Comparative study of hematopoietic differentiation between human embryonic stem cell lines

Directed differentiation of human embryonic stem cells (hESCs) into any desired cell type has been hailed as a therapeutic promise to cure many human diseases. However, substantial roadblocks still exist for in vitro differentiation of hESCs into distinct cell types, including T lymphocytes. Here we examined the hematopoietic differentiation potential of six different hESC lines. We compare their ability to develop into CD34(+) or CD34(+)CD45(+) hematopoietic precursor populations under several differentiation conditions. Comparison of lymphoid potential of hESC derived- and fetal tissue derived-hematopoietic precursors was also made. We found diverse hematopoietic potential between hESC lines depending on the culture or passage conditions. In contrast to fetal-derived hematopoietic precursors, none of the CD34(+) precursors differentiated from hESCs were able to develop further into T cells. These data underscore the difficulties in the current strategy of hESC forward differentiation and highlight distinct differences between CD34(+) hematopoietic precursors generated in vitro versus in vivo.     

Expression of the human gamma-globin gene after retroviral transfer to transformed erythroid cells.

Regulation of the human fetal (gamma) globin gene and a series of mutant gamma-globin genes was studied after retroviral transfer into erythroid cells with fetal or adult patterns of endogenous globin gene expression. Steady-state RNA from a virally transferred A gamma-globin gene with a normal promoter increased after induction of erythroid maturation of murine erythroleukemia cells and comprised from 2% to 23% of the mouse beta maj-globin RNA level. RNA expression from the virally transferred A gamma-globin gene comprised 23% of the endogenous G gamma- + A gamma-globin expression in K 562 cells after treatment with hemin. Expression from a virally transferred gamma- or beta-globin gene exceeded endogenous gamma- or beta-globin expression by a factor of 6 or more in the human erythroleukemia line KMOE, in which the endogenous globin genes are weakly inducible. In these experiments, no difference in expression was observed between the gene with the normal promoter and an A gamma-globin gene with a point mutation in its promoter (-196 C-to-T) that has been associated with hereditary persistence of fetal hemoglobin (HPFH). To test for cis-acting determinants located within the introns of the gamma-globin gene, expression was measured from a set of gamma-globin genes configured with either intron alone or with neither intron. In contrast to an intronless beta-globin gene, which is not expressed in MEL cells, the intronless gamma-globin gene was expressed in MEL cells at 24% of the level of an intron-containing gene.(ABSTRACT TRUNCATED AT 250 WORDS)     

Bacterial infection of human hematopoietic stem cells induces monocytic differentiation

Differentiation of hematopoietic stem cells (HSCs) can be influenced by different stimuli, including cytotoxic agents, certain cytokines, and contact with pathogens. Infection may result in dysregulation of these important progenitor cells and therefore interfere with the availability of blood cells. In this study we analyzed the effect of bacterial infection on HSCs concerning surface marker expression and cytokine release. Listeria monocytogenes and Yersinia enterocolitica accelerated maturation of hematopoietic progenitor cells along the myeloid lineage, as demonstrated by the upregulation of CD13, CD14, and costimulatory signals. By screening cytokine secretion, granulocyte-macrophage colony-stimulating factor, interleukin (IL)-6, IL-8, IL-10, IL-12, and tumor necrosis factor-alpha were found to be induced by bacterial infection. These data indicate that infection of HSCs with L. monocytogenes and Y. enterocolitica affects the differentiation of CD34(+) hematopoietic progenitors in vitro and may lead to secretion of cytokines that can influence the HSC differentiation capacity and immune response.     

Advances in retroviral transduction of hematopoietic stem cells for the gene therapy of atherosclerosis

PURPOSE OF REVIEW: Atherosclerosis is a chronic inflammatory disease that is the primary cause of morbidity and mortality in the developed world. Many studies have shown that macrophages and T-cells play critical roles in multiple aspects of the pathogenesis of the disease. Given that these cells are ultimately derived from bone marrow precursors, the concept of performing gene therapy for atherosclerosis through the retroviral transduction of hematopoietic stem cells has received much attention. This review will highlight recent advances that will help bring this goal closer. RECENT FINDINGS: The clinical application of retroviral gene transfer into hematopoietic stem cells has been hampered, in part, by the absence of vectors that can direct long-lasting, cell-type specific gene expression. In this review we will detail recent developments in the design of novel retroviral and lentiviral vectors that appear to overcome these problems, offering approaches to express therapeutic genes in specific cell-types within atherosclerotic lesions. We will also highlight advances in our understanding of the pathogenesis of atherosclerosis that may offer new gene therapeutic targets. SUMMARY: The use of retroviral transduction of hematopoietic stem cells for treatment of patients with atherosclerosis still remains a long-term goal. However, the recent development of retroviral vectors capable of directing expression to specific cell types within the lesion will allow more targeted therapeutic strategies to be devised. In addition, these vectors will provide powerful experimental tools to further our understanding of the pathogenesis of the disease.     

