Normal Stem Cell Populations Research Articles

CD52 Expression In Leukemic Stem/Progenitor Cells

AbstractAbstract 2743CD52 is a cell surface glycoprotein of unknown function that is expressed in B and T lymphocytes, macrophages, and monocytes, but is not expressed in normal hematopoietic stem/progenitor cells. CD52 is also expressed in chronic lymphocytic leukemia (CLL), B-cell acute lymphoblastic leukemia (ALL), and some cases of T-ALL. Alemtuzumab, a recombinant humanized monoclonal antibody, targets CD52 and is used to treat CLL. In contrast to normal hematopoietic stem/progenitor cells, CD52 expression has been described in acute myeloid leukemia (AML) and in blast crisis (BC) chronic myeloid leukemia (CML). Based on these observations we were curious whether CD52 expression distinguished normal from malignant or more mature from immature stem/progenitors cells, and whether these cells were sensitive to alemtuzumab.CD52 expression was examined in three blast cell populations (CD34+/CD38-, CD34+/CD38+, and CD34-) in patients with myeloid (44) and lymphoid (18) neoplasms, and normal patients (6). In normal hematopoietic cells, stems cells are enriched in the first population; more mature cells are characterized by increasing CD38 expression and loss of CD34 expression. In AML and CML leukemia stem cells may arise within either CD34+ population and possibly in the CD34- population. Relative to normal lymphocytes average CD52 expression could be characterized as low to moderate. Using an expression cutoff of > 20%, in contrast to normal patients, CD52 was detected in at least one of three blast populations in almost all patients. Using a more stringent cutoff of > 50%, CD52 was expressed in CD34+/CD38- cells in 7/11 B-ALL and 6/7 T-ALL cases and was concordantly expressed in the other two populations. Using the same criteria in myeloid malignancies (Table 1), expression occurred more frequently in AML, AML arising from myelodysplastic syndrome (MDS), and BC CML. In AML and AML arising from MDS, CD52 was expressed in the 34+/38- population in 7/15 cases (47%) and 4/7 cases (57%), respectively; it was expressed in both BC CML patients. In AML and BC CML patients, CD52 was expressed at similar levels in the CD34+/CD38+ fraction. No clear association between CD52 expression and cytogenetic abnormalities was found. We then examined whether CD52 expression differentiated normal from malignant blasts (CD34+/CD38- and CD34+/CD38+) in two CML myeloid BC patients. FISH and quantitative PCR demonstrated that BCR-ABL was expressed in all 4 populations, which were also morphologically distinct. Colony forming unit (CFU) assays demonstrated a significantly decreased ability to form CFU (on average 5–20 fold decrease) in CD52+/CD34+/CD38- CML cells suggesting CD52 cells may be more mature. Lastly and not previously described, we found that several BC CML cell lines express CD52, and complement-mediated cell cytotoxicity was similar in the highest expressing cell lines to that seen in EHEB (B-CLL) cells known to be targeted by alemtuzumab. Thus, alemtuzumab may have clinical efficacy in BC CML.In conclusion, CD52 is expressed on blast populations enriched for leukemic stem cells. Whether the absence or presence of CD52 more precisely segregates a leukemia stem cell containing population currently remains unknown and requires functional testing in a murine model. Our preliminary experiments in CML suggest CD52 may not differentiate between normal and malignant stem/progenitor cells. However, CD52 expression may distinguish normal and malignant stem cell populations in cases where CD52 and CD38 are more highly expressed. The observation that CD52 expression is increased in acute vs. chronic leukemias raises the intriguing possibility that CD52, if not directly involved, may be a marker for genes or pathways contributing to the block in differentiation seen with progression to acute leukemia. Furthermore, given that CD52 expression is heterogeneous in chronic disorders, it is possible that CD52 expression within these populations may correlate with poor prognosis or impending leukemic conversion. [Display omitted] Disclosure:Oehler:Pfizer: Research Funding. Radich:Novartis: Consultancy, Honoraria, Research Funding; Bristol-Myers Squibb: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria.

