Frequency of BCR-ABL⁺ cells in CD34⁺38⁺ or CD34⁺38⁻ populations. (A) A schematic of experimental and analytical procedures for measurement of the frequency of BCR-ABL–positive cells within flow cytometry selected CD34⁺CD38⁻ and CD34⁺CD38⁺ cells using limiting dilution analysis is shown. (B) The frequencies of BCR-ABL⁺ cells within the CD34⁺CD38⁺ (black bars) and CD34⁺CD38⁻ (grey bars) subpopulations in 14 samples obtained at different time points from 6 patients is shown (2-3 serial samples per patient).