Distinct signals control the hematopoiesis of lymphoid-related dendritic cells

IL-10 in the microenvironment of HNSCC inhibits the CpG ODN induced IFN-α secretion of pDCs

It has been shown that head and neck squamous cell carcinoma (HNSCC) are infiltrated by plasmacytoid dendritic cells (pDCs). The HNSCC TH2 biased microenvironment leads to strong alterations of the cellular functions of pDC and thus impairs the initiation and function of adequate immune responses. In this work we comprehensively analyzed the capacity of CpG-oligonucleotides to activate interferon (IFN)-α secretion of human pDC in the presence of HNSCC. IFN-α secretion was measured using the ELISA Technique. Class A CpG dinucleotide 2216 was used in different concentrations and time frames to stimulate the IFN-α production of human pDC from peripheral blood in the absence and presence of the HNSCC microenvironment. To elucidate single components that might induce the reduction of IFN-α secretion, pDC were exposed to different concentrations of HNSCC relevant cytokines such as IL-6, IL-8 and IL-10. In accordance to former experiments we found that HNSCC micro milieu severely depresses up to 75% of IFN-α secretion capacity of pDCs, if the stimulating Class A CpG 2216 is added to the culture. Preincubation of HNSCC supernatant leads to unrestorable reduction of IFN-α secretion in pDC and can not be restored by CpG 2216. Incubation of pDCs with single cytokines relevant for cancer progression within the HNSCC micro milieu show that IL-6 or IL-8 have no influence on the IFN-α secretion in pDCs, whereas IL-10 massively impairs the secretion in a dose dependent manner. This effect can be potentiated by synergistic incubation with IL-6 and can be abrogated by blocking antibodies to the IL-10 receptor. Interestingly, incubation with IL-10 is not the only factor that impairs the IFN-α secretion, as incubation with the whole HNSCC supernatant is even more effective in reducing the secretion, implying that additional factors play a role. We conclude that restoration of HNSCC induced TH2 bias could be improved by the inhibition of immune cell cytokine receptors in addition to immunostimulating approaches with CpG motifs.

Regulation of PI3K signaling in T-cell acute lymphoblastic leukemia: a novel PTEN/Ikaros/miR-26b mechanism reveals a critical targetable role for PIK3CD

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy, and T-ALL patients are prone to early disease relapse and suffer from poor outcomes. The PTEN, PI3K/AKT, and Notch pathways are frequently altered in T-ALL. PTEN is a tumor suppressor that inactivates the PI3K pathway. We profiled miRNAs in Pten-deficient mouse T-ALL and identified miR-26b as a potentially dysregulated gene. We validated decreased expression levels of miR-26b in mouse and human T-ALL cells. In addition, expression of exogenous miR-26b reduced proliferation and promoted apoptosis of T-ALL cells in vitro, and hindered progression of T-ALL in vivo. Furthermore, miR-26b inhibited the PI3K/AKT pathway by directly targeting PIK3CD, the gene encoding PI3Kδ, in human T-ALL cell lines. ShRNA for PIK3CD and CAL-101, a PIK3CD inhibitor, reduced the growth and increased apoptosis of T-ALL cells. Finally, we showed that PTEN induced miR-26b expression by regulating the differential expression of Ikaros isoforms that are transcriptional regulators of miR-26b. These results suggest that miR-26b functions as a tumor suppressor in the development of T-ALL. Further characterization of targets and regulators of miR-26b may be promising for the development of novel therapies.

IKAROS: a multifunctional regulator of the polymerase II transcription cycle

Transcription factors are important determinants of lineage specification during hematopoiesis. They favor recruitment of cofactors involved in epigenetic regulation, thereby defining patterns of gene expression in a development- and lineage-specific manner. Additionally, transcription factors can facilitate transcription preinitiation complex (PIC) formation and assembly on chromatin. Interestingly, a few lineage-specific transcription factors, including IKAROS, also regulate transcription elongation. IKAROS is a tumor suppressor frequently inactivated in leukemia and associated with a poor prognosis. It forms a complex with the nucleosome remodeling and deacetylase (NuRD) complex and the positive transcription elongation factor b (P-TEFb), which is required for productive transcription elongation. It has also been reported that IKAROS interacts with factors involved in transcription termination. Here we review these and other recent findings that establish IKAROS as the first transcription factor found to act as a multifunctional regulator of the transcription cycle in hematopoietic cells.

Dextromethorphan inhibits activations and functions in dendritic cells

Dendritic cells (DCs) play an important role in connecting innate and adaptive immunity. Thus, DCs have been regarded as a major target for the development of immunomodulators. In this study, we examined the effect of dextromethorphan (DXM), a common cough suppressant with a high safety profile, on the activation and function of DCs. In the presence of DXM, the LPS-induced expression of the costimulatory molecules in murine bone marrow-derived dendritic cells (BMDCs) was significantly suppressed. In addition, DXM treatment reduced the production of reactive oxygen species (ROS), proinflammatory cytokines, and chemokines in maturing BMDCs that were activated by LPS. Therefore, DXM abrogated the ability of LPS-stimulated DCs to induce Ag-specific T-cell activation, as determined by their decreased proliferation and IFN-γ secretion in mixed leukocyte cultures. Moreover, the inhibition of LPS-induced MAPK activation and NF-κB translocation may contribute to the suppressive effect of DXM on BMDCs. Remarkably, DXM decreased the LPS-induced surface expression of CD80, CD83, and HLA-DR and the secretion of IL-6 and IL-12 in human monocyte-derived dendritic cells (MDDCs). These findings provide a new insight into the impact of DXM treatment on DCs and suggest that DXM has the potential to be used in treating DC-related acute and chronic diseases.

