Kegg Pathway: Hematopoietic cell lineage

Epigenetics. 2009 Nov 16; 4(8):
Ramírez J, Hagman J

The Mi-2/NuRD chromatin remodeling complex links multiple transcriptional regulatory processes including histone deacetylation, histone demethylation, nucleosome mobilization and recruitment of other regulatory proteins. In some contexts, Mi-2/NuRD functions as a barrier to transcriptional activation by working in opposition to other chromatin remodelers such as SWI/SNF. Alternatively, the Mi-2beta ATPase subunit of Mi-2/NuRD can promote transcription. Together, these gatekeeper functions of Mi-2/NuRD influence cell fate decisions by modulating transcriptional activity. Recent studies have shown the importance of Mi-2/NuRD both in maintaining Hematopoietic stem cell (HSC) pools and in normal lineage progression. Furthermore, components of Mi-2/NuRD complexes are modular co-repressors/co-activators comprising multiple protein subunits that have been linked directly to oncogenesis and have potential as therapeutic targets for cancer treatment. Mi-2/NuRD's essential functions in metazoan cell fates and activities underscore its importance as a focal point of epigenetic research.

J Immunol. 2009 Dec 1; 183(11): 7352-7361
Carrizosa E, Gomez TS, Labno CM, Klos Dehring DA, Liu X, Freedman BD, Billadeau DD, Burkhardt JK

Productive T cell activation requires efficient reorganization of the actin cytoskeleton. We showed previously that the actin-regulatory protein, Hematopoietic lineage cell-specific protein 1 (HS1), is required for the stabilization of F-actin and Vav1 at the immunological synapse and for efficient calcium responses. The Tec family kinase IL-2-inducible T cell kinase (Itk) regulates similar aspects of T cell activation, suggesting that these proteins act in the same pathway. Using video microscopy, we show that T cells lacking Itk or HS1 exhibited similar defects in actin responses, extending unstable lamellipodial protrusions upon TCR stimulation. HS1 and Itk could be coimmunoprecipitated from T cell lysates, and GST-pulldown studies showed that Itk's Src homology 2 domain binds directly to two phosphotyrosines in HS1. In the absence of Itk, or in T cells overexpressing an Itk Src homology 2 domain mutant, HS1 failed to localize to the immunological synapse, indicating that Itk serves to recruit HS1 to sites of TCR engagement. Because Itk is required for phospholipase C (PLC)gamma1 phosphorylation and calcium store release, we examined the calcium signaling pathway in HS1(-/-) T cells in greater detail. In response to TCR engagement, T cells lacking HS1 exhibited diminished calcium store release, but TCR-dependent PLCgamma1 phosphorylation was intact, indicating that HS1's role in calcium signaling is distinct from that of Itk. HS1-deficient T cells exhibited defective cytoskeletal association of PLCgamma1 and altered formation of PLCgamma1 microclusters. We conclude that HS1 functions as an effector of Itk in the T cell actin-regulatory pathway, and directs the spatial organization of PLCgamma1 signaling complexes.

Biochem Biophys Res Commun. 2009 Nov 11;
Seifinejad A, Taei A, Totonchi M, Vazirinasab H, Hasani SN, Aghdami N, Shahbazi E, Salekdeh GH, Baharvand H

Bombay phenotype is one of the rare phenotypes in the ABO blood group system that fails to express ABH antigens on red blood cells. Nonsense or missense mutations in fucosyltransfrase1 (FUT1) and fucosyltransfrase2 (FUT2) genes are known to create this phenotype. This blood group is compatible with all other blood groups as a donor, as it does not express the H antigen on the red blood cells. In this study, we describe the establishment of human induced pluripotent stem cells (iPSCs) from the dermal fibroblasts of a Bombay blood-type individual by the ectopic expression of established transcription factors Klf4, Oct4, Sox2, and c-Myc. Sequence analyses of fibroblasts and iPSCs revealed a nonsense mutation 826C to T (276 Gln to Ter) in the FUT1 gene and a missense mutation 739G to A (247 Gly to Ser) in the FUT2 gene in the Bombay phenotype under study. The established iPSCs resemble human embryonic stem cells in morphology, passaging, surface and pluripotency markers, normal karyotype, gene expression, DNA methylation of critical pluripotency genes, and in-vitro differentiation. The directed differentiation of the iPSCs into Hematopoietic lineage cells displayed increased expression of the Hematopoietic lineage markers such as CD34, CD133, RUNX1, KDR, alpha-globulin, and gamma-globulin. Such specific stem cells provide an unprecedented opportunity to produce a universal blood group donor, in-vitro, thus enabling cellular replacement therapies, once the safety issue is resolved.

