Functional modulation of dendritic cells to suppress adaptive immune responses

Immunopathogenesis of oral submucous fibrosis by chewing the areca nut

Oral submucous fibrosis (OSF) is a chronic, progressive, scarring, and premalignant disease of the oral mucosa. Its pathogenic factors are complex and include chewing areca nuts or other spicy food items, nutrition, and genetic and immune factors. Recently, immune factors have become the focus of medical research, with increased attention being paid to the role of immune regulation in diseases, particularly tumors. OSF is accompanied by obvious changes in the immune microenvironment. The aim of this review is to discuss the potential relationship of OSF and areca nuts genetic with the immune system, including lymphocytes, macrophage, Langerhans cell, mast cell, and substances released by activated immune cells, to determine the pathogenesis and treatment of OSF from an immunologic viewpoint.

Evaluation of mast cells and burning sensation in various stages of Oral Submucous Fibrosis

Background

Oral Submucous Fibrosis (OSMF) is a potentially malignant disorder and burning sensation is the initial complaint among these patients. Scientific literature has established that mast cells play a major role in various inflammatory disorders. However, OSMF being an inflammatory disorder, the role of mast cells is yet to be established. Hence the aim of this study was to evaluate mast cells and burning sensation in various stages of Oral Submucous Fibrosis.

Methods

The study population comprised of forty subjects, thirty were clinically confirmed cases of OSMF and ten healthy individuals served as control. A complete history and clinical examination followed by an incisional biopsy was performed. Samples obtained were subjected to routine histopathological examination and mast cells evaluation.

Results

Mean number of total mast cells in Stage I, II and III OSMF were 8.5 ± 0.7, 11.31 ± 8.8 and 24.7 ± 21.2 respectively. There was a significant difference in total mast cell count between cases and controls. Degranulated mast cells was a significant predictor (p = 0.028), indicating role in clinical staging of OSMF. Degranulated mast cells had a significant role and was a positive predictor (B = 0.763, OR 2.145[95%CI 1.055-4.630]) at moderate levels of burning sensation. A significant difference (p = 0.029) in burning sensation across histopathological grades was also observed in the study.

Conclusion

Degranulated mast cells were found to have a significant influence in mild to moderate levels of burning sensation among OSMF patients. Role of degranulated mast cells were also found to be significant in various clinical stages of OSMF.

Properdin and factor H production by human dendritic cells modulates their T-cell stimulatory capacity and is regulated by IFN-γ

Dendritic cells (DCs) and complement are both key members of the innate and adaptive immune response. Recent experimental mouse models have shown that production of alternative pathway (AP) components by DCs strongly affects their ability to activate and regulate T-cell responses. In this study we investigated the production and regulation of properdin (fP) and factor H (fH) both integral regulators of the AP, by DCs and tolerogenic DCs (tolDCs). Both fP and fH were produced by DCs, with significantly higher levels of both AP components produced by tolDCs. Upon activation with IFN-γ both cells increased fH production, while simultaneously decreasing production of fP. IL-27, a member of the IL-12 family, increased fH, but production of fP remained unaffected. The functional capacity of fP and fH produced by DCs and tolDCs was confirmed by their ability to bind C3b. Inhibition of fH production by DCs resulted in a greater ability to induce allogenic CD4⁺ T-cell proliferation. In contrast, inhibition of fP production led to a significantly reduced allostimulatory capacity. In summary, this study shows that production of fP and fH by DCs, differentially regulates their immunogenicity, and that the local cytokine environment can profoundly affect the production of fP and fH.

CD40 Ligand-Dependent Maturation of Human Monocyte-Derived Dendritic Cells by Activated Platelets

Atherosclerosis is defined as an inflammatory immunological disease that is triggered by platelet activation, endothelial injury and consequent innate and adaptive immune processes. Dendritic cells are critical for the cell-mediated arm of the immune response as they activate naïve T cells after maturation. Platelets play a crucial role in thrombus formation in the injured vessel walls. We investigated the role of resting and thrombin-activated platelets in dendritic cell maturation in vitro using platelets and monocyte-derived dendritic cells from healthy donors. Resting platelet supernatants did not affect maturation, whereas supernatants from thrombin-activated platelets induced dendritic cell maturation as demonstrated by FACS analysis of HLA-DR expression. This effect was inhibited by anti CD40 ligand antibody, but not by aspirin pretreatment of platelets. Supernatants of platelet-dendritic cell co-cultures induced augmented monocyte migration when platelets were activated by thrombin, again reversible by blocking CD40 ligand. These data show that activated platelets trigger dendritic cell maturation independent of cyclooxygenase-derived arachidonic acid metabolites by mechanisms involving CD40 ligand, which is also involved in monocyte chemotactic mediator release from platelets and dendritic cells. The results of this study suggest a role of CD40 ligand from activated platelets in connecting innate and adaptive immunity.