Interleukin-34 induces monocytic-like differentiation in leukemia cell lines

Interleukin-34 (IL-34) is a cytokine consisting of a 39kD homodimer, shown to be a ligand for both the Macrophage Colony Stimulating Factor (M-CSF/CSF-1) receptor and the Receptor-like protein tyrosine phosphatase-zeta (RPTP-ƺ). IL-34 has been shown to promote monocyte viability and proliferation as well as the differentiation of bone marrow cells into macrophage progenitors. Published work on IL-34 involves its effects on normal hematopoietic and osteoclast progenitors. However, it is not known whether IL-34 has biologic effects in cancer, including leukemia. Here we report that the biological effects of IL-34 include induction of differential expression of Interleukins-1α and -1β as well as induction of differentiation of U937, HL-60 and THP-1 leukemia cell lines demonstrating monocyte-like characteristics. The ability of IL-34 to induce monocytic-like differentiation is supported by strong morphological and functional evidence. Cell surface markers of myeloid lineage, CD64 and CD86, remain constant while the levels of CD11b and CD71 decline with IL-34 treatment. IL-34 also induced increases in CD14 and CD68 expression, further supporting maturation toward monocytic character. IL-34-induced differentiated U937 and THP-1 cell lines exhibited biological functions such as endocytosis and respiratory burst activities. Collectively, we conclude that while IL-34 does not induce cell growth or proliferation, it is able to induce differentiation of leukemia cell lines from monoblastic precursor cells towards monocyte- and macrophage-like cells, mediated through the JAK/STAT and PI3K/Akt pathways. To our knowledge, this is the first report that IL-34 induces differentiation in human leukemic cells, let alone any cancer model.     

Changing modified regions in the genome in hematopoietic stem cell differentiation

In the process of hematopoietic stem cell (CD133⁺ cell) differentiation, a drastic change in gene expression occurs which must be regulated by epigenetic mechanisms. One strategy for CD133⁺ cell differentiation analysis is to identify genomic DNA regions that have been modified in the process of differentiation. However, it is difficult to obtain large amounts of genomic DNA from uniform CD133⁺ cells. Based on this situation, we screened genomic DNA regions where modifications change during the process of differentiation in human CD133⁺ cells using differential methylation site scanning (DMSS), which is a method of identifying differentially methylated regions of the genome from a small number of cells. As a result, we cloned three DNA fragments which corresponded to centrosomal protein 68 kDA (Cep68), TRIO and F-actin binding protein (TRIOBP), and AMP-activated protein kinase beta (AMPKb).     

Expression of CD34 in hematopoietic cancer cell lines reflects tightly regulated stem/progenitor-like state

Hematopoietic cancer stem cells preserve cellular hierarchy in a manner similar to normal stem cells, yet the underlying regulatory mechanisms are poorly understood. It is known that both normal and malignant stem/progenitor cells express CD34. Here, we demonstrate that several cell lines (HL-60, U266) derived from hematopoietic malignancies contain not only CD34(-) but also CD34(+) subpopulations. The CD34(+) cells displayed a stem/progenitor-like phenotype since, in contrast to CD34(-) cells, they frequently underwent cellular division and rapidly formed colonies in methylcellulose-based medium. Strikingly, a constant fraction of the CD34(+) and CD34(-) cell subpopulations, when separated, rapidly switched their phenotype. Consequently, both separated fractions could generate tumors in immunocompromised NOD/LtSz-scid/scid mice. Cultures in vitro showed that the proportion of CD34(+) stem/progenitor-like cells in the population was decreased by cell-cell contact and increased by soluble factors secreted by the cells. Using cytokine arrays, we identified some of these factors, notably thymopoietin that was able to increase the proportion of CD34(+) cells and overall colony-forming capacity in tested cell lines. This action of thymopoietin was conserved in mononuclear cells from bone marrow. Therefore, we propose that hematopoietic cancer cell lines containing subpopulations of CD34(+) cells can provide an in vitro model for studies of cancer stem/progenitor cells.     