Ikaros-Notch axis in host hematopoietic cells regulates experimental graft-versus-host disease

Host hematopoietically derived APCs play a vital role in the initiation of GVH responses. However, the APC autonomous molecular mechanisms that are critical for the induction of GVHD are not known. We report here that the Ikaros-Notch axis in host hematopoietically derived APCs regulates the severity of acute GVHD across multiple clinically relevant murine models of experimental bone marrow transplantation. In the present study, Ikaros deficiency (Ik(-/-)) limited to host hematopoietically derived APCs enhanced donor T-cell expansion and intensified acute GVHD, as determined by survival and other GVHD-specific parameters. The Ik(-/-) conventional CD8(+) and CD8(-)CD11c(+) dendritic cells (DCs), the most potent APCs, showed no increase in the expression of activation markers or in response to TLR stimulation compared with wild-type controls. However, Ik(-/-) DCs demonstrated an enhanced stimulation of allogeneic T cells. Deficiency of Ikaros in the conventional CD8(+) and CD8(-)CD11c(+) DCs was associated with an increase in Notch signaling, the blockade of which mitigated the enhanced in vitro and in vivo allostimulatory capacity. Therefore, the Ikaros-Notch axis is a novel pathway that modulates DC biology in general, and targeting this pathway in host hematopoietically derived APCs may reduce GVHD.

Ikaros confers early temporal competence to mouse retinal progenitor cells

In the developing mouse retina, multipotent retinal progenitor cells (RPCs) give rise to specific retinal cell types at different times, but the molecular mechanisms regulating how RPCs change over time remain unclear. In the Drosophila neuroblast lineage, the zinc finger transcription factor Hunchback (Hb) is both necessary and sufficient to specify early-born neuronal identity. We show here that Ikaros, a mouse ortholog of Hb, is expressed in all early embryonic RPCs, which then give rise to Ikaros-negative RPCs at later stages in the lineage. Remarkably, misexpression of Ikaros in late RPCs is sufficient to confer competence to generate early-born neurons. Conversely, Ikaros mutant mice have reduced numbers of early-born cell types, whereas late-born cell types are not affected. These results suggest a model in which Ikaros expression is both necessary and sufficient to confer early temporal competence to RPCs and raise the possibility that a similar strategy might be used to control the sequential order of cell birth in other parts of the nervous system.

The role of Ikaros in human erythroid differentiation

Ikaros—a factor that positively or negatively controls gene transcription—is active in murine adult erythroid cells, and involved in fetal to adult globin switching. Mice with Ikaros mutations have defects in erythropoiesis and anemia. In this paper, we have studied the role of Ikaros in human erythroid development for the first time. Using a gene-transfer strategy, we expressed Ikaros 6 (Ik6)—a known dominant-negative protein that interferes with normal Ikaros activity—in cord blood or apheresis CD34+ cells that were induced to differentiate along the erythroid pathway. Lentivirally induced Ik6-forced expression resulted in increased cell death, decreased cell proliferation, and decreased expression of erythroid-specific genes, including GATA1 and fetal and adult globins. In contrast, we observed the maintenance of a residual myeloid population that can be detected in this culture system, with a relative increase of myeloid gene expression, including PU1. In secondary cultures, expression of Ik6 favored reversion of sorted and phenotypically defined erythroid cells into myeloid cells, and prevented reversion of myeloid cells into erythroid cells. We conclude that Ikaros is involved in human adult or fetal erythroid differentiation as well as in the commitment between erythroid and myeloid cells.

Development of human lymphoid cells

The lymphocytes, T, B, and NK cells, and a proportion of dendritic cells (DCs) have a common developmental origin. Lymphocytes develop from hematopoietic stem cells via common lymphocyte and various lineage-restricted precursors. This review discusses the current knowledge of human lymphocyte development and the phenotypes and functions of the rare intermediate populations that together form the pathways of development into T, B, and NK cells and DCs. Clearly, development of hematopoietic cells is supported by cytokines. The studies of patients with genetic deficiencies in cytokine receptors that are discussed here have illuminated the importance of cytokines in lymphoid development. Lineage decisions are under control of transcription factors, and studies performed in the past decade have provided insight into transcriptional control of human lymphoid development, the results of which are summarized and discussed in this review.

The aging of early B-cell precursors

B-cell genesis in the bone marrow declines with advancing age. In this review, we discuss our current understanding of why B-cell production rates decline with age with a special emphasis on why age-related factors might target very early lymphoid precursors. We consider the impact of aging on cytokine responsiveness and how current models for lineage relationships for very early B- and T-cell precursors might influence interpretations of experiments addressing age-associated declines in B- and T-cell differentiation. This discussion centers on the notion that aging affects events associated with the process by which hematopoietic stem cells are guided toward the B-cell pathway. Finally, we present a model in which the age-associated loss of early B-cell precursors is linked to suboptimal function of key transcriptional regulators of very early B-cell development.