Quiescent, Slow-Cycling Stem Cell Populations in Cancer: A Review of the Evidence and Discussion of Significance

Long-lived cancer stem cells (CSCs) with indefinite proliferative potential have been identified in multiple epithelial cancer types. These cells are likely derived from transformed adult stem cells and are thought to share many characteristics with their parental population, including a quiescent slow-cycling phenotype. Various label-retaining techniques have been used to identify normal slow cycling adult stem cell populations and offer a unique methodology to functionally identify and isolate cancer stem cells. The quiescent nature of CSCs represents an inherent mechanism that at least partially explains chemotherapy resistance and recurrence in posttherapy cancer patients. Isolating and understanding the cell cycle regulatory mechanisms of quiescent cancer cells will be a key component to creation of future therapies that better target CSCs and totally eradicate tumors. Here we review the evidence for quiescent CSC populations and explore potential cell cycle regulators that may serve as future targets for elimination of these cells.

Abstract 4294: Differentiated colorectal cancer cells protect tumor-initiating cells from irinotecan

Abstract Normal colon tissue stem cells drive tissue turnover by generating daughter stem cells and a rapidly proliferating pool of progenitor cells that give rise to differentiated cell types with specialized functions. This functional hierarchy is preserved in colon tumors in which a tumor-initiating cell (or cancer stem cell) compartment drives the formation of proliferating and differentiated cell types with reduced tumorigenic potential. Normal colon stem cells possess a variety of resistance mechanisms that allow them to endure a lifetime of genotoxic insults. By inheriting these traits, tumor-initiating cells (TIC) are thought to be endowed with an intrinsic resistance to chemotherapy. However, the relationship between chemo-resistance and tumor-initiating potential in colon tumors is poorly understood. We studied this relationship using a series colonosphere cultures isolated from freshly resected primary colon tumors and liver metastases. These cultures are highly enriched for TIC, based on their high clone and tumor-forming potential and expression of the stem cell marker ALDH1. The TIC-enriched cultures display resistance to the toposomerase I inhibitor irinotecan. However, drug resistance is mediated by a small subpopulation of non-tumorigenic differentiated ALDH1-negative cells expressing the drug efflux pump ABCB1. ABCB1 is localized to the brush border of cells at the colonosphere periphery and of cells forming intra-spheroid tubules. In human colorectal liver metastases ABCB1 is predominantly localized to the luminal side of differentiated tubule-forming cells. These ABCB1 drug-resistant cells are proliferation-competent but unable to initiate tumor formation. Conversely, tumor-initiating cells are ABCB1-negative and drug-sensitive, but could generate non-tumorigenic drug-resistant offspring in vitro and in tumor xenografts. Our work shows that colorectal tumor-initiating cells do not display intrinsic resistance to irinotecan, most likely because they are derived from a normal stem cell population that does not express ABC transporters. Tumor-initiating cells generate a protective shield of drug-resistant ABCB1-positive offspring. Furthermore, the preservation of tumor-initiating capacity following irinotecan exposure requires the cooperative action of drug-sensitive tumor-initiating cells and their drug-resistant differentiated offspring. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4294.

Abstract 4256: Neuroendocrine, stem, and stromal cell interactions involved in the organization of the normal colonic stem cell niche which become disorganized during colon tumorigenesis

