Human mesenchymal stem cells license adult CD34+ hemopoietic progenitor cells to differentiate into regulatory dendritic cells through activation of the Notch pathway

The mechanisms underlying the immunomodulatory functions of mesenchymal stem cells (MSC) on dendritic cells (DC) have been shown to involve soluble factors, such as IL-6 or TGF-beta, or cell-cell contact, or both depending on the report referenced. In this study, we intend to clarify these mechanisms by examining the immunosuppressive effect of human adult MSC on adult DC differentiated from CD34(+) hemopoietic progenitor cells (HPC). MSC have been shown to inhibit interstitial DC differentiation from monocytes and umbilical CD34(+) HPC. In this study, we confirm that MSC not only halt interstitial DC but also Langerhans cell differentiation from adult CD34(+) HPC, as assessed by the decreased expression of CD1a, CD14, CD86, CD80, and CD83 Ags on their cell surface. Accordingly, the functional capacity of CD34(+) HPC-derived DC (CD34-DC) to stimulate alloreactive T cells was impaired. Furthermore, we showed that 1) MSC inhibited commitment of CD34(+) HPC into immature DC, but not maturation of CD34-DC, 2) this inhibitory effect was reversible, and 3) DC generated in coculture with MSC (MSC-DC) induced the generation of alloantigen-specific regulatory T cells following secondary allostimulation. Conditioned medium from MSC cultures showed some inhibitory effect independent of IL-6, M-CSF, and TGF-beta. In comparison, direct coculture of MSC with CD34(+) HPC resulted in much stronger immunosuppressive effect and led to an activation of the Notch pathway as assessed by the overexpression of Hes1 in MSC-DC. Finally, DAPT, a gamma-secretase inhibitor that inhibits Notch signaling, was able to overcome MSC-DC defects. In conclusion, our data suggest that MSC license adult CD34(+) HPC to differentiate into regulatory DC through activation of the Notch pathway.     

Leukemia inhibitory factor induces endothelial differentiation in cardiac stem cells

The importance of interleukin 6 (IL-6)-related cytokines in cardiac homeostasis has been studied extensively; however, little is known about their biological significance in cardiac stem cells. Here we describe that leukemia inhibitory factor (LIF), a member of IL-6-related cytokines, activated STAT3 and ERK1/2 in cardiac Sca-1+ stem cells. LIF stimulation resulted in the induction of endothelial cell-specific genes, including VE-cadherin, Flk-1, and CD31, whereas neither smooth muscle nor cardiac muscle marker genes such as GATA4, GATA6, Nkx-2.5, and calponin were up-regulated. Immunocytochemical examination showed that about 25% of total cells were positively stained with anti-CD31 antibody 14 days after LIF stimulation. Immunofluorescent microscopic analyses identified the Sca-1+ cells that were also positively stained with anti-von Willebrand factor antibody, indicating the differentiating process of Sca-1+ cells into the endothelial cells. IL-6, which did not activate STAT3 and ERK1/2, failed to induce the differentiation of cardiac stem cells into the endothelial cells. In cardiac stem cells, the transduction with dominant negative STAT3 abrogated the LIF-induced endothelial differentiation. And the inhibition of ERK1/2 with the MEK1/2 inhibitor U0126 also prevented the differentiation of Sca-1+ cells into endothelial cells. Thus, both STAT3 and ERK1/2 are required for LIF-mediated endothelial differentiation in cardiac stem cells. Collectively, it is proposed that LIF regulates the commitment of cardiac stem cells into the endothelial cell lineage, contributing to neovascularization in the process of tissue remodeling and/or regeneration.     

