技术资料

Efficient gene transfer into human hematopoietic stem cells (HSCs) is an important goal in the study of the hematopoietic system as well as for gene therapy of hematopoietic disorders. A lentiviral vector based on the human immunodeficiency virus (HIV) was able to transduce human CD34+ cells capable of stable,long-term reconstitution of nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. High-efficiency transduction occurred in the absence of cytokine stimulation and resulted in transgene expression in multiple lineages of human hematopoietic cells for up to 22 weeks after transplantation. View Publication

We report that embryonic stem cells efficiently undergo differentiation in vitro to mesoderm and hematopoietic cells and that this in vitro system recapitulates days 6.5 to 7.5 of mouse hematopoietic development. Embryonic stem cells differentiated as embryoid bodies (EBs) develop erythroid precursors by day 4 of differentiation,and by day 6,more than 85% of EBs contain such cells. A comparative reverse transcriptase-mediated polymerase chain reaction profile of marker genes for primitive endoderm (collagen alpha IV) and mesoderm (Brachyury) indicates that both cell types are present in the developing EBs as well in normal embryos prior to the onset of hematopoiesis. GATA-1,GATA-3,and vav are expressed in both the EBs and embryos just prior to and/or during the early onset of hematopoiesis,indicating that they could play a role in the early stages of hematopoietic development both in vivo and in vitro. The initial stages of hematopoietic development within the EBs occur in the absence of added growth factors and are not significantly influenced by the addition of a broad spectrum of factors,including interleukin-3 (IL-3),IL-1,IL-6,IL-11,erythropoietin,and Kit ligand. At days 10 and 14 of differentiation,EB hematopoiesis is significantly enhanced by the addition of both Kit ligand and IL-11 to the cultures. Kinetic analysis indicates that hematopoietic precursors develop within the EBs in an ordered pattern. Precursors of the primitive erythroid lineage appear first,approximately 24 h before precursors of the macrophage and definitive erythroid lineages. Bipotential neutrophil/macrophage and multilineage precursors appear next,and precursors of the mast cell lineage develop last. The kinetics of precursor development,as well as the growth factor responsiveness of these early cells,is similar to that found in the yolk sac and early fetal liver,indicating that the onset of hematopoiesis within the EBs parallels that found in the embryo. View Publication

Reliance on volunteer blood donors can lead to transfusion product shortages,and current liquid storage of red blood cells (RBCs) is associated with biochemical changes over time,known as 'the storage lesion'. Thus,there is a need for alternative sources of transfusable RBCs to supplement conventional blood donations. Extracorporeal production of stem cell-derived RBCs (stemRBCs) is a potential and yet untapped source of fresh,transfusable RBCs. A number of groups have attempted RBC differentiation from CD34+ cells. However,it is still unclear whether these stemRBCs could eventually be effective substitutes for traditional RBCs due to potential differences in oxygen carrying capacity,viability,deformability,and other critical parameters. We have generated ex vivo stemRBCs from primary human cord blood CD34+ cells and compared them to donor-derived RBCs based on a number of in vitro parameters. In vivo,we assessed stemRBC circulation kinetics in an animal model of transfusion and oxygen delivery in a mouse model of exercise performance. Our novel,chronically anemic,SCID mouse model can evaluate the potential of stemRBCs to deliver oxygen to tissues (muscle) under resting and exercise-induced hypoxic conditions. Based on our data,stem cell-derived RBCs have a similar biochemical profile compared to donor-derived RBCs. While certain key differences remain between donor-derived RBCs and stemRBCs,the ability of stemRBCs to deliver oxygen in a living organism provides support for further development as a transfusion product. View Publication

