PBMCs of COVID-19 convalescent individuals (n=11) were stimulated with the Spike MPs corresponding to the ancestral reference strain (Wu, black) and the B.1.1.7 (UK, grey), B.1.351 (SA, red), P.1 (BR, orange) and CAL.20C (CA, light blue) SARS-CoV-2 variants. A) Percentages of AIM+ (OX40+CD137+) CD4+T cells. B) Percentages of AIM+ (CD69+CD137+) CD8+ T cells. C) IFNγ spot forming cells (SFC) per million PBMCs D) IL-5 SFC per million PBMCs. Paired comparisons of Wuhan S MP versus each of the variants were performed by Wilcoxon test and are indicated by the p values in panels A-C. The data shown in panels A and B are plotted to show the Spike MPs titration (1 μg/mL, 0.1 μg/mL, 0.01 μg/mL) for CD4+ (E) and CD8+ (F) T cells in each SARS-CoV-2 variant and the geometric mean of the 0.1ug/mL condition is listed above each titration. In all panels, the bars represent the geometric mean.