Human tolerogenic dendritic cells produce IL-35 in the absence of other IL-12 family members

IL-35 is a cytokine of the IL-12 family, existing as a heterodimer of IL-12p35 and Ebi3. IL-35 has anti-inflammatory properties and is produced by regulatory T cells in humans and mice, where it is required for optimal suppression of immune responses. Distinct from other IL-12 cytokines, the expression of IL-35 has not been described in antigen-presenting cells. In view of the immune-regulatory properties of IL-35, we investigated the expression, regulation, and function of IL-12p35 and Ebi3 in human monocyte-derived dendritic cells and tolerogenic DCs (tolDCs). These tolDCs do not produce IL-12p70 or the homodimer IL-12p40. We demonstrate that tolDCs completely lack transcriptional expression of IL-12p40. However, tolDCs maintain mRNA expression of IL-12p35 and Ebi3. Using intracellular flow cytometry and Western blot analysis, we show that tolDCs produce Ebi3 and IL-12p35, and both can be enhanced upon stimulation with IFN-γ, LPS, or CD40L. tolDCs supernatants have the capacity to suppress T-cell activation. Using IL12A silencing, we demonstrate that IL-12p35 is required for tolDCs to reach their full suppressive potential. Taken together, our results indicate that tolDCs produce IL-35, providing an additional novel mechanism by which tolDCs elicit their tolerogenic potential.

Induction of indoleamine 2, 3-dioxygenase in human dendritic cells by a cholera toxin B subunit-proinsulin vaccine

Dendritic cells (DC) interact with naïve T cells to regulate the delicate balance between immunity and tolerance required to maintain immunological homeostasis. In this study, immature human dendritic cells (iDC) were inoculated with a chimeric fusion protein vaccine containing the pancreatic β-cell auto-antigen proinsulin linked to a mucosal adjuvant the cholera toxin B subunit (CTB-INS). Proteomic analysis of vaccine inoculated DCs revealed strong up-regulation of the tryptophan catabolic enzyme indoleamine 2, 3-dioxygenase (IDO1). Increased biosynthesis of the immunosuppressive enzyme was detected in DCs inoculated with the CTB-INS fusion protein but not in DCs inoculated with proinsulin, CTB, or an unlinked combination of the two proteins. Immunoblot and PCR analyses of vaccine treated DCs detected IDO1mRNA by 3 hours and IDO1 protein synthesis by 6 hours after vaccine inoculation. Determination of IDO1 activity in vaccinated DCs by measurement of tryptophan degradation products (kynurenines) showed increased tryptophan cleavage into N-formyl kynurenine. Vaccination did not interfere with monocytes differentiation into DC, suggesting the vaccine can function safely in the human immune system. Treatment of vaccinated DCs with pharmacological NF-κB inhibitors ACHP or DHMEQ significantly inhibited IDO1 biosynthesis, suggesting a role for NF-κB signaling in vaccine up-regulation of dendritic cell IDO1. Heat map analysis of the proteomic data revealed an overall down-regulation of vaccinated DC functions, suggesting vaccine suppression of DC maturation. Together, our experimental data indicate that CTB-INS vaccine induction of IDO1 biosynthesis in human DCs may result in the inhibition of DC maturation generating a durable state of immunological tolerance. Understanding how CTB-INS modulates IDO1 activity in human DCs will facilitate vaccine efficacy and safety, moving this immunosuppressive strategy closer to clinical applications for prevention of type 1 diabetes autoimmunity.

Inhibition of vascular endothelial growth factor by small interfering RNA upregulates differentiation, maturation and function of dendritic cells

This study aimed to investigate the effects of vascular endothelial growth factor (VEGF) secreted by MCF-7 breast cancer cells on the differentiation, maturation and function of dendritic cells (DCs). Small interfering RNAs (siRNAs) directed against the VEGF gene were designed and transfected into MCF-7 breast cancer cells at an optimal concentration (100 nmol/l) using cationic liposome transfection reagent, whereas the control group was transfected with only transfection reagent. Western blot analysis and ELISA were used to determine VEGF protein expression and VEGF concentration, respectively. Mononuclear cells were cultured with the culture supernatants from primary MCF-7 cells (control group) and siRNA-treated MCF-7 cells (siRNA group). The DC phenotypes, including CD1a, CD80, CD83, CD86 and HLA-DR, were evaluated by flow cytometry. The MTT assay was used to assess the cytotoxicity of DC-mediated tumor-specific cytotoxic T lymphocytes (CTLs) against MCF-7 cells in the two different culture supernatants. The VEGF-targeted constructed siRNA inhibited VEGF expression in MCF-7 cells. Cultivation with the culture supernatants from MCF-7 cells treated with siRNA affected DC morphology. DCs in the siRNA group exhibited a significantly higher expression of CD86, CD80, CD83 and HLA-DR compared to the cells in the control group, whereas the expression of CD1a in the siRNA group was significantly lower compared to that in the control group. The cytotoxic activity of CTLs mediated by DCs was significantly altered by siRNA transfection. These results indicated that VEGF may play a significant role in tumor development, progression and immunosuppression.