Abstract In development of colorectal cancer (CRC), stem cell (SC) overpopulation underlies tumor initiation and progression, but it is incompletely understood which dysregulated mechanisms cause SC overpopulation. Because neuroendocrine cell (NEC) and SC populations both reside in the SC niche at the normal crypt bottom, we hypothesized that i) NECs play a role in maintaining the SC population, and ii) changes in the NEC population contributes to SC overpopulation and altered epithelial: stromal interactions during tumorigenesis. Immunofluorescence mapping and flow cytometry were used to analyze SC niche structure and cell-cell interactions in normal and neoplastic colonic tissues from Caucasian and African-American patients. In normal colonic crypts, most cells (77%) staining positively for the colonic SC marker ALDH1, also co-stained for the NE cell marker chromogranin-A (CGA). In the progression from normal to normal-appearing FAP to adenomatous to malignant colonic tissue, the proportion of ALDH1+/CGA+ cells progressively diminished while the proportion of ALDH1+/CGA- cells increased. The epithelial phenotype of tumor cells was confirmed by co-staining for pancytokeratin. These data suggest that colonic SC express a NE phenotype, and loss of this phenotype is associated with an increased number of SC during colon tumorigenesis. Our studies using flow cytometry and CRC cell lines (COLO320, DiFi, LIM1863, LoVo, SW480, HCT116 & HT29) revealed that each line is characterized by the proportion of cells having a SC phenotype (ALDEFLUOR+) and NEC phenotype (SSTR+ or GLPR2+). have a low proportion. These findings suggest that these proportions are maintained constant through feedback mechanisms involving SC and NEC subpopulations. Our studies of epithelial-stromal interactions used immunofluorescence mapping of basement membrane proteins (Perlecan; collagen IV), inflammation markers (Cox2; Caveolin 1), pericryptal fibroblasts (smooth muscle actin), endothelial cells (CD34) and macrophages (CD68). Our results show that the stroma undergoes progressive disorganization (particularly pericryptal fibroblasts & basement membrane) in parallel with increasing size of the SC population during colon tumorigenesis. These results suggest that genetic changes occurring during colon tumorigenesis lead to breakdown of stromal-epithelial interactions that are crucial to the maintenance of the stem cell niche, which contributes to colonic tissue disorganization that is a cardinal feature of cancer. Taken together, our investigations yield insights into: (i) the control of normal SC populations (including how the SC niche is maintained), (ii) molecular mechanisms underlying SC overpopulation in tumorigenesis, and (iii) potential targets for novel anti-cancer therapeutic strategies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4256.

PSF1, a DNA Replication Factor Expressed Widely in Stem and Progenitor Cells, Drives Tumorigenic and Metastatic Properties

PSF1 (partner of sld five 1) is an evolutionarily conserved DNA replication factor implicated in DNA replication in lower species that is strongly expressed in a wide range of normal stem cell populations and progenitor cell populations. Because stem and progenitor cells possess high proliferative capacity, we hypothesized that PSF1 may play an important role in tumor growth. To begin to investigate PSF1 function in cancer cells, we cloned the mouse PSF1 promoter and generated lung and colon carcinoma cells that stably express a PSF1 promoter-reporter gene. Reporter expression in cells correlated with endogenous PSF1 mRNA expression. In a tumor cell xenograft model, high levels of reporter expression correlated with high proliferative activity, serial transplantation potential, and metastatic capability. Notably, cancer cells expressing reporter levels localized to perivascular regions in tumors and displayed expression signatures related to embryonic stem cells. RNAi-mediated silencing of endogenous PSF1 inhibited cancer cell growth by disrupting DNA synthesis and chromosomal segregation. These findings implicate PSF1 in tumorigenesis and offer initial evidence of its potential as a theranostic target.

Single-Cell STAT5 Signal Transduction Profiling in Normal and Leukemic Stem and Progenitor Cell Populations Reveals Highly Distinct Cytokine Responses