PLoS Comput Biol. 2009 Sep; 5(9): e1000518
Palani S, Sarkar CA

Autoregulation of transcription factors and cross-antagonism between lineage-specific transcription factors are a recurrent theme in cell differentiation. An equally prevalent event that is frequently overlooked in lineage commitment models is the upregulation of lineage-specific receptors, often through lineage-specific transcription factors. Here, we use a minimal model that combines cell-extrinsic and cell-intrinsic elements of regulation in order to understand how both instructive and stochastic events can inform cell commitment decisions in hematopoiesis. Our results suggest that cytokine-mediated positive receptor feedback can induce a "switch-like" response to external stimuli during multilineage differentiation by providing robustness to both bipotent and committed states while protecting progenitors from noise-induced differentiation or decommitment. Our model provides support to both the instructive and stochastic theories of commitment: cell fates are ultimately driven by lineage-specific transcription factors, but cytokine signaling can strongly bias lineage commitment by regulating these inherently noisy cell-fate decisions with complex, pertinent behaviors such as ligand-mediated ultrasensitivity and robust multistability. The simulations further suggest that the kinetics of differentiation to a mature cell state can depend on the starting progenitor state as well as on the route of commitment that is chosen. Lastly, our model shows good agreement with lineage-specific receptor expression kinetics from microarray experiments and provides a computational framework that can integrate both classical and alternative commitment paths in hematopoiesis that have been observed experimentally.

Blood Rev. 2009 Nov 10;
Lengerke C, Daley GQ

The discovery of human embryonic stem cells (hESCs) raised promises for a universal resource for cell based therapies in regenerative medicine. Recently, fast-paced progress has been made towards the generation of pluripotent stem cells (PSCs) amenable for clinical applications, culminating in reprogramming of adult somatic cells to autologous PSCs that can be indefinitely expanded in vitro. However, besides the efficient generation of bona fide, clinically safe PSCs (e.g., without the use of oncoproteins and gene transfer based on viruses inserting randomly into the genome), a major challenge in the field remains how to efficiently differentiate PSCs to specific lineages and how to select cells that will function normally upon transplantation in adults. In this review, we analyse the in vitro differentiation potential of PSCs to the Hematopoietic lineage by discussing blood cell types that can be currently obtained, limitations in derivation of adult-type HSCs and prospects for clinical application of PSCs-derived blood cells.

Virol J. 2009; 6: 196
Cox C, Cao S, Lu Y

BACKGROUND: Human Noroviruses are the predominant cause of non-bacterial gastroenteritis worldwide. To facilitate prevention and control, a norovirus isolated from mice can provide a model to understand human noroviruses. To establish optimal viral infectivity conditions for murine noroviruses, several cell lines of Hematopoietic lineage, including murine BV-2, RAW 264.7, and TIB, as well as human CHME-5, were tested comparatively for their sensitivity to murine norovirus-1. RESULTS: Except for CHME-5, all three murine-derived cell lines were susceptible to MNV infection. Viral infection of these cells was confirmed by RT-PCR. Using both viral plaque and replication assays, BV-2 and RAW 264.7 cells were determined to have comparable sensitivities to MNV-1 infection. Comparisons of cell growth characteristics, general laboratory handling and potential in-field applications suggest the use of BV-2 to be more advantageous. CONCLUSION: Results obtained from these studies demonstrate that an immortalized microglial cell line can support MNV-1 replication and provides a more efficient method to detect and study murine noroviruses, facilitating future investigations using MNV-1 as a model to study, detect, and control Human Norovirus.

