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A quantitative trait locus (QTL) controlling HbF levels has previously been mapped to chromosome 6q23 in an Asian-Indian kindred with beta thalassemia and heterocellular hereditary persistence of fetal hemoglobin (HPFH). Five protein-coding genes,ALDH8A1,HBS1L,cMYB,AHI1,and PDE7B reside in this 1.5-megabase (Mb) candidate interval of 6q23. To direct sequencing efforts we compared the expression profiles of these 5 genes between 12 individuals with elevated and 14 individuals with normal HbF levels during adult erythropoiesis by real-time quantitative reverse transcription-polymerase chain reaction (RT-PCR). Two genes,cMYB and HBS1L,demonstrated simultaneous transcriptional down-regulation in individuals with elevated HbF levels. Transfection of K562 cells encoding human cDNA of cMYB and HBS1L genes showed that,although overexpression of ectopic cMYB inhibited gamma-globin gene expression,overexpression of HBS1L had no effect. Low levels of cMYB were associated with low cell expansions,accelerated erythroid maturation,and higher number of macrophages in erythroid cell culture. These observations suggest that differences in the intrinsic levels of cMYB may account for some of the variation in adult HbF levels. The possible mechanism of cMYB influencing gamma- to beta-globin switching is discussed. View Publication

Differentiation of embryonic stem (ES) cells typically requires cell-cell aggregation in the form of embryoid bodies (EBs). This process is not very well controlled and final cell numbers can be limited by EB agglomeration and the inability to drive differentiation towards a desired cell type. This study compares three-dimensional (3D) fibrin culture to conventional two-dimensional (2D) suspension culture and to culture in a semisolid methylcellulose medium solution. Two types of fibrin culture were evaluated,including a PEGylated fibrin gel. PEGylation with a difunctional PEG derivative retarded fibrinogen migration during through sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) as a result of crosslinking,similarly,degradation was slowed in the PEGylated gel. ES cell proliferation was higher in both the fibrin and PEGylated fibrin gels versus 2D and methylcellulose controls. FACS analysis and real-time-PCR revealed differences in patterns of differentiation for the various culture systems. Culture in PEGylated fibrin or methylcellulose culture demonstrated features characteristic of less extensive differentiation relative to fibrin and 2D culture as evidenced by the transcription factor Oct-4. Fibrin gels showed gene and protein expression similar to that in 2D culture. Both fibrin and 2D cultures demonstrated statistically greater cell numbers positive for the vascular mesoderm marker,VE-cadherin. View Publication

Ex vivo expansion of hematopoietic stem cells (HSCs) has been explored in the fields of stem cell biology,gene therapy,and clinical transplantation. Here,we demonstrate efficient ex vivo expansion of HSCs measured by long-term severe combined immunodeficient (SCID) repopulating cells (SRCs) from human cord blood CD133-sorted cells using a soluble form of Delta1. After a 3-week culture on immobilized Delta1 supplemented with stem cell factor,thrombopoietin,Flt-3 ligand,interleukin (IL)-3,and IL-6/soluble IL-6 receptor chimeric protein (FP6) in a serum- and stromal cell-free condition,we achieved approximately sixfold expansion of SRCs when evaluated by limiting dilution/transplantation assays. The maintenance of full multipotency and self-renewal capacity during culture was confirmed by transplantation to nonobese diabetic/SCID/gammac(null) mice,which showed myeloid,B,T,and natural killer cells as well as CD133(+)CD34(+) cells,and hematopoietic reconstitution in the secondary recipients. Interestingly,the CD133-sorted cells contained approximately 4.5 times more SRCs than the CD34-sorted cells. The present study provides a promising method to expand HSCs and encourages future trials on clinical transplantation. View Publication

Aldehyde dehydrogenase (ALDH) is an enzyme that is expressed in the liver and is required for the conversion of retinol (vitamin A) to retinoic acids. ALDH is also highly enriched in hematopoietic stem cells (HSCs) and is considered a selectable marker of human HSCs,although its contribution to stem cell fate remains unknown. In this study,we demonstrate that ALDH is a key regulator of HSC differentiation. Inhibition of ALDH with diethylaminobenzaldehyde (DEAB) delayed the differentiation of human HSCs that otherwise occurred in response to cytokines. Moreover,short-term culture with DEAB caused a 3.4-fold expansion in the most primitive assayable human cells,the nonobese diabetic/severe combined immunodeficiency mouse repopulating cells,compared with day 0 CD34(+)CD38(-)lin(-) cells. The effects of DEAB on HSC differentiation could be reversed by the coadministration of the retinoic acid receptor agonist,all-trans-retinoic acid,suggesting that the ability of ALDH to generate retinoic acids is important in determining HSC fate. DEAB treatment also caused a decrease in retinoic acid receptor-mediated signaling within human HSCs,suggesting directly that inhibition of ALDH promotes HSC self-renewal via reduction of retinoic acid activity. Modulation of ALDH activity and retinoid signaling is a previously unrecognized and effective strategy to amplify human HSCs. View Publication

