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Several hematopoietic growth factors,including interleukin-10 (IL-10) and transforming growth factor-beta1 (TGF-beta1),promote the differentiation of tolerogenic dendritic cells (DCs). Hepatocyte growth factor (HGF) is a pleiotropic cytokine whose effects on human DC differentiation and function have not been investigated. Monocytes cultured with HGF (HGFMo) differentiated into accessory cells with DC-like morphology,released low amounts of IL-12p70 and up-regulated IL-10 both at the mRNA and at the protein level. Upon activation with HGFMo,allogeneic CD4+CD25- T cells expressed the T regulatory (Treg)-associated transcription factor FoxP3,proliferated poorly,and released high levels of IL-10. Interestingly,blockade of surface immunoglobulin-like transcript 3 (ILT3) on HGFMo or neutralization of secreted IL-10 translated into partial restoration of T-cell proliferation. Secondary stimulation of HGFMo-primed CD4+ T cells with immunogenic DCs differentiated with granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-4 from monocytes of the same donor resulted in measurable T-cell proliferation. HGFMo-primed CD4+ T cells significantly inhibited the proliferation of naive CD4+CD25- T cells in a cell-contact-dependent manner. Finally,DNA microarray analysis revealed a unique gene-expression profile of HGF-activated monocytes. Collectively,our findings point to a novel role for HGF in the regulation of monocyte/DC functions that might be exploited therapeutically. View Publication

The t(16:16) and inv(16) are associated with FAB M4Eo myeloid leukemias and result in fusion of the CBFB gene to the MYH11 gene (encoding smooth muscle myosin heavy chain [SMMHC]). Knockout of CBFbeta causes embryonic lethality due to lack of definitive hematopoiesis. Although knock-in of CBFB-MYH11 is not sufficient to cause disease,expression increases the incidence of leukemia when combined with cooperating events. Although mouse models are valuable tools in the study of leukemogenesis,little is known about the contribution of CBFbeta-SMMHC to human hematopoietic stem and progenitor cell self-renewal. We introduced the CBFbeta-MYH11 cDNA into human CD34+ cells via retroviral transduction. Transduced cells displayed an initial repression of progenitor activity but eventually dominated the culture,resulting in the proliferation of clonal populations for up to 7 months. Long-term cultures displayed a myelomonocytic morphology while retaining multilineage progenitor activity and engraftment in NOD/SCID-B2M-/- mice. Progenitor cells from long-term cultures showed altered expression of genes defining inv(16) identified in microarray studies of human patient samples. This system will be useful in examining the effects of CBFbeta-SMMHC on gene expression in the human preleukemic cell,in characterizing the effect of this oncogene on human stem cell biology,and in defining its contribution to the development of leukemia. View Publication

Chronic treatment with antidepressants increases neurogenesis in the adult hippocampus. This increase in the production of new neurons may be required for the behavioral effects of antidepressants. However,it is not known which class of cells within the neuronal differentiation cascade is targeted by the drugs. We have generated a reporter mouse line,which allows identification and classification of early neuronal progenitors. It also allows accurate quantitation of changes induced by neurogenic agents in these distinct subclasses of neuronal precursors. We use this line to demonstrate that the selective serotonin reuptake inhibitor antidepressant fluoxetine does not affect division of stem-like cells in the dentate gyrus but increases symmetric divisions of an early progenitor cell class. We further demonstrate that these cells are the sole class of neuronal progenitors targeted by fluoxetine in the adult brain and suggest that the fluoxetine-induced increase in new neurons arises as a result of the expansion of this cell class. This finding defines a cellular target for antidepressant drug therapies. View Publication

Langerhans cells (LC) are a unique subset of dendritic cells (DC),present in the epidermis and serving as the first line of defense against pathogens invading the skin. To investigate the role of human LCs in innate immune responses,we examined TLR expression and function of LC-like DCs derived from CD34+ progenitor cells and compared them to DCs derived from peripheral blood monocytes (monocyte-derived DC; Mo-DC). LC-like DCs and Mo-DCs expressed TLR1-10 mRNAs at comparable levels. Although many of the TLR-induced cytokine patterns were similar between the two cell types,stimulation with the TLR3 agonist poly(I:C) triggered significantly higher amounts of the IFN-inducible chemokines CXCL9 (monokine induced by IFN-gamma) and CXCL11 (IFN-gamma-inducible T cell alpha chemoattractant) in LC-like DCs as compared with Mo-DCs. Supernatants from TLR3-activated LC-like DCs reduced intracellular replication of vesicular stomatitis virus in a type I IFN-dependent manner. Finally,CXCL9 colocalized with LCs in skin biopsy specimens from viral infections. Together,our data suggest that LCs exhibit a direct antiviral activity that is dependent on type I IFN as part of the innate immune system. View Publication

