Project description:MLL-AF9 expression in normal human umbilical cord blood CD34+ cells leads to long-term proliferation of a myeloid progenitor cell with leukemogenic potential. Expression of a Core Binding Factor leukemia fusion (AML1-ETO or CBFbeta-SMMHC) in human CD34+ cells results in self-renewal of primitive progenitor cells with multilineage potential and stem cell ability, but these cells do not induce leukemia in immunodeficient mice. This comparative microarray study was initiated to determine how faithful these cell cultures are to the transcriptome of patient samples expressing each of these different fusion proteins, and to analyze the signaling pathways that are unique to CBF cultures and MLL-fusion cultures, with the hope of determining why the MLL-fusion cells are leukemogenic while the CBF cells are not. Experiment Overall Design: We have established a culture system whereby we retrovirally transduce human CD34+ cells, obtained from cord blood, with the leukemia fusion genes MLL-AF9 (MA9), AML1-ETO (AE) or CBFbetaMYH11 (CM). Cells expressing each of these fusion proteins are able to proliferate long-term in vitro in a cytokine dependent manner. These cultures resemble somewhat the blast samples from patients that contain these different fusion proteins, in that MA9 cells are predominantly monocytic (M5-like), AE cells have a large population of primitive CD34+ cells with continued abnormal differentiation (M2-like) and CM cells also contain a population of primitive CD34+ cells with continued abnormal differentiation but also have a significant population of abnormal eosinophils (M4Eo). We grow these cells in the presence of fetal bovine serum (FBS), and also grow them in serum-free conditions using the BIT supplement from Stem Cell Technologies. For the current experiments we used cell cultures that had been proliferating in vitro for 8-12 weeks, in either serum-free conditions or with FBS. Replicate samples were included in some instances, and the same clonal cultures that were grown under either BIT or FBS were also included.

Project description:Malignant transformation in a multipotential precursor has recently been shown to underlie mixed phenotype acute leukaemias. In contrast, and despite the conclusive demonstration that MLL-AF4 infant ALL arises in utero. In order to address this we purified haematopoietic stem/progenitor cell (HSPC) populations from four non-lineage switching presentation infant ALL cases and one ALL presentation which went on to lineage switch at relapse. The specific MLL-AF4 fusion event was determined in unsorted samples by LDI-PCR and identified in purified populations by nested PCR. In three cases where non-lineage restricted populations were able to be purified, MLL-AF4 was identified in the CD34+CD38-CD45RA+ population (LK228, LK230, LS01), the CD34+CD38-CD45RA-CD90- multipotential progenitor population (MPP, LS01) and even a candidate CD34+CD38-CD45RA-CD90+ haematopoietic stem cell (HSC) population (LK228) Interestingly, in a single non-switched MLL-AF9 case analysed for external comparison, the fusion was only identified in CD19+ blast/B cell populations, not in any HSPC population. Unexpectedly, we were also able to identify the presence of the MLL-AF4 fusion in apparently normally differentiated CD34-CD19/3-HLA-DR+CD14/11c+ monocytes/dendritic cells from the peripheral blood/bone marrow of 4/5 cases examined. This finding was further supported by single cell analysis of LS01PALL which identified the fusion in 2/22 CD34-CD19/3-HLA-DR+CD14/11c+ monocytes/dendritic cells analysed. Furthermore, the matched AML sample (LS01RAML) also contained MLL-AF4 positive mature T lymphoid cells. These data imply that MLL-AF4 does not impose a complete block on normal haematopoietic differentiation, and raise the question of what additional factors contribute to leukaemic lineage determination in the setting of the MLL-AF4 translocation. To examine the functional capacity of MLL-AF4 transformed precursor cells we generated a patient-derived xenograft model using NOD-scid/IL2Rγ-/- (NSG) mice. Serial xenotransplantation identified an MLL-AF4 positive clone persisting within the human CD34+CD38-CD45RA-CD90+ compartment across four generations of mice, confirming self-renewal of this population. Together these data identify an early multipotent progenitor or HSC as the putative cell of origin for MLL-AF4 ALL. Furthermore, they demonstrate that MLL-AF4, uniquely amongst MLL fusion genes, imposes a profound lymphoid bias on the developing leukemia but without completely abolishing broader, non-malignant, haematopoietic differentiation.

Project description:Contemporary treatment of pediatric acute myeloid leukemia (AML) requires the assignment of patients to specific risk groups. To explore whether expression profiling of leukemic blasts could accurately distinguish between the known risk groups of AML, we analyzed 130 pediatric and 20 adult AML diagnostic bone marrow or peripheral blood samples using the Affymetrix U133A microarray. Class discriminating genes were identified for each of the major prognostic subtypes of pediatric AML, including t(15;17)[PML-RARalpha], t(8;21)[AML1-ETO], inv(16) [CBFbeta-MYH11], MLL chimeric fusion genes, and cases classified as FAB-M7. When subsets of these genes were used in supervised learning algorithms, an overall classification accuracy of more than 93% was achieved. Moreover, we were able to use the expression signatures generated from the pediatric samples to accurately classify adult de novo AMLs with the same genetic lesions. The class discriminating genes also provided novel insights into the molecular pathobiology of these leukemias. Finally, using a combined pediatric data set of 130 AMLs and 137 acute lymphoblastic leukemias, we identified an expression signature for cases with MLL chimeric fusion genes irrespective of lineage. Surprisingly, AMLs containing partial tandem duplications of MLL failed to cluster with MLL chimeric fusion gene cases, suggesting a significant difference in their underlying mechanism of transformation. All the gene expression arrays are available through http://www.stjuderesearch.org/site/data/AML1/ in the original study (PMID:15226186). To study the RAS gene expression in the human AML patients, a total of 104 AML cases with known KRAS and NRAS status (including 72 gene expression arrays in the original study and 32 additional arrays acquired later on), as well as 4 CD34+ normal bone marrow cases deposited in GEO GSE33315, were including in this depository. Gene expression profiling was performed on 104 single diagnosis tumor samples and 4 CD34+ normal bone marrow samples

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Leukemia fusion-gene transduced human cord blood cells

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