Fig. 4: Immunization with adjuvanted S-VLPs induces SARS-CoV-2-neutralizing, protective responses in rodents.

a* Humoral immune response titers (total anti-spike IgG) in vaccinated mice with different S-VLP formulations. Anti-S geometric mean titers (GMT) at day 28 from naïve and treated groups were determined by ELISA. b* Quantification of spike-specific T cells. Isolated splenocytes from vaccinated mice with S-VLP formulations were co-incubated with a spike peptide library. Quantification of IFN-γ+ secreting cells was performed by ELISpot and results were expressed as the mean of IFN-γ+/10⁶ splenocytes. c** Cell-based (hACE2-HEK293T) surrogate neutralization assay. The percentage neutralization means for SARS-CoV-2 was determined from dilutions of 1:25 in unadjuvanted and Adju-phos or 1:75 in AS01b conditions. a–c Data are presented as geometric mean ± SEM (10 mice per group). Black dots represent naïve animals, blue for unadjuvanted, red for Adju-phos, and green for AS01b S-VLPs. d Body weight change in immunized hamsters infected with SARS-CoV-2 (ancestral strain). The line graph represents daily body weight measurements of naïve and vaccinated animals post-challenge. e** Virus quantification by plaque assay. Plaque forming units (PFUs) were quantified in Vero E6 cells infected with hamster lung homogenates. Virus load (log10) is displayed in PFU per gram of lung. f** Viral RNA quantification in hamster lungs. RNA samples from naïve and vaccinated animals at five days post-challenge were subjected to viral RNA detection by RT-qPCR. SARS-CoV-2 RNA concentration is displayed by gRNA copies/lung (log10). d–f Data are presented as mean ± SEM (6 animals per group). Black dots (gray bars) represent naïve animals, blue is unadjuvanted S-VLPs, orange AS01b and green represents S-VLPs+AS01b. *A one-way ANOVA with Tukey’s or **Dunnette’s multiple comparison tests was performed to assess significance. p ≤ 0.0001, p ≤ 0.001, p ≤ 0.01 and p ≤ 0.05 are represented by four, three, two, and one asterisks, respectively, and p > 0.05 as not significant (NS).