Identification and characterization of pDC-like cells in normal mouse skin and melanomas treated with imiquimod

Among the different subsets of dendritic cells (DC) described in humans and mice, epidermal Langerhans cells and dermal DCs represent the only DC populations resident in normal skin. In this study we describe a population of CD4(+)CD3(-) plasmacytoid DC (pDC)-like cells that accumulate in the dermis and spleens of mice topically treated with imiquimod, a low m.w. immune response modifier with potent antiviral and antitumor activities. These CD4(+)CD3(-) cells coexpress GR-1, B220, MHC class II, and, to a lesser extent, CD11c and display the phenotypic features of pDCs described in lymphoid organs. The accumulation of pDC-like cells after imiquimod treatment was detected not only in normal skin, but also in intradermally induced melanomas. Imiquimod treatment leads either to complete regression or to a significant reduction of the tumors. The number of pDCs correlates well with the clinical response of the tumors to the drug, suggesting that the antitumor effects of imiquimod could be mediated at least in part by the recruitment of pDC-like cells to the skin. Therefore, strategies aimed at activating and directing these cells into neoplastic tissues may be a promising and novel approach for the immunotherapy of various types of cancer.

Regulation of IFN Regulatory Factor-7 and IFN-α Production by Enveloped Virus and Lipopolysaccharide in Human Plasmacytoid Dendritic Cells

Human plasmacytoid dendritic cells (PDC) are a major source of IFN-alpha upon exposure to enveloped viruses and TLR-7 and TLR-9 ligands. Although IFN regulatory factor-7 (IRF-7) is known to play an essential role in virus-activated transcription of IFN-alpha genes, the molecular mechanisms of IFN-alpha production in human PDC remain poorly understood. We and others have recently reported high constitutive levels of IRF-7 expression in PDC as compared with other PBMC. In this study, we demonstrate that both LPS and HSV up-regulate the expression of IRF-7 in PDC, and that this enhancement of IRF-7 is dependent on NF-kappa B activation. The NF-kappa B inhibitors MG132 and pyrrolidinedithiocarbamate efficiently inhibited the induction of IRF-7 by HSV or LPS, and also down-regulated the constitutive expression of IRF-7 in PDC and blocked the HSV-induced production of IFN-alpha. In addition, we found that nuclear translocation of IRF-7 occurred rapidly in response to HSV stimulation, but not in response to LPS, which is consistent with the stimulation of IFN-alpha production by virus and not by LPS. Although LPS by itself was not able to induce IFN-alpha production, it led to rapid up-regulation of TLR-4 on PDC and increased the magnitude and accelerated the kinetics of HSV-induced IFN-alpha production in PDC, providing a mechanism that might be operative in a scenario of mixed infection. In contrast to the current concept of IFN-alpha regulation established in cell lines, this study strongly supports the immediate availability of high constitutive levels of IRF-7 expression in PDC, and suggests an activation required for IRF-7 that contributes to IFN-alpha production in virus-stimulated PDC.

Virally stimulated plasmacytoid dendritic cells produce chemokines and induce migration of T and NK cells

The natural interferon (IFN)-producing cell is now known to be identical to the plasmacytoid dendritic cell (PDC). These are Lin-, CD123+, CD11c-, and human leukocyte antigen-DR+ cells that secrete large amounts of IFN-alpha (1-2 IU/cell) when stimulated by enveloped viruses such as herpes simplex virus. In the current study, we have evaluated chemokine expression by virally stimulated PDC. Up-regulation of mRNA for CCL4, CCL3, CCL5, CCL2, and CXC chemokine ligand (CXCL)10 in herpes simplex virus-stimulated PDC was detected by RNAse protection assays. In contrast, PDC-depleted peripheral blood mononuclear cells did not up-regulate these mRNA species upon viral stimulation. Enzyme-linked immunosorbent assay and/or intracellular flow cytometry confirmed production of these proteins, and studies indicated overlapping production of IFN-alpha and the other cytokines/chemokines by PDC. Endocytosis plays a critical role in chemokine induction, as disruption of the pathway inhibits the response. However, transcription of viral genes is not required for chemokine induction. Autocrine IFN-alpha signaling in the PDC could account for a portion of the CXCL10 and CCL2 production in virally stimulated PDC but was not responsible for the induction of the other chemokines. To evaluate the functional role of the chemokines, chemotaxis assays were performed using supernatants from virally stimulated PDC. Activated T cells and natural killer cells, but not naïve T cells, were preferentially recruited by these PDC supernatants. Migration was subsequently inhibited by addition of neutralizing antibody to CCL4 and CXCL10. We hypothesize that virally induced chemokine production plays a pivotal role in the homing of leukocytes to PDC.