In vitro-generated DC with tolerogenic functions: perspectives for in vivo cellular therapy

Dendritic cells (DCs) have a central role in immune regulation and serve as an essential link between innate and adaptive immunity. Their broad range of powerful immune stimulatory as well as regulatory functions has made DCs a target for vaccine development strategies. One approach to promote the tolerogenicity of DCs is to suppress their maturation by pharmacological agents, including the glucocorticoid dexamethasone. In this chapter, we describe methods to generate tolerogenic Dex-DC derived from either human peripheral blood monocytes or rat bone marrow cells.

Dendritic cell tolerogenicity: a key mechanism in immunomodulation by vitamin D receptor agonists

Dendritic cells (DC) induce or tolerize T cells, and tolerogenic DCs can promote the development of regulatory T cells (Treg) with suppressive activity. Thus, the possibility of manipulating DCs and enhancing their tolerogenic properties using different pharmacologic or biologic agents could be exploited to control a variety of chronic immuno-mediated inflammatory conditions. Among agents able to promote induction of tolerogenic DCs, vitamin D receptor (VDR) agonists have attracted considerable attention, also because of their potential in clinical translation. DCs are key targets for the immunomodulatory effects of VDR agonists, which shape DC phenotype and function, enhancing their tolerogenicity in adaptive immune responses. Tolerogenic DCs induced by a short treatment with VDR agonists promote CD4+CD25+Foxp3+ Treg cells that are able to mediate transplantation tolerance and to arrest the development of autoimmune diseases. VDR agonists not only favor induction of CD4+CD25+ Treg cells, but can also enhance their recruitment at inflammatory sites. The tolerogenic properties induced by VDR agonists in DCs, leading to enhanced Treg cell development, likely contribute to the beneficial activity of these hormone-like molecules in autoimmune disease and graft rejection models, highlighting their applicability to the treatment of chronic inflammatory conditions sustained by autoreactive or alloreactive immune responses.

Epithelial metaplasia: adult stem cell reprogramming and (pre)neoplastic transformation mediated by inflammation?

Throughout adult life, new developmental commitment of adult stem cells causes metaplastic conversions to occur frequently in some organs. These reversible epithelial replacements are almost always observed in association with chronic inflammation and persistent irritation. Although metaplasia is not synonymous with dysplasia, clinical surveillance has demonstrated that these adaptive processes have an increased susceptibility to evolve into cancer. We propose that cytokines and other soluble factors released by both epithelial and inflammatory cells might alter the transcription-factor expression profile of stem cells and lead to the development of metaplasia. Furthermore, inflammatory mediators might also promote the malignant transformation of epithelial metaplasia by inducing genetic and epigenetic changes and by preventing the immune system from mounting an efficient anti-tumour immune response. A better understanding of the molecular mechanisms leading to metaplasia might help in the design of new therapies for neoplastic and degenerative diseases.

Handbook of experimental pharmacology "dendritic cells": the use of dexamethasone in the induction of tolerogenic DCs

Dendritic cells (DCs) have a central role in immune regulation, ranging from tolerance induction to the induction of specific immune responses. DCs serve as an essential link between innate and adaptive immunity. This broad range of powerful immune stimulatory as well as regulatory functions has made DCs as targets for vaccine development strategies. One approach to promote the tolerogenicity of DCs is to suppress their maturation by pharmacological agents, including glucocorticoids (GCs). In the present chapter we will review GCs used in vitro with cultured DCs, applied in vivo, or used to generate tolerogenic DCs for cellular therapy.