Chem Biol Interact. 2009 Nov 5;
Gasiewicz TA, Singh KP, Casado FL

The aryl hydrocarbon receptor (AhR) belongs to the basic helix-loop-helix (bHLH) Per-Arnt-Sim (PAS) family of transcription factors. Many of these proteins are involved in regulating responses to signals in the tissue environment such as hypoxia, oxidation-reduction status, and circadian rhythms. Although the AhR is well studied as a mediator of the toxicity of certain xenobiotics, the normal physiological function remains unknown. However, accumulating data support a hypothesis that the AhR has an important function in the regulation of Hematopoietic stem cells (HSCs). Persistent AhR activation by dioxin, a potent xenobiotic AhR agonist, results in altered numbers and function of HSCs in mouse bone marrow. Analysis of HSCs from AhR null-allele mice also indicates that lack of AhR expression results in altered characteristics and function of these cells. HSCs from these animals are hyperproliferative and have altered cell cycle. In addition, aging AhR-KO mice show characteristics consistent with premature bone marrow senescence and are prone to Hematopoietic disease. Finally, some data suggest that the expression of the Ahr gene is regulated under conditions that control HSC proliferation. The presence of a normal functioning AhR may provide an important advantage to organisms by regulating the balance between quiescence and proliferation and preventing the premature exhaustion of HSCs and sensitivity to genetic alterations. This function assists in the preservation of HSC function and long-term multi-lineage generation over the lifespan of the organism. This also implicates a role for the AhR in the aging process. Furthermore, these functions may affect the sensitivity of HSCs to certain xenobiotics, including benzene. Defining the molecular mechanisms by which these events occur may lead to the identification of previously undefined roles of this transcription factor in human diseases, particularly those caused or affected by xenobiotics.

Stem cells. 2009 Nov 4;
Zhao X, Ren G, Liang L, Ai PZ, Zheng B, Tischfield JA, Shi Y, Shao C

The balance between Th1 and Th2 cells is critical for homeostasis of the immune system. Th1 cells can also regulate Hematopoietic progenitor cell homeostasis by production of oncostatin M. Here we show that Th1 cell products, but not those of Th2 cells, caused a rapid expansion of lineage(low)Sca-1(+)C-kit(+) (LSK) cells in vivo and in vitro. Among Th1 cytokines, IFNgamma was found to play a major role in this expansion by activating the expression of Sca-1 in lineage(low)Sca-1(-)C-kit(+) cells. This process was dependent on IFNgammaR1 signaling and the STAT1 pathway. Furthermore, those IFNgamma-induced LSK cells had a higher proliferation potential than control LSK cells. In addition, while the overall production of colony forming units (CFUs) in bone marrow was decreased after IFNgamma treatment, the sorted LSK cells could give rise to a higher yield of CFUs. Finally, the IFNgamma-induced hematopoiesis was biased toward the differentiation of myeloid lineages. Therefore, our findings demonstrated a novel role of IFNgamma in activating Hematopoietic progenitor cells and provide a new insight into the clinical application of interferon.

J Immunol. 2009 Dec 1; 183(11): 7084-7094
Dudakov JA, Goldberg GL, Reiseger JJ, Vlahos K, Chidgey AP, Boyd RL

Cytotoxic antineoplastic therapy is widely used in the clinic as a treatment for malignant diseases. The treatment itself, however, leads to long-term depletion of the adaptive immune system, which is more pronounced in older patients, predominantly due to thymic atrophy. We and others have previously shown that withdrawal of sex steroids is able to regenerate the aged thymus and enhance recovery from autologous and allogeneic Hematopoietic stem cell transplant. In this study we have examined the effects of sex steroid ablation (SSA) on the recovery of lymphopoiesis in the bone marrow (BM) and thymus following treatment with the chemotherapeutic agent cyclophosphamide (Cy) in middle-aged and old mice. Furthermore, we have also examined the impact of this regeneration on peripheral immunity. SSA enhanced the recovery of BM resident Hematopoietic stem cells and lymphoid progenitors and promoted lymphopoiesis. Interestingly, Cy alone caused a profound increase in the recently described common lymphoid progenitor 2 (CLP-2) population in the BM. In the thymus, SSA caused a profound increase in cellularity as well as all intrathymic T-lineage progenitors including early T-lineage progenitors (ETPs) and non-canonical T cell progenitors such as the CLP-2. We also found that these transferred into numerical increases in the periphery with enhanced B and T cell numbers. Furthermore, these lymphocytes were found to have an enhanced functional capacity with no perturbation of the TCR repertoire. Taken together, these results provide the basis for the use of SSA in the clinic to enhance treatment outcomes from cytotoxic antineoplastic therapy.

