CD8+ T-cell responses to PR1 and WT1 vaccination by intracellular IFN-γ assay. (A-C) Longitudinal data on IFN-γ production by CD8+ T cells in PBMC samples from patient 8, cultured for 6 hours with PR1 (A), with WT1 (B), or without peptide (negative control [C]) are presented. Results are expressed as percentages of total CD8+ T cells. (D,E) Frequencies of PR1- and WT1-specific CD8+ T cells by tetramer analysis and IFN-γ production were compared and found to be highly correlated; P < .001.