Lentivirus vector-mediated hematopoietic stem cell gene transfer of common gamma-chain cytokine receptor in rhesus macaques

Nonhuman primate model systems of autologous CD34+ cell transplant are the most effective means to assess the safety and capabilities of lentivirus vectors. Toward this end, we tested the efficiency of marking, gene expression, and transplant of bone marrow and peripheral blood CD34+ cells using a self-inactivating lentivirus vector (CS-Rh-MLV-E) bearing an internal murine leukemia virus long terminal repeat derived from a murine retrovirus adapted to replicate in rhesus macaques. In vitro cytokine stimulation was not required to achieve efficient transduction of CD34+ cells resulting in marking and gene expression of the reporter gene encoding enhanced green fluorescent protein (EGFP) following transplant of the CD34+ cells. Monkeys transplanted with mobilized peripheral blood CD34+ cells resulted in EGFP expression in 1 to 10% of multilineage peripheral blood cells, including red blood cells and platelets, stable for 15 months to date. The relative level of gene expression utilizing this vector is 2- to 10-fold greater than that utilizing a non-self-inactivating lentivirus vector bearing the cytomegalovirus immediate-early promoter. In contrast, in animals transplanted with autologous bone marrow CD34+ cells, multilineage EGFP expression was evident initially but diminished over time. We further tested our lentivirus vector system by demonstrating gene transfer of the human common gamma-chain cytokine receptor gene (gamma(c)), deficient in X-linked SCID patients and recently successfully used to treat disease. Marking was 0.42 and.001 HIV-1 vector DNA copy per 100 cells in two animals. To date, all EGFP- and gamma(c)-transplanted animals are healthy. This system may prove useful for expression of therapeutic genes in human hematopoietic cells.     

Diverse hematopoietic potentials of five human embryonic stem cell lines

Despite a growing body of literature concerning the hematopoietic differentiation of human embryonic stem cells (hESCs), the full hematopoietic potential of the majority of existing hESC lines remains unknown. In this study, the hematopoietic response of five NIH-approved hESC lines (H1, hSF6, BG01, BG02, and BG03) was compared. Our data show that despite expressing similar hESC markers under self-renewing conditions and initiating mesodermal differentiation under spontaneous differentiation conditions, marked differences in subsequent hematopoietic differentiation potential among these lines existed. A high degree of hematopoietic differentiation was attained only by H1 and BG02, whereas this process appeared to be abortive in nature for hSF6, BG01, and BG03. This difference in hematopoietic differentiation predisposition was readily apparent during spontaneous differentiation, and further augmented under hematopoietic-inducing conditions. This predisposition appeared to be intrinsic to the specific hESC line and independent of passage number or gender karyotype. Interestingly, H1 and BG02 displayed remarkable similarities in their kinetics of hematopoietic marker expression, hematopoietic colony formation, erythroid differentiation, and globin expression, suggesting that a similar, predetermined differentiation sequence is followed. The identification of intrinsic and extrinsic factors governing the hematopoietic differentiation potential of hESCs will be of great importance for the putative clinical utility of hESC lines.     

Adoptive transfer of T-cell precursors enhances T-cell reconstitution after allogeneic hematopoietic stem cell transplantation

Immunoincompetence after allogeneic hematopoietic stem cell transplantation (HSCT) affects in particular the T-cell lineage and is associated with an increased risk for infections, graft failure and malignant relapse. To generate large numbers of T-cell precursors for adoptive therapy, we cultured mouse hematopoietic stem cells (HSCs) in vitro on OP9 mouse stromal cells expressing the Notch-1 ligand Delta-like-1 (OP9-DL1). We infused these cells, together with T-cell-depleted mouse bone marrow or purified HSCs, into lethally irradiated allogeneic recipients and determined their effect on T-cell reconstitution after transplantation. Recipients of OP9-DL1-derived T-cell precursors showed increased thymic cellularity and substantially improved donor T-cell chimerism (versus recipients of bone marrow or HSCs only). OP9-DL1-derived T-cell precursors gave rise to host-tolerant CD4+ and CD8+ populations with normal T-cell antigen receptor repertoires, cytokine secretion and proliferative responses to antigen. Administration of OP9-DL1-derived T-cell precursors increased resistance to infection with Listeria monocytogenes and mediated significant graft-versus-tumor (GVT) activity but not graft-versus-host disease (GVHD). We conclude that the adoptive transfer of OP9-DL1-derived T-cell precursors markedly enhances T-cell reconstitution after transplantation, resulting in GVT activity without GVHD.     