BackgroundSignal Transducer and Activator of Transcription 5 (STAT5) plays critical roles in normal and leukemic hematopoiesis. However, the manner in which STAT5 responds to early-acting and lineage-restricted cytokines, particularly in leukemic stem/progenitor cells, is largely unknown.Methodology/Principal FindingsWe optimized a multiparametric flow cytometry protocol to analyze STAT5 phosphorylation upon cytokine stimulation in stem and progenitor cell compartments at a single-cell level. In normal cord blood (CB) cells, STAT5 phosphorylation was efficiently induced by TPO, IL-3 and GM-CSF within CD34+CD38− hematopoietic stem cells (HSCs). EPO- and SCF-induced STAT5 phosphorylation was largely restricted to the megakaryocyte-erythroid progenitor (MEP) compartment, while G-CSF as well IL-3 and GM-CSF were most efficient in inducing STAT5 phosphorylation in the myeloid progenitor compartments. Strikingly, mobilized adult peripheral blood (PB) CD34+ cells responded much less efficiently to cytokine-induced STAT5 activation, with the exception of TPO. In leukemic stem and progenitor cells, highly distinct cytokine responses were observed, differing significantly from their normal counterparts. These responses could not be predicted by the expression level of cytokine receptors. Also, heterogeneity existed in cytokine requirements for long-term expansion of AML CD34+ cells on stroma.Conclusions/SignificanceIn conclusion, our optimized multiparametric flow cytometry protocols allow the analysis of signal transduction at the single cell level in normal and leukemic stem and progenitor cells. Our study demonstrates highly distinctive cytokine responses in STAT5 phosphorylation in both normal and leukemic stem/progenitor cells.

Single-Cell STAT5 Signal Transduction Profiling in Normal and Leukemic Stem and Progenitor Cell Populations Reveals Highly Distinct Cytokine Responses.

Abstract 2510Poster Board II-487Signal Transducer and Activator of Transcription 5 (STAT5) plays critical roles in normal and leukemic hematopoiesis. We have observed that introduction of activated STAT5A in human stem/progenitor cells enhances long-term stem cell self-renewal, while lentiviral downmodulation of STAT5 expression in both normal as well as primary leukemic CD34+ cells impairs long-term growth and self-renewal. Many cytokines that act on the immature human stem cell compartment are known to be able to activate STAT5, such as TPO and SCF. Yet, little is known about the specificity and kinetics of STAT5 signaling in response to early-acting and lineage-restricted cytokines in specifically defined stem cell and progenitor compartments, particularly in the case of acute myeloid leukemia. We optimized a multiparametric flow cytometry protocol to analyze STAT5 phosphorylation upon cytokine stimulation in stem and progenitor cell compartments at the single-cell level. In normal cord blood (CB) cells, STAT5 phosphorylation was efficiently induced by TPO, IL-3 and GM-CSF within CD34+CD38− hematopoietic stem cells (HSCs). EPO and SCF-induced STAT5 phosphorylation was largely restricted to the megakaryocyte-erythroid progenitor (MEP) compartment, while G-CSF, as well IL-3 and GM-CSF were most efficient in inducing STAT5 phosphorylation in the myeloid progenitor compartments. Strikingly, mobilized adult peripheral blood (PB) CD34+ cells responded much less efficiently to cytokine-induced STAT5 activation, with the exception of TPO. In leukemic stem and progenitor cells, highly distinct cytokine responses were observed, differing significantly from their normal counterparts. A number of different types of responses were observed, being a) a strong STAT5 activation induced by TPO only; b) a strong STAT5 activation induced by IL3 and GM-CSF, but not TPO; c) STAT5 activation induced by various cytokines; and d) constitutive STAT5 phosphorylation that could not significantly be further induced by cytokines. These responses could not be predicted by the expression level of cytokine receptors. Also, heterogeneity existed in cytokine requirements for long-term expansion of AML CD34+ cells on stroma. In most examined cases multiple cytokines acted in an additive fashion in inducing long-term growth of primary AML CD34+ cells in bone marrow stromal cocultures, and in only 1 out of 10 cases cytokine-independent growth was observed. In none of the cases only IL3 or TPO were sufficient to induced long-term expansion of primary AML CD34+ cells. In conclusion, our study demonstrates variable cytokine responses in STAT5 phosphorylation in both normal and leukemic stem/progenitor cells. Disclosures:No relevant conflicts of interest to declare.

