Veto activity of CD34⁺ cells: the veto activity is specific for CTL-p against CD34⁺ donor cells.

Responder cells (1 × 10⁶/mL) were simultaneously cultured with irradiated stimulators (0.7 × 10⁶/mL) from the donor of the CD34⁺ cells (○) and a third party (▵) for 5 days in the absence (○,▵) or presence (●,▴) of CD34⁺ cells added at a veto-to-responder ratio of 0.4:1. The responder cells were then divided equally, and each fraction was cultured again for 7 days under limiting dilution with stimulators from the donor of the CD34⁺ cells (A) or stimulators from the third-party donor (B). The CTL activity was determined by⁵¹Cr-release assay with the relevant target cells. The CTL-p frequency was calculated. The parameters for the different regression lines were as follows. (A) CTL-p frequency against stimulators from the CD34⁺ donor in the absence of CD34⁺ cells (○) was ln y = − 13.8 × 10⁻⁵x + ln 118.6 (R² = 0.955, SE(f) = 2.1 × 10⁻⁵,P = .022, f with 95% confidence interval [CI] = 4.7 × 10⁻⁵ to 2.3 × 10⁻⁴). In the presence of CD34⁺ cells (●), ln y = −0.84 × 10⁻⁵x + ln 102.9 (R² = 0.873, SE(f) = 2.2 × 10^-6,P = .065, f with 95% CI = − 1.3 × 10⁻⁶ to 1.8 × 10⁻⁵). In the presence of CD34⁺ cells (●), f was significantly lower (P < .005) than in the absence of these cells (○). (B) Anti–third-party CTL-p frequency in the absence of CD34⁺ cells (▵) was ln y = − 2.6 × 10⁻⁵ x + ln 103.6 (R² = 0.982, SE(f) = 2.4 × 10⁻⁶,P = .008, f with 95% CI = 1.5 × 10⁻⁵ to 3.7 × 10⁻⁵). In the presence of CD34⁺ cells (▴): ln y = − 2 × 10⁻⁵ x + ln 97.8 (R² = 0.898, SE(f) = 3.8 × 10⁻⁶,P = .014, f with 95% CI = 7.6 × 10⁻⁶ to 3.2 × 10⁻⁵). There was no significant difference between f in the presence (▴) and absence (▵) of CD34⁺cells (P > .1).