4-1BB-ligand is regulated on human dendritic cells and induces the production of IL-12

Co-stimulation via 4-1BB and its ligand 4-1BB ligand (4-1BB-L) plays an important role in cytotoxic and pro-inflammatory immune responses. 4-1BB-L is generally described on activated antigen-presenting cells but there is limited information on its expression and function in human dendritic cells (DC). We herein compared purified CD1a+CD14- DC issued from monocytes or from hematopoietic progenitor cells (HPC). These DC expressed 4-1BB-L mRNA transcripts with highest cell surface levels on HPC-derived DC cultured with IL-1. Pro-inflammatory activation, particularly CD40 ligand+IL-1, up-regulated 4-1BB-L on DC. We confirmed reverse signaling via 4-1BB-L as immobilized 4-1BB in conjunction with CD40-L, enhanced IL-12beta mRNA and the secretion of IL-12 p70 in various APC, including monocytes. Altogether, DC may differ in T cell co-stimulation properties due to variable and regulated levels of 4-1BB-L. Data illustrate reciprocal stimulations between T cells and APC via up-regulated receptor/ligands and production of key cytokines that consolidate cellular immune responses.

Activation with CpG-A and CpG-B oligonucleotides reveals two distinct regulatory pathways of type I IFN synthesis in human plasmacytoid dendritic cells

Two different CpG oligonucleotides (ODN) were used to study the regulation of type I IFN in human plasmacytoid dendritic cells (PDC): ODN 2216, a CpG-A ODN, known to induce high amounts of IFN-alpha in PDC, and ODN 2006, a CpG-B ODN, which is potent at stimulating B cells. CpG-A ODN showed higher and prolonged kinetics of type I IFN production compared with that of CpG-B ODN. In contrast, CpG-B ODN was more active than CpG-A ODN in stimulating IL-8 production and increasing costimulatory and Ag-presenting molecules, suggesting that CpG-A and CpG-B trigger distinct regulatory pathways in PDC. Indeed, CpG-A ODN, but not CpG-B ODN, activated the type I IFNR-mediated autocrine feedback loop. PDC were found to express high constitutive levels of IFN regulatory factor (IRF)7. IRF7 and STAT1, but not IRF3, were equally up-regulated by both CpG-A and CpG-B. CD40 ligand synergistically increased CpG-B-induced IFN-alpha independent of the IFNR but did not affect CpG-B-induced IFN-beta. In conclusion, our studies provide evidence for the existence of two distinct regulatory pathways of type I IFN synthesis in human PDC, one dependent on and one independent of the IFNR-mediated feedback loop. The alternate use of these pathways is based on the type of stimulus rather than the quantity of IFN-alphabeta available to trigger the IFNR. Constitutive expression of IRF7 and the ability to produce considerable amounts of IFN-alpha independent of the IFNR seem to represent characteristic features of PDC.

Plasmacytoid dendritic cells: a new cutaneous dendritic cell subset with distinct role in inflammatory skin diseases

Epidermal dendritic cells found in inflamed skin include Langerhans cells and the recently identified population of inflammatory dendritic epidermal cells. Another subset of dendritic cells in humans is the plasmacytoid dendritic cell in peripheral blood, which is characterized by the production of large amounts of type I interferon (interferon-alpha and interferon-beta) upon viral infection. We hypothesized that plasmacytoid dendritic cells might be involved in anti-viral defense mechanisms of the skin. Here we investigated plasmacytoid dendritic cells, inflammatory dendritic epidermal cells, and Langerhans cells in epidermal single cell suspensions of normal looking skin from healthy volunteers and of lesional skin from patients with different inflammatory skin diseases. Langerhans cells were found in normal and in inflamed skin samples. In normal skin, plasmacytoid dendritic cells and inflammatory dendritic epidermal cells were low or absent. Lesional skin samples from patients with psoriasis vulgaris and contact dermatitis contained relatively high numbers of both inflammatory dendritic epidermal cells and plasmacytoid dendritic cells. In contrast, many inflammatory dendritic epidermal cells but only very few plasmacytoid dendritic cells could be detected in atopic dermatitis lesions. Lupus erythematosus was characterized by high numbers of plasmacytoid dendritic cells but low numbers of inflammatory dendritic epidermal cells. These results demonstrate that in addition to resident Langerhans cells, plasmacytoid dendritic cells and inflammatory dendritic epidermal cells are selectively recruited to the skin lesions depending on the type of skin disease. The lack of plasmacytoid dendritic cells in atopic dermatitis may predispose atopic dermatitis patients to viral infections such as eczema herpeticum, a secondary infection of atopic dermatitis lesions with herpes simplex virus. The composition of dendritic cell subsets may help to clarify the etiology of inflammatory skin diseases and forms the basis for therapeutic intervention with selective microbial molecules such as immunostimulatory CpG oligonucleotides.

Human hematopoietic lineage commitment

The ultimate goal of developmental immunology is to understand the normal processes that give rise to the immune system in order to diagnose and develop effective treatments for diseases that occur as a consequence of immune system defects. Central to achieving this goal is understanding the complex interplay between microenvironmental signals and transcription factors that direct human hematopoietic differentiation and lineage commitment. The ability to isolate highly purified populations of human hematopoietic cells at critical points in differentiation make it possible to answer very specific questions about the hematopoietic process and lineage restriction. This review describes the use of surface immunophenotypes to identify human hematopoietic cells at particular points in differentiation or with particular patterns of lineage restriction. Culture models are discussed in the context of the ability to detect, characterize and determine the lineage potential of human hematopoietic stem cells and progenitors. Variations in hematopoeises that correspond to ontogeny will be examined. Potential roles for the HOX and Ikaros proteins in human lineage commitment will be considered. Also included will be discussion of a number of factors that provide challenges to experimental design, to experimental interpretation, and to the development of a comprehensive model of human hematopoiesis.

