技术资料

The efficacy of cardiac repair by stem cell administration relies on a successful functional integration of injected cells into the host myocardium. Safety concerns have been raised about the possibility that stem cells may induce foci of arrhythmia in the ischemic myocardium. In a previous work (36),we showed that human cord blood CD34(+) cells,when cocultured on neonatal mouse cardiomyocytes,exhibit excitation-contraction coupling features similar to those of cardiomyocytes,even though no human genes were upregulated. The aims of the present work are to investigate whether human CD34(+) cells,isolated after 1 wk of coculture with neonatal ventricular myocytes,possess molecular and functional properties of cardiomyocytes and to discriminate,using a reporter gene system,whether cardiac differentiation derives from a (trans)differentiation or a cell fusion process. Umbilical cord blood CD34(+) cells were isolated by a magnetic cell sorting method,transduced with a lentiviral vector carrying the enhanced green fluorescent protein (EGFP) gene,and seeded onto primary cultures of spontaneously beating rat neonatal cardiomyocytes. Cocultured EGFP(+)/CD34(+)-derived cells were analyzed for their electrophysiological features at different time points. After 1 wk in coculture,EGFP(+) cells,in contact with cardiomyocytes,were spontaneously contracting and had a maximum diastolic potential (MDP) of -53.1 mV,while those that remained isolated from the surrounding myocytes did not contract and had a depolarized resting potential of -11.4 mV. Cells were then resuspended and cultured at low density to identify EGFP(+) progenitor cell derivatives. Under these conditions,we observed single EGFP(+) beating cells that had acquired an hyperpolarization-activated current typical of neonatal cardiomyocytes (EGFP(+) cells,-2.24 ± 0.89 pA/pF; myocytes,-1.99 ± 0.63 pA/pF,at -125 mV). To discriminate between cell autonomous differentiation and fusion,EGFP(+)/CD34(+) cells were cocultured with cardiac myocytes infected with a red fluorescence protein-lentiviral vector; under these conditions we found that 100% of EGFP(+) cells were also red fluorescent protein positive,suggesting cell fusion as the mechanism by which cardiac functional features are acquired. View Publication

Two critical concerns in clinical cord blood transplantation are the initial time to engraftment and the subsequent restoration of immune function. These studies measured the impact of progenitor cell dose on both the pace and strength of hematopoietic reconstitution by transplanting nonobese diabetic/severe combined immunodeficiency/interleukin-2 receptor-gamma-null (NSγ) mice with lineage-depleted aldehyde dehydrogenase-bright CD34(+) human cord blood progenitors. The progress of each transplant was monitored over an extended time course by repeatedly analyzing the peripheral blood for human hematopoietic cells. In vivo human hematopoietic development was complete. After long-term transplantation assays (≥ 19 weeks),human T-cell development was documented within multiple tissues in 16 of 32 NSγ mice. Human T-cell differentiation was active within NSγ thymuses,as documented by the presence of CD4(+) CD8(+) T-cell progenitors as well as T-cell receptor excision circles. It is important to note that although myeloid and B-cell engraftment was detected as early as 4 weeks after transplantation,human T-cell development was exclusively late onset. High progenitor cell doses were associated with a robust human hematopoietic chimerism that accelerated both initial time to engraftment and subsequent T-cell development. At lower progenitor cell doses,the chimerism was weak and the human hematopoietic lineage development was frequently incomplete. View Publication

Defining the molecular mechanisms underpinning fetal (gamma) globin gene silencing may provide strategies for reactivation of gamma-gene expression,a major therapeutic objective in patients with beta-thalassemia and sickle cell disease (SCD). We have previously demonstrated that symmetric methylation of histone H4 Arginine 3 (H4R3me2s) by the protein arginine methyltransferase PRMT5 is required for recruitment of the DNA methyltransferase DNMT3A to the gamma-promoter,and subsequent DNA methylation and gene silencing. Here we show in an erythroid cell line,and in primary adult erythroid progenitors that PRMT5 induces additional repressive epigenetic marks at the gamma-promoter through the assembly of a multiprotein repressor complex containing the histone modifying enzymes SUV4-20h1,casein kinase 2alpha (CK2alpha),and components of the nucleosome remodeling and histone deacetylation complex. Expression of a mutant form of PRMT5 lacking methyltransferase activity or shRNA-mediated knockdown of SUV4-20h1 resulted in loss of complex binding to the gamma-promoter,reversal of both histone and DNA repressive epigenetic marks,and increased gamma-gene expression. The repressive H4K20me3 mark induced by SUV4-20h1 is enriched on the gamma-promoter in erythroid progenitors from adult bone marrow compared with cord blood,suggesting developmental specificity. These studies define coordinated epigenetic events linked to fetal globin gene silencing,and provide potential therapeutic targets for the treatment of beta-thalassemia and SCD. View Publication

