Fig. 7. SARS-CoV-2 Kb spike (539–546)-specific MHC class I restricted CD8 + T cells in response to SpFN vaccine following booster vaccination.

a Frequency of antigen-specific CD8 + T cells in splenocytes of naïve and vaccinated mice as determined by flow cytometry-based SARS-CoV-2 spike (539–546)-specific tetramer staining. b Representative flow plots depicting the frequency of Kb spike (539–546)-specific CD8 + T cells at week 6 in all the groups. Bar graphs and representative flow plots demonstrate the significantly higher percentage of spike (539–546)-specific-, c TNF-α +, d IFN-γ + CD8 + T cells. e Bar graph and representative flow plots depicting the significant differences in the frequency of the SARS-Cov-2 spike-specific CD8 + T cells concomitantly producing both IFN-γ and TNF-α. Bars represent the mean + SD and significant differences between the groups were calculated using nonparametric two-tailed Mann–Whitney U-test in Graphpad prism version 8. f CD8 + T cell polyfunctionality: Differences in the ability of CD8 + T cells stimulated with SARS-CoV-2 spike peptides to secrete more than one cytokine. Boolean gating was applied to identify all combinations of CD8 + T cell effector functions. The pie chart depicts the average proportion of spike-specific CD8 + T cells producing all three (IFN-γ, IL-2, or TNF-α), any two, or any one cytokine. The graphs show cytokine-secreting peptide-specific CD8⁺ T cells for each individual mouse (n = 5 /group) in response to each adjuvant formulation and the horizontal line represents the mean. This analysis was performed using the SPICE software version 5.1⁶⁵.