Cutaneous lymphoblastic lymphoma of putative plasmacytoid dendritic cell-precursor origin: two cases

Although the neoplasm of relatively mature type plasmacytoid dendritic cells (pDC) was recently reported, that of pDC-precursor has not yet been defined. We experienced two elderly male Japanese patients with reddish skin tumors. The histology of the tumors in both patients showed terminal deoxinucleotidyl transferase (TdT)-positive lymphoblastic lymphoma (LBL). The pathological cells did not express T, B or NK markers, and no rearranged bands were shown for immunoglobulin (Ig)-JH, T cell receptor (TCR)-C beta, J gamma, J delta1, and c-myc. In addition, no Epstein-Barr virus (EBV)-derived DNA was detected in either case. The cells were (CD45, CD43, CD74, CD10, and HLA-DR)-positive in both cases, and one of the cases showed (CD4, CD36, CD54, CD58 and CD86)-positive plasmacytoid lymphoblasts, which appeared to be compatible with intermediate cells between human bone marrow lymphoid precursors and mature lymphoid DC. The cutaneous LBL in the two cases may, therefore, have been of pDC-precursor origin.

Haematopoietic cell-fate decisions, chromatin regulation and ikaros

The regulated production of several terminally differentiated cell types of the blood and immune systems (haematopoiesis) has been the focus of many studies on cell-fate determination. Chromatin and the control of its structure have been implicated in the regulation of cell-fate decisions and in the maintenance of the determined states. Here, I review advances in the field, emphasizing the potential role of chromatin in lineage commitment and differentiation. In this context, I discuss Ikaros, an essential regulator of lymphocyte development and an integral component of a functionally diverse chromatin remodelling network that operates from the early stages of haematopoiesis to the mature lymphocytes.

High frequency of Ikaros isoform 6 expression in acute myelomonocytic and monocytic leukemias: implications for up-regulation of the antiapoptotic protein Bcl-XL in leukemogenesis

While studying Ikaros proteins in childhood acute myeloid leukemia (AML), Ikaros isoform 6 (Ik6) expression was detected in 7 of 10 cases of M4 and M5 leukemia, but in none of the remaining French-American-British subtypes (M2, 8 cases; M7, 6 cases). The spliced Ikaros isoforms 4 to 8 (Ik4-8) suppress the function of full-length Ik1 or Ik2 in a dominant-negative manner, owing to their reduced numbers of DNA binding sites. Thus, dominant-negative Ikaros isoforms may inhibit the normal transcriptional regulation of hematopoietic cell development. To clarify the function of Ik6 in developing blood cells, this isoform was transiently transfected into an Ik2(+), interleukin-3 (IL-3)-dependent 32D murine myeloid precursor cell line and studied the expression of Bcl-2 family proteins in relation to in vitro cell growth, using a tetracycline-inducible TREx system. The possibility of aberrant cell regulation due to Ikaros functional changes was examined by cotransfecting both Ik2 and Ik6 into Ikaros/Aiolos/Helios triple-negative Cos-7 cells. The results demonstrated IL-3-independent growth by Ik6-transfected 32D clones coincident with up-regulation of the antiapoptotic protein Bcl-XL. Up-regulation of Bcl-XL, but not of other Bcl-2 family proteins, was associated with the suppression of functional Ik2 by Ik6 in a dominant-negative fashion. Thus, the pathogenesis of myelomonocytic/monocytic AML may involve aberrant regulation of apoptosis due to unscheduled expression of the Ik6 isoform.

Acute T-lymphoblastic leukemia relapsed with the character of myeloid/natural killer cell precursor phenotype: a case report

The leukemic lymphoblasts of a patient expressed CD7, CD13, CD33, CD34, HLA-DR and cytoplasmic CD3varepsilon. He was diagnosed with acute lymphoblastic leukemia (ALL), and successfully treated with a conventional chemotherapy for ALL. The disease relapsed three times, and the character of the cells gradually altered, i.e. CD56 expression increased and CD13, CD7 and cCD3 epsilon decreased. The phenotype of the relapsed ALL was, therefore, compatible with myeloid/natural killer cell precursor acute leukemia (M/NK-AL). Some of M/NK-AL may be closely related with T/myeloid-biphenotypic pro-T blasts, and both types of acute leukemia may develop a tendency to express myeloid antigens, and they may belong to the category of immature T lymphoid precursors.

Enforced expression of the Ikaros isoform IK5 decreases the numbers of extrathymic intraepithelial lymphocytes and natural killer 1.1+ T cells

The zinc-finger protein Ikaros plays an important role in lymphoid homeostasis, and loss of Ikaros expression through germline disruption impairs lymphoid development. However, the role played by Ikaros after commitment to the T-cell lineage is unclear. To address this question, this study used the lck proximal promoter to drive the expression in T-cell progenitors of a naturally occurring short Ikaros isoform (IK5), which lacks the DNA-binding domain, reasoning that IK5 will form heterodimers with long isoforms and perturb their function. The IK5 transgene led to a selective and dramatic decrease in extrathymic intestinal intraepithelial lymphocytes (IELs) and natural killer 1.1+ T (NK T) cells with little effect on conventional alphabeta T cells, which resembles the T-cell phenotype of interleukin-15 receptor alpha chain (IL-15Ralpha) and IL-2/IL-15 receptor beta chain (IL-2Rbeta) knockout mice. The expression of IL-2Rbeta on double-negative T-cell progenitors of bi-5 was reduced, but enforced expression of IL-2Rbeta did not rescue IELs or NK T cells in bi-5 transgenic mice, suggesting that Ikaros or Ikaros family members regulate the expression of additional genes that are essential for the development of IELs and NK T cells. The study concludes that modest changes in the ratio of short to long Ikaros isoforms can substantially perturb T-cell development, and the development of IELs and NK T cells is particularly sensitive to such changes.

