Fig. 6. Characterization of CD8⁺ T memory cells after breakthrough infection and the 4^th vaccine dose.

Reactivation capacity of spike-specific CD8⁺ T cells 1 month after symptom onset and 4^th vaccination. Median values are depicted with 95% confidence interval error bars with n = 6 for Omicron and n = 2 for Delta breakthrough infections, and n = 4 individuals receiving a 4^th vaccination (a). t-SNE representation of spike-specific CD8⁺ T cells 1 month after symptom onset and 4^th vaccination. Expression levels of CD38, CCR7, TCF- and BCL-2 are depicted (b). Calculated ex vivo frequencies of BCL-2^hi non-naïve spike-specific CD8⁺ T cells before and after breakthrough infection and 4^th vaccination (c). Antibody neutralization activity as 50% plaque reduction neutralization tests (PRNT50) for SARS-CoV-2 variants B.1, B.1.617.2 and B.1.1.529 after breakthrough infection and 4^th vaccination with n = 11 for Omicron and n = 1 for Delta breakthrough infection, and n = 2 individuals receiving a 4^th vaccination (d). Statistical significance was calculated by Kruskal-Wallis test (a) to compare the effect of the antigen triggers on expansion (p_exp) and interferon production (p_inf) and two-way ANOVA with main model (c, d) to compare the effects of antigen triggers (p_a) on epitope-specific T cell frequencies (c) or the effects of VOCs (p_v) and time course (p_t). Source data are provided as a Source Data file.