Competent dendritic cells derived from CD34+ progenitors express CMRF-44 antigen early in the differentiation pathway

Differentiation of CD34(+) haematopoietic stem cells into functional dendritic cells (DC) was investigated using the mAb CMRF-44 and other mAb against DC-associated markers. GM-CSF mobilized peripheral blood stem cells were obtained from healthy donors by leukapheresis. CD34(+) cells were purified using CD34(+)-positive selection,and subsequent immunomagnetic depletion of CD14 and CD2 cells. CD34(+) cells were cultured in medium supplemented with one or more of GM-CSF,TNF-alpha, IL-4 or IL-6. CMRF-44 Ag expression was monitored by flow cytometry, and DC function by allogeneic MLR and tetanus toxoid(TT) presentation assays. CD34(+) cells quickly acquired the CMRF-44 Ag when cultured in the presence of TNF-alpha.By day 3, more than 50% of the cells were double-positive for CD34 and CMRF-44. CD34 expression was gradually lost, so that by day 9, the majority of the cells were CD34(-)/CMRF-44(+).GM-CSF and TNF-alpha also induced CD40 expression, and up-regulation of CD54 and MHC class II on CD34(+) cells; their expression was correlated to the CMRF-44 Ag. Day 3 CD34(+)/CMRF-44(+) cells,but not CD34(+)/CMRF-44(-) cells, become potent APC when cultured further with GM-CSF plus TNF-alpha. These CMRF-44(+) cells were potent inducers of Th1-type immune response in the primary allogeneic MLR and present TT to autologous CD4(+) T cells. TNF-alpha alone is sufficient to induce CMRF-44 expression on CD34(+) cells, but in combination with GM-CSF expands the CMRF-44(+) population. CMRF-44 expression correlates with DC function and may be a useful early marker for commitment of CD34(+) cells to the DC differentiation pathway.     

Immunoregulatory effects of human dental pulp-derived stem cells on T cells: comparison of transwell co-culture and mixed lymphocyte reaction systems

BACKGROUND AIMS. Studies performed using human and animal models have indicated the immunoregulatory capability of mesenchymal stromal cells in several lineages. We investigated whether human dental pulp-derived stem cells (hDP-SC) have regulatory effects on phytohemagglutinin (PHA)-activated CD3(+) T cells. We aimed to define the regulatory mechanisms associated with hDP-SC that occur in mixed lymphocyte reaction (MLR) and transwell systems with PHA-CD3(+) T cells and hDP-SC at a ratio of 1:1. METHODS. Proliferation, apoptosis and pro- and anti-inflammatory cytokines of PHA-CD3(+)T cells, the expression of Regulatory T cells (Treg) markers and some regulatory factors related to hDP-SC, were studied in Both transwell and MLR are co-cultures systems. RESULTS. Anti-proliferative and apoptotic effects of hDP-SC were determined in co-culture systems. Elevated expression levels of human leukocyte antigen (HLA)-G, hepatocyte growth factor (HGF)-β1, intracellular adhesion molecule (ICAM-1)-1, interleukin (IL)-6, IL-10, transforming growth factor (TGF)-β1, vascular adhesion molecule (VCAM)-1 and vascular endothelial growth factor (VEGF) by hDP-SC were detected in the co-culture systems. We observed decreased expression levels of pro-inflammatory cytokines [interferon (IFN)-γ, IL-2, IL-6 receptor (R), IL-12, Interleukin-17A (IL-17A), tumor necrosis factor (TNF)-α] and increased expression levels of anti-inflammatory cytokine [inducible protein (IP)-10] from PHA-CD3(+) T cells in the transwell system. Expression of Treg (CD4(+) CD25(+) Foxp3(+)) markers was significantly induced by hDP-SC in both co-culture systems. We observed apoptosis of PHA-CD3(+) T cells with 24 h using time-lapse camera photographs and active caspase labeling; it is likely that paracrine soluble factors and molecular signals secreted by hDP-SC led this apoptosis. CONCLUSIONS. We suggest that hDP-SC have potent immunoregulatory functions because of their soluble factors and cytokines via paracrine mechanisms associated with PHA-CD3(+) T cells, which could contribute to clinical therapies.     