Phenotypic markers associated with human hematopoietic stem cells (HSCs) were developed and validated using uncultured cells. Because phenotype and function can be dissociated during culture,better markers to prospectively track and isolate HSCs in ex vivo cultures could be instrumental in advancing HSC-based therapies. Using an expansion system previously shown to increase hematopoietic progenitors and SCID-repopulating cells (SRCs),we demonstrated that the rhodamine-low phenotype was lost,whereas AC133 expression was retained throughout culture. Furthermore,the AC133(+)CD38(-) subpopulation was significantly enriched in long-term culture-initiating cells (LTC-IC) and SRCs after culture. Preculture and postculture analysis of total nucleated cell and LTC-IC number,and limiting dilution analysis in NOD/SCID mice,showed a 43-fold expansion of the AC133(+)CD38(-) subpopulation that corresponded to a 7.3-fold and 4.4-fold expansion of LTC-ICs and SRCs in this subpopulation,respectively. Thus,AC133(+)CD38(-) is an improved marker that tracks and enriches for LTC-IC and SRC in ex vivo cultures. View Publication

Beta glucans are cell wall constituents of yeast,fungi and bacteria,as well as mushrooms and barley. Glucans are not expressed on mammalian cells and are recognized as pathogen-associated molecular patterns (PAMPS) by pattern recognition receptors (PRR). Beta glucans have potential activity as biological response modifiers for hematopoiesis and enhancement of bone marrow recovery after injury. We have reported that Maitake beta glucan (MBG) enhanced mouse bone marrow (BMC) and human umbilical cord blood (CB) cell granulocyte-monocyte colony forming unit (GM-CFU) activity in vitro and protected GM-CFU forming stem cells from doxorubicin (DOX) toxicity. The objective of this study was to determine the effects of MBG on expansion of phenotypically distinct subpopulations of progenitor and stem cells in CB from full-term infants cultured ex vivo and on homing and engraftment in vivo in the nonobese diabetic/severe combined immunodeficient (NOD/SCID) mouse. MBG promoted a greater expansion of CD34+CD33+CD38- human committed hematopoietic progenitor (HPC) cells compared to the conventional stem cell culture medium (P = 0.002 by ANOVA). CD34+CXCR4+CD38- early,uncommitted human hematopoietic stem cell (HSC) numbers showed a trend towards increase in response to MBG. The fate of CD34+ enriched CB cells after injection into the sublethally irradiated NOS/SCID mouse was evaluated after retrieval of xenografted human CB from marrow and spleen by flow cytometric analysis. Oral administration of MBG to recipient NOS/SCID mice led to enhanced homing at 3 days and engraftment at 6 days in mouse bone marrow (P = 0.002 and P = 0.0005,respectively) compared to control mice. More CD34+ human CB cells were also retrieved from mouse spleen in MBG treated mice at 6 days after transplantation. The studies suggest that MBG promotes hematopoiesis through effects on CD34+ progenitor cell expansion ex vivo and when given to the transplant recipient could enhance CD34+ precursor cell homing and support engraftment. View Publication