Dendritic cells: a complex simplicity

Dendritic cells (DC) are essential antigen-presenting cells that initiate and regulate adaptive immune responses. There are distinct DC populations of diverse origins, which develop from hematopoietic progenitors already committed to the lymphoid or the myeloid lineages and, in the latter case, even from terminally differentiated macrophages. One may assume that DC of lymphoid origin are dedicated to the adaptive immune system, along which they have phylogenetically co-evolved, whereas myeloid DC would be more involved as an interface between the innate and adaptive immune systems. However, any DC can ultimately present antigens in either an immunogenic or tolerogenic manner according to whether they are more or less or not at all activated towards maturation, depending on the condition under which they encountered antigen. Hence, DC either induce the appropriate immune response to pathogens or prevent autoimmune reactivity. Thus, besides default programming, which should be necessary to face the challenges of their usual setting, each type of DC can also display functions that are similar, in an instructive mode, to elicit immune responses deemed necessary for unexpected stimuli. In such a system, DC provide enough flexibility and sufficient redundancy to ensure that an essential function of the immune system, i.e., passing information from its innate to adaptive arms and affecting the latter's responses, occurs under optimal conditions. Working on the basis of such a unified theory of DC diversity should be useful for learning to adequately manipulate the immune system for the development of cellular immunotherapy.

Ikaros gene expression and leukemia

The Ikaros (Ik) protein, or LyF1, was initially described as a protein binding to regulatory sequences of a number of genes expressed in murine lymphoid cells. Ikaros is a critical regulator of normal hematopoietic stem cell differentiation, as evidenced by dramatic defects in the lymphoid compartments, in homozygous animals with gene inactivation. Because differential splicing produces multiple isoforms with potentially different functions, Ikaros provides a unique model to study how post-transcriptional mechanisms may be involved in neoplastic processes. Indeed, several groups including ours have underlined evidences that expression of different Ikaros isoforms vary among different types of leukemias. The predominance of short isoforms in certain subsets is intriguing. Here, additional observations reinforced the hypothesis that Ikaros expression may be deregulated in human leukemias. Whether this is a cause or a consequence of the leukemic process remains speculative. Other human diseases however, provide examples of abnormal post-transcriptional regulations that have been further characterized.

Forced expression of the Ikaros 6 isoform in human placental blood CD34(+) cells impairs their ability to differentiate toward the B-lymphoid lineage

Studies in mice suggest that the Ikaros (Ik) gene encodes several isoforms and is a critical regulator of hematolymphoid differentiation. Little is known on the role of Ikaros in human stem cell differentiation. Herein, the biological consequences of the forced expression of Ikaros 6 (Ik6) in human placental blood CD34(+) progenitors are evaluated. Ik6 is one of the isoforms produced from the Ikaros premessenger RNA by alternative splicing and is thought to behave as a dominant negative isoform of the gene product because it lacks the DNA binding domain present in transcriptionally active isoforms. The results demonstrate that human cord blood CD34(+) cells that express high levels of Ik6 as a result of retrovirally mediated gene transfer have a reduced capacity to produce lymphoid B cells in 2 independent assays: (1) in vitro reinitiation of human hematopoiesis during coculture with the MS-5 murine stromal cell line and (2) xenotransplantation in nonobese diabetic-severe combined immunodeficient mice. These results suggest that Ikaros plays an important role in stem cell commitment in humans and that the balance between the different isoforms is a key element of this regulatory system; they support the hypothesis that posttranscriptional events can participate in the control of human hematopoietic differentiation.

Delineation of intrathymic T, NK, and dendritic cell (DC) progenitors in fetal and adult rats: demonstration of a bipotent T/DC intermediate precursor

We previously published study results stating that the early rat fetal liver contains a high frequency of T/dendritic cells (DCs), but rarely T/NK bipotent common progenitors. Now, by using xenogenic rat/SCID mouse fetal thymic organ cultures, we extend these observations to the thymus, in which conflicting data have been published in human and mouse. On the one hand, enriched adult intrathymic CD45+CD2- triple negative for CD8, CD4, and CD3 Ag cell progenitors, which contained both rearranged TCRbeta chain and pre-Talpha chain transcripts, completely lacked NKR-P1A expressing cells, and upon limiting dilution conditions, generated T- and T/DC-containing lobes, but no T/NK or NK ones were found. On the other hand, the CD45+CD2- triple negative for CD8, CD4, and CD3 Ags cell population obtained from 15- and 16-day-old fetal rat thymus can be divided into NKR-P1A- and NKR-P1A(low) cell subpopulations that differ in several aspects. Both cell subsets expressed pre-TCRalpha chain transcripts, but only the former contained fully rearranged TCRbeta chain transcripts. Upon limiting dilution, T cell-committed progenitors were only found in the NKR-P1A- cell population, whereas NK-committed progenitors were present in the NKR-P1A(low) population. More importantly, bipotential T/NK progenitors were very rare and were found only in the NKR-P1A(low) cell population, whereas bipotential T/DC progenitors, only previously suggested in the adult mouse thymus, were observed frequently in the NKR-P1A-CD2- cell subpopulation. Our results demonstrate, therefore, that a common intrathymic T/DC intermediate represents the main T cell developmental pathway in rat thymus.