Induction of tolerogenic dendritic cells by vitamin D receptor agonists

Dendritic cells induce and regulate T cell responses, and tolerogenic dendritic cells (DCs) can promote the development of regulatory T cells with suppressive activity. Thus, the possibility to manipulate DCs using different pharmacological or biological agents enables them to exert tolerogenic activities, could be exploited to better control a variety of chronic inflammatory conditions, from autoimmune diseases to allograft rejection. A variety of both biological and pharmacological agents can induce tolerogenic DCs, and several in vitro studies have demonstrated that human regulatory T cells can be induced by DCs manipulated to acquire and/or enhance tolerogenic properties, with in vivo data also accumulating. Within this context, we have explored the immunoregulatory activities of vitamin D receptor (VDR) agonists, secosteroid hormones able to induce tolerogenic DCs and regulatory T cells. Tolerogenic DCs induced by a short treatment with VDR agonists promote CD4(+) CD25(+) Foxp3(+) suppressor T cells that are able to mediate transplantation tolerance and to arrest the development of autoimmune diseases. VDR agonists not only favour the induction of CD4(+) CD25(+) regulatory T cells, but can also enhance their recruitment to inflammatory sites. VDR agonists have been proven effective and safe drugs in a variety of autoimmune disease and graft rejection models, highlighting their potential applicability to chronic inflammatory conditions sustained by autoreactive or alloreactive immune responses. In addition to the topical treatment of psoriasis, a Th1-mediated autoimmune disease of the skin where VDR agonists are the most used topical drugs; these agents might eventually find a broader application in the treatment of inflammatory conditions, where their modulatory effects on DCs enhancing T cells with regulatory functions could turn out to be quite beneficial.

Differentially modulated dendritic cells induce regulatory T cells with different characteristics

Dexamethason (DEX) treated DC display several features that establish them as candidates for specific allogeneic tolerance induction. We report the results of in vitro studies of polarization of the alloimmune T cell response with two types of differentially modulated human DC. Both DEX treated DC triggered by LPS for 6 h (DEX6-DC) and DEX treated DC triggered by LPS for 48 h (DEX48-DC) acquired low levels of costimulatory, adhesion, and MHC class II molecules compared with mature DC (mDC). In contrast to mDC, both DEX6-DC and DEX48-DC did not produce any IL-12. DEX6-DC were able to produce significant amounts of IL-10 whereas DEX48-DC did not actively produce IL-10. Conversely, the induction of IL-10 producing cells was significantly increased when PBL were stimulated with DEX48-DC compared with DEX6-DC. Both stimulation of PBL with DEX6-DC and DEX48-DC led to the induction of cell populations able to suppress the proliferative alloimmune response of primed T cells in a cell-cell contact independent and antigen-nonspecific manner. Tregs obtained after stimulation with DEX48-DC were also able to inhibit the IFN-gamma production of the effector cells and this effect could be blocked by anti-IL-10. Tregs induced by DEX6-DC produced similar amounts of IL-10, yet were not able to inhibit IFN-gamma production of the effector T cells, indicating a different mechanism. In summary, we show that differential modulation of DC results in the induction of different populations of regulatory T cells.

Cholera toxin B subunit promotes the induction of regulatory T cells by preventing human dendritic cell maturation

Cholera toxin B subunit (CTB) is an efficient mucosal carrier molecule for the generation of immune responses to linked antigens. There is also good evidence that CTB acts as an immunosuppressant, as it is able to down-modulate human monocyte/macrophage cell line activation and to suppress Th1-type responses. In the present study, we examined the possibility that recombinant CTB (rCTB) may affect human dendritic cell (DC) functions in response to LPS stimulation and may induce the generation of DC with the capacity to generate CD4(+) regulatory T cells (Tregs). Our findings show that rCTB partially prevents the LPS-induced maturation process of monocyte-derived DC (MDDC) and decreases their IL-12 production with no relevant effect on IL-10 production. LPS-stimulated MDDC pretreated with rCTB are able to promote the induction of low proliferating T cells, which show an enhanced IL-10 production associated with a reduced IFN-gamma production and the same high levels of TGF-beta as the control. These T cells suppress proliferation of activated autologous T cells. Transwell experiments and blockade of IL-10R and TGF-beta showed that the immunomodulatory effect is mediated by soluble factors. Thus, T cells induced by rCTB-conditioned MDDC acquire a regulatory phenotype and activity similar to those described for type 1 Tregs.

Tumor-specific regulatory T cells in cancer patients

A large body of evidence indicates that the presence of regulatory T cells (Tregs) in tumors is associated with a dampened tumor-specific immune response and a clear negative impact on survival. Many different subsets of Tregs have been identified, which all act through similar or distinct pathways to suppress tumor-specific effector cells. The observation that tumor-infiltrating Tregs are able to recognize tumor-derived antigens and can be expanded by vaccines that primarily aim at reinforcing the effector arm of the antitumor response stresses the need to study Tregs for each type of cancer targeted by immunotherapy. Current protocols enable us to isolate and culture tumor-infiltrating Tregs. Ultimately, this will not only lead to a full comprehension of the specificity and working mechanisms of Tregs but also facilitate the development of successful interventions strategies for the immunotherapy of cancer.

