Cynthia E Dunbar

National Heart, Lung, and Blood Institute, 베서스다, Maryland, United States

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Publications (240)1853.75 Total impact

  • Leukemia Research 04/2015; 39:S26-S27. DOI:10.1016/S0145-2126(15)30057-6 · 2.69 Impact Factor
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    ABSTRACT: The high risk of insertional oncogenesis reported in clinical trials utilizing integrating retroviral vectors to genetically-modify hematopoietic stem and progenitor cells (HSPC) requires the development of safety strategies to minimize risks associated with novel cell and gene therapies. The ability to ablate genetically modified cells in vivo is desirable, should an abnormal clone emerge. Inclusion of “suicide genes” in vectors to facilitate targeted ablation of vector-containing abnormal clones in vivo is one potential safety approach. We tested whether the inclusion of the “inducible Caspase-9” (iCasp9) suicide gene in a gamma-retroviral vector facilitated efficient elimination of vector-containing HSPCs and their hematopoietic progeny in vivo long-term, in an autologous non-human primate transplantation model. Following stable engraftment of iCasp9 expressing hematopoietic cells in rhesus macaques, administration of AP1903, a chemical inducer of dimerization able to activate iCasp9, specifically eliminated vector-containing cells in all hematopoietic lineages long-term, suggesting activity at the HSPC level. Between 75-94% of vector-containing cells were eliminated by well-tolerated AP1903 dosing, but lack of complete ablation was linked to lower iCasp9 expression in residual cells. Further investigation of resistance mechanisms demonstrated upregulation of Bcl-2 in hematopoietic cell lines transduced with the vector and resistant to AP1903 ablation. These results demonstrate both the potential and the limitations of safety approaches utilizing iCasp9 to HSPC-targeted gene therapy settings, in a model with great relevance to clinical development. Stem Cells 2014
    Stem Cells 01/2015; 33(1). DOI:10.1002/stem.1869 · 7.70 Impact Factor
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    ABSTRACT: The treatment of aplastic anemia is currently with immunosuppressive therapy (IST) with anti-thymocyte globulin (ATG) and cyclosporine, to which two thirds of patients respond. However, a significant proportion of these responders relapse and many have persistent cytopenias. The management of these patients is challenging. Modifications to this standard approach using alternative immunosuppressive agents or adding hematopoietic cytokines such as granulocyte colony-stimulating factor (G-CSF) and erythropoietin (EPO) have not improved outcome. A recent trial has shown that eltrombopag, a thrombopoeitin mimetic, is efficacious in the treatment of patients with severe aplastic anemia (SAA) refractory to IST. There is evidence that this drug works by directly stimulating marrow stem and progenitor cells thereby promoting hematopoietic recovery in patients with bone marrow failure. Several trials are ongoing in our institution using this very promising drug in combination therapy in the upfront treatment of SAA, in IST-refractory SAA and in moderate disease. Published by Elsevier Inc.
    Seminars in Hematology 01/2015; 52(1):31-37. DOI:10.1053/j.seminhematol.2014.10.002 · 2.46 Impact Factor
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    ABSTRACT: Dyskeratosis congenita (DC) is an inherited multi-system disorder, characterized by oral leukoplakia, nail dystrophy, and abnormal skin pigmentation, as well as high rates of bone marrow failure, solid tumors, and other medical problems such as osteopenia. DC and telomere biology disorders (collectively referred to as TBD here) are caused by germline mutations in telomere biology genes leading to very short telomeres and limited proliferative potential of hematopoietic stem cells. We found that skeletal stem cells (SSCs) within the bone marrow stromal cell population (BMSCs, also known as bone marrow-derived mesenchymal stem cells), may contribute to the hematological phenotype. TBD-BMSCs exhibited reduced clonogenicity, spontaneous differentiation into adipocytes and fibrotic cells, and increased senescence in vitro. Upon in vivo transplantation into mice, TBD-BMSCs failed to form bone or support hematopoiesis, unlike normal BMSCs. TERC reduction (a TBD-associated gene) in normal BMSCs by siTERC-RNA recapitulated the TBD-BMSC phenotype by reducing proliferation and secondary colony forming efficiency, and by accelerating senescence in vitro. Microarray profiles of control and siTERC-BMSCs showed decreased hematopoietic factors at the mRNA level, and decreased secretion of factors at the protein level. These findings are consistent with defects in SSCs/BMSCs contributing to bone marrow failure in TBD. Copyright © 2014 American Society of Hematology.
