Figure 3.

Pre-existing memory cells expand poorly upon vaccination

(A) Spearman correlation between the frequencies of spike-reactive Tmems pre-vaccination (x axis) and the fold expansion post-second vaccination (y axis).

(B–D) Donors were grouped by their pre-vaccination frequencies of spike-reactive Tmems (<1.5, n = 8; 1.5–2.5, n = 14; 2.5–5, n = 10; >5, n = 11). Donors >80 years of age (n = 6) are depicted as separate group. For each bin, the (B) fold expansion post-second vaccination, (C) percentage of IL-21 production within CD154⁺ Tmems, and (D) functional avidity of expanded spike-reactive T cells is indicated.

(E) Spearman correlation between the proportion of spike-reactive naive cells pre-vaccination (x axis) and the fold expansion post-second vaccination (y axis).

(F–H) Donors were grouped by their pre-vaccination proportion of spike-reactive naive cells (<20, n = 9; 20–30, n = 11; 30–45, n = 12; >45, n = 11). Donors >80 years of age (n = 6) are depicted as separate group. For each bin, the (F) fold expansion post-second vaccination, (G) percentage of IL-21 production within CD154⁺ Tmems, and (H) functional avidity of expanded spike-reactive T cells is indicated. Each symbol in (A–H) represents one donor; horizontal lines indicate mean in (B, C, F, G) and geometric mean in (D, H). Statistical differences: Kruskal-Wallis test with Dunn’s post hoc test in (B–D, F–H). To determine differences between the younger age groups, donors >80 years of age were excluded from statistical analysis. See also Figure S3.