High- and low-avidity CD8⁺ T-cell responses determined by sensitivity to peptide concentration in healthy donors and patients with CML. Stimulating CD8⁺ T cells with 0.1 μM and 10 μM CMV pp65 (□), PR1 (○), WT1 (▵), and BCR-ABL (⋄) determined high- and low-avidity responses, respectively. Results shown are the ratios of high- to low-avidity CD8⁺ T-cell responses, calculated for individual healthy donors (filled symbols) and patients with CML (open symbols). Ratios were obtained by the following calculation: (number of IFN-γ mRNA copies/10⁴ CD8 copies with 0.1 μM peptide)/(number of IFN-γ mRNA copies/10⁴ CD8 copies with 10 μM peptide). Bars represent the median high- and low-avidity ratio for each condition. CD8⁺ T-cell responses to PR1, WT1, and BCR-ABL in patients with CML were mostly low avidity, whereas CD8⁺ T-cell responses in healthy donors were skewed toward high-avidity responses (P = .01 and P < .05, respectively). CMV responses were not statistically different in the 2 groups (P = .12). Dashed line represents a median ratio of 1.