BACKGROUND: Excessive maturation of hematopoietic cells leads to a reduction of long-term proliferative capability during cord blood (CB) expansion. In this study,we report the effects of anit-CD52 (Alemtuzumab,Campath) on both short- and long-term ex vivo expansion of CB hematopoietic stem cells (HSC) by evaluating the potential role of Alemtuzumab in preserving the repopulating capability in CB HSC and nonlymphoid progenitors. METHODS: Ex vivo expansion experiments were carried out using freshly purified CB CD34(+)cells in StemSpantrade mark SFEM medium in the presence of stem cell factor,Flt3-Ligand and thrombopoietin at 50 ng/ml. Alemtuzumab (10 microg/ml) was used to deplete CD52(+) cells during the cultures. Flow cytometry was used to monitor CB HSC and their differentiation. Colony forming unit (CFU) assays and long term culture-initiating cell (LTC-IC) assays were performed on cells obtained from day 0 (before culture) and day 14 after cultures. Secondary cultures was performed using CD34(+) cells isolated at 35 days from primary cultures and further cultured in StemSpantrade mark SFEM medium for another 14 days to confirm the long term effect of alemtuzumab in liquid cultures. RESULTS: Compared to cytokines alone,addition of alemtuzumab resulted in a significant increase in total nucleated cells,absolute CD34(+) cells,myeloid and megakaryocytic progenitors,multi-lineage and myeloid CFU and LTC-IC. CONCLUSION: The results from current study suggested that the use of alemtuzumab for ex vivo expansion of CBHSC maybe advantageous. Our findings may improve current technologies for CBHSC expansion and increase the availability of CB units for transplantation. However,in vivo studies using animal models are likely needed in further studies to test the hematopoietic effects using such expanded CB products. View Publication

Umbilical cord blood (UCB) is increasingly being used for human hematopoietic stem cell (HSC) transplantation in children but often requires pooling multiple cords to obtain sufficient numbers for transplantation in adults. To overcome this limitation,we have used an ex vivo two-week culture system to expand the number of hematopoietic CD34(+) cells in cord blood. To assess the in vivo function of these expanded CD34(+) cells,cultured human UCB containing 1 x 10(6) CD34(+) cells were transplanted into conditioned NOD-scid IL2rgamma(null) mice. The expanded CD34(+) cells displayed short- and long-term repopulating cell activity. The cultured human cells differentiated into myeloid,B-lymphoid,and erythroid lineages,but not T lymphocytes. Administration of human recombinant TNFalpha to recipient mice immediately prior to transplantation promoted human thymocyte and T-cell development. These T cells proliferated vigorously in response to TCR cross-linking by anti-CD3 antibody. Engrafted TNFalpha-treated mice generated antibodies in response to T-dependent and T-independent immunization,which was enhanced when mice were co-treated with the B cell cytokine BLyS. Ex vivo expanded CD34(+) human UCB cells have the capacity to generate multiple hematopoietic lineages and a functional human immune system upon transplantation into TNFalpha-treated NOD-scid IL2rgamma(null) mice. View Publication

Prior in vitro studies suggested that different types of hematopoietic stem cells may differentiate into cardiomyocytes. The present work examined whether human CD34(+) cells from the human umbilical cord blood (hUCB),cocultured with neonatal mouse cardiomyocytes,acquire the functional properties of myocardial cells and express human cardiac genes. hUCB CD34(+) cells were cocultured onto cardiomyocytes following an infection with a lentivirus-encoding enhanced green fluorescent protein (EGFP). After 7 days,mononucleated EGFP(+) cells were tested for their electrophysiological features by patch clamp and for cytosolic [Ca(2+)] ([Ca(2+)](i)) homeostasis by [Ca(2+)](i) imaging of X-rhod1-loaded cells. Human Nkx2.5 and GATA-4 expression was examined in cocultured cell populations by real-time RT-PCR. EGFP(+) cells were connected to surrounding cells by gap junctions,acquired electrophysiological properties similar to those of cardiomyocytes,and showed action potential-associated [Ca(2+)](i) transients. These cells also exhibited spontaneous sarcoplasmic reticulum [Ca(2+)](i) oscillations and the associated membrane potential depolarization. However,RT-PCR of both cell populations showed no upregulation of human-specific cardiac genes. In conclusion,under our experimental conditions,hUCB CD34(+) cells cocultured with murine cardiomyocytes formed cells that exhibited excitation-contraction coupling features similar to those of cardiomyocytes. However,the expression of human-specific cardiac genes was undetectable by RT-PCR. View Publication

