Signaling via Src family kinases is required for normal internalization of the receptor c-Kit.
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Stem cell factor (SCF) exerts its biological effects by binding to a specific receptor, the tyrosine kinase c-Kit, which is expressed on the cell surface. Although normal cellular trafficking of growth factor receptors may play a critical role in the modulation of receptor function, the mechanisms that regulate the distribution of c-Kit on the cell surface and the internalization of c-Kit have not been fully defined. We investigated whether signal transduction via Src family kinases is required for normal c-Kit trafficking. Treatment of the SCF-responsive human hematopoietic cell line MO7e with the inhibitor of Src family kinases PP1 blocked SCF-induced capping of c-Kit and internalization of c-Kit. c-Kit was able to associate with clathrin in the presence of PP1, suggesting that entry of c-Kit into clathrin-coated pits occurs independently of Src family kinases. SCF-induced internalization of c-Kit was also diminished in the D33-3 lymphoid cell line in which expression of Lyn kinase was disrupted by homologous recombination. These results indicate that Src family kinases play a role in ligand-induced trafficking of c-Kit. (+info)
Direct evidence for multiple self-renewal divisions of human in vivo repopulating hematopoietic cells in short-term culture.
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Recently, culture conditions that stimulate the proliferation of primitive hematopoietic cells defined by various phenotypic and functional endpoints in vitro have been identified. However, evidence that they support a high probability of self-renewal leading to a large net expansion in vitro of transplantable cells with lympho-myeloid repopulating ability has been more difficult to obtain. The present study was designed to investigate whether the low overall expansion of human repopulating hematopoietic cells seen in vitro reflects a selective unresponsiveness of these rare cells to the growth factors currently used to stimulate them or, alternatively, whether they do proliferate in vitro but lose engrafting potential. For this, we used a high-resolution procedure for tracking and reisolating cells as a function of their proliferation history based on the loss of cellular fluorescence after staining with (5- and 6-) carboxyfluorescein diacetate succinimidyl ester. The results show that the vast majority of long-term culture-initiating cells and in vivo lympho-myeloid competitive repopulating units present in 5-day suspension cultures initiated with CD34(+) human cord blood and fetal liver cells are the progeny of cells that have divided at least once in response to stimulation by interleukin-3, interleukin-6, granulocyte colony-stimulating factor, Steel factor, and Flt3-ligand. Thus, most human repopulating cells from these two sources are stimulated to undergo multiple divisions under currently used short-term suspension culture conditions and a proportion of these retain engraftment potential. (+info)
Efficient and durable gene marking of hematopoietic progenitor cells in nonhuman primates after nonablative conditioning.
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Optimization of mobilization, harvest, and transduction of hematopoietic stem cells is critical to successful stem cell gene therapy. We evaluated the utility of a novel protocol involving Flt3-ligand (Flt3-L) and granulocyte colony-stimulating factor (G-CSF) mobilization of peripheral blood stem cells and retrovirus transduction using hematopoietic growth factors to introduce a reporter gene, murine CD24 (mCD24), into hematopoietic stem cells in nonhuman primates. Rhesus macaques were treated with Flt3-L (200 microgram/kg) and G-CSF (20 microgram/kg) for 7 days and autologous CD34(+) peripheral blood stem cells harvested by leukapheresis. CD34(+) cells were transduced with an MFGS-based retrovirus vector encoding mCD24 using 4 daily transductions with centrifugations in the presence of Flt3-L (100 ng/mL), human stem cell factor (50 ng/mL), and PIXY321 (50 ng/mL) in serum-free medium. An important and novel feature of this study is that enhanced in vivo engraftment of transduced stem cells was achieved by conditioning the animals with a low-morbidity regimen of sublethal irradiation (320 to 400 cGy) on the day of transplantation. Engraftment was monitored sequentially in the bone marrow and blood using both multiparameter flow cytometry and semi-quantitative DNA polymerase chain reaction (PCR). Our data show successful and persistent engraftment of transduced primitive progenitors capable of giving rise to marked cells of multiple hematopoietic lineages, including granulocytes, monocytes, and B and T lymphocytes. At 4 to 6 weeks posttransplantation, 47% +/- 32% (n = 4) of granulocytes expressed mCD24 antigen at the cell surface. Peak in vivo levels of genetically modified peripheral blood lymphocytes approached 35% +/- 22% (n = 4) as assessed both by flow cytometry and PCR 6 to 10 weeks posttransplantation. In addition, naive (CD45RA(+) and CD62L(+)) CD4(+) and CD8(+) cells were the predominant phenotype of the marked CD3(+) T cells detected at early time points. A high level of marking persisted at between 10% and 15% of peripheral blood leukocytes for 4 months and at lower levels past 6 months in some animals. A cytotoxic T-lymphocyte response against mCD24 was detected in only 1 animal. This degree of persistent long-lived, high-level gene marking of multiple hematopoietic lineages, including naive T cells, using a nonablative marrow conditioning regimen represents an important step toward the ultimate goal of high-level permanent transduced gene expression in stem cells. (+info)
The use of granulocyte colony-stimulating factor during retroviral transduction on fibronectin fragment CH-296 enhances gene transfer into hematopoietic repopulating cells in dogs.