We show here that the process of megakaryocytic differentiation requires the presence of the recently discovered protein tescalcin. Tescalcin is dramatically upregulated during the differentiation and maturation of primary megakaryocytes or upon PMA-induced differentiation of K562 cells. This upregulation requires sustained signaling through the ERK pathway. Overexpression of tescalcin in K562 cells initiates events of spontaneous megakaryocytic differentiation,such as expression of specific cell surface antigens,inhibition of cell proliferation,and polyploidization. Conversely,knockdown of this protein in primary CD34+ hematopoietic progenitors and cell lines by RNA interference suppresses megakaryocytic differentiation. In cells lacking tescalcin,the expression of Fli-1,Ets-1,and Ets-2 transcription factors,but not GATA-1 or MafB,is blocked. Thus,tescalcin is essential for the coupling of ERK cascade activation with the expression of Ets family genes in megakaryocytic differentiation. View Publication

BACKGROUND: ALDH(br) cells express high aldehyde dehydrogenase (ALDH) activity and have progenitor cell activity in several contexts. We characterized human BM ALDH(br) cells to determine whether cell sorting based on ALDH activity isolates potentially useful populations for cell therapy. METHOD: We measured the expression of ALDH and cell-surface Ag by flow cytometry and compared the ability of sorted ALDH(br),and BM populations remaining after ALDH(br) cells were removed (ALDH(dim) populations),to develop into several cell lineages in culture. RESULTS: The ALDH(br) population comprised 1.2+/-0.8% (mean+/-SD,n=30) nucleated cells and was enriched in cells expressing CD34,CD117,CD105,CD127,CD133 and CD166,and in primitive CD34(+) CD38(-) and CD34(+) CD133(+) progenitors. Most of the CD34(+) and CD133(+) cells were ALDH(dim). ALDH(br) populations had 144-fold more hematopoietic colony-forming activity than ALDH(dim) cells and included all megakaryocyte progenitors. ALDH(br) populations readily established endothelial cell monolayers in cultures. Cells generating endothelial colonies in 7 days were 435-fold more frequent in ALDH(br) than ALDH(dim) populations. CFU-F were 9.5-fold more frequent in ALDH(br) than ALDH(dim) cells,and ALDH(br) cells gave rise to multipotential mesenchymal cell cultures that could be driven to develop into adipocytes,osteoblasts and chondrocytes. DISCUSSION: Hematopoietic,endothelial and mesenchymal progenitor cells can be isolated simultaneously from human BM by cell sorting based on ALDH activity. BM ALDH(br) populations may be useful in several cell therapy applications. View Publication

Efficient in vivo selection increases survival of gene-corrected hematopoietic stem cells (HSCs) and protects hematopoiesis,even if initial gene transfer efficiency is low. Moreover,selection of a limited number of transduced HSCs lowers the number of cell clones at risk of gene activation by insertional mutagenesis. However,a limited clonal repertoire greatly increases the proliferation stress of each individual clone. Therefore,understanding the impact of in vivo selection on proliferation and lineage differentiation of stem-cell clones is essential for its clinical use. We established minimal cell and drug dosage requirements for selection of P140K mutant O6-methylguanine-DNA-methyltransferase (MGMT P140K)-expressing HSCs and monitored their differentiation potential and clonality under long-term selective stress. Up to 17 administrations of O6-benzylguanine (O6-BG) and 1,3-bis(2-chloroethyl)-1-nitroso-urea (BCNU) did not impair long-term differentiation and proliferation of MGMT P140K-expressing stem-cell clones in mice that underwent serial transplantation and did not lead to clonal exhaustion. Interestingly,not all gene-modified hematopoietic repopulating cell clones were efficiently selectable. Our studies demonstrate that the normal function of murine hematopoietic stem and progenitor cells is not compromised by reduced-intensity long-term in vivo selection,thus underscoring the potential value of MGMT P140K selection for clinical gene therapy. View Publication