Corticosteroids prevent generation of CD34+-derived dermal dendritic cells but do not inhibit Langerhans cell development

Corticosteroids (CS) have been shown to exert strong inhibitory effects on dendritic cell (DC) differentiation and function. Those studies were mostly performed with monocyte-derived DC, which represents only one subpopulation from the wide variety of DC types. In the present study the effects of the CS dexamethasone and prednisolone were investigated on the differentiation of CD34(+) hemopoietic progenitor cells into 1) Langerhans cells (LC), which differentiate directly into CD1a(+) DC; and 2) dermal/interstitial DC, which differentiate via a CD14(+)CD1a(-) phenotype into CD14(-)CD1a(+) DC. CS present during the entire 11-day culture period, resulting in fully differentiated CD1a(+) DC, increased the percentage of langerin(+) DC within the CD1a(+) population. In line with these data, CS treatment during the first 6 days of differentiation reduced the development of CD14(+) dermal DC precursors and thereby seemed to support the generation of CD1a(+) LC precursors. Addition of CS from day 6 onward specifically blocked the development of CD1a(+) dermal DC by both inhibition of spontaneous and IL-4-induced differentiation of CD14(+) DC precursors into CD1a(+) DC as well as induction of apoptosis in CD14(+) DC precursors. Apoptosis was not found in CD14(+) macrophage precursors derived from the same CD34(+) progenitors. The development and function of LC were not affected by CS, as demonstrated by a normal T cell stimulatory capacity and IL-12 production. These data demonstrate that CS interfere with the normal development of DC from CD34(+) progenitors by specific induction of apoptosis in precursors of dermal/interstitial DC. In view of the different functional capacities of dermal/interstitial DC and Langerhans cells, this might affect the overall cellular immune response.     

DAP12 promotes IRAK-M expression and IL-10 production by liver myeloid dendritic cells and restrains their T cell allostimulatory ability

Freshly isolated hepatic dendritic cells (DC) are comparatively immature, relatively resistant to maturation, and can downmodulate effector T cell responses. Molecular mechanisms that underlie these properties are ill defined. DNAX-activating protein of 12 kDa (DAP12) is an ITAM-bearing transmembrane adaptor protein that integrates signals through several receptors, including triggering receptor expressed on myeloid cells-1, -2, and CD200R. Notably, DC propagated from DAP12-deficient mice exhibit enhanced maturation in response to TLR ligation. Given the constitutive exposure of liver DC to endotoxin draining from the gut, we hypothesized that DAP12 might regulate liver DC maturation. We show that DAP12 is expressed by freshly isolated liver, spleen, kidney, and lung myeloid DC. Moreover, inhibition of DAP12 expression by liver DC using small interfering RNA promotes their phenotypic and functional maturation, resulting in enhanced TNF-α, IL-6, and IL-12p70 production, reduced secretion of IL-10, and enhanced CD4(+) and CD8(+) T cell proliferation. Furthermore, DAP12 silencing correlates with decreased STAT3 phosphorylation in mature liver DC and with diminished expression of the IL-1R-associated kinase-M, a negative regulator of TLR signaling. These findings highlight a regulatory role for DAP12 in hepatic DC maturation, and suggest a mechanism whereby this function may be induced/maintained.     

Two phenotypically distinct subsets of spleen dendritic cells in rats exhibit different cytokine production and T cell stimulatory activity

