Figure 1. T-cell Responses to the Ancestral and Omicron Spike Protein of SARS-CoV-2.

Representative flow cytometry plots gated on CD4⁺ or CD8⁺ T cells showing upregulation of activation markers (CD69 and CD40 ligand [CD40L] for CD4⁺ cells and CD69 and CD137 for CD8⁺ cells) following overnight stimulation with a pool of overlapping peptides covering the whole spike protein from the ancestral vaccine strain (Pool_S), a peptide pool covering only the mutated regions of the Spike protein from the Omicron variant (Pool_Mut) or a peptide pool covering the same regions as Pool_Mut, but from the ancestral strain (Pool_Ref). Ctr indicates unstimulated control; numbers, percentages of activation induced marker cells within each gate.