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A competitive repopulation assay in the dog was used to develop improved gene transfer protocols for hematopoietic stem cell gene therapy. Using this assay, we previously showed improved gene transfer into canine hematopoietic repopulating cells when CD34-enriched marrow cells were cocultivated on gibbon ape leukemia virus (GALV)-based retrovirus vector-producing cells. In the present study, we have investigated the use of fibronectin fragment CH-296 and 2 growth factor combinations to further improve gene transfer efficiency. CD34-enriched marrow cells from each dog were prestimulated for 24 hours and then divided into 3 equal fractions. Two fractions were placed into flasks coated with either CH-296 or bovine serum albumin (BSA) and virus-containing medium supplemented with growth factors, and protamine sulfate was replaced 4 times over a 48-hour period. One fraction was cocultivated on irradiated PG13 (GALV-pseudotype) packaging cells for 48 hours. In 2 animals, cells of the different fractions were transduced in the presence of human FLT-3 ligand (FLT3L), canine stem cell factor (cSCF), and human megakaryocyte growth and development factor (MGDF), and in 2 other dogs, transduction was performed in the presence of FLT3L, cSCF, and canine granulocyte-colony stimulating factor (cG-CSF). The vectors used contained small sequence differences, allowing differentiation of cells genetically marked by the different vectors. After transduction, nonadherent and adherent cells from all 3 fractions were pooled and infused into lethally irradiated dogs. Polymerase chain reaction and Southern blot analysis were used to determine the persistence of the transferred vectors in the peripheral blood and marrow cells after transplantation. The highest levels of gene transfer were obtained when cells were transduced in the presence of FLT3L, cSCF, and cG-CSF (gene transfer levels of more than 10% for more than 8 months so far). Compared with the 2 animals that received cells transduced with FLT3L, cSCF, and MGDF, gene transfer levels were significantly higher when dogs received cells that were transduced in the presence of cG-CSF. Transduction on CH-296 resulted in gene transfer levels that were at least as high as transduction by cocultivation. In summary, the overall levels of gene transfer obtained with these conditions should be sufficiently high to allow stem cell gene therapy studies aimed at correcting genetic diseases in dogs as a model for human gene therapy. (+info)
Rapid induction of CD40 on a subset of granulocyte colony-stimulating factor-mobilized CD34(+) blood cells identifies myeloid committed progenitors and permits selection of nonimmunogenic CD40(-) progenitor cells.
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CD40 antigen is a costimulatory molecule highly expressed on dendritic cells (DC) and activated B cells, which induces T-cell proliferation through the binding with CD40L receptor. In this study, we evaluated CD40 expression on normal CD34(+) blood cells and functionally characterized CD34(+)CD40(+) and CD34(+)CD40(-) cell subsets. CD40, CD80, and CD86 antigens were constitutively expressed on 3.2% +/- 4.5%, 0%, and 1.8% +/- 1.2% CD34(+) blood cells, respectively. However, after 24 hours in liquid culture with medium alone, or with tumor-necrosis-factor-alpha (TNF-alpha), or with allogeneic mononuclear cells 10.8% +/- 3.8%, 75.3% +/- 15.0% and 53. 7% +/- 17.0% CD34(+) blood cells, respectively, became CD40(+). After incubation for 24 hours with TNF-alpha CD34(+)CD40(+) blood cells expressed only myeloid markers and contained less than 5% CD86(+) and CD80(+) cells. Also, a 24-hour priming with TNF-alpha or ligation of CD40 significantly increased the CD34(+) blood cells alloantigen presenting function. Finally, purified CD34(+)CD40(+) blood cells stimulated an alloreactive T-cell response in MLC, were enriched in granulocytic, monocytic, and dendritic precursors, and generated high numbers of DC in 11-14 d liquid cultures with GM-CSF, SCF, TNF-alpha and FLT-3L. In contrast, CD34(+)CD40(-) cells were poorly immunogenic, contained committed granulocytic and erythroid precursors and early progenitors, and differentiated poorly toward the DC lineage. In conclusion, a short incubation with TNF-alpha allows the selection of CD40(+) blood progenitors, which may be a useful source of DC precursors for antitumor vaccine studies, and also a CD34(+)CD40(-) blood cell fraction that could be exploited in innovative strategies of allogeneic transplantation across HLA barriers. (+info)
Retroviral-mediated gene transduction of c-kit into single hematopoietic progenitor cells from cord blood enhances erythroid colony formation and decreases sensitivity to inhibition by tumor necrosis factor-alpha and transforming growth factor-beta1.