Blood. 2009 Nov 3;
Weishaupt H, Sigvardsson M, Attema JL

Heritable epigenetic signatures are proposed to serve as an important regulatory mechanism in lineage fate determination. To investigate this, we profiled chromatin modifications in murine Hematopoietic stem cells, lineage restricted progenitors and CD4(+) T cells using modified genome-scale miniChIP technology. We show that genes involved in mature Hematopoietic cell function associate with distinct chromatin states in stem and progenitor cells, prior to their activation or silencing upon cellular maturation. Many lineage-restricted promoters are associated with bivalent histone methylation and highly combinatorial histone modification patterns, which may determine their selective priming of gene expression during lineage commitment. These bivalent chromatin states are conserved in mammalian evolution, with a particular over-representation of promoters encoding key regulators of hematopoiesis. Following differentiation into progenitors and T cells, activating histone modifications persist at transcriptionally repressed promoters, suggesting that these transcriptional programs might be reactivated after lineage restriction. Collectively, our data reveal the epigenetic framework that underlies the cell fate options of Hematopoietic stem cells.

Stem cells Dev. 2009 Nov 3;
Sørensen AL, Timoskainen S, West FD, Vekterud K, Boquest AC, Ahrlund-Richter L, Stice SL, Collas P

Mesenchymal stem cells (MSCs) can differentiate into multiple mesodermal cell types in vitro; however their differentiation capacity is influenced by their tissue of origin. To what extent epigenetic information on promoters of lineage-specification genes in human progenitors influences transcriptional activation and differentiation potential remains unclear. We produced bisulfite sequencing maps of DNA methylation in adipogenic, myogenic and endothelial promoters in relation to gene expression and differentiation capacity, and unravel a similarity in DNA methylation profiles between MSCs isolated from human adipose tissue, bone marrow and muscle. This similarity is irrespective of promoter CpG content. Methylation patterns of MSCs are distinct from those of Hematopoietic progenitor cells, pluripotent human embryonic stem cells (hESCs) and multipotent hESC-derived mesenchymal cells. Moreover, in vitro MSC differentiation does not affect lineage-specific promoter methylation states, arguing that these methylation patterns in differentiated cells are already established at the progenitor stage. Further, we find a correlation between lineage-specific promoter hypermethylation and lack of differentiation capacity toward that lineage, but no relationship between weak promoter methylation and capacity of transcriptional activation or differentiation. Thus, only part of the restriction in differentiation capacity of tissue-specific stem cells is programmed by promoter DNA methylation: hypermethylation seems to constitute a barrier to differentiation, however no or weak methylation has no predictive value for differentiation potential.

cell. 2009 Oct 30; 139(3): 535-46
Yue R, Kang J, Zhao C, Hu W, Tang Y, Liu X, Pei G

Beta-arrestin1 is a multifunctional protein critically involved in signal transduction. Recently, it is also identified as a nuclear transcriptional regulator, but the underlying mechanisms and physiological significance remain to be explored. Here, we identified beta-arrestin1 as an evolutionarily conserved protein essential for zebrafish development. Zebrafish embryos depleted of beta-arrestin1 displayed severe posterior defects and especially failed to undergo hematopoiesis. In addition, the expression of cdx4, a critical regulator of embryonic blood formation, and its downstream hox genes were downregulated by depletion of beta-arrestin1, while injection of cdx4, hoxa9a or hoxb4a mRNA rescued the Hematopoietic defects. Further mechanistic studies revealed that beta-arrestin1 bound to and sequestered the polycomb group (PcG) recruiter YY1, and relieved PcG-mediated repression of cdx4-hox pathway, thus regulating Hematopoietic lineage specification. Taken together, this study demonstrated a critical role of beta-arrestin1 during zebrafish primitive hematopoiesis, as well as an important regulator of PcG proteins and cdx4-hox pathway.