The B-cell receptor (BCR) transmits life and death signals throughout B-cell development,and altered BCR signaling may be required for survival of B-lymphoma cells. We used single-cell signaling profiles to compare follicular lymphoma (FL) B cells and nonmalignant host B cells within individual patient biopsies and identified BCR-mediated signaling events specific to lymphoma B cells. Expression of CD20,Bcl-2,and BCR light chain isotype (kappa or lambda) distinguished FL tumor B-cell and nontumor host B-cell subsets within FL patient biopsies. BCR-mediated signaling via phosphorylation of Btk,Syk,Erk1/2,and p38 occurred more rapidly in tumor B cells from FL samples than in infiltrating nontumor B cells,achieved greater levels of per-cell signaling,and sustained this level of signaling for hours longer than nontumor B cells. The timing and magnitude of BCR-mediated signaling in nontumor B cells within an FL sample instead resembled that observed in mature B cells from the peripheral blood of healthy subjects. BCR signaling pathways that are potentiated specifically in lymphoma cells should provide new targets for therapeutic attention. View Publication

B-cell functions in antitumor immunity are not well understood. In this study,we evaluated the role of B cells in the development of antitumor immunity using Friend murine leukemia virus gag-expressing mouse EL-4 (EL-4 gag),D5 mouse melanoma,or MCA304 mouse sarcoma cells. To screen tumors for susceptibility to B-cell-deficient immune environments,spleen cells from naive C57BL/6 [wild-type (WT)] and B-cell knockout (BKO) mice were cultured with irradiated tumor cells in vitro. When cells were stimulated with EL-4 gag or D5 (but not MCA304 tumors),IFN-gamma production from CD8 T cells and natural killer cells was markedly decreased in WT compared with BKO cultures. IFN-gamma production was correlated with CD40 ligand expression on the tumor and inversely with interleukin-10 (IL-10) production by B cells. Sorted WT B cells produced more IL-10 than CD40 knockout (CD40KO) B cells when cocultured with EL-4 gag or D5 (but not MCA304). IFN-gamma production by BKO cells was reduced by the addition of sorted naive WT B cells (partially by CD40KO B cells) or recombinant mouse IL-10. In vivo tumor progression mirrored in vitro studies in that WT mice were unable to control tumor growth whereas EL-4 gag and D5 tumors (but not MCA304) were eliminated in BKO mice. Robust in vivo antitumor CTLs developed only in BKO tumor-challenged mice. Our studies provide the first mechanistic basis for the concept that B-cell depletion could therapeutically enhance antitumor immune responses to certain tumors by decreasing IL-10 production from B cells. View Publication

In herpesvirus infections,the virus persists for life but is contained through T-cell-mediated immune surveillance. How this immune surveillance operates is poorly understood. Recent studies of other persistent infections have indicated that virus persistence is associated with functional deficits in the CD8(+) T-cell response. To test whether this is the case in a herpesvirus infection,we used a mutant murine gammaherpesvirus that is defective in its ability to persist in the host. By comparing the immune response to this virus with a revertant virus that can persist,we were able to dissect the changes in the antiviral CD8(+) T-cell response that are induced by virus persistence. Surprisingly,persistently infected mice controlled a secondary challenge infection more rapidly than nonpersistently infected mice,indicating enhanced rather than diminished effector functions. Consistent with this,virus-specific CD8 T cells from these mice exhibited faster upregulation of the cytotoxic mediator granzyme B. Another unexpected finding was that CD8(+) T cells from neither infection responded efficiently to homeostatic cytokines. The unresponsiveness of the memory cells from the nonpersistently infected mice appears to be linked to the prolonged replication of virus within the lungs. Other changes seen in different chronic infection models were also observed,such as changes in Bcl-2 levels,interleukin-2 production,and the immunodominance hierarchy. These data show persistence of gammaherpesvirus type 68 alters the properties of CD8(+) T cells and illustrates that immune surveillance does not require CD8 T cells with the same attributes as classical" memory CD8(+) T cells." View Publication