    Blood 12/2014; Blood Online First Edition(Advance Online Publication). DOI:10.1182/blood-2014-06-566810 · 10.43 Impact Factor
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    ABSTRACT: There are 5 genetic forms of chronic granulomatous disease (CGD), resulting from mutations in any of 5 subunits of phagocyte oxidase, an enzyme complex in neutrophils, monocytes and macrophages that produces microbicidal reactive oxygen species. We generated induced pluripotent stem cells (iPSCs) from peripheral blood CD34(+) hematopoietic stem cells of patients with each of 5 CGD genotypes. We used zinc finger nuclease (ZFN) targeting the AAVS1 safe harbor site together with CGD genotype-specific minigene plasmids with flanking AAVS1 sequence to target correction of iPSC representing each form of CGD. We achieved targeted insertion with constitutive expression of desired oxidase subunit in 70-80% percent of selected iPSC clones. Neutrophils and macrophages differentiated from corrected CGD iPSCs demonstrated restored oxidase activity and antimicrobial function against CGD bacterial pathogens Staphylococcus aureus and Granulibacter bethesdensis. Using a standard platform that combines iPSC generation from peripheral blood CD34(+) cells and ZFN mediated AAVS1 safe harbor minigene targeting, we demonstrate efficient generation of genetically corrected iPSCs using an identical approach for all 5 genetic forms of CGD. This safe harbor minigene targeting platform is broadly applicable to a wide range of inherited single gene metabolic disorders.Molecular Therapy (2014); doi:10.1038/mt.2014.195.
    Molecular Therapy 10/2014; 23(1). DOI:10.1038/mt.2014.195 · 6.43 Impact Factor
  • Daniela Malide, Jean-Yves Metais, Cynthia E. Dunbar
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    ABSTRACT: We developed and validated a fluorescent marking methodology for clonal tracking of hematopoietic stem and progenitor cells (HSPCs) with high spatial and temporal resolution to study in vivo hematopoiesis using the murine bone marrow transplant experimental model. Genetic combinatorial marking using lentiviral vectors encoding fluorescent proteins (FPs) enabled cell fate mapping through advanced microscopy imaging. Vectors encoding five different FPs: Cerulean, EGFP, Venus, tdTomato, and mCherry were used to concurrently transduce HSPCs, creating a diverse palette of color marked cells. Imaging using confocal/two-photon hybrid microscopy enables simultaneous high resolution assessment of uniquely marked cells and their progeny in conjunction with structural components of the tissues. Volumetric analyses over large areas reveal that spectrally coded HSPC-derived cells can be detected non-invasively in various intact tissues, including the bone marrow (BM), for extensive periods of time following transplantation. Live studies combining video-rate multiphoton and confocal time-lapse imaging in 4D demonstrate the possibility of dynamic cellular and clonal tracking in a quantitative manner.
    Journal of Visualized Experiments 08/2014; DOI:10.3791/51669
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    ABSTRACT: Myeloid derived suppressor cells (MDSCs) play a critical role in suppression of immune responses in cancer and inflammation. Here, we describe how regulation of Bcl2a1 by cytokines controls the suppressor function of CD11b(+) Gr-1(high) granulocytic MDSCs. Co-culture of CD11b(+) Gr-1(high) granulocytic MDSCs with antigen-stimulated T cells and simultaneous blockade of IFN-γ by the use of anti-IFN-γ blocking antibody, IFN-γ(-/-) effector T cells, IFN-γR(-/-) MDSCs or STAT1(-/-) MDSCs led to up-regulation of Bcl2a1 in CD11b(+) Gr-1(high) cells, improved survival and enhanced their suppressor function. Molecular studies revealed that GM-CSF released by antigen-stimulated CD8(+) T cells induced Bcl2a1 up-regulation, which was repressed in the presence of IFN-γ by a direct interaction of phosphorylated STAT-1 with the Bcl2a1 promotor. Bcl2a1 overexpressing granulocytic MDSCs demonstrated prolonged survival and enhanced suppressor function in vitro. Our data suggest that IFN-γ/ STAT1-dependent regulation of Bcl2a1 regulates survival and thereby suppressor function of granulocytic MDSCs. This article is protected by copyright. All rights reserved.