Cancer cell. 2009 Nov 6; 16(5): 390-400
Bereshchenko O, Mancini E, Moore S, Bilbao D, Månsson R, Luc S, Grover A, Jacobsen SE, Bryder D, Nerlov C

We here use knockin mutagenesis in the mouse to model the spectrum of acquired CEBPA mutations in human acute myeloid leukemia. We find that C-terminal C/EBPalpha mutations increase the proliferation of long-term Hematopoietic stem cells (LT-HSCs) in a cell-intrinsic manner and override normal HSC homeostasis, leading to expansion of premalignant HSCs. However, such mutations impair myeloid programming of HSCs and block myeloid lineage commitment when homozygous. In contrast, N-terminal C/EBPalpha mutations are silent with regards to HSC expansion, but allow the formation of committed myeloid progenitors, the templates for leukemia-initiating cells. The combination of N- and C-terminal C/EBPalpha mutations incorporates both features, accelerating disease development and explaining the clinical prevalence of this configuration of CEBPA mutations.

Cytotherapy. 2009; 11(6): 768-77
Singh K, Srivastava A, Mathur N, Kumar S, Kumar L, Mukhopadhyay A, Konchupillai V

BACKGROUND AIMS: The application of cord blood (CB)-derived Hematopoietic cells in allogeneic transplantation has been restricted because of the unavailability of adequate cell numbers from one unit of CB and their delayed engraftment in recipients. The main purpose of this study was to develop an economic process for isolating nucleated cells from CB and expanding enriched CD133(+) cells. METHODS: Four protocols for processing CB, using different combinations of density-gradient centrifugation, hydroxyethyl starch (HES) and NH4Cl treatment, were compared regarding the yields of CD45(+), CD34(+)/CD133(+) and colony-forming cells. CD133-enriched cells were expanded for 10 days in the presence of Hematopoietic growth factor-supplemented medium. The performance of the culture was evaluated by analyzing colony-forming potential, fold-expansion of primitive Hematopoietic stem cells (HSC) and lineage commitment by flow cytometry. RESULTS: A two-step treatment of CB with HES followed by NH4Cl resulted in the highest recovery of CD45(+) (84.3%) and CD34(+) (69.1%) cells compared with that present in umbilical CB. A suspension culture of CD133-enriched cells resulted in an average 150-fold increase in nucleated cells, of which CD133(+), CD34(+) and CD34(+) CD38 cell expansions were 17.2+/-1.3, 40+/-4.6, and 6.9+/-1.1 fold, respectively. The total myeloid colony-forming cell count was almost 3800-fold higher than that present in the processed CB. CONCLUSIONS: The highest yields of nucleated and progenitor stem cells were obtained with a two-step processing of CB. The CD133(+) cells obtained by this method are expected to yield enough Hematopoietic progenitors for potential allogeneic transplantation.

PLoS One. 2009; 4(10): e7661
Zheng X, Oancea C, Henschler R, Moore MA, Ruthardt M

BACKGROUND: t(9;22) is a balanced translocation, and the chromosome 22 breakpoints (Philadelphia chromosome--Ph+) determine formation of different fusion genes that are associated with either Ph+ acute lymphatic leukemia (Ph+ ALL) or chronic myeloid leukemia (CML). The "minor" breakpoint in Ph+ ALL encodes p185(BCR/ABL) from der22 and p96(ABL/BCR) from der9. The "major" breakpoint in CML encodes p210(BCR/ABL) and p40(ABL/BCR). Herein, we investigated the leukemogenic potential of the der9-associated p96(ABL/BCR) and p40(ABL/BCR) fusion proteins and their roles in the lineage commitment of Hematopoietic stem cells in comparison to BCR/ABL. METHODOLOGY: All t(9;22) derived proteins were retrovirally expressed in murine Hematopoietic stem cells (SL cells) and human umbilical cord blood cells (UCBC). Stem cell potential was determined by replating efficiency, colony forming--spleen and competitive repopulating assays. The leukemic potential of the ABL/BCR fusion proteins was assessed by in a transduction/transplantation model. Effects on the lineage commitment and differentiation were investigated by culturing the cells under conditions driving either myeloid or lymphoid commitment. Expression of key factors of the B-cell differentiation and components of the preB-cell receptor were determined by qRT-PCR. PRINCIPAL FINDINGS: Both p96(ABL/BCR) and p40(ABL/BCR) increased proliferation of early progenitors and the short term stem cell capacity of SL-cells and exhibited own leukemogenic potential. Interestingly, BCR/ABL gave origin exclusively to a myeloid phenotype independently from the culture conditions whereas p96(ABL/BCR) and to a minor extent p40(ABL/BCR) forced the B-cell commitment of SL-cells and UCBC. CONCLUSIONS/SIGNIFICANCE: Our here presented data establish the reciprocal ABL/BCR fusion proteins as second oncogenes encoded by the t(9;22) in addition to BCR/ABL and suggest that ABL/BCR contribute to the determination of the leukemic phenotype through their influence on the lineage commitment.