Anti CD25 treatment of human dendritic cells modulates both their cytokine synthesis profiles and their capacity to activate allogeneic CD4 T cells: a potential tolerogenic effect

Recently, attention has been focused on the role for dendritic cells (DCs) in the promotion of peripheral tolerance. It is currently believed that the maturation/activation state of DCs might be a control point for the induction of graft tolerance through modifications of the activation state of T cells. We have observed IL-2, and IL-2 receptor gene expression by reverse transcriptase-polymerase chain reaction (RT-PCR) in human DC lysates following bacterial stimulation. It has been demonstrated in the present study IL-2R alpha (CD25) expression on human DCs upon LPS activation. DCs differentiated from monocytes were exposed to anti CD25 during maturation, anti CD25 treatment affected the abilities of human DCs to induce CD4+ T cell proliferation in response to alloantigens, maintained endocytic capacity, Anti CD25 treated DCs produce low levels of IL-12 and IFN and high level of IL-10. All these characteristics suggest that DCs may be used in cellular therapy either to induce allograft tolerance (anti CD25 treated DCs) or to restore immunity against tumors (IL-2 treated DCs).

Impairment of circulating myeloid dendritic cells in immunosuppressed liver transplant recipients

The aim of the present study was to elucidate the impact of liver transplantation (LTX) on myeloid dendritic cell (MDC) homeostasis. We observed a threefold reduction of circulating CD1c(+) MDC immediately after LTX (n = 16; P < 0.01), and normalization between 3 and 12 months after LTX. This decline was not due to recruitment of MDC into the liver graft, as numbers of MDC in post-LTX liver graft biopsies were not increased compared to pre-LTX biopsies (n = 7). Moreover, no change in chemokine receptor expression on circulating MDC was observed, suggesting that their homing properties were not altered. Normalization of circulating MDC was associated with withdrawal of corticosteroid therapy, and not with changes in calcineurin inhibitor intake, indicating that corticosteroids are responsible for the observed changes in numbers of circulating MDC. During high-dose corticosteroid treatment early after LTX, circulating MDC showed a lowered maturation status with decreased expression of human leucocyte antigen D-related (HLA-DR) and CD86 compared to pre-LTX values (P < 0.01). However, when MDC from blood of LTX recipients were matured ex vivo, they up-regulated HLA-DR and co-stimulatory molecules to a comparable extent as MDC from healthy individuals. In addition, ex vivo matured MDC from both groups had equal allogeneic T cell stimulatory capacity. In conclusion, during the first months after LTX numbers and maturational status of circulating MDC are impaired significantly, probably due to a suppressive effect of corticosteroids on MDC. However, corticosteroid therapy does not imprint MDC with an intrinsic resistance to maturation stimuli.

Sanglifehrin a blocks key dendritic cell functions in vivo and promotes long-term allograft survival together with low-dose CsA

Sanglifehrin A (SFA) is a novel compound with unsurpassed cyclophilin-binding affinity, but relatively low direct antilymphocytic activity. Here, we report the capacity of SFA to selectively inhibit key dendritic cell (DC) functions in vivo and to suppress acute and chronic heart allograft rejection. We show that in vivo, SFA profoundly decreases DC receptor-mediated endocytosis and macropinocytosis and DC-T-cell allostimulatory activity. Furthermore, SFA abrogates >90% of IL-12p70 production in vivo while having no significant effect on IL-10 and TNF-alpha production. In a rat vascularized heart transplant model, SFA alone did not prevent graft rejection and rejection occurred within 23 days after low-dose CsA, whereas addition of SFA to low-dose CsA promoted long-term graft survival (median survival time >100 days; p = 0.0007). With respect to chronic rejection, SFA + CsA almost completely prevented graft arteriosclerosis compared to animals treated with CsA alone and controls. We propose that SFA represents a novel class of immunophilin-binding immunosuppressants with high activity against DCs and the development of graft vasculopathy in CsA-treated recipients.

Toll-like receptor activation enhances cell-mediated immunity induced by an antibody vaccine targeting human dendritic cells

Previously, we have successfully targeted the mannose receptor (MR) expressed on monocyte-derived dendritic cells (DCs) using a fully human MR-specific antibody, B11, as a vehicle to deliver whole protein tumor antigens such as the human chorionic gonadotropin hormone (hCGbeta). Since MRs play a role in bridging innate immunity with adaptive immunity we have explored several toll-like receptor (TLR)-specific ligands that may synergize with MR targeting and be applicable as adjuvants in the clinic. We demonstrate that antigen-specific helper and cytolytic T cells from both healthy donors and cancer patients were effectively primed with B11-hCGbeta-treated autologous DCs when a combination of one or several TLR ligands is used. Specifically, concomitant signaling of DCs via TLR3 with dsRNA (poly I:C) and DC TLR 7/8 with Resiquimod (R-848), respectively, elicited efficient antigen presentation-mediated by MR-targeting. We demonstrate that MR and TLRs contribute towards maturation and activation of DCs by a mechanism that may be driven by a combination of adjuvant and antibody vaccines that specifically deliver antigenic targets to DCs.

