Comparison of BCR-ABL transcripts and BCR-ABL, P-Tyr, and P-CrKL protein expression levels between MNC, CD34⁺, and CD34⁺CD38^– CML cells. (A) The expression level of BCR-ABL was determined by quantitative RT-PCR and normalized to cell number used in the assay. Five patient samples were tested in this way and the results combined. The figure shows the expression level of BCR-ABL in the sorted cell populations as a product of the MNC population level (P = .016 for MNC versus CD34⁺ cells and P = .031 for MNC versus CD34⁺CD38^– cells). These results show that the expression levels differ by at least 10-fold between the MNC population and the 2 stem cell populations. There was no significant difference between the CD34⁺ and the CD 34⁺CD38^– populations. BCR-ABL (B), P-Tyr (C), and P-CrKL (D) protein expression levels in total MNCs and CD34⁺ and CD34⁺CD38^– CML cells from 3 newly diagnosed chronic phase CML patients were assessed by Western blotting. Protein expression was quantified using relative densitometry (bar charts above blots). These experiments showed that BCR-ABL, P-Tyr, and P-CrKL were highest in the most primitive CD34⁺CD38^– subpopulation and lowest in the mature total MNC fraction. RD indicates relative density.