Figure 3.

T-cell immune responses against spike antigens of wild-type and delta variant SARS-CoV-2 in samples from vaccinated participants

IFNγ (A), IL-2 (B), and IFNγ (C) concentrations in culture supernatant of peripheral blood mononuclear cells stimulated with peptide pools of wild-type and delta variant spike protein for 48 h (n=48; 47 of 48 samples responded to stimulation). Intracellular cytokine staining for IFNγ (D), IL-2 (E), and TNFα (F) in CD4 cells, and granzyme B (G), IFNγ (H), and perforin (I) in CD8 cells stimulated with peptide pools of wild-type and delta variant spike protein for 18–20 h; graphs show the proportions of cells expressing these molecules (n=41). Activation-induced marker assay of CD4 T cells (J) and CD8 T cells (K) stimulated with peptide pools of wild-type and delta variant spike protein for 24 h; graphs show the proportions of cells expressing these activation markers (n=38). (L) Antigen-specific activation of T cells by peptide pools exclusively covering the mutant regions of the delta variant spike protein compared with the homologous wild-type reference peptide pool (n=19; 19 of 24 samples responded to simulation; mean 63·78 SFCs/10⁶ PBMCs for wild-type, and 45.68 SFCs/10⁶ PBMCs for the delta variant). Each datapoint represents the readings from the peptide pool-stimulated wells for one study participant, after subtraction of the dimethyl sulfoxide-stimulated wells. IFNγ=interferon γ. SFCs=spot forming cells. TNFα=tumour necrosis factor α.