Markers Distinguishing Cancer Stem Cells from Normal Human Neuronal Stem Cell Populations in Malignant Glioma Patients

Markers Distinguishing Cancer Stem Cells from Normal Human Neuronal Stem Cell Populations in Malignant Glioma Patients

Dysregulated gene expression networks in human acute myelogenous leukemia stem cells

We performed the first genome-wide expression analysis directly comparing the expression profile of highly enriched normal human hematopoietic stem cells (HSC) and leukemic stem cells (LSC) from patients with acute myeloid leukemia (AML). Comparing the expression signature of normal HSC to that of LSC, we identified 3,005 differentially expressed genes. Using 2 independent analyses, we identified multiple pathways that are aberrantly regulated in leukemic stem cells compared with normal HSC. Several pathways, including Wnt signaling, MAP Kinase signaling, and Adherens Junction, are well known for their role in cancer development and stem cell biology. Other pathways have not been previously implicated in the regulation of cancer stem cell functions, including Ribosome and T Cell Receptor Signaling pathway. This study demonstrates that combining global gene expression analysis with detailed annotated pathway resources applied to highly enriched normal and malignant stem cell populations, can yield an understanding of the critical pathways regulating cancer stem cells.

Normal stem cells in cancer prone epithelial tissues.

The concept of a cancer stem cell is not a new one, being first suggested over 100 years ago. Over recent years the concept has enjoyed renewed enthusiasm, partly because of our growing understanding of the nature of somatic stem cells, but also because of a growing realisation that the development of strategies that target cancer stem cells may offer considerable advantages over conventional approaches. However, despite this renewed enthusiasm the existence of cancer stem cells remains controversial in many tumour types and any potential relationship to the normal stem cell pool remains poorly defined. This review summarises key elements of our understanding of the normal stem cell populations within animal models of the predominant cancer prone epithelial tissues, and further investigates the potential links between these populations and putative cancer stem cells.

Comparative Transcriptome Analysis of Different Subsets of CD34+ Normal and Chronic Myeloid Leukemia Cells Identifies Novel Perturbations in the CML Stem Cell Population.

Chronic myeloid leukemia (CML) arises from a hematopoietic stem cell that acquires a BCR-ABL fusion gene. During the chronic phase of the disease, this cell produces an expanding multi-lineage clone that usually comes to dominate all terminal stages of myelopoiesis. However, eventually, further mutations are acquired which cause progression to a rapidly fatal acute leukemia. To obtain new insights into the molecular perturbations that cause CML stem cells to initiate chronic phase disease, we generated Long Serial Analysis of Gene Expression (LongSAGE) libraries (∼200,000 tags/library) from extracts of highly purified lin−CD34+CD45RA−CD36−CD71−CD7−CD38+ and lin−CD34+CD45RA−CD36−CD71−CD7−CD38− normal bone marrow (BM) and G-CSF-mobilized peripheral blood (G-mPB) cells as well as cells from 3 chronic phase CML patients with predominantly Ph+/BCR-ABL+ cells in both of these very primitive cell subsets. Long term culture-initiating cell (LTC-IC) and direct colony-forming cell (CFC) assays performed on an aliquot of each of these cell populations showed the frequency of LTC-IC were 4 to 130-fold higher in the 34+38− cells than in the matching 34+38+ cells with the opposite trend for the CFCs. Comparison of the tags present in the pooled CML and pooled normal BM and G-mPB libraries revealed many differentially expressed genes. Real-time RT-PCR analysis of lin−CD34+ cells from 14 chronic phase CML patients and 3 normal BMs confirmed the differential expression of 14 candidate transcripts identified by SAGE (changes ranging from 3-fold lower to 80-fold higher in the CML cells, p<0.05). The altered levels of expression of 5 of these genes (i.e., beta-catenin, MLLT3, IL1R1, LY6E and GAS2) were highly correlated with the relative levels of BCR-ABL transcripts in the same cells (r ≥0.6). 5 of the 14 genes (IL1R1, vWF, SOX4, SELL and RHOB) were found to be differentially expressed in the 3-day post-transduction progeny of CD34+ cord blood cells exposed to a BCR/ABL-IRES-GFP vs a control GFP- lentivirus preparation (n=2). 3 (GAS2, DUSP1 and TP53BP2) were upregulated (5 to 11-fold) in imatinib-treated K562 cells (as compared to untreated K562 cells) but their expression remained unchanged in similarly treated KG1 cells (a primitive BCR-ABL-negative human AML cell line) providing further evidence that their deregulated expression is secondary to the kinase activity of p210BCR-ABL. In addition, from a comparison of the meta-library for the 34+38− CML cells with the meta-libraries for both the normal 34+38− and 34+38+ cells, the meta-library for the 34+38+ CML cells and most publicly accessible SAGE data, we were able to identify 65 novel tags in the 34+38− CML cells. 32 of these unique tags were located within conserved genomic regions and >2 kb away from known transcripts, and of these 32, 3 were confirmed to represent novel transcripts using a PCR approach. These results illustrate the potential of SAGE to reveal novel as well as known components in the transcriptomes of rare normal and cancer stem cell populations. Investigation of their roles in primitive human cells transduced with BCR-ABL and BCR-ABL+cell lines indicates the utility of these models for further delineation of the complex effects of BCR-ABL expression in chronic phase CML stem cells.