    European Journal of Immunology 08/2014; 44(8). DOI:10.1002/eji.201444497 · 4.52 Impact Factor
  • Bone Marrow Transplantation 07/2014; DOI:10.1038/bmt.2014.162 · 3.47 Impact Factor
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    ABSTRACT: Induced pluripotent stem cell (iPSC)-based cell therapies have great potential for regenerative medicine but are also potentially associated with tumorigenic risks. Current rodent models are not optimal predictors of efficiency and safety for clinical application. Therefore, we developed a clinically relevant nonhuman primate model to assess the tumorigenic potential and in vivo efficacy of both undifferentiated and differentiated iPSCs in autologous settings without immunosuppression. Undifferentiated autologous iPSCs indeed form mature teratomas in a dose-dependent manner. However, tumor formation is accompanied by an inflammatory reaction. On the other hand, iPSC-derived mesodermal stromal-like cells form new bone in vivo without any evidence of teratoma formation. We therefore show in a large animal model that closely resembles human physiology that undifferentiated autologous iPSCs form teratomas, and that iPSC-derived progenitor cells can give rise to a functional tissue in vivo.
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    ABSTRACT: In mice, clonal tracking of hematopoietic stem cells (HSCs) has revealed variations in repopulation characteristics. However, it is unclear whether similar properties apply in primates. Here, we examined this issue through tracking of thousands of hematopoietic stem and progenitor cells (HSPCs) in rhesus macaques for up to 12 years. Approximately half of the clones analyzed contributed to long-term repopulation (over 3-10 years), arising in sequential groups and likely representing self-renewing HSCs. The remainder contributed primarily for the first year. The long-lived clones could be further subdivided into functional groups contributing primarily to myeloid, lymphoid, or both myeloid and lymphoid lineages. Over time, the 4%-10% of clones with robust dual lineage contribution predominated in repopulation. HSPCs expressing a CCR5 shRNA transgene behaved similarly to controls. Our study therefore documents HSPC behavior in a clinically relevant model over a long time frame and provides a substantial system-level data set that is a reference point for future work.
    Cell stem cell 04/2014; 14(4):473-85. DOI:10.1016/j.stem.2013.12.012 · 22.15 Impact Factor
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    ABSTRACT: Analysis of hematopoietic stem cell function in nonhuman primates provides insights that are relevant for human biology and therapeutic strategies. In this study, we applied quantitative genetic barcoding to track the clonal output of transplanted autologous rhesus macaque hematopoietic stem and progenitor cells over a time period of up to 9.5 months. We found that unilineage short-term progenitors reconstituted myeloid and lymphoid lineages at 1 month but were supplanted over time by multilineage clones, initially myeloid restricted, then myeloid-B clones, and then stable myeloid-B-T multilineage, long-term repopulating clones. Surprisingly, reconstitution of the natural killer (NK) cell lineage, and particularly the major CD16(+)/CD56(-) peripheral blood NK compartment, showed limited clonal overlap with T, B, or myeloid lineages, and therefore appears to be ontologically distinct. Thus, in addition to providing insights into clonal behavior over time, our analysis suggests an unexpected paradigm for the relationship between NK cells and other hematopoietic lineages in primates.
    Cell stem cell 04/2014; 14(4):486-99. DOI:10.1016/j.stem.2014.01.020 · 22.15 Impact Factor
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    ABSTRACT: Induced pluripotent stem cell (iPSC) therapies offer a promising path for patient-specific regenerative medicine. However, tumor formation from residual undifferentiated iPSC or transformation of iPSC or their derivatives is a risk. Inclusion of a suicide gene is one approach to risk mitigation. We introduced a dimerizable-"inducible caspase-9" (iCasp9) suicide gene into mouse iPSC (miPSC) and rhesus iPSC (RhiPSC) via a lentivirus, driving expression from either a cytomegalovirus (CMV), elongation factor-1 α (EF1α) or pluripotency-specific EOS-C(3+) promoter. Exposure of the iPSC to the synthetic chemical dimerizer, AP1903, in vitro induced effective apoptosis in EF1α-iCasp9-expressing (EF1α)-iPSC, with less effective killing of EOS-C(3+)-iPSC and CMV-iPSC, proportional to transgene expression in these cells. AP1903 treatment of EF1α-iCasp9 miPSC in vitro delayed or prevented teratomas. AP1903 administration following subcutaneous or intravenous delivery of EF1α-iPSC resulted in delayed teratoma progression but did not ablate tumors. EF1α-iCasp9 expression was downregulated during in vitro and in vivo differentiation due to DNA methylation at CpG islands within the promoter, and methylation, and thus decreased expression, could be reversed by 5-azacytidine treatment. The level and stability of suicide gene expression will be important for the development of suicide gene strategies in iPSC regenerative medicine.