Cancer immunosuppression and autoimmune disease: beyond immunosuppressive networks for tumour immunity

Cancer immunosuppression evolves by constitution of an immunosuppressive network extending from a primary tumour site to secondary lymphoid organs and peripheral vessels and is mediated by several tumour-derived soluble factors (TDSFs) such as interleukin-10 (IL-10), transforming growth factor-beta (TGF-beta) and vascular endothelial growth factor (VEGF). TDSFs induce immature myeloid cells and regulatory T cells in accordance with tumour progression, resulting in the inhibition of dendritic cell maturation and T-cell activation in a tumour-specific immune response. Tumour cells grow by exploiting a pro-inflammatory situation in the tumour microenvironment, whereas immune cells are regulated by TDSFs during anti-inflammatory situations--mediated by impaired clearance of apoptotic cells--that cause the release of IL-10, TGF-beta, and prostaglandin E2 (PGE2) by macrophages. Accumulation of impaired apoptotic cells induces anti-DNA antibodies directed against self antigens, which resembles a pseudo-autoimmune status. Systemic lupus erythematosus is a prototype of autoimmune disease that is characterized by defective tolerance of self antigens, the presence of anti-DNA antibodies and a pro-inflammatory response. The anti-DNA antibodies can be produced by impaired clearance of apoptotic cells, which is the result of a hereditary deficiency of complements C1q, C3 and C4, which are involved in the recognition of phagocytosis by macrophages. Thus, it is likely that impaired clearance of apoptotic cells is able to provoke different types of immune dysfunction in cancer and autoimmune disease in which some are similar and others are critically different. This review discusses a comparison of immunological dysfunctions in cancer and autoimmune disease with the aim of exploring new insights beyond cancer immunosuppression in tumour immunity.

Proteasomal chymotrypsin-like peptidase activity is required for essential functions of human monocyte-derived dendritic cells

The ubiquitin-proteasome pathway is the principal system for extralysosomal protein degradation in eukaryotic cells, and is essential for the regulation and maintenance of basic cellular processes, including differentiation, proliferation, cell cycling, gene transcription and apoptosis. The 26S proteasome, a large multicatalytic protease complex, constitutes the system's proteolytic core machinery that exhibits different proteolytic activities residing in defined proteasomal subunits. We have identified proteasome inhibitors - bortezomib, epoxomicin and lactacystin - which selectively inhibit the proteasomal beta5 subunit-located chymotrypsin-like peptidase activity in human monocyte-derived dendritic cells (DCs). Inhibition of proteasomal chymotrypsin-like peptidase activity in immature and mature DCs impairs the cell-surface expression of CD40, CD86, CD80, human leucocyte antigen (HLA)-DR, CD206 and CD209, induces apoptosis, and impairs maturation of DCs, as demonstrated by decreased cell-surface expression of CD83 and lack of nuclear translocation of RelA and RelB. Inhibition of chymotrypsin-like peptidase activity abrogates macropinocytosis and receptor-mediated endocytosis of macromolecular antigens in immature DCs, and inhibits the synthesis of interleukin (IL)-12p70 and IL-12p40 in mature DCs. As a functional consequence, DCs fail to stimulate allogeneic CD4(+) and CD8(+) T cells and autologous CD4(+) T cells sufficiently in response to inhibition of chymotrypsin-like peptidase activity. Thus, proteasomal chymotrypsin-like peptidase activity is required for essential functions of human DCs, and inhibition of proteasomal chymotrypsin-like peptidase activity by selective inhibitors, or by targeting beta5 subunit expression, may provide a novel therapeutic strategy for suppression of deregulated and unwanted immune responses.