Blood. 2009 Oct 27;
Nakahara F, Sakata-Yanagimoto M, Komeno Y, Kato N, Uchida T, Haraguchi K, Kumano K, Harada Y, Harada H, Kitaura J, Ogawa S, Kurokawa M, Kitamura T, Chiba S

Hairy enhancer of split 1 (Hes1) is a basic helix-loop-helix transcriptional repressor that affects differentiation and often helps maintain cells in an immature state in various tissues. Here we show that retroviral expression of Hes1 immortalizes common myeloid progenitors (CMPs) and granulocyte-macrophage progenitors (GMPs) in the presence of interleukin-3, conferring permanent replating capability on these cells. Whereas these cells did not develop myeloproliferative neoplasms when intravenously administered into irradiated mice, the combination of Hes1 and BCR-ABL in CMPs and GMPs caused acute leukemia resembling blast crisis of chronic myelogenous leukemia (CML), resulting in rapid death of the recipient mice. On the other hand, BCR-ABL alone caused CML-like disease when expressed in c-Kit-positive, Sca-1-positive, and lineage-negative Hematopoietic stem cells (KSLs), but not committed progenitors CMPs or GMPs, as previously reported. Leukemic cells derived from Hes1 and BCR-ABL-expressing CMPs and GMPs were more immature than those derived from BCR-ABL-expressing KSLs. Intriguingly, Hes1 was highly expressed in eight of 20 patients with CML in blast crisis, but not in the chronic phase, and dominant negative Hes1 retarded the growth of some CML cell lines expressing Hes1. These results suggest that Hes1 is a key molecule in blast crisis transition in CML.

Leuk Lymphoma. 2009 Sep 30;
Sevilla DW, Emmons FN, Colovai AI, Beaubier NT, Baker C, Bhatia M, Bhagat G, Alobeid B

Acquired aplastic anemia (AA) and myelodysplastic syndromes (MDS) are bone marrow (BM) failure syndromes with overlapping clinical features, and at least a subset appears to share common pathophysiologic mechanisms. Recent studies of MDS have shown down-regulation of genes involved in B-cell development and decreased B-cell precursors (hematogones). We explored the possibility that AA, similar to MDS, might also be associated with defects in development of lymphoid cells, especially B-cells, by using flow cytometry to assess the presence of hematogones and mature lymphocytes in BM samples from 25 children with AA and 41 age-matched controls. We observed that the percentage of total and early (stage I) hematogones were significantly decreased in AA compared to controls, and they returned to normal numbers after Hematopoietic stem-cell transplant. This demonstrates early B-cell lineage involvement in AA, similar to recent findings in MDS. Our findings suggest dysfunction of an early multilineage progenitor in the pathogenesis of AA.

Chem Biol Interact. 2009 Oct 24;
Vardiman JW

The World Health Organization (WHO) classification of myeloid and lymphoid neoplasms utilizes morphology, immunophenotype, genetics and clinical features to define disease entities of clinical significance. It is a consensus classification in which a number of experts have agreed on the classification and diagnostic criteria. In general, the classification stratifies neoplasms according to their lineage (myeloid, lymphoid, histiocytic/dendritic) and distinguishes neoplasms of precursor cells from those comprised of functionally mature cells. Lymphoid neoplasms are derived from cells that frequently have features that recapitulate stages of normal B-, T-, and NK-cell differentiation and function, so to some extent they can be classified according to the corresponding normal counterpart, although additional features, such as genotype, clinical features and even location of the tumor figure into the final classification listing as well. Five major subgroups of myeloid neoplasms are recognized based mainly on their degree of maturation and biologic properties: myeloproliferative neoplasms (MPNs) which are comprised primarily of mature cells with effective proliferation; myeloid (and lymphoid) neoplasms with eosinophilia and abnormalities of PDGFRA, PDGFRB and FGFR1, defined largely by the finding of significant eosinophilia and specific genetic abnormalities; myelodysplastic/myeloproliferative neoplasms (MDS/MPN), comprised mainly of mature cells with both effective and ineffective proliferation of various lineages; myelodysplastic syndromes (MDS), in which immature and mature cells are found with abnormal, dysplastic and ineffective maturation, and acute myeloid leukemia (AML), comprised of precursor cells with impaired maturation. Genetic abnormalities play an important role as diagnostic criteria for further sub-classification of some myeloid neoplasms, particularly of AML. Although therapy-related MDS and AML (t-MDS/AML) often have genetic defects identical to those found in de novo AML and de novo MDS, they are classified separately from de novo AML and MDS in order to emphasize their unique clinical and biologic properties.

