Figure 2.

Reduced antigenic repertoire of SARS-CoV-2 specific primary CD8⁺ T-cell responses in older adults. (A–D) PBMCs (7 × 10⁷) were primed in vitro with a pool of 37 SARS-CoV-2-derived peptides. After ten days, the frequency of epitope-specific primed naive CD8⁺ T cells was measured upon restimulation with 12 different matrixes composed of six peptides each or with the YLQ peptide (matrix 13) by IFNγ ELISpot. Responses above the threshold of 50 SFU/million cells were considered positive. Individual (A) and median values + S.E.M. (B) of responses to single matrixes are shown. Since each peptide is contained in two different matrixes, when responses to both matrixes were above 50 SFU/million cells, the response toward that single peptide was counted as positive and marked in black (C). The total number of recognized peptides by each donor was calculated and shown (D); the lines represent the median values. Statistical significance was determined by Mann–Whitney test, *p < 0.05 and **p < 0.01.