Figure 1.

High- and low-quality CD4⁺ T cell responses develop upon SARS-CoV-2 vaccination

(A) Overview of the study design. Blood was drawn at the indicated time points and analyzed for SARS-CoV-2-specific CD4⁺ T cells and IgG. 34 individuals of our study received two doses of the BioNTech/Pfizer BNT162b2 mRNA vaccine, while 16 individuals received a heterologous immunization with AstraZeneca ChAdOx1 followed by Moderna mRNA-1273.

(B) Representative dot plot examples for the ex vivo detection of SARS-CoV-2 spike-reactive CD4⁺ T cells by ARTE pre- and post-vaccination. Absolute cell counts after magnetic CD154⁺ enrichment from 1x10e7 PBMCs are indicated.

(C) Serum anti-spike IgG antibody concentrations pre- and post-second vaccination.

(D) Frequencies of SARS-CoV-2 spike-reactive Tmems pre- and post-vaccination (left) in comparison to convalescent COVID-19 patients with mild (non-hospitalized) or severe disease (based on WHO criteria WHO4–7) (right).

(E) Vaccination-induced expansion of spike-reactive CD4⁺ Tmems was calculated for each donor based on the frequency pre-vaccination and after the second vaccination. Individuals with the lowest (“bottom 10”) and highest (“top 10”) expansion rate are indicated in blue or orange, respectively.

(F) Bottom 10 and top 10 expanders were determined as described in (E) and compared for spike-reactive Tmem frequencies.

(G) Spike-reactive CD154⁺ Tmems were FACS-purified, expanded, and re-stimulated with decreasing antigen concentration in the presence of autologous antigen-presenting cells. Reactive cells were determined by re-expression of CD154 and TNF-α, and EC50 values were calculated from dose-response curves.

(H) Ex vivo IL-21 production of spike-reactive T cells, within CD154⁺ Tmems (left) or within total CD4⁺ T cells (right).

(I) Dot plot example of spike-specific IL-21 and IL-2 production of a bottom 10 or top 10 donor.

(J and K) Anti-spike IgG concentrations (J) and SARS-CoV-2 serum neutralization titers (K) at 6–8 weeks and 6 months post-second vaccination.

(L) Spearman correlation of the fold expansion of spike-reactive CD4⁺ T cells and anti-spike IgG concentrations measured 6–8 weeks post-second vaccination. Each symbol in (C, D, F–H, J–L) represents one donor; horizontal lines indicate geometric mean in (C, D). Box-and-whisker plots display quartiles and range in (F–H, J, K). Statistical differences: Friedman test with Dunn’s post hoc test in (D, left); two-tailed Mann-Whitney test in (D, right) and (C, F–H, J, K). See also Figures S1–S3.