Quantitative expression of regulatory and differentiation-related genes in the key steps of human hematopoiesis: The LeukoStage Database.

Differentiation during hematopoiesis leads to the generation of many cell types with specific functions. At various stages of maturation, the cells may change pathologically, leading to diseases including acute leukemias (ALs). Expression levels of regulatory molecules (such as the IKZF, GATA, HOX, FOX, NOTCH and CEBP families, as well as SPI-1/PU1 and PAX5) and lineage-specific molecules (including CD2, CD14, CD79A, and BLNK) may be compared between pathological and physiological cells. Although the key steps of differentiation are known, the available databases focus mainly on fully differentiated cells as a reference. Precursor cells may be a more appropriate reference point for diseases that evolve at immature stages. Therefore, we developed a quantitative real-time polymerase chain reaction (qPCR) array to investigate 90 genes that are characteristic of the lymphoid or myeloid lineages and/or are thought to be involved in their regulation. Using this array, sorted cells of granulocytic, monocytic, T and B lineages were analyzed. For each of these lineages, 3-5 differentiation stages were selected (17 stages total), and cells were sorted from 3 different donors per stage. The qPCR results were compared to similarly processed AL cells of lymphoblastic (n=18) or myeloid (n=6) origins and biphenotypic AL cells of B cell origin with myeloid involvement (n=5). Molecules characteristic of each lineage were found. In addition, cells of a newly discovered switching lymphoblastic AL (swALL) were sorted at various phases during the supposed transdifferentiation from an immature B cell to a monocytic phenotype. As demonstrated previously, gene expression changed along with the immunophenotype. The qPCR data are publicly available in the LeukoStage Database in which gene expression in malignant and non-malignant cells of different lineages can be explored graphically and differentially expressed genes can be identified. In addition, the LeukoStage Database can aid the functional analyses of next-generation sequencing data.

CD2-positive B-cell precursor acute lymphoblastic leukemia with an early switch to the monocytic lineage.

Switches from the lymphoid to myeloid lineage during B-cell precursor acute lymphoblastic leukemia (BCP-ALL) treatment are considered rare and thus far have been detected in MLL-rearranged leukemia. Here, we describe a novel BCP-ALL subset, switching BCP-ALL or swALL, which demonstrated monocytosis early during treatment. Despite their monocytic phenotype, 'monocytoids' share immunoreceptor gene rearrangements with leukemic B lymphoblasts. All swALLs demonstrated BCP-ALL with CD2 positivity and no MLL alterations, and the proportion of swALLs cases among BCP-ALLs was unexpectedly high (4%). The upregulation of CEBPα and demethylation of the CEBPA gene were significant in blasts at diagnosis, prior to the time when most of the switching occurs. Intermediate stages between CD14(neg)CD19(pos)CD34(pos) B lymphoblasts and CD14(pos)CD19(neg)CD34(neg) 'monocytoids' were detected, and changes in the expression of PAX5, PU1, M-CSFR, GM-CSFR and other genes accompanied the switch. Alterations in the Ikaros and ERG genes were more frequent in swALL patients; however, both were altered in only a minority of swALLs. Moreover, switching could be recapitulated in vitro and in mouse xenografts. Although children with swALL respond slowly to initial therapy, risk-based ALL therapy appears the treatment of choice for swALL. SwALL shows that transdifferentiating into monocytic lineage is specifically associated with CEBPα changes and CD2 expression.