Stem cell leukemia/T cell acute leukemia 1 (SCL/TAL1) plays a key role in the development of murine primitive hematopoiesis but its functions in adult definitive hematopoiesis are still unclear. Using lentiviral delivery of TAL1-directed shRNA in human hematopoietic cells,we show that decreased expression of TAL1 induced major disorders at different levels of adult hematopoietic cell development. Erythroid and myeloid cell production in cultures was dramatically decreased in TAL1-directed shRNA-expressing cells,whereas lymphoid B-cell development was normal. These results confirm the role of TAL1 in the erythroid compartment and show TLA1's implication in the function of myeloid committed progenitors. Moreover,long-term cultures and transplantation of TAL1-directed shRNA-expressing CD34+ cells into irradiated nonobese diabetic-severe combined immunodeficient (NOD-SCID) mice led to dramatically low levels of human cells of all lineages including the B-lymphoid lineage,strongly suggesting that TAL1 has a role in the early commitment of hematopoietic stem cells (HSCs) in humans. Cultures and transplantation experiments performed with mouse Sca1+ cells gave identical results. Altogether,these observations definitively show that TAL1 participates in the regulation of hematopoiesis from HSCs to myeloid progenitors,and pinpoint TAL1 as a master protein of human and murine adult hematopoiesis. View Publication

MafB is a member of the large Maf family of transcription factors that share similar basic region/leucine zipper DNA binding motifs and N-terminal activation domains. Although it is well known that MafB is specifically expressed in glomerular epithelial cells (podocytes) and macrophages,characterization of the null mutant phenotype in these tissues has not been previously reported. To investigate suspected MafB functions in the kidney and in macrophages,we generated mafB/green fluorescent protein (GFP) knock-in null mutant mice. MafB homozygous mutants displayed renal dysgenesis with abnormal podocyte differentiation as well as tubular apoptosis. Interestingly,these kidney phenotypes were associated with diminished expression of several kidney disease-related genes. In hematopoietic cells,GFP fluorescence was observed in both Mac-1- and F4/80-expressing macrophages in the fetal liver. Interestingly,F4/80 expression in macrophages was suppressed in the homozygous mutant,although development of the Mac-1-positive macrophage population was unaffected. In primary cultures of fetal liver hematopoietic cells,MafB deficiency was found to dramatically suppress F4/80 expression in nonadherent macrophages,whereas the Mac-1-positive macrophage population developed normally. These results demonstrate that MafB is essential for podocyte differentiation,renal tubule survival,and F4/80 maturation in a distinct subpopulation of nonadherent mature macrophages. View Publication

Activating mutations of c-KIT lead to ligand-independent growth. Internal tandem duplications (ITDs) of exon 11,which encodes the juxtamembrane domain (JMD),are constitutively activating mutations found in 7% of gastrointestinal stromal tumors (GISTs) but have not been described in childhood acute myeloid leukemia (AML). DNA and cDNA from 60 children with AML were screened by polymerase chain reaction (PCR) for mutations of the JMD. A complex ITD (kit cITD) involving exon 11 and exon 12 was identified with a relative frequency of 7% (4/60). The human kit cITDs were inserted into the murine c-Kit backbone and expressed in Ba/F3 cells. KIT cITD induced factorindependent growth and apoptosis resistance,and exhibited constitutive autophosphorylation. KIT cITD constitutively activated the PI3K/AKT pathway and phosphorylated STAT1,STAT3,STAT5,and SHP-2. Imatinib (IM) or rapamycin (Rap) led to complete inhibition of growth,with IC50 values at nanomolar levels. IM and Rap synergistically inhibited growth and surmounted KIT cITD-induced apoptosis resistance. IM but not LY294002 inhibited phosphorylation of STAT3 and STAT5,suggesting aberrant cross talk between PI3K- and STAT-activating pathways. The findings presented may have immediate therapeutic impact for a subgroup of childhood AML-expressing c-KIT mutations. View Publication

Adenosine deaminase (ADA) deficiency is caused by a purine metabolic dysfunction,leading to severe combined immunodeficiency (SCID) and multiple organ damage. To investigate the efficacy of ex vivo gene therapy with self-inactivating lentiviral vectors (LVs) in correcting this complex phenotype,we used an ADA(-/-) mouse model characterized by early postnatal lethality. LV-mediated ADA gene transfer into bone marrow cells combined with low-dose irradiation rescued mice from lethality and restored their growth,as did transplantation of wild-type bone marrow. Mixed chimerism with multilineage engraftment of transduced cells was detected in the long term in animals that underwent transplantation. ADA activity was normalized in lymphocytes and partially corrected in red blood cells (RBCs),resulting in full metabolic detoxification and prevention of severe pulmonary insufficiency. Moreover,gene therapy restored normal lymphoid differentiation and immune functions,including antigen-specific antibody production. Similar degrees of detoxification and immune reconstitution were obtained in mice treated early after birth or after 1 month of enzyme-replacement therapy,mimicking 2 potential applications for ADA-SCID. Overall,this study demonstrates the efficacy of LV gene transfer in correcting both the immunological and metabolic phenotypes of ADA-SCID and supports the future clinical use of this approach. View Publication