Unraveling the complex nature of prostate cancer stem cells

The identification of distinct prostate cancer stem cell biomarkers is necessary as researchers attempt to isolate, characterize, and therapeutically target these tumor initiating cells. However, in reading the current literature it is frequently difficult to discern which biomarkers and cellular characteristics identify prostate cancer stem cells as opposed to the general population of prostate cancer cells or normal prostate stem cells. Within this review, we address this issue by dissecting out the cell surface markers, adhesion and cytoskeletal proteins, signaling pathways, epigenetic modifications, and the effects of androgens that are specific to and help to define the prostate cancer stem cell.

Hierarchical Organization of Prostate Cancer Cells in Xenograft Tumors: The CD44+α2β1+ Cell Population Is Enriched in Tumor-Initiating Cells

Prostate cancer cells are heterogeneous in their tumorigenicity. For example, the side population cells isolated from LAPC9 xenografts are 100 to 1,000 times more tumorigenic than the corresponding non-side population cells. Highly purified CD44(+) prostate cancer cells from several xenografts are also enriched in prostate cancer stem/progenitor cells. Because the CD44(+) prostate cancer cell population is still heterogeneous, we wonder whether we could further enrich for tumorigenic prostate cancer cells in this population using other markers. Integrin alpha2beta1 has been proposed to mark a population of normal human prostate stem cells. Therefore, we first asked whether the alpha2beta1(+/hi) cells in prostate tumors might also represent prostate cancer stem cells. Highly purified (> or =98%) alpha2beta1(+/hi) cells from three human xenograft tumors, Du145, LAPC4, and LAPC9, show higher clonal and clonogenic potential than the alpha2beta1(-/lo) cells in vitro. However, when injected into the nonobese diabetic/severe combined immunodeficient (NOD/SCID) mouse prostate or s.c., the alpha2beta1(+/hi) prostate cancer cells are no more tumorigenic than the alpha2beta1(-/lo) cells. Immunofluorescence studies reveal that CD44 and alpha2beta1 identify an overlapping and inclusive population of prostate cancer cells in that approximately 70% of alpha2beta1(+/hi) cells are CD44(+) and 20% to 30% of CD44(+) cells are distributed in the alpha2beta1(-/lo) cell population. Subsequently, we sorted out CD44(+)alpha2beta1(+/hi), CD44(+)alpha2beta1(-/lo), CD44(-)alpha2beta1(+/hi), and CD44(-)alpha2beta1(-/lo) cells from LAPC9 tumors and carried out tumorigenicity experiments. The results revealed a hierarchy in tumorigenic potential in the order of CD44(+)alpha2beta1(+/hi) approximately CD44(+)alpha2beta1(-/lo) > CD44(-)alpha2beta1(+/hi) >> CD44(-)alpha2beta1(-/lo). These observations together suggest that prostate cancer cells are organized as a hierarchy.