Blood. 2009 Oct 23;
Lemoli RM, Salvestrini V, Bianchi E, Bertolini F, Fogli M, Amabile M, Tafuri A, Salati S, Zini R, Testoni N, Rabascio C, Rossi L, Martin-Padura I, Castagnetti F, Marighetti P, Martinelli G, Baccarani M, Ferrari S, Manfredini R

We show the molecular and functional characterization of a novel population of lineage-negative CD34-negative (Lin(-)CD34(-)) Hematopoietic stem cells from chronic myelogenous leukemia (CML) patients at diagnosis. Molecular karyotyping and quantitative analysis of BCR-ABL transcript demonstrated that about one third of CD34(-) cells are leukemic. CML Lin(-)CD34(-) cells showed kinetic quiescence and limited clonogenic capacity. However, stroma-dependent cultures induced CD34 expression on some cells, cell cycling, increased clonogenic activity and expression of BCR-ABL transcript. Lin(-)CD34(-) cells showed Hematopoietic cell engraftment rate in two immunodeficient mouse strains similar to Lin(-)CD34(+) cells whereas endothelial cell engraftment was significantly higher. Gene expression profiling revealed the down-regulation of cell cycle arrest genes, genes involved in antigen presentation and processing, while the expression of genes related to tumor progression, such as angiogenic factors, was strongly up-regulated when compared to normal counterparts. Phenotypic analysis confirmed the significant down-regulation of HLA class I and II molecules in CML Lin(-)CD34(-)cells. Imatinib mesylate did not reduce fusion transcript levels, BCR-ABL kinase activity and clonogenic efficiency of CML Lin(-)CD34(-) cells in vitro. Moreover, leukemic CD34(-) cells survived exposure to BCR-ABL inhibitors in vivo. Thus, we identified a novel CD34(-) leukemic stem cell subset in CML with peculiar molecular and functional characteristics.

Proc Natl Acad Sci U S A. 2009 Nov 10; 106(45): 19102-7
Metcalf D, Ng AP, Loughran SJ, Phipson B, Smyth GK, Di Rago L, Mifsud S

Two distinct bone marrow-derived blast colony-forming cells can generate colonies of lineage-restricted progenitor cells in agar cultures of murine bone marrow. Both cell types selectively had a Kit(+) ScaI(+) phenotype distinguishing them from most lineage-restricted progenitor cells. Multicentric blast colony-forming cells stimulated by stem cell factor plus interleukin-6 (IL-6) (BL-CFC-S) were separable from most dispersed blast colony-forming cells stimulated by Flt3 ligand and IL-6 (BL-CFC-F) using CD34 and Flt3R probes. Multicentric BL-CFC-S cofractionated with colony-forming units, spleen (CFU-S) supporting the possibility that the 2 cells may be identical. The colony populations generated by BL-CFC-S were similar in their phenotype and proliferative capacity to progenitor cells in whole bone marrow but the progeny of BL-CFC-F were skewed with an abnormally high proportion of Kit(-) Flt3R(+) cells whose clonogenic cells tended to generate only macrophage progeny. Both blast colony populations had a high percentage of GR1(+) and Mac1(+) cells but BL-CFC-F colonies also contained a significant population of B220(+) and IL-7R(+) cells relevant to the superior ability of BL-CFC-F colony cells to generate B lymphocytes and the known dependency of this process on Flt3 ligand and IL-7. The commitment events and phenotypic changes during the generation of differing progenitor cells in blast colonies can now be clonally analyzed in a convenient in vitro culture system.