We recently reported that splenic dendritic cells (DC) in rats can be separated into CD4(+) and CD4(-) subsets and that the CD4(-) subset exhibited a natural cytotoxic activity in vitro against tumor cells. Moreover, a recent report suggests that CD4(-) DC could have tolerogenic properties in vivo. In this study, we have analyzed the phenotype and in vitro T cell stimulatory activity of freshly isolated splenic DC subsets. Unlike the CD4(-) subset, CD4(+) splenic DC expressed CD5, CD90, and signal regulatory protein alpha molecules. Both fresh CD4(-) and CD4(+) DC displayed an immature phenotype, although CD4(+) cells constitutively expressed moderate levels of CD80. The half-life of the CD4(-), but not CD4(+) DC in vitro was extremely short but cells could be rescued from death by CD40 ligand, IL-3, or GM-CSF. The CD4(-) DC produced large amounts of the proinflammatory cytokines IL-12 and TNF-alpha and induced Th1 responses in allogeneic CD4(+) T cells, whereas the CD4(+) DC produced low amounts of IL-12 and no TNF-alpha, but induced Th1 and Th2 responses. As compared with the CD4(+) DC that strongly stimulated the proliferation of purified CD8(+) T cells, the CD4(-) DC exhibited a poor CD8(+) T cell stimulatory capacity that was substantially increased by CD40 stimulation. Therefore, as previously shown in mice and humans, we have identified the existence of a high IL-12-producing DC subset in the rat that induces Th1 responses. The fact that both the CD4(+) and CD4(-) DC subsets produced low amounts of IFN-alpha upon viral infection suggests that they are not related to plasmacytoid DC.     

IL-9 enhances the growth of human mast cell progenitors under stimulation with stem cell factor

We examined the effects of IL-9 on human mast cell development from CD34(+) cord blood (CB) and peripheral blood cells in serum-deprived cultures. IL-9 apparently enhanced cell production under stimulation with stem cell factor (SCF) from CD34(+) CB cells. A great majority of the cultured cells grown with SCF + IL-9 became positive for tryptase at 4 wk. In methylcellulose cultures of CD34(+) CB cells, IL-9 increased both the number and size of mast cell colonies grown with SCF. Furthermore, SCF + IL-9 caused an exclusive expansion of mast cell colony-forming cells in a 2-wk liquid culture of CD34(+) CB cells, at a level markedly greater than for SCF alone. Clonal cell cultures and RT-PCR analysis showed that the targets of SCF + IL-9 were the CD34(+)CD38(+) CB cells rather than the CD34(+)CD38(-) CB cells. IL-9 neither augmented the SCF-dependent generation of progeny nor supported the survival of 6-wk-cultured mast cells. Moreover, there was no difference in the appearance of tryptase(+) cells and histamine content in the cultured cells between SCF and SCF + IL-9. The addition of IL-9 increased numbers of mast cell colonies grown with SCF from CD34(+) peripheral blood cells in children with or without asthma. It is of interest that mast cell progenitors of asthmatic patients responded to SCF + IL-9 to a greater extent than those of normal controls. Taken together, IL-9 appears to act as a potent enhancer for the SCF-dependent growth of mast cell progenitors in humans, particularly asthmatic patients.     

Modulation of haematopoietic progenitor development by FLT-3 ligand.

The Flt-3 receptor is expressed in primitive haematopoietic cells and its ligand exerts proliferative effects on these cells in vitro in synergy with other cytokines. To increase our knowledge of the functional properties of the human Flt-3 ligand (FL) as relating to in vitro expansion of haematopoietic stem cells, the effects on murine haematopoiesis of FL alone or in combination with other growth factors were studied. Analysis of Flk-2/Flt-3 mRNA expression indicated that Flk-2/Flt-3 was preferentially expressed in primitive haematopoietic cell populations. To examine the expression of the Flk-2/Flt-3 receptor on megakaryocyte progenitors (CFU-Meg), Flk-2/Flt-3 positive and negative CD34(+)populations were separated from human bone marrow and cultured in a plasma clot culture system. CFU-Meg colonies were found in the Flk-2/Flt-3 negative fraction. Myeloid (CFU-GM) derived colonies appeared in the presence of FL alone. Neither FL+IL-3 nor FL+IL-3+IL-6 had any effect on the generation of megakaryocyte colonies (CFU-MK), due to the lack of FL receptor expression on megakaryocyte progenitors. Bone marrow cells remaining after 5-fluorouracil (5-FU) treatment of mice represent a very primitive population of progenitors enriched for reconstituting stem cells. This cell population expressed FL receptors, as revealed by RT-PCR analysis. Addition of FL alone did not enhance the replication of such cells in liquid cultures as compared to controls. However, a significantly greater generation of myeloid progenitors (CFU-GM) in clonogenic assays was observed in the presence of FL+IL-3, FL+GM-CSF or FL+CSF-1. In addition, the effects of FL on in vitro expansion of murine haematopoietic stem cells were studied using lineage-negative (lin(-)) Sca-1 positive (Sca-1(+)) c-kit positive (c-kit(+)) marrow cells from 5-FU treated mice. FL enhanced the survival of primitive murine lin(-)Sca-1(+)c-kit(+)cells. FL and IL-6 were able to significantly expand murine progenitor stem cells in vitro and promote their survival. These studies strongly suggest that FL significantly and selectively enhanced the generation of myeloid progenitors in vitro and increased myeloid progenitor responsiveness to later acting growth factors. In addition, FL synergized with IL-6 to support in vitro expansion of haematopoietic progenitors and promoted the survival of lin(-)Sca-1(+)c-kit(+)cells.     