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The c-kit receptor and its ligand, steel factor (SLF), are critical for optimal hematopoiesis. We evaluated effects of transducing cord blood (CB) progenitor cells with a retrovirus encoding human c-kit cDNA. CD34(+) cells were sorted as a population or as 1 cell/well for cells expressing high levels of CD34 and different levels of c-kit (++,+,Lo/-), transduced and then cultured in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), IL-6, erythropoietin (Epo) +/- SLF in the absence of serum. At a single-cell level, transduction with c-kit, but not with control (neo only), virus significantly increased colony formation, especially by erythroid and multipotential progenitors. The enhancing effect of c-kit transduction was inversely correlated with expression of c-kit protein before transduction. The greatest enhancing effects were noted in CD34KitLo+/- cells transduced with c-kit. The stimulating effect was apparent even in the absence of exogenously added SLF, but in the presence of GM-CSF, IL-3, IL-6, and Epo. Enzyme-linked immunosorbent assay (ELISA) of SLF protein, reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of SLF mRNA expression in CD34+ cells, and use of neutralizing antibodies to SLF and/or c-kit suggested the presence of endogenous, although probably very low level, expression of SLF by these progenitor cells. Transduction of c-kit significantly decreased sensitivity of progenitor cells to the inhibitory effects of transforming growth factor-beta1 and tumor necrosis factor-alpha. c-kit-transduced cells had increased expression of c-kit protein and decreased spontaneous or cytokine-induced apoptosis. Our results suggest that transduced c-kit into selected progenitor cells can enhance proliferation and decrease apoptosis and that endogenous SLF may mediate this effect. (+info)
Demonstration that human mast cells arise from a progenitor cell population that is CD34(+), c-kit(+), and expresses aminopeptidase N (CD13).
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Human mast cells are known to arise from a CD34(+)/c-kit(+) progenitor cell population that also gives rise to neutrophils, eosinophils, basophils, and monocytes. To further characterize cells within the CD34(+)/c-kit(+) population that yield mast cells, this progenitor was additionally sorted for CD13, a myeloid marker known to appear early on rodent mast cells and cultured human mast cells, but not expressed or expressed at low levels on human tissue mast cells; and cultured in recombinant human (rh) stem cell factor (rhSCF), rh interleukin-3 (rhIL-3; first week only), and rhIL-6. Initial sorts revealed that although the majority of cells in culture arose from the CD34(+)/c-kit(+)/CD13(-) cell population, mast cells arose from a CD34(+)/c-kit(+)/CD13(+) progenitor cell that also gave rise to a population of monocytes. Sequential sorting confirmed that CD34(+)/c-kit(+)/CD13(+) cells in CD34(+)/c-kit(+)/CD13(-) sorts gave rise to the few mast cells observed in CD13(-) sorted cells. CD34(+)/c-kit(+)/CD13(+) cells plated as single cells in the presence of various cytokine combinations gave rise to pure mast cell, monocyte, or mixed mast cell/monocyte progeny. Addition of either rh granulocyte-macrophage colony-stimulating factor (rhGM-CSF) or rhIL-5 to the CD34(+)/c-kit(+)/CD13(+) progenitor cell population cultured in rhSCF, rhIL-3, and rhIL-6 did increase the number of total cells cultured and in the case of rhIL-5, did increase total mast cell numbers. Neither rhGM-CSF or rhIL-5 led to additional cell populations, ie, even with the addition of rhGM-CSF or rhIL-5, only mast cells and monocytes grew from CD34(+)/c-kit(+)/CD13(+) cells. Thus, human mast cells and a population of monocytes arise from precursor cells that express CD34, c-kit, and CD13; and within which, are mast cell, monocyte, and mast/monocyte (bipotential) precursors. (+info)
Matrix metalloproteinase-9 production, a newly identified function of mast cell progenitors, is downregulated by c-kit receptor activation.
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Mast cell precursors invade from the peripheral blood into local tissues where they differentiate to their mature phenotypes. However, the mechanism of this migration process has been unclear. We clearly demonstrated here the production and release of matrix metalloproteinase-9 (MMP-9), a matrix-degrading enzyme necessary for leukocyte transmigration, by interleukin-3-dependent mouse mast cell progenitors: bone marrow-derived cultured mast cells and IC-2 mast cells. Because several interleukin-3-independent mast cell lines with active mutations in the c-kit gene did not release MMP-9, the possible involvement of c-kit receptor activation in downregulation of MMP-9 production was predicted. c-kit receptor activation by stem cell factor led to a significant decrease in MMP-9 production of cultured mast cells and IC-2 mast cells transfected with the c-kit gene. Thus, the present results suggest that mast cell precursors are able to produce MMP-9, which may be essential for mast cell migration into tissues, and that stem cell factor may downregulate the MMP-9 production, resulting in engagement of mast cells to matrix components. (+info)