Project description:BACKGROUND: BCR-ABL1+ chronic myeloid leukemia (CML) is characterized by abnormal production of leukemic stem (LSC) and progenitor cells and their spread from the bone marrow into the blood resulting in extramedullary myeloproliferation. So far, little is known about specific markers and functions of LSC in CML. METHODS: We examined the phenotype and function of CD34+/CD38─/Lin─ CML LSC by a multi-parameter screen approach employing antibody-phenotyping, mRNA expression profiling, and functional studies, including LSC repopulation experiments in irradiated NOD-SCID-IL-2Rgamma-/- (NSG) mice, followed by marker-validation using diverse control-cohorts and follow-up samples of CML patients treated with imatinib. RESULTS: Of all LSC markers examined, dipeptidylpeptidase IV (DPPIV=CD26) was identified as specific and functionally relevant surface marker-enzyme on CD34+/CD38─ CML LSC. CD26 was not detected on normal CD34+/CD38─ stem cells or LSC in other hematopoietic malignancies. The percentage of CD26+ CML LSC decreased to undetectable levels during successful treatment with imatinib in all patients (p<0.001). Whereas the sorted CD26─ stem cells obtained from CML patients engrafted irradiated NSG mice with multilineage BCR-ABL1-negative hematopoiesis, CD26+ LSC engrafted NSG mice with BCR-ABL1+ cells. Functionally, CD26 was identified as target-enzyme disrupting the SDF-1alpha-CXCR4-axis by cleaving SDF-1alpha a chemotaxin for CXCR4+ stem cells. Whereas CD26 was found to inhibit SDF-1alpha-induced migration, CD26-targeting gliptins reverted this effect and blocked the mobilization of CML LSC in a stroma co-culture assay. CONCLUSIONS: CD26 is a robust biomarker of LSC and a useful tool for their quantification and isolation in patients with BCR/ABL1+ CML. Moreover, CD26 expression may explain the extramedullary spread of LSC in CML. To define specific mRNA expression patterns and to identify specific LSC markers in CML LSC, gene array analyses were performed. RNA was isolated from sorted CD34+/CD45+/CD38─ CML LSC, CD34+/CD45+/CD38+ CML progenitor cells, CML MNC, sorted CD34+/CD38─ cord blood (CB) SC, CB-derived CD34+/CD38+ progenitor cells, and CB MNC. Total RNA was extracted from sorted cells using RNeasy Micro-Kit (Qiagen) and used (100 ng total RNA) for Gene Chip analyses. Preparation of terminal-labeled cRNA, hybridization to genome-wide human PrimeView GeneChips (Affymetrix, Santa Clara, CA, USA) and scanning of arrays were carried out according to the manufacturer's protocols (https://www.affymetrix.com). Robust Multichip Average (RMA) signal extraction and normalization were performed according to http://www.bioconductor.org/ as described.18 Differences in mRNA expression levels (from multiple paired samples) were calculated as mRNA ratio of i) CML LSC versus CB SC, ii) CML LSC versus CD34+/CD38+ CML progenitors, and normal cord blood SC versus cord blood progenitors. To calculate differential gene expression between individual sample groups where appropriate, we performed a statistical comparison using the LIMMA package as described previously. Briefly, LIMMA estimates the fold change between predefined sample groups by fitting a linear model and using an empirical Bayes method to moderate the standard errors of the estimated log-fold changes for each probe set.

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).

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Lin-, CD38-, CD34+ Hematopoietic Stem Cells.

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