The effect of sustained exposure to nicotine,a major constituent of cigarette smoke,on hematopoiesis in the bone marrow (BM) and spleen was evaluated in a murine model. BALB/c mice were exposed to nicotine subcutaneously using 21-day slow-release pellets. Exposure to nicotine had no effect on the proliferation of long-term BM cultures or on their ability to form colonies. However,there was a significant decrease in the generation of lineage-specific progenitor cells,specifically eosinophil (colony-forming unit [CFU]-Eos) progenitors,in the BM of nicotine-exposed mice compared with control mice. Surprisingly,sustained exposure of mice to nicotine was found to induce significant hematopoiesis in the spleen. There was a significant increase in total colony formation as well as eosinophil-,granulocyte-macrophage-,and B-lymphocyte-specific progenitors (CFU-Eos,CFU-GM,and CFU-B,respectively) in nicotine-exposed mice but not in control mice. Sustained exposure to nicotine was associated with significant inhibition of rolling and migration of enriched hematopoietic stem/progenitor cells (HSPCs) across BM endothelial cells (BMECs) in vitro as well as decreased expression of beta2 integrin on the surface of these cells. Although sustained exposure to nicotine has only a modest effect on BM hematopoiesis,our studies indicate that it significantly induces extramedullary hematopoiesis in the spleen. Decreased interaction of nicotine-exposed HSPCs with BMECs (i.e.,rolling and migration) may result in altered BM homing of these cells,leading to their seeding and proliferation at extramedullary sites such as the spleen. View Publication

Retroviral vectors with long terminal repeats (LTRs),which contain strong enhancer/promoter sequences at both ends of their genome,are widely used for stable gene transfer into hematopoietic cells. However,recent clinical data and mouse models point to insertional activation of cellular proto-oncogenes as a dose-limiting side effect of retroviral gene delivery that potentially induces leukemia. Self-inactivating (SIN) retroviral vectors do not contain the terminal repetition of the enhancer/promoter,theoretically attenuating the interaction with neighboring cellular genes. With a new assay based on in vitro expansion of primary murine hematopoietic cells and selection in limiting dilution,we showed that SIN vectors using a strong internal retroviral enhancer/promoter may also transform cells by insertional mutagenesis. Most transformed clones,including those obtained after dose escalation of SIN vectors,showed insertions upstream of the third exon of Evi1 and in reverse orientation to its transcriptional orientation. Normalizing for the vector copy number,we found the transforming capacity of SIN vectors to be significantly reduced when compared with corresponding LTR vectors. Additional modifications of SIN vectors may further increase safety. Improved cell-culture assays will likely play an important role in the evaluation of insertional mutagenesis. View Publication

Hematopoietic progenitor cell trafficking is an important phenomenon throughout life. It is thought to occur in sequential steps,similar to what has been described for mature leukocytes. Molecular actors have been identified for each step of leukocyte migration; recently,CD99 was shown to play a part during transendothelial migration. We explored the expression and role of CD99 on human hematopoietic progenitors. We demonstrate that (1) CD34+ cells express CD99,albeit with various intensities; (2) subsets of CD34+ cells with high or low levels of CD99 expression produce different numbers of erythroid,natural killer (NK),or dendritic cells in the in vitro differentiation assays; (3) the level of CD99 expression is related to the ability to differentiate toward B cells; (4) CD34+ cells that migrate through an endothelial monolayer in response to SDF-1alpha and SCF display the highest level of CD99 expression; (5) binding of a neutralizing antibody to CD99 partially inhibits transendothelial migration of CD34+ progenitors in an in vitro assay; and (6) binding of a neutralizing antibody to CD99 reduces homing of CD34+ progenitors xenotransplanted in NOD-SCID mice. We conclude that expression of CD99 on human CD34+ progenitors has functional significance and that CD99 may be involved in transendothelial migration of progenitors. View Publication

Transcription factors are critical for instructing the development of B lymphocytes from multipotential progenitor cells in the bone marrow (BM). Here,we show that the absence of STAT3 impaired B-cell development. Mice selectively lacking STAT3 in BM progenitor cells displayed reduced numbers of mature B cells,both in the BM and in the periphery. The reduction in the B-cell compartment included reduced percentages and numbers of pro-B,pre-B,and immature B cells in the absence of STAT3,whereas the number of pre-pro-B cells was increased. We found that pro-B and pre-B-cell populations lacking STAT3 were hyporesponsive to IL-7 because of a decreased number of IL-7-responsive cells rather than decreased expression or signaling of IL-7Ralpha. Moreover,STAT3-deficient mice displayed enhanced apoptosis in the pro-B population when deprived of survival factors,suggesting that at least 2 mechanisms (impaired differentiation and enhanced apoptosis) are involved in the mutant phenotype. Last,BM transplantation confirmed that impaired B lymphopoiesis in the absence of STAT3 was caused by a cell autonomous defect. In sum,these studies defined a specific role for STAT3 in early B-cell development,probably acting at the pre-pro-B transition by contributing to the survival of IL-7-responsive progenitors. View Publication