Hematopoietic stem cells (HSCs) are the basis of bone marrow transplantation and are attractive target cells for hematopoietic gene therapy,but these important clinical applications have been severely hampered by difficulties in ex vivo expansion of HSCs. In particular,the use of cord blood for adult transplantation is greatly limited by the number of HSCs. Previously we identified angiopoietin-like proteins and IGF-binding protein 2 (IGFBP2) as new hormones that,together with other factors,can expand mouse bone marrow HSCs in culture. Here,we measure the activity of multipotent human severe combined immunodeficient (SCID)-repopulating cells (SRCs) by transplantation into the nonobese diabetic SCID (NOD/SCID) mice; secondary transplantation was performed to evaluate the self-renewal potential of SRCs. A serum-free medium containing SCF,TPO,and FGF-1 or Flt3-L cannot significantly support expansion of the SRCs present in human cord blood CD133+ cells. Addition of either angiopoietin-like 5 or IGF-binding protein 2 to the cultures led to a sizable expansion of HSC numbers,as assayed by NOD/SCID transplantation. A serum-free culture containing SCF,TPO,FGF-1,angiopoietin-like 5,and IGFBP2 supports an approximately 20-fold net expansion of repopulating human cord blood HSCs,a number potentially applicable to several clinical processes including HSC transplantation. View Publication

The histo-blood group i and I antigens have been characterized as straight and branched repeats of N-acetyllactosamine,respectively,and the conversion of the straight-chain i to the branched-chain I structure on red cells is regulated to occur after birth. It has been demonstrated that the human I locus expresses 3 IGnT transcripts,IGnTA,IGnTB,and IGnTC,and that the last of these is responsible for the I branching formation on red cells. In the present investigation,the K-562 cell line was used as a model to show that the i-to-I transition in erythroid differentiation is determined by the transcription factor CCAAT/enhancer binding protein alpha (C/EBPalpha),which enhances transcription of the IGnTC gene,consequently leading to formation of the I antigen. Further investigation suggested that C/EBPalpha IGnTC-activation activity is modulated at a posttranslational level,and that the phosphorylation status of C/EBPalpha may have a crucial effect. Results from studies using adult and cord erythropoietic cells agreed with those derived using the K-562 cell model,with lentiviral expression of C/EBPalpha in CD34(+) hemopoietic cells demonstrating the determining role of C/EBPalpha in the induction of the IGnTC gene as well as in I antigen expression. View Publication

Human cord blood (CB)-derived CD133+ cells carry characteristics of primitive hematopoietic cells and proffer an alternative for CD34+ cells in hematopoietic stem cell (HSC) transplantation. To characterize the CD133+ cell population on a genetic level,a global expression analysis of CD133+ cells was performed using oligonucleotide microarrays. CD133+ cells were purified from four fresh CB units by immunomagnetic selection. All four CD133+ samples showed significant similarity in their gene expression pattern,whereas they differed clearly from the CD133- control samples. In all,690 transcripts were differentially expressed between CD133+ and CD133- cells. Of these,393 were increased and 297 were decreased in CD133+ cells. The highest overexpression was noted in genes associated with metabolism,cellular physiological processes,cell communication,and development. A set of 257 transcripts expressed solely in the CD133+ cell population was identified. Colony-forming unit (CFU) assay was used to detect the clonal progeny of precursors present in the studied cell populations. The results demonstrate that CD133+ cells express primitive markers and possess clonogenic progenitor capacity. This study provides a gene expression profile for human CD133+ cells. It presents a set of genes that may be used to unravel the properties of the CD133+ cell population,assumed to be highly enriched in HSCs. View Publication

Although significant advances have been made over the last decade with respect to our understanding of stem cell biology,progress has been limited in the development of successful techniques for clinically significant ex vivo expansion of hematopoietic stem and progenitor cells. We here describe the effect of Notch ligand density on induction of Notch signaling and subsequent cell fate of human CD34+CD38- cord blood progenitors. Lower densities of Delta1(ext-IgG) enhanced the generation of CD34+ cells as well as CD14+ and CD7+ cells,consistent with early myeloid and lymphoid differentiation,respectively. However,culture with increased amounts of Delta1(ext-IgG) induced apoptosis of CD34+ precursors resulting in decreased cell numbers,without affecting generation of CD7+ cells. RNA interference studies revealed that the promotion of lymphoid differentiation was primarily mediated by Delta1 activation of Notch1. Furthermore,enhanced generation of NOD/SCID repopulating cells was seen following culture with lower but not higher densities of ligand. These studies indicate critical,quantitative aspects of Notch signaling in affecting hematopoietic precursor cell-fate outcomes and suggest that density of Notch ligands in different organ systems may be an important determinant in regulating cell-fate outcomes. Moreover,these findings contribute to the development of methodology for manipulation of hematopoietic precursors for therapeutic purposes. View Publication