Ratio of Ph⁺ cells to Ph⁻cells. Ph chromosomes were found in myeloid cells and B lymphocytes but not in mature T and NK cells. BCR/ABL fusion signals were found in pluripotent stem cells (CD34⁺Thy-1⁺), B progenitor cells (CD34⁺CD19⁺), and T progenitor cells (CD34⁺CD7⁺ cells or CD34⁺CD7⁺CD5⁺) at a frequency equal to that in all CD34⁺ cells. T lymphocytes showed a marked decrease of Ph⁺ cells between progenitor cells and mature cells. The incidence ratios of Ph⁺ cells in mature T cells and NK cells were below the cutoff value.