Maturation-resistant dendritic cells induce hyporesponsiveness in alloreactive CD45RA+ and CD45RO+ T-cell populations

Dendritic cells (DCs) play a crucial role in the induction of antigen-specific immunity and tolerance. Considering in vivo application of DCs prior to human organ transplantation, a protocol to develop tolerogenic DCs that not only induce unresponsiveness in naive (CD45RA+) T cells, but also in alloreactive memory (CD45RO+) T cells is required. The present study shows that dexamethasone (Dex) alters the differentiation of human monocyte-derived DCs. DexDCs cocultured with allogeneic CD4+ T cells induced low proliferating and low IFNgamma producing T cells. This is caused by lack of both costimulation via CD28 and hampered production of a soluble factor, as well as additional active suppression via B7-H1 and IL-10. T cells primed by DexDCs demonstrated hyporesponsiveness upon restimulation with mature DCs seemingly via the induction of anergy, since these cells showed no enhanced apoptosis and only a limited suppressive capacity. Interestingly, not only cocultures of allogeneic CD45RA+, but also of CD45RO+ T cells with DexDCs rendered T-cell populations hyporesponsive to restimulation with mature DCs. The finding that also alloreactive memory T cells can be regulated supports the rationale of cell-based therapies to obtain allograft-specific tolerance in transplant recipients.

Interleukin-10-secreting type 1 regulatory T cells in rodents and humans

Interleukin-10 (IL-10)-secreting T regulatory type 1 (Tr1) cells are defined by their specific cytokine production profile, which includes the secretion of high levels of IL-10 and transforming growth factor-beta(TGF-beta), and by their ability to suppress antigen-specific effector T-cell responses via a cytokine-dependent mechanism. In contrast to the naturally occurring CD4+ CD25+ T regulatory cells (Tregs) that emerge directly from the thymus, Tr1 cells are induced by antigen stimulation via an IL-10-dependent process in vitro and in vivo. Specialized IL-10-producing dendritic cells, such as those in an immature state or those modulated by tolerogenic stimuli, play a key role in this process. We propose to use the term Tr1 cells for all IL-10-producing T-cell populations that are induced by IL-10 and have regulatory activity. The full biological characterization of Tr1 cells has been hampered by the difficulty in generating these cells in vitro and by the lack of specific marker molecules. However, it is clear that Tr1 cells play a key role in regulating adaptive immune responses both in mice and in humans. Further work to delineate the specific molecular signature of Tr1 cells, to determine their relationship with CD4+ CD25+ Tregs, and to elucidate their respective role in maintaining peripheral tolerance is crucial to advance our knowledge on this Treg subset. Furthermore, results from clinical protocols using Tr1 cells to modulate immune responses in vivo in autoimmunity, transplantation, and chronic inflammatory diseases will undoubtedly prove the biological relevance of these cells in immunotolerance.

Dendritic cell deficiency in the blood of kidney transplant patients on long-term immunosuppression: results of a prospective matched-cohort study

Evidence from in vitro studies suggests that immunosuppressive drugs interfere with key functions of dendritic cells (DCs), but the in vivo relevance of these findings is elusive. We prospectively analyzed the major DC precursor subsets in the blood of kidney transplant recipients on long-term immunosuppression (> or =1 year). A total of 87 patients were compared to 87 age- and sex-matched controls. Total DC numbers and the precursor subsets, myeloid type 1 DCs, myeloid type 2 DCs (mDC1, mDC2) and plasmacytoid DCs (pDCs) were identified by four color flow cytometry. Long-term immunosuppression was associated with significant reduction of all major DC subsets in comparison to healthy controls (mDC1 p < 0.001; mDC2 p < 0.0001; two-tailed Mann-Whitney U-test) with the strongest negative impact on pDCs (p < 0.00001). In contrast, total leukocyte numbers were not significantly affected. Analysis of the relative impact of different agents revealed a significant impact of prednisolone on pDCs (p = 0.009) and mDCs2 (p = 0.006). The functional relevance of pDC deficiency was confirmed independently by Interferon-alpha analysis after Toll-like receptor 7 (p < or = 0.001) and 9 (p < 0.05) stimulation. These results indicate for the first time a profound negative impact of long-term immunosuppression on major DC subsets in kidney transplant recipients. DC deficiency may have important implications with respect to viral infections and tumor development.

Dexamethasone Induces IL-10-Producing Monocyte-Derived Dendritic Cells with Durable Immaturity

