Fig. 2. Antibody and T-cell responses against the SARS-CoV-2 spike protein after homologous COVID-19 vaccine regimens or heterologous ChAdOx-priming and BNT- or mRNA-1273-boosting.

Cellular and humoral immune parameters were analyzed 13–18 days post vaccination and compared between individuals with different homologous or heterologous COVID-19 vaccine regimens: homologous ChAdOx vaccination (n = 62), heterologous ChAdOx/BNT vaccination (n = 66), heterologous ChAdOx/mRNA-1273-vaccination (n = 101), homologous BNT vaccination (n = 43) or homologous mRNA-1273-vaccination (n = 58). a ELISA and surrogate neutralization assays were performed to quantify levels of spike-specific IgG and neutralizing antibodies. Intracellular cytokine staining after antigen-specific stimulation of whole blood samples allowed for flow-cytometrical determination of SARS-CoV-2 spike-specific (b) and SEB-reactive (c) CD4 and CD8 T-cell levels. Reactive cells were identified by co-expression of CD69 and IFNγ among CD4 or CD8 T cells and subtraction of reactivity of respective negative control stimulations. CTLA-4 expression was determined on d spike-specific and e SEB-reactive CD4 and CD8 T cells in all samples with at least 20 cytokine-positive CD4 and CD8 T cells. f Correlation matrix of spike-specific T-cell and antibody responses among each group. Bars in a–e represent medians with interquartile ranges. Differences between the groups were calculated using two-sided Kruskal–Wallis test with Dunn´s multiple comparisons post-test. Correlations in f were analyzed according to two-tailed Spearman (see also Supplementary Table 1). Dotted lines indicate detection limits for antibodies in a, indicating negative, intermediate, and positive levels or levels of inhibition, respectively as per manufacturer’s instructions, and detection limits for SARS-CoV-2-specific CD4 T cells in b and c. Source data are provided as a Source Data file. IFN Interferon, MFI median fluorescence intensitiy, SEB Staphylococcus aureus enterotoxin B.