The immunophenotypes of blast cells in B-cell precursor acute lymphoblastic leukemia: how different are they from their normal counterparts?

Currently, there are three major maturational stages of CD19 antigen expressing B-cell precursors (hematogones). In B-cell precursor acute lymphoblastic leukemia (BCP-ALL), the malignant counterpart of hematogones, the leukemic blasts share common phenotypic features. The aim of the study was to enumerate the actual differences between the leukemic blasts in the CD10+ and CD10- subgroups of BCP-ALL and hematogones by assessing the expression of the antigens: TdT, CD34, CD45, CD10, CD38, CD20 and CD22. To enable quantitative assessment of antigen expression on the different cell types, an objective scale of antigen expression was developed, the basis of which was direct fluorescence measurement using multicolor flow cytometry. All cases of CD10+ BCP-ALL clustered with type 1 hematogones. Among CD10-- BCP-ALL subgroup, 54.5%, 27.3% and 18.2% of cases clustered with type 1, 2 and 3 hematogones, respectively. In contrast to the CD10- blasts, the CD10+ blasts exhibited significantly higher levels of TdT, CD22, CD34 and CD20 expression. Conversely, CD10- blasts showed significantly higher expression of CD45 than CD10+ blasts, and a higher rate of CD45 antigen overexpression than CD10+ blasts (54.5% vs. 14.9% of cases, respectively). Multiparameter flow cytometry combined with the use of absolute antigen expression scale based on direct fluorescence measurement, has enabled a clear distinction between blasts in BCP-ALL cases and their normal counterparts. This novel and previously undescribed method has allowed the comparative analysis of antigen expression between leukemic blasts and different types of their normal counterparts.