    01/2014; 1:14053. DOI:10.1038/mtm.2014.53
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    ABSTRACT: About a quarter of patients with severe aplastic anemia (SAA) remain pancytopenic despite immunosuppressive therapy. We have previously demonstrated that eltrombopag has efficacy in this setting with 44% (11/25) of patients having clinically significant hematologic responses. We now report safety and efficacy data on a further 18 patients and long term follow up on the entire cohort of 43 patients. The overall response rate was 17/43 (40%) at 3-4 months, including tri and bi-lineage responses. The majority of patients who remained on eltrombopag in an extension study (14/17) continued to show improvement, and 7 eventually had significant increases in neutrophil, red cell and platelet lineages. Five patients with robust near-normalization of blood counts had drug discontinued at a median of 28.5 months after entry (range 9 to 37), and all maintained stable counts a median of 13 months (range 1-15) off eltrombopag. 8 patients, including 6 non-responders and 2 responders, developed new cytogenetic abnormalities on eltrombopag, including 5 with chromosome 7 loss or partial deletion. None evolved to acute myeloid leukemia to date. Eltrombopag is efficacious in a subset of patients with aplastic anemia refractory to IST, with frequent multilineage responses, and maintenance of normalized hematopoiesis off treatment. This study is registered at, identifier: NCT00922883.
    Blood 12/2013; 123(12). DOI:10.1182/blood-2013-10-534743 · 10.43 Impact Factor
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    ABSTRACT: Plerixafor (Mozobil) is a CXCR4 antagonist that rapidly mobilizes CD34(+) cells into circulation. Recently, plerixafor has been used as a single agent to mobilize peripheral blood stem cells for allogeneic hematopoietic cell transplantation. Although G-CSF mobilization is known to alter the phenotype and cytokine polarization of transplanted T cells, the effects of plerixafor mobilization on T cells have not been well characterized. In this study, we show that alterations in the T cell phenotype and cytokine gene expression profiles characteristic of G-CSF mobilization do not occur after mobilization with plerixafor. Compared with nonmobilized T cells, plerixafor-mobilized T cells had similar phenotype, mixed lymphocyte reactivity, and Foxp3 gene expression levels in CD4(+) T cells, and did not undergo a change in expression levels of 84 genes associated with Th1/Th2/Th3 pathways. In contrast with plerixafor, G-CSF mobilization decreased CD62L expression on both CD4 and CD8(+) T cells and altered expression levels of 16 cytokine-associated genes in CD3(+) T cells. To assess the clinical relevance of these findings, we explored a murine model of graft-versus-host disease in which transplant recipients received plerixafor or G-CSF mobilized allograft from MHC-matched, minor histocompatibility-mismatched donors; recipients of plerixafor mobilized peripheral blood stem cells had a significantly higher incidence of skin graft-versus-host disease compared with mice receiving G-CSF mobilized transplants (100 versus 50%, respectively, p = 0.02). These preclinical data show plerixafor, in contrast with G-CSF, does not alter the phenotype and cytokine polarization of T cells, which raises the possibility that T cell-mediated immune sequelae of allogeneic transplantation in humans may differ when donor allografts are mobilized with plerixafor compared with G-CSF.