The Challenges of Targeting Chronic Myeloid Leukemia Stem Cells

Chronic myeloid leukemia (CML) is sustained by a clonally amplified population of Bcr-Abl–positive pluripotent stem cells. Persistence of a large, functionally intact yet suppressed residual normal hematopoietic stem cell population in most patients with CML has made it possible to aim at the development of curative therapies. However, achieving this goal requires the identification of agents that will eradicate the leukemic stem cell population. Several potent Bcr-Abl–targeted drugs have now been introduced into clinical practice with remarkable effects. Nevertheless, accumulating data indicate that the leukemic CML stem cells in patients with chronic phase CML are less responsive to these agents than the bulk of the neoplastic cells. In this article, we review emerging evidence that CML stem cells have a number of unusual properties that underlie their relative insensitivity to treatment, including those that specifically target the Bcr-Abl oncoprotein. The biology of the neoplastic stem cells in patients with CML is clearly important to the future attainment of cures and might also prove a paradigm relevant to other types of malignancies that are sustained by transformed stem cell populations.

Advances in study of acute leukemia stem cells

白血病干细胞很可能是起源于发生了突变的正常造血干细胞.除与正常造血干细胞具有相同的CD34+、CD38-、HLA-DR-等细胞表型外,急性髓系白血病干细胞还具有自己特有的CD90-、CD117-、CD123+细胞表型、对热更敏感、持续活化的核因子κB以及比正常造血干细胞具有更高的自我更新和分化增殖能力等特征.核因子κB的异常活化、白细胞介素受体3以及PI3K信号传导等通路可能参与白血病干细胞生长和生存的调节,在白血病的发生与发展中起着重要的作用。

Effects of structural and “mixed” isomers of Glu-Trp dipeptide on normal hemopoietic stem cells

We studied the effects of optical (dd-, ll-, dl-, and ld-dipeptides with alpha-bond, EW) structural isomers and cyclic (dd-, ll-, dl-, and ld-dipeptides with gamma-bond, iEW) analogs of Glu-Trp synthetic dipeptide on the population of normal hemopoietic stem cells. Dipeptides containing lGlu (lGlu-lTrp, lGlu-dTrp) injected to mice were inert towards committed bone marrow CFU-S; dGlu-containing dipeptides (dGlu-dTrp, dGlu-lTrp) inhibited the growth of CFU-S-8; and LiGlu-dTrp stimulated these cells. Inhibitory or stimulatory effects of optical and chemical isomers of Glu-Trp dipeptide are determined by optical orientation and nature of peptide bond of Glu residue. The effects of cyclic and mixed peptides towards colony formation are similar to those of the corresponding linear dipeptides.

Transforming Growth Factor-beta2 protects the small intestine during methotrexate treatment in rats possibly by reducing stem cell cycling.

During chemo- and radiation therapy, the balance between epithelial cell proliferation, differentiation, and cell death at the villus tip is disrupted by premature death of dividing epithelial cells. This will subsequently lead to the onset of mucosal barrier injury in the whole gastrointestinal tract. Up till now there is no validated method to treat side effects occurring due to therapy. An approach to manage this side effect might be to reversibly arrest growth of epithelial stem cells during therapy using Transforming Growth Factor-β2. A Transforming Growth Factor-β2 enriched fraction prepared from bovine milk was shown to protect small intestinal epithelial cells against cell cycle specific chemotherapeutic agents by arresting the cells in G1-phase. Secondly, in a rat model for induced small intestinal damage, oral supplementation of rats exposed to methotrexate with the Transforming Growth Factor-β2 enriched fraction significantly reduced the chemotherapy-associated weight loss and ileal villus atrophy by reducing cell proliferation in the normal stem cell population. Thus oral supplementation with a bovine milk fraction enriched for Transforming Growth Factor-β2 attenuated the side effects of chemotherapy in the small intestine in rats.British Journal of Cancer (2002) 87, 113–118. doi:10.1038/sj.bjc.6600342 www.bjcancer.com© 2002 Cancer Research UK

Evidence that ceramide mediates the ability of tumor necrosis factor to modulate primitive human hematopoietic cell fates

