Tetramers. CD3⁺ T cells from the same culture described in Figure 3 were stained with WT1-A/HLA-A0201 tetramer with mAbs to CD8 and other T-cell markers. Percentage of tetramer-positive CD8⁺ T cells (number shown in upper left corner of each histogram) were gated on CD3⁺ events after passing through the small lymphocyte gate. Cells from prevaccine, postvaccine 3, and postvaccine 6 are shown as T0, T3, and T6, respectively. The data are representative staining from triplicate cultures. After vaccination, a robust increase in percentage of WT1-specific CD8⁺ T cells was noted in cultures with WT1-A, WT1-A1, and 122A1 peptides (top axis). Peptide 122A stimulation induced a weak but significant response.