    The Journal of Immunology 11/2013; 191(12). DOI:10.4049/jimmunol.1301148 · 5.36 Impact Factor
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    ABSTRACT: Hematopoietic stem cell (HSC) gene therapy using integrating vectors has a potential leukemogenic risk due to insertional mutagenesis. To reduce this risk, a limitation of ≤2 average vector copy number (VCN) per cell is generally accepted. We developed an assay for VCN among transduced CD34(+) cells that reliably predicts in vivo VCN in 16 rhesus recipients of CD34(+) cells transduced with a green fluorescent protein (GFP) (or yellow fluorescent protein (YFP))-encoding lentiviral vector. Using GFP (or YFP)-specific probe/primers by real-time PCR, VCN among transduced CD34(+) cells had no correlation with VCN among granulocytes or lymphocytes in vivo assayed 6 months post-transplantation. This was a likely result of residual plasmids present in the vector preparation. We then designed self-inactivating long terminal repeat (SIN-LTR)-specific probe/primers, which detect only integrated provirus. Evaluation with SIN-LTR probe/primers resulted in a positive correlation of VCN among transduced CD34(+) cells with granulocytes and lymphocytes in vivo. The transduced CD34(+) cells had higher VCN (25.1 ± 5.6) as compared with granulocytes (2.8 ± 1) and lymphocytes (2.4 ± 0.7). In summary, an integrated provirus-specific real-time PCR system demonstrated nine- to tenfold higher VCN in transduced CD34(+) cells in vitro, as compared with VCN in vivo. Therefore, the restriction of ≤2 VCN before infusion might unnecessarily limit gene transfer efficacy.Molecular Therapy-Nucleic Acids (2013) 2, e122; doi:10.1038/mtna.2013.49; published online 17 September 2013.
    09/2013; 2(9):e122. DOI:10.1038/mtna.2013.49
  • Cancer Research 08/2013; 73(8 Supplement):467-467. DOI:10.1158/1538-7445.AM2013-467 · 9.28 Impact Factor
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    ABSTRACT: The occurrence of clonal perturbations and leukemia in patients transplanted with gamma retroviral vector-transduced autologous hematopoietic stem and progenitor cells (HSPCs) has stimulated extensive investigation, demonstrating that proviral insertions mayperturb adjacent proto-oncogene expression. Although enhancer-deleted lentiviruses are less likely to result in insertional oncogenesis, there is evidence that they may perturb transcript splicing, and one patient with a benign clonal expansion of lentivirally-transduced HPSC has been reported. The rhesus macaque model provides an opportunity for informative long-term analysis to ask whether transduction impacts on long-term HSPCproperties. We utilized two techniques to examine whether lentivirally-transduced HSPCs from eight rhesus macaques transplanted 1-13.5 years previously are perturbed at a population level, comparing telomere length as a measure of replicative history and gene expression profile of vector positive versus vector negative cells. There were no differences in telomere lengths between sorted GFP+ and GFP- blood cells, suggesting that lentiviral transduction did not globally disrupt replicative patterns. Bone marrow GFP+ and GFP- CD34+ cells showed no differences in gene expression using unsupervised and principal component analysis. These studies did not uncover any global long-term perturbation of proliferation, differentiation, or other important functional parameters of transduced HSPCs in the rhesus macaque model.Molecular Therapy (2013); accepted article preview online 18 July 2013; doi:10.1038/mt.2013.168.
    Molecular Therapy 07/2013; 22(1). DOI:10.1038/mt.2013.168 · 6.43 Impact Factor
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    ABSTRACT: Chronic GVHD (cGVHD) is a major complication of allogeneic hematopoietic SCT. Post transplant thrombocytopenia in patients with cGVHD has been associated with poor outcome and its etiology is unclear. We investigated whether thrombopoiesis, assessed via measurement of the absolute immature platelet number (AIPN) in the blood, is impaired in cGVHD, and whether the level of thrombopoiesis correlates with the severity and activity of cGVHD as assessed via the National Institutes of Health (NIH) organ scoring system. We used a cohort of 110 well-characterized cGVHD patients, including 83 (75%) with severe cGVHD per NIH global score. Higher AIPN was associated with active therapeutic intent (P=0.026), lower Karnofsky score (P=0.0013), worse joint/fascia cGVHD (P=0.0005) and worse skin cGVHD (P=0.0044). AIPN correlated with platelet counts and was not correlated with ANC, WBC, C-reactive protein (CRP), absolute lymphocyte count (ALC), albumin, total and average NIH scores, or number of prior systemic therapies. AIPN values for cGVHD patients substantially overlapped those of the normal population. Higher AIPN, as marker of active thrombopoiesisis, was associated with worse severity and activity of cGVHD, especially skin and joints/fascia manifestations. Among patients with stable moderate or severe cGVHD, there was no evidence of hypoproduction of platelets. Future studies should further investigate the role of thrombopoiesis in cGVHD.Bone Marrow Transplantation advance online publication, 8 July 2013; doi:10.1038/bmt.2013.95.