In this study, it is shown that short-term exposure of normal human marrow CD34+CD38− cells to low concentrations of tumor necrosis factor (TNF) in the presence of 100 ng/mL Flt3 ligand and Steel factor and 20 ng/mL interleukin-3 (IL-3), IL-6, and granulocyte colony-stimulating factor, in either bulk or single-cell serum-free cultures, markedly reduces their ability subsequently to generate colony-forming cells (CFCs) in 6-week stromal cell–containing long-term cultures without affecting their viability, mitogenic response, or short-term ability to produce CFCs. A similar differential effect on the functional attributes of CD34+CD38− cells was seen when C2- or C6-ceramide, but not dihydro-C2-ceramide (an inactive analog of ceramide), was substituted for TNF. The addition of D-erythro-MAPP (a specific inhibitor of intracellular ceramide degradation) enhanced the ability of TNF to selectively eliminate long-term culture–initiating cell (LTC-IC) activity. These findings indicate that TNF can directly modulate the ability of CD34+CD38− cells to maintain their LTC-IC function at doses below those required to initiate apoptosis, cell cycle arrest, or both, and they suggest that this may be mediated by the TNF-induced generation of intracellular ceramide. Identification of a signaling intermediate that can influence primitive hematopoietic cell fate decisions offers a new approach to the investigation of signaling mechanisms in normal stem cell populations and to how these may be altered in leukemic cells.

Evidence that ceramide mediates the ability of tumor necrosis factor to modulate primitive human hematopoietic cell fates

AbstractIn this study, it is shown that short-term exposure of normal human marrow CD34+CD38− cells to low concentrations of tumor necrosis factor (TNF) in the presence of 100 ng/mL Flt3 ligand and Steel factor and 20 ng/mL interleukin-3 (IL-3), IL-6, and granulocyte colony-stimulating factor, in either bulk or single-cell serum-free cultures, markedly reduces their ability subsequently to generate colony-forming cells (CFCs) in 6-week stromal cell–containing long-term cultures without affecting their viability, mitogenic response, or short-term ability to produce CFCs. A similar differential effect on the functional attributes of CD34+CD38− cells was seen when C2- or C6-ceramide, but not dihydro-C2-ceramide (an inactive analog of ceramide), was substituted for TNF. The addition of D-erythro-MAPP (a specific inhibitor of intracellular ceramide degradation) enhanced the ability of TNF to selectively eliminate long-term culture–initiating cell (LTC-IC) activity. These findings indicate that TNF can directly modulate the ability of CD34+CD38− cells to maintain their LTC-IC function at doses below those required to initiate apoptosis, cell cycle arrest, or both, and they suggest that this may be mediated by the TNF-induced generation of intracellular ceramide. Identification of a signaling intermediate that can influence primitive hematopoietic cell fate decisions offers a new approach to the investigation of signaling mechanisms in normal stem cell populations and to how these may be altered in leukemic cells.

Kinetics of in vivo homing and recruitment into cycle of hematopoietic cells are organ-specific but CD44-independent.

In this study, we investigated the homing and initiation of division of fluorescently labelled adult mouse bone marrow cells after their intravenous injection into lethally irradiated congenic mice. After 2 h, only 3% of the transplanted cells remained in the blood, and approximately 35% could be retrieved from the marrow, liver and spleen in approximately equal numbers. Subsequently, the proportion of injected cells found in blood, liver and spleen decreased further, but increased slightly (to approximately 17%) in the marrow. Homing of progenitors followed a similar pattern. At 22 h post transplant, almost half of the injected cells in the blood, liver and spleen had completed a first mitosis; although these did not include progenitors with in vitro clonogenic ability. At the same time, >90% of the injected cells recovered from the marrow had not yet divided. Parallel studies with CD44-/- mice showed these to contain a numerically and functionally normal stem cell population whose homing and activation in either CD44+/+ or CD44-/- hosts appeared unaltered. These results indicate homing mechanisms that favor more stable retention of transplanted marrow cells in the marrow of the recipient, more rapid activation of some of those cells that home to other sites, and a lack of change in either of these responses when either the transplanted or the recipient cells do not express CD44.