Salmonella infection does not increase expression and activity of the high affinity IL-12 receptor

Expression of high affinity IL-12 receptors is required for IL-12-mediated IFN-gamma production. Activation of this pathway has been shown to be critical in generating optimal cell-mediated immunity. Therefore, increased IL-12 receptor expression might be expected in the host response after infection by an intracellular bacterial pathogen. In the present study, we have made the surprising discovery that infection with Salmonella results in an early reduction of high affinity IL-12 receptor expression and activation. After oral inoculation with Salmonella, the level of mRNA expression encoding IL-12 receptor beta2 (IL-12Rbeta2) subunit was diminished 12 h postinfection in the mesenteric lymph nodes and subsequently in the spleen. Furthermore, decreased IL-12Rbeta2 mRNA expression was observed in CD4+ T lymphocytes isolated from the mesenteric lymph nodes and spleens of infected mice. Attenuated IL-12Rbeta2 mRNA expression correlated with reduced receptor signaling, as demonstrated by reduced IL-12-induced STAT4 phosphorylation in enriched T lymphocytes isolated from the mesenteric lymph nodes and spleens of Salmonella-infected mice. These in vivo results were substantiated with an in vitro model system. In this model system, T lymphocytes cocultured with Salmonella-infected macrophages expressed less IL-12Rbeta2 mRNA. The cocultured T cells were also less responsive to IL-12 as assessed by reduced phosphorylation of STAT4 and limited IFN-gamma secretion. Together, these studies suggest that Salmonella can limit an optimal host immune response by reducing the expression and activity of high affinity IL-12 receptors.     

Development of dendritic cells in culture from human and murine thymic precursor cells.

The earliest T-precursor population in the adult murine thymus can give rise to dendritic cells (DC) in culture if stimulated with a cocktail of cytokines that includes interleukin (IL)-3, but not with cytokine mixes based on granulocyte-macrophage colony stimulating factor (GM-CSF), normally used to generate myeloid-derived DC. This and other evidence led to the proposal that two different lineages of DC exist, one lymphoid-related and the other myeloid-related. To determine whether this selective response to cytokines was restricted to murine DC, early human thymic T-precursors were isolated and their capacity to generate DC in response to various cytokines directly compared to their murine counterparts. In contrast to cultures of murine thymic precursors, CD34+CD1a- lineage marker negative (Lin-) precursor cells from the human thymus proliferated and generated DC with both the IL-3-containing cytokine mix lacking GM-CSF and with GM-CSF based cytokine mixes. These CD34+CD1a-Lin- human precursor cells also gave rise to NK cells under appropriate culture conditions, but produced no granulocyte, monocyte, eosinophil, megakaryocyte or erythroid cells in standard soft-agar colony-forming cell assays. Thus, although apparently lymphoid-restricted, the human thymic DC precursors responded to the myeloid factor GM-CSF as well as to the cytokines selective for murine lymphoid-related DC.     