Identification of CpG oligonucleotide sequences with high induction of IFN-alpha/beta in plasmacytoid dendritic cells

The immature plasmacytoid dendritic cell (PDC) is identical with the principal type I IFN-producing cell upon viral infection. Oligodeoxynucleotides which contain unmethylated CpG motifs (CpG ODN) are recognized by the vertebrate immune system. Previously, we described CpG ODN that strongly activate human B cells and human blood dendritic cells. Here we describe distinct CpG-containing oligonucleotide sequences which, in contrast to previously described CpG ODN, induced high amounts of IFN-alpha and IFN-beta in peripheral blood mononuclear cells (PBMC). Intracellular staining for IFN-alpha revealed that within PBMC CpG ODN-induced IFN-alpha is produced exclusively by PDC. Unlike IFN-alpha, TNF-alpha is up-regulated in PDC by all CpG ODN tested. Purified PDC responded to CpG ODN, demonstrating direct activation of PDC by CpG ODN. The most active sequence induced the production of up to 5 pg IFN-alpha per single PDC, resulting in more than 400 ng/ml IFN-alpha in the supernatant of PBMC enriched for PDC. The potency of CpG ODN to stimulate IFN-alpha correlated with their ability to stimulate NK cell lytic activity, while purified NK cells did not respond to CpG ODN. IFNgamma production in PBMC was dependent on CpG ODN-induced IFN-alpha/beta as demonstrated by IFN-alpha/beta blocking antibodies. IFN-alpha-inducing CpG ODN strongly supported IFN-gamma production of TCR-triggered CD4 T cells but were less active than other CpG ODN in stimulating B cells. In conclusion our results demonstrate that particular CpG ODN sequences exist which, due to high IFN-alpha/beta induction in PDC, induce a set of immune responses typical for viral infection.

Regulation of T cell cytokine production by dendritic cells generated in vitro from hematopoietic progenitor cells

When dendritic cells (DC) present antigens to T cells, reciprocal cellular interactions occur that lead to cytokine production. This cytokine response is regulated by specific properties of DC, notably their maturation/activation status and perhaps their origin. The latter possibility prompted us to determine if DC produced along distinct developmental pathways induced distinct T cell responses. Hematopoietic progenitor cells with the potential to differentiate into multiple lineages of cells were induced to differentiate into DC along two pathways. One leads to the formation of lymphoid-related DC but not of monocyte-derived DC and is induced by culture of CD34(+) cells with flt-3 ligand (F), c-kit ligand (K), GM-CSF (Gm), IL-1beta ("1"), and IL-7 ("7") (FKGm17). Another pathway with distinct molecular requirements supports in part monocyte-derived DC and is induced by the cytokines F, K, Gm, TNF-alpha (T), and IL-4 ("4") (FKGmT4). DC produced along these two pathways were isolated by flow cytometry and compared. They differed only slightly in phenotype and morphology and both induced Th1-type cytokine production in MLR (mixed lymphocyte reactions). However, on a cell-per-cell basis, FKGm17-DC produced more IL-18 or IL-12 and induced more IFN-gamma by T cells in MLR. Such superior properties were not intrinsically determined by the origin of the DC but were induced by FKGm17 cytokines. We conclude that lymphoid-related DC have the potential to induce Th1 T cell responses but that environmental signals strongly influence T-cell-stimulating properties of DC.

Derivation of dendritic cells from myeloid and lymphoid precursors

The antigen presenting dendritic cells (DC) found in mouse and human lymphoid tissues are heterogeneous. Several subsets of mature DC have been described and these may correspond to distinct lineages. In this review, we present evidence obtained from a series of studies on the lineage origin of DC. This evidence points to the existence of at least three pathways for DC development, namely one from myeloid progenitors, a second from lymphoid progenitors and the third for Langerhans cells from precursors whose relationship to myeloid or lymphoid cell types is not yet clearly defined.

Effects of cytokines on the culture and differentiation of dendritic cells in vitro

The ability to culture dendritic cells (DC) in vitro has been integral to the dramatic increase in research in the area of immunotherapy. Over time, a number of methods for generating these cells have been developed. This article will provide an overview of the isolation and generation of DC and will give a detailed description of the role specific cytokines play in this process from the mobilization of precursors to the final maturation of DC.

