FLU-specific cells proliferate better than CMV-specific cells. (A) Dot plots gated on CD8⁺ lymphocytes in which FLU or CMV tetramer staining is plotted against CFSE to visualize cell divisions. Total PBMCs were cultured for 6 days in the presence of IL-7, IL-15, FLU peptide, CMV peptide, or the specific peptide in combination with FLU or CMV antigen, respectively. (top panels) Staining with the FLU tetramer. (bottom panels) Staining with the CMV tetramer. For clarity, only 50% of the measured events is shown in the CMV tetramer staining. Representative data are shown from 1 of 3 independent experiments with healthy donors. (B) Precursor frequencies of FLU-specific (▪) and CMV-specific cells (▴) from one donor on dose titrations of IL-7 and IL-15 in 6-day total PBMC cultures. (C) Percentage of CMV B7 tetramer⁺ cells within CD8⁺ T cells before culture (unstimulated) and after 6 days' stimulation with the CMV B7 peptide, cytokines, or CMV antigen, alone or in combination. Representative data are shown from 2 independent experiments with healthy donors.