BACKGROUND AND OBJECTIVES: Primitive human hematopoietic cells contain higher levels of aldehyde dehydrogenase (ALDH) activity than their terminally differentiating progeny but the particular stages when ALDH levels change have not been well defined. The objective of this study was to compare ALDH levels among the earliest stages of hematopoietic cell differentiation and to determine whether these could be exploited to obtain improved purity of human cord blood cells with long-term lympho-myeloid repopulating activity in vivo. DESIGN AND METHODS: ALDEFLUOR-stained human cord blood cells displaying different levels of ALDH activity were first analyzed for co-expression of various surface markers. Subsets of these cells were then isolated by multi-parameter flow cytometry and assessed for short-and long-term repopulating activity in sublethally irradiated immunodeficient mice. RESULTS: Most short-term myeloid repopulating cells (STRC-M) and all long-term lympho-myeloid repopulating cells (LTRC-ML) stained selectively as ALDH+. Limiting dilution analysis of the frequencies of both STRC-M and LTRC-ML showed that they were similarly and most highly enriched in the 10% top ALDH+ cells. Removal of cells expressing CD2,CD3,CD7,CD14,CD16,CD24,CD36,CD38,CD56,CD66b,or glycophorin A from the ALDH+ low-density fraction of human cord blood cells with low light side-scattering properties yielded a population containing LTRC-ML at a frequency of 1/360. INTERPRETATION AND CONCLUSION: Elevated ALDH activity is a broadly inclusive property of primitive human cord blood cells that,in combination with other markers,allows easy isolation of the stem cell fraction at unprecedented purities. View Publication

Chronic phase-to-blast crisis transition in chronic myelogenous leukemia (CML) is associated with differentiation arrest and down-regulation of C/EBPalpha,a transcription factor essential for granulocyte differentiation. Patients with CML in blast crisis (CML-BC) became rapidly resistant to therapy with the breakpoint cluster region-Abelson murine leukemia (BCR/ABL) kinase inhibitor imatinib (STI571) because of mutations in the kinase domain that interfere with drug binding. We show here that the restoration of C/EBPalpha activity in STI571-sensitive or -resistant 32D-BCR/ABL cells induced granulocyte differentiation,inhibited proliferation in vitro and in mice,and suppressed leukemogenesis. Moreover,activation of C/EBPalpha eradicated leukemia in 4 of 10 and in 6 of 7 mice injected with STI571-sensitive or -resistant 32D-BCR/ABL cells,respectively. Differentiation induction and proliferation inhibition were required for optimal suppression of leukemogenesis,as indicated by the effects of p42 C/EBPalpha,which were more potent than those of K298E C/EBPalpha,a mutant defective in DNA binding and transcription activation that failed to induce granulocyte differentiation. Activation of C/EBPalpha in blast cells from 4 patients with CML-BC,including one resistant to STI571 and BMS-354825 and carrying the T315I Abl kinase domain mutation,also induced granulocyte differentiation. Thus,these data indicate that C/EBPalpha has potent antileukemia effects even in cells resistant to ATP-binding competitive tyrosine kinase inhibitors,and they portend the development of anti-leukemia therapies that rely on C/EBPalpha activation. View Publication

The mechanisms underlying deregulation of HOX gene expression in AML are poorly understood. The ParaHox gene CDX2 was shown to act as positive upstream regulator of several HOX genes. In this study,constitutive expression of Cdx2 caused perturbation of leukemogenic Hox genes such as Hoxa10 and Hoxb8 in murine hematopoietic progenitors. Deletion of the N-terminal domain of Cdx2 abrogated its ability to perturb Hox gene expression and to cause acute myeloid leukemia (AML) in mice. In contrast inactivation of the putative Pbx interacting site of Cdx2 did not change the leukemogenic potential of the gene. In an analysis of 115 patients with AML,expression levels of CDX2 were closely correlated with deregulated HOX gene expression. Patients with normal karyotype showed a 14-fold higher expression of CDX2 and deregulated HOX gene expression compared with patients with chromosomal translocations such as t(8:21) or t(15;17). All patients with AML with normal karyotype tested were negative for CDX1 and CDX4 expression. These data link the leukemogenic potential of Cdx2 to its ability to dysregulate Hox genes. They furthermore correlate the level of CDX2 expression with HOX gene expression in human AML and support a potential role of CDX2 in the development of human AML with aberrant Hox gene expression. View Publication