization were incubated with 30 PFU of SARS-CoV-2 for 1 h at 37 °C; serial dilutions of virus-serum mixtures were added onto Vero E6 cell monolayers and plates were fixed and stained after 3 days of culture. (A) PRNT (Plaque Reduction Neutralization Test) antibody titer ID50 was defined as the highest serum dilution resulting in 50% reduction of plaques. Serum samples from day 60 post-immunization and anti-S1 positive control antibodies were subjected to ELISAs (read as absorbance) for reactivity against SARS-CoV-2 variants, including WT (Wuhan) and variants of concern (B-M). The data are represented as the mean ± SEM and represent one (A) or two (B-M) independent experiments. p values are shown for entirety of study using one-way ANOVA test with post hoc Tukey’s multiple comparisons; *, p < 0.05; **, p < 0.01; ***, p < 0.001; ****, p < 0.0001.