Expression of the long form of human FLIP by retroviral gene transfer of hemopoietic stem cells exacerbates experimental autoimmune encephalomyelitis

Subsidence of inflammation and clinical recovery in experimental autoimmune encephalomyelitis (EAE) is postulated to involve apoptosis of inflammatory cells. To test this concept, we examined the effects of overexpressing the long form of human FLICE-inhibitory protein, a potent inhibitor of death receptor-mediated apoptosis, in myelin oligodendrocyte glycoprotein-induced EAE in DBA/1 mice. We found that overexpression of the long form of human FLICE-inhibitory protein by retroviral gene transfer of hemopoietic stem cells led to a clinically more severe EAE in these mice compared with control mice receiving the retroviral vector alone. The exacerbated disease was evident by an enhanced and prolonged inflammatory reaction in the CNS of these animals compared with control mice. The acute phase of EAE was characterized by a massive infiltration of macrophages and granulocytes and a simultaneous increase in TNF-alpha production in the CNS. In the chronic phase of the disease, there was a prolonged inflammatory response in the form of persistent CD4(+) T and B cells in the CNS and a peripheral Th1 cytokine bias caused by elevated levels of IFN-gamma and reduced levels of IL-4 in the spleen. Our findings demonstrate that death receptor-mediated apoptosis can be important in the pathogenesis of EAE and further emphasize the need for effective apoptotic elimination of inflammatory cells to achieve disease remission.     

Expression of the human beta-globin gene after retroviral transfer into murine erythroleukemia cells and human BFU-E cells.

Replication-defective amphotropic retrovirus vectors containing either the human beta-globin gene with introns or an intronless beta-globin minigene were constructed and used to study beta-globin expression following gene transfer into hematopoietic cells. The beta-globin genes were marked by introducing a 6-base-pair insertion into the region corresponding to the 5' untranslated region of the beta-globin mRNA to allow detection of RNA encoded by the new gene in human cells expressing normal human beta-globin RNA. Introduction of a virus containing the beta-globin gene with introns into murine erythroleukemia cells resulted in inducible expression of human beta-globin RNA and protein, while the viruses containing the minigene were inactive. The introduced human beta-globin gene was 6 to 110% as active as the endogenous mouse beta maj-globin genes in six randomly chosen cell clones. Introduction of the viruses into human BFU-E cells, followed by analysis of marked and unmarked globin RNAs in differentiated erythroid colonies, revealed that the introduced beta-globin gene was about 5% as active as the endogenous genes in these normal human erythroid cells and that again the minigene was inactive. These data are discussed in terms of the potential treatment of genetic disease by gene therapy.     

Expression from cell type-specific enhancer-modified retroviral vectors after transduction: influence of marker gene stability

The enhanced green fluorescent protein (EGFP) is increasingly used as a reporter gene in viral vectors for a number of applications. To establish a system to study the activity of cis-acting cellular regulatory sequences, we deleted the viral enhancer in EGFP-carrying retroviral vectors and replaced it with cell type-specific elements. In this study, we use this system to demonstrate the activity of the human CD2 lymphoid-specific and the Tie2 endothelial cell type-specific enhancers in cell lines and in primary cells transduced by retroviral vectors. Furthermore, we compare findings obtained with EGFP as the reporter gene to those obtained replacing EGFP with d2EGFP, an unstable variant of EGFP characterized by a much shorter half-life compared to EGFP, and by reduced accumulation in the cells. d2EGFP-carrying vectors were generated at titers which were not different from those generated by the corresponding vectors carrying EGFP. Moreover, the activity of a Moloney murine leukemia virus enhancer could be readily detected following transduction of target cells with either EGFP- or d2EGFP-carrying vectors. However, the activity of the relatively weak CD2 and Tie2 enhancers was exclusively detected using EGFP as the reporter gene.These findings indicate that enhancer replacement is a feasible and promising approach to address the function of cell type-specific regulatory elements in retroviral vectors carrying the EGFP gene.