    Bone marrow transplantation 07/2013; 48(12). DOI:10.1038/bmt.2013.95 · 3.47 Impact Factor
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    ABSTRACT: Aplastic anemia is a bone marrow failure syndrome that causes pancytopenia and can lead to life-threatening complications. Bone marrow transplantation remains the standard of care for younger patients and those with a good performance status but many patients may not have a suitable donor. Immunosuppressive therapy is able to resolve cytopenias in a majority of patients with aplastic anemia but relapses are not uncommon and some patients remain refractory to this approach. Patients may require frequent blood and platelet transfusion support which is expensive and inconvenient. Life-threatening bleeding complications still occur despite prophylactic platelet transfusion. Thrombopoietin (TPO) mimetics, such as romiplostim and eltrombopag, were developed to treat patients with refractory immune thrombocytopenia but are now being investigated for the treatment of bone marrow failure syndromes. TPO is the main regulator for platelet production and its receptor (c-Mpl) is present on megakaryocytes and hematopoietic stem cells. Trilineage hematopoietic responses were observed in a recent clinical trial using eltrombopag in patients with severe aplastic anemia refractory to immunosuppression suggesting that these agents can provide a new therapeutic option for enhancing blood production. In this review, we discuss these recent results and ongoing investigation of TPO mimetics for aplastic anemia and other bone marrow failure states like myelodysplastic syndromes. Clonal evolution or progression to acute myeloid leukemia remains a concern when using these drugs in bone marrow failure and patients should only be treated in the setting of a clinical trial.
    International journal of hematology 05/2013; 98(1). DOI:10.1007/s12185-013-1352-6 · 1.68 Impact Factor
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    ABSTRACT: Critically short telomeres activate p53-mediated apoptosis, resulting in organ failure and leading to malignant transformation. Mutations in genes responsible for telomere maintenance are linked to a number of human diseases. We derived induced pluripotent stem cells (iPSCs) from 4 patients with aplastic anemia or hypocellular bone marrow carrying heterozygous mutations in the telomerase reverse transcriptase (TERT) or the telomerase RNA component (TERC) telomerase genes. Both mutant and control iPSCs upregulated TERT and TERC expression compared with parental fibroblasts, but mutant iPSCs elongated telomeres at a lower rate compared with healthy iPSCs, and the deficit correlated with the mutations' impact on telomerase activity. There was no evidence for alternative lengthening of telomere (ALT) pathway activation. Elongation varied among iPSC clones derived from the same patient and among clones from siblings harboring identical mutations. Clonal heterogeneity was linked to genetic and environmental factors, but was not influenced by residual expression of reprogramming transgenes. Hypoxia increased telomere extension in both mutant and normal iPSCs. Additionally, telomerase-mutant iPSCs showed defective hematopoietic differentiation in vitro, mirroring the clinical phenotype observed in patients and demonstrating that human telomere diseases can be modeled utilizing iPSCs. Our data support the necessity of studying multiple clones when using iPSCs to model disease.
    The Journal of clinical investigation 05/2013; 123(5). DOI:10.1172/JCI67146 · 13.77 Impact Factor

Publication Stats

11k Citations
1,853.75 Total Impact Points

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  • 1989–2015
    • National Heart, Lung, and Blood Institute
      • Hematology Branch
      베서스다, Maryland, United States
  • 1989–2011
    • National Institutes of Health
      • • Department of Laboratory Medicine
      • • Branch of Dermatology
      • • Branch of Molecular and Clinical Hematology (MCHB)
      베서스다, Maryland, United States
  • 2005–2006
    • University of Freiburg
      Freiburg, Baden-Württemberg, Germany
    • University of Ferrara
      Ferrare, Emilia-Romagna, Italy
  • 2002
    • University of Texas MD Anderson Cancer Center
      Houston, Texas, United States
  • 2001–2002
    • The National Institute of Diabetes and Digestive and Kidney Diseases
      베서스다, Maryland, United States
    • Mayo Clinic - Rochester
      Rochester, Minnesota, United States
  • 2000
    • Jichi Medical University
      • Department of Genetic Therapeutics
      Totigi, Tochigi, Japan
  • 1997
    • University of Massachusetts Medical School
      Worcester, Massachusetts, United States
  • 1995
    • Cincinnati Children's Hospital Medical Center
      Cincinnati, Ohio, United States
  • 1994
    • St. Jude Children's Research Hospital
      Memphis, Tennessee, United States