Project description:Differences in chemo-sensitivity of subpopulations of AML stem cells could have important clinical implications. Using in vitro cytotoxicity, xenograft models and colony forming assays, we compared chemotherapy sensitivity between Lineage (Lin-)CD34-CD38-, Lin-CD34-CD38+, Lin-CD34+CD38- and Lin-CD34+CD38+ populations from 26 primary AMLs (19 paediatric and 7 adult). We identified a common recurring pattern of chemo-response associated with a poor clinical outcome: In each of 16/26 (62%) AMLs, Lin-CD34-CD38- cells were the most chemoresistant of the four subpopulations to daunorubicin in vitro. Cytarabine-resistant colonies formed only from Lin-CD34-CD38- populations following tertiary passages through both NOG mice and methylcellulose in these AMLs The presence of chemo-resistant Lin-CD34-CD38- populations was signficantly associated with reduced relapse-free survival in childhood AML. Consistently, CD34 negativity was significantly associated with an increased risk of relapse in a larger retropsective cohort (n=89). Samples enriched for chemo-resistant Lin-CD34-CD38- LSCs with a stem cell profile and an undifferentiated genotype revealed pathways likely to confer chemo-resistance, These strongly indicated dependence of chemo-resistant Lin-CD34-CD38- LSCs on their niche environment as well as deregulated DNA damage responses, lipid and Notch1 signalling, Our findings have major implications for the risk stratification of childhood AML and could lead to the development of novel therapeutic approaches. 3 subpopulations of leukemia stem cells from 9 patients with primary childhood AML were analysed. We compared gene expression profiles of Lin-CD34+CD38- (Q1), Lin-CD34+CD38+ (Q2) and Lin-CD34-CD38- (Q3) cells between 3 AMLs in which the CD34+ cells were most chemo-resistant (AML-1P, AML-6P and AML-10P) and the same cells from the remaining AMLs in which the Lin-CD34-CD38- cells were the most chemo-resistant population. We also compared the gene expression profiles of Lin-CD34-CD38- (Q3) cells in the 3 samples with the highest LC50 values (AML-15P, AML-17P and AML-19P) with that of the 3 AMLs exhibiting the lowest LC50 values (AML-2P, AML-5P and AML-11P).

Project description:Human embryonic stem cells (hESCs) offer an important model for investigating the human hematopoietic celldevelopment. Here, we used long serial analysis of gene expression and quantitative real-time PCR to characterize two subsets of primitive hematopoietic cells derived in vitro from hESCs. This revealed differences in their expression of genes associated with lymphoid and myeloid development, cellular biosynthetic processes, and cell cycle regulation. Further comparisons with analogous data for primitive hematopoietic cells isolated from first trimester human fetal liver and newborn cord blood showed a strong similarity between the transcriptomes of the most primitive hESC- and in vivo-derived populations, with the main differences involving genes that regulate HSC development, self-renewal and homing, chromatin remodeling, AP1 transcription complex genes, and non-coding RNAs. These data suggest that primitive hematopoietic cells are generated from hESCs in vitro by processes similar to those operative during human embryogenesis in vivo, although some differences were also detected. Human embryonic stem cells (hESCs) are capable of indefinite self-renewal but can also be induced to undergo a stepwise process of differentiation into a spectrum of recognizable mature blood cell types. However, a clear understanding of the molecular mechanism by which the first hematopoietic stem cells (HSCs) acquire their unique defining properties of self-renewal and repopulating potential is lacking. As a first step towards obtaining the information needed to close this gap, we have undertaken a comparative gene expression analysis of different highly purified primitive human hematopoietic subpopulations (erythroid-megakaryocytic progenitor enriched CD43+CD235a+CD41a+/- cells, mutiplepotent progenitor enriched lin-CD34+CD43+CD45-, and lin-CD34+CD43+CD45+ cells) generated either in vitro from hESCs or in vivo from fetal (human fetal liver lin-CD34+CD38- cells) or neonatal hematopoietic primitive cells (human cord blood lin-CD34+CD38- and lin-CD34+CD38+ cells). This involved preparing a long serial analysis of gene expression (LongSAGE) library from an extracts of each prospectively isolated subpopulation and then sequencing each library to a depth of 200,000 tags.

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