CD8(+) but not CD8(-) dendritic cells cross-prime cytotoxic T cells in vivo

Bone marrow-derived antigen-presenting cells (APCs) take up cell-associated antigens and present them in the context of major histocompatibility complex (MHC) class I molecules to CD8(+) T cells in a process referred to as cross-priming. Cross-priming is essential for the induction of CD8(+) T cell responses directed towards antigens not expressed in professional APCs. Although in vitro experiments have shown that dendritic cells (DCs) and macrophages are capable of presenting exogenous antigens in association with MHC class I, the cross-presenting cell in vivo has not been identified. We have isolated splenic DCs after in vivo priming with ovalbumin-loaded beta2-microglobulin-deficient splenocytes and show that they indeed present cell-associated antigens in the context of MHC class I molecules. This process is transporter associated with antigen presentation (TAP) dependent, suggesting an endosome to cytosol transport. To determine whether a specific subset of splenic DCs is involved in this cross-presentation, we negatively and positively selected for CD8(-) and CD8(+) DCs. Only the CD8(+), and not the CD8(-), DC subset demonstrates cross-priming ability. FACS((R)) studies after injection of splenocytes loaded with fluorescent beads showed that 1 and 0.6% of the CD8(+) and the CD8(-) DC subsets, respectively, had one or more associated beads. These results indicate that CD8(+) DCs play an important role in the generation of cytotoxic T lymphocyte responses specific for cell-associated antigens.

Characterization of dendritic cell differentiation pathways from cord blood CD34+CD7+CD45RA+hematopoietic progenitor cells

To better characterize human dendritic cells (DCs) that originate from lymphoid progenitors, the authors examined the DC differentiation pathways from a novel CD7+CD45RA+ progenitor population found among cord blood CD34+ cells. Unlike CD7−CD45RA+ and CD7+CD45RA− progenitors, this population displayed high natural killer (NK) cell differentiation capacity when cultured with stem cell factor (SCF), interleukin (IL)-2, IL-7, and IL-15, attesting to its lymphoid potential. In cultures with SCF, Flt3 ligand (FL), granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor (TNF)-α (standard condition), CD7+CD45RA+ progenitors expanded less (37- vs 155-fold) but yielded 2-fold higher CD1a+ DC percentages than CD7−CD45RA+ or CD7+CD45RA− progenitors. As reported for CD34+CD1a− thymocytes, cloning experiments demonstrated that CD7+CD45RA+ cells comprised bipotent NK/DC progenitors. DCs differentiated from CD7−CD45RA+ and CD7+CD45RA+ progenitors differed as to E-cadherin CD123, CD116, and CD127 expression, but none of these was really discriminant. Only CD7+CD45RA+ or thymic progenitors differentiated into Lag+S100+Langerhans cells in the absence of exogenous transforming growth factor (TGF)-β1. Analysis of the DC differentiation pathways showed that CD7+CD45RA+ progenitors generated CD1a+CD14− precursors that were macrophage-colony stimulating factor (M-CSF) resistant and CD1a−CD14+ precursors that readily differentiated into DCs under the standard condition. Accordingly, CD7+CD45RA+ progenitor-derived mature DCs produced 2- to 4-fold more IL-6, IL-12, and TNF-α on CD40 ligation and elicited 3- to 6-fold higher allogeneic T-lymphocyte reactivity than CD7−CD45RA+ progenitor-derived DCs. Altogether, these findings provide evidence that the DCs that differentiate from cord blood CD34+CD7+CD45RA+ progenitors represent an original population for their developmental pathways and function.

Characterization of dendritic cell differentiation pathways from cord blood CD34+CD7+CD45RA+hematopoietic progenitor cells

To better characterize human dendritic cells (DCs) that originate from lymphoid progenitors, the authors examined the DC differentiation pathways from a novel CD7+CD45RA+ progenitor population found among cord blood CD34+ cells. Unlike CD7−CD45RA+ and CD7+CD45RA− progenitors, this population displayed high natural killer (NK) cell differentiation capacity when cultured with stem cell factor (SCF), interleukin (IL)-2, IL-7, and IL-15, attesting to its lymphoid potential. In cultures with SCF, Flt3 ligand (FL), granulocyte-macrophage colony-stimulating factor (GM-CSF), and tumor necrosis factor (TNF)-α (standard condition), CD7+CD45RA+ progenitors expanded less (37- vs 155-fold) but yielded 2-fold higher CD1a+ DC percentages than CD7−CD45RA+ or CD7+CD45RA− progenitors. As reported for CD34+CD1a− thymocytes, cloning experiments demonstrated that CD7+CD45RA+ cells comprised bipotent NK/DC progenitors. DCs differentiated from CD7−CD45RA+ and CD7+CD45RA+ progenitors differed as to E-cadherin CD123, CD116, and CD127 expression, but none of these was really discriminant. Only CD7+CD45RA+ or thymic progenitors differentiated into Lag+S100+Langerhans cells in the absence of exogenous transforming growth factor (TGF)-β1. Analysis of the DC differentiation pathways showed that CD7+CD45RA+ progenitors generated CD1a+CD14− precursors that were macrophage-colony stimulating factor (M-CSF) resistant and CD1a−CD14+ precursors that readily differentiated into DCs under the standard condition. Accordingly, CD7+CD45RA+ progenitor-derived mature DCs produced 2- to 4-fold more IL-6, IL-12, and TNF-α on CD40 ligation and elicited 3- to 6-fold higher allogeneic T-lymphocyte reactivity than CD7−CD45RA+ progenitor-derived DCs. Altogether, these findings provide evidence that the DCs that differentiate from cord blood CD34+CD7+CD45RA+ progenitors represent an original population for their developmental pathways and function.