While during the first trimester of pregnancy natural killer (NK) cells represent the most abundant lymphocyte population in the decidua,their actual function at this site is still debated. In this study we analyzed NK cells isolated from decidual tissue for their surface phenotype and functional capability. We show that decidual NK (dNK) cells express normal surface levels of certain activating receptors,including NKp46,NKG2D,and 2B4,as well as of killer cell immunoglobulin-like receptors (KIRs) and CD94/NKG2A inhibitory receptor. In addition,they are characterized by high levels of cytoplasmic granules despite their CD56(bright) CD16- surface phenotype. Moreover,we provide evidence that in dNK cells,activating NK receptors display normal triggering capability whereas 2B4 functions as an inhibitory receptor. Thus,cross-linking of 2B4 resulted in inhibition of both cytolytic activity and interferon-gamma (IFN-gamma) production. Clonal analysis revealed that,in the majority of dNK cell clones,the 2B4 inhibitory function is related to the deficient expression of signaling lymphocyte activation molecule (SLAM)-associated protein (SAP) mRNA. Moreover,biochemical analysis revealed low levels of SAP in the dNK polyclonal population. This might suggest that dNK cells,although potentially capable of killing,are inhibited in their function when interacting with cells expressing CD48. View Publication

Definitive mesoderm arises from a bipotent mesendodermal population,and to study processes controlling its development at this stage,embryonic stem (ES) cells can be employed. SHB (Src homology 2 protein in beta-cells) is an adapter protein previously found to be involved in ES cell differentiation to mesoderm. To further study the role of SHB in this context,we have established ES cell lines deficient for one (SHB+/-) or both SHB alleles (SHB-/-). Differentiating embryoid bodies (EBs) derived from these ES cell lines were used for gene expression analysis. Alternatively,EBs were stained for the blood vessel marker CD31. For hematopoietic differentiation,EBs were differentiated in methylcellulose. SHB-/- EBs exhibited delayed down-regulation of the early mesodermal marker Brachyury. Later mesodermal markers relatively specific for the hematopoietic,vascular,and cardiac lineages were expressed at lower levels on day 6 or 8 of differentiation in EBs lacking SHB. The expression of vascular endothelial growth factor receptor-2 and fibroblast growth factor receptor-1 was also reduced in SHB-/- EBs. SHB-/- EBs demonstrated impaired blood vessel formation after vascular endothelial growth factor stimulation. In addition,the SHB-/- ES cells formed fewer blood cell colonies than SHB+/+ ES cells. It is concluded that SHB is required for appropriate hematopoietic and vascular differentiation and that delayed down-regulation of Brachyury expression may play a role in this context. View Publication

Toll-like receptors (TLRs) play a key role in pathogen recognition and regulation of the innate and adaptive immune responses. Although TLR expression and signaling have been investigated in blood cells,it is currently unknown whether their bone marrow ancestors express TLRs and respond to their ligands. Here we found that TLRs (e.g. TLR4,TLR7 and TLR8) were expressed by freshly isolated human bone marrow (BM) hematopoietic CD34+ progenitor cells. Incubation of these primitive cells with TLR ligands such as immunostimulatory small interfering RNAs and R848,a specific ligand for TLR7/8,induced cytokine production (e.g. IL1-beta,IL6,IL8,TNF-alpha,GM-CSF). Moreover,TLR7/8 signaling induced the differentiation of BM CD34+ progenitors into cells with the morphology of macrophages and monocytic dendritic precursors characterized by the expression of CD13,CD14 and/or CD11c markers. By contrast,R848 ligand did not induce the expression of glycophorin A,an early marker for erythropoiesis. Collectively,the data indicate for the first time that human BM CD34+ progenitor cells constitutively express functional TLR7/TLR8,whose ligation can induce leukopoiesis without the addition of any exogenous cytokines. Thus,TLR signaling may regulate BM cell development in humans. View Publication

Of paramount importance for the development of cell therapies to treat diabetes is the production of sufficient numbers of pancreatic endocrine cells that function similarly to primary islets. We have developed a differentiation process that converts human embryonic stem (hES) cells to endocrine cells capable of synthesizing the pancreatic hormones insulin,glucagon,somatostatin,pancreatic polypeptide and ghrelin. This process mimics in vivo pancreatic organogenesis by directing cells through stages resembling definitive endoderm,gut-tube endoderm,pancreatic endoderm and endocrine precursor--en route to cells that express endocrine hormones. The hES cell-derived insulin-expressing cells have an insulin content approaching that of adult islets. Similar to fetal beta-cells,they release C-peptide in response to multiple secretory stimuli,but only minimally to glucose. Production of these hES cell-derived endocrine cells may represent a critical step in the development of a renewable source of cells for diabetes cell therapy. View Publication

Recent population studies provide clues that the use of metformin may be associated with reduced incidence and improved prognosis of certain cancers. This drug is widely used in the treatment of type 2 diabetes,where it is often referred to as an insulin sensitizer" because it not only lowers blood glucose but also reduces the hyperinsulinemia associated with insulin resistance. As insulin and insulin-like growth factors stimulate proliferation of many normal and transformed cell types� View Publication