Analysis of CTL-mediated killing of CD34⁺cell populations purified from patients with leukemia and normal donors.

(A) Representative experiment showing the level of killing by anti-P126 CTL against purified CD34⁺ and CD34⁻ cell populations isolated from patients with CML who were either HLA-A0201⁺ or A0201⁻. CD34⁻/A0201⁺ cells were not recognized by the CTL unless coated with P126 peptide. The leukemic cell line BV173 and the TAP-deficient T2 cells coated with P126 or the control E7 peptide were used as positive and negative controls in all experiments. (B) Cold target competition experiment. Shown is the killing by anti-P126 CTL against chromium-labeled CD34⁺ targets from an A0201⁺ patient with CML in the absence or presence of a 30-fold excess of cold BV173 and C1R-A2 targets. The killing of chromium-labeled BV173 and C1R-A2 is shown for comparison. (C) Average of the level of specific CTL killing of purified CD34⁺cells from 11 different HLA-A0201⁺ patients with CML and from 6 normal donors. The level of killing of CD34⁻cells purified from patients with CML and against the positive control cells BV173 is also shown. The figure shows the mean level and standard deviation of specific CTL killing. (D) Representative experiment showing the level of killing by anti-P126 CTL of purified CD34⁺ and CD34⁻ cell populations isolated from HLA-A0201⁺ normal donors. No CTL killing was detectable unless target cells were coated with P126 peptide.