Immunophenotypic and gene expression patterns of distinct BLL subpopulations. Immunophenotypic analysis performed by flow cytometry revealed 2 distinct BLL subpopulations in (A) patient 2073 and (B) patient 2279. Cells in the representative dot plots are colored according to the expression of 2 other CD markers measured within the same tube. Although the 2 distinct subpopulations are clearly visible in patient 2073, the immunophenotypic architecture of the leukemic clone in patient 2279 is more complex (see supplemental Figure 1). However, by using a combination of several markers, which are displayed in the sorting algorithms below the dot plots, it was possible to sort 2 nonoverlapping subpopulations in both patients: preT and myeloid (My) in patient 2073 and biphenotypic preT-myeloid (preT-My) and preT in patient 2279. (*) The presence or absence of intracellular myeloperoxidase (iMPO) was determined in a different tube. (C) A heat map representing the expression levels of the 200 top-scoring genes that are differentially expressed in preT (2279-T, 2073-T) compared with myeloid/preT-myeloid (2279-M, 2073-M) subpopulations. Expression values were transformed into a scale ranging from −1 to +1; for each gene, the minimal value was set to −1, and the maximal value was set to +1. (D) The normalized expression levels (ncounts) of selected lineage-specific genes involved in the 200-gene set represented in panel C document the distinct lineage characteristics of sorted subpopulations.