Nonviral transfection of human umbilical cord blood dendritic cells is feasible, but the yield of dendritic cells with transgene expression limits the application of this method in cancer immunotherapy

Dendritic cells (DC) generated from human umbilical cord blood might replace patients' DC in attempts to elicit tumor-specific immune response in cancer patients. We studied the efficiency of transfection of human cord blood DC with plasmid DNA carrying the enhanced version of green fluorescent protein (EGFP) as a reporter gene, to test if nonviral gene transfer would be a method to load DC with protein antigens for immunotherapy purposes. Cord blood mononuclear cells were cultured in serum-free medium in the presence of granulocyte-monocyte colony stimulating factor (GM-CSF), stem cell factor (SCF) and Flt-3 ligand (FL), to generate DC from their precursors, and thereafter transfected by electroporation. Maturation of DC was induced by stimulation with GM-CSF, SCF, FL and phorbol myristate acetate (PMA). Transfected DC strongly expressed EGFP, but transfection efficiency of DC, defined as HLA-DR(+) cells lacking lineage-specific markers, did not exceed 2.5%. Expression of the reporter gene was also demonstrated in the DC generated from transfected, purified CD34(+) cord blood cells, by stimulation with GM-CSF, SCF, FL, and tumor necrosis factor alpha (TNF-alpha). Transfection of CD34(+) cells was very efficient, but proliferation of the transfected cells was much reduced as compared to the untransfected cells. Therefore, the yield of transgene-expressing DC was relatively low. In conclusion, nonviral transfection of cord blood DC proved feasible, but considering the requirements for immunotherapy in cancer patients, transfection of differentiated DC or generation of DC from transfected hematopoietic stem cells provide only a limited number of DC expressing the transgene.     

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.     

Tumors promote altered maturation and early apoptosis of monocyte-derived dendritic cells

Tumors produce a number of immunosuppressive factors that block the maturation of CD34+ stem cells into dendritic cells (DC). We hypothesized that tumors might also interfere with the maturation and/or function of human monocyte-derived DC. In contrast to stem cells, we found that CD14+ cells responded to tumor culture supernatant (TSN) by increasing expression of APC surface markers, up-regulating nuclear translocation of RelB, and developing allostimulatory activity. Although displaying these characteristics of mature DC, TSN-exposed DC lacked the capacity to produce IL-12, did not acquire full allostimulatory activity, and rapidly underwent apoptosis. The effects of TSN appeared to be specific for maturing DC, and were not reversed by Abs against known DC regulatory factors including IL-10, vascular endothelial growth factor, TGF-beta, or PGE2. Supernatants collected from nonmalignant cell sources had no effect on DC maturation. The altered maturation and early apoptosis of monocyte-derived DC may represent another mechanism by which tumors evade immune detection.     

Quiescence of CD34-negative haematopoietic stem cells is mediated by downregulation of Cyclin B and no stat activation

The CD34-negative, adherent growing, fibroblast-like canine haematopoietic stem cell line D064 was recently identified as the earliest progenitor population in the bone marrow. D064 cells are predominately quiescent. Quiescence is mediated by the accumulation of the cyclin-dependent kinase inhibitor p27(kip-1)and in parallel, by the downregulation of Cyclin B, leading to an accumulation of quiescent cells in the G(0)/G(1)-phase of the cell cycle. Stem cell factor (SCF), the ligand for the tyrosine kinase receptor c-kit, usually induces differentiation of the CD34-negative stem cells into CD34-positive haematopoietic precursors. SCF also suppresses the expression of c-myc-dependent Cyclin E, which is not transcribed initially, but expression occurs later on. Interleukin 6 (IL-6) instead rather promotes proliferation, but fails to induce proliferation in the majority of CD34-negative stem cells due to no STAT activation in quiescent cells. Nevertheless, the potential of quiescent D064 cells to proliferate eventually, becomes apparent by the low-level expression of IL-6 dependent STAT factors. D064 cells also spontaneously start to express Bax, while Bcl-2 is downregulated in parallel. In summary, CD34-negative haematopoietic stem cells dwell in the marrow or other niches as quiescent cells, until they can respond to autocrine or paracrine growth factor-mediated signals.