Fig. 4.

Within-donor differences of peptide pool reactive CD4 (a) and CD8 (b) T-cell responses are shown for freshly isolated versus cryopreserved PBMC. Depicted are the within-donor differences of detected CD4 (a) and CD8 (b) T-cell responses upon stimulation of freshly isolated versus cryopreserved PBMC with peptide pools of EBV-BZLF1 (n = 30), EBV-EBNA3A (n = 30), HCMV-IE1 (n = 19), and HCMV-pp65 (n = 19) proteins. To determine the bias between freshly isolated and cryopreserved PBMC the frequencies of antigen-reactive CD4 (a) or CD8 (b) T cells in cryopreserved PBMC was subtracted from that of respective freshly isolated PBMC for each donor. Each dot represents the respective fresh minus cryopreserved difference of CD4 (a) and CD8 (b) TP-reactive T-cell responses of each single donor. Bars represent the median difference of antigen-reactive CD4 (a) or CD8 (b) T-cell responses of all tested donors. All statistics are based on paired Wilcoxon signed rank tests. PP peptide pool, TP T-activated protein