It is highly desirable that immature dendritic cells (DC) used for tolerance induction maintain steady immature state with predominant interleukin (IL)-10 production. In this study, we attempted to develop DC with durable immaturity and other tolerogenic features by using dexamethasone (Dex). We found DC derived from human monocytes in the presence of 10(-7) m Dex were negative for CD1a. Compared with control transduced DC (Ctrl-DC), Dex-DC expressed lower CD40, CD80 and CD86 but equivalent human leucocyte antigen-DR. Both immature Dex- and Ctrl-DC did not express CD83. Nevertheless, upon stimulation of lipopolysaccharide (LPS) or CD40 ligand, the expression of CD40, CD80, CD83 and CD86 was upregulated on Ctrl-DC but not on Dex-DC. The immaturity of Dex-DC was durable following Dex removal. Interestingly, Dex-DC maintained production of large amount of IL-10 and little IL-12 five days after Dex removed. Further study indicated that high-level IL-10 production by Dex-DC was associated with high-level phosphorylation of extracellular signal-regulated kinase (ERK) as blockade of this enzyme markedly attenuated IL-10 production. Furthermore, Dex-DC sustained the capability of high phosphorylation of ERK and IL-10 production 5 days after Dex removal. In addition, Dex-DC had significantly lower activity in stimulating T-cell proliferation. Neutralization of IL-10, to some extent, promoted DC maturation activated by LPS, as well as T-cell stimulatory activity of Dex-DC. The above findings suggest that IL-10-producing Dex-DC with durable immaturity are potentially useful for induction of immune tolerance.

Manipulating dendritic cells to induce regulatory T cells

Dendritic cells (DCs) induce and regulate T-cell responses, and tolerogenic DCs can promote the development of regulatory T cells with suppressive activity. The possibility of manipulating DCs using different pharmacological or biological agents, enabling them to exert tolerogenic activities, could be exploited to better control a variety of chronic inflammatory conditions, from autoimmune diseases to allograft rejection.

Cell-mediated immunity and head and neck cancer: with special emphasis on betel quid chewing habit

Betel quid (BQ) chewing is popular in Taiwan, India, and many southeast-Asian countries. BQ chewing has strong association with the risk of oral leukoplakia (OL), oral submucous fibrosis (OSF), and oral cancer (OC). BQ components exhibit genotoxicity and may alter the structure of DNA, proteins and lipids, resulting in production of antigenicity. BQ ingredients are also shown to induce keratinocyte inflammation by stimulating the production of prostaglandins, TNF-alpha, IL-6, IL-8, and granulocyte-macrophage colony-stimulating factor (GM-CSF) in keratinocytes. These events may provoke tissue inflammation, early cell-mediated immunity (CMI), and immune surveillance in BQ chewers. However, BQ components also directly affect the functional activities of immunocompotent cells, and moreover tumor cells may hypo-respond to the CMI via diverse mechanisms such as induction of apoptosis of lymphocytes, induction of production of suppressor T cells, downregulation of MHC molecules in tumor cells, etc. Clinically, an alteration in lymphocyte subsets, a decrease in total number of lymphocytes, and a reduction in functional activities of CMI have been observed in isolated peripheral blood mononuclear cells (PBMC) and tumor infiltrated lymphocytes (TIL) in patients with OSF, OL or OC. Adaptation of tumor cells to immune system may promote clonal selection of resistant tumor cells, leading to immune tolerance. Future studies on effects of BQ components on CMI and humoral immunity in vitro and in vivo can be helpful for chemoprevention of BQ-related oral mucosal diseases. To elucidate how virus infection, tobacco, alcohol and BQ consumption, and other environmental exposure affect the immune status of patients with oral premalignant lesions or OC will help us to understand the immunopathogenesis of OC and to develop immunotherapeutic strategies for OC.

Polyunsaturated fatty acids block dendritic cell activation and function independently of NF-kappaB activation

Polyunsaturated fatty acids (PUFAs) modulate immune responses leading to clinically significant beneficial effects in a variety of inflammatory disorders. PUFA effects on T cells have been extensively studied, but their influence on human dendritic cells (DCs), which are the most potent antigen-presenting cells and play a key role in initiating immune responses, has not been elucidated so far. Here we show that PUFAs of the n-3 and n-6 series (arachidonic and eicosapentaenoic acid) affect human monocyte-derived DC differentiation and inhibit their activation by LPS, resulting in altered DC surface molecule expression and diminished cytokine secretion. Furthermore, the potency to stimulate T cells was markedly inhibited in PUFA-treated DCs. The PUFA-mediated block in LPS-induced DC activation is reflected by diminished TNF-alpha, IL-12p40, CD40, and COX-2 mRNA levels. Strikingly, typical LPS-induced signaling events such as degradation of IkappaB and activation of NF-kappaB were not affected by PUFAs, even though DC membrane lipid composition was markedly altered. Arachidonic and eicosapentaenoic acid both altered DC prostaglandin production, but inhibitors of cyclooxygenases and lipoxygenases did not abolish PUFA effects, indicating that the observed PUFA actions on DCs were independent of autoregulation via eicosanoids. These data demonstrate a unique interference with DC activation and function that could significantly contribute to the well known anti-inflammatory effects of PUFAs.

1α,25-Dihydroxyvitamin D3 or analogue treated dendritic cells modulate human autoreactive T cells via the selective induction of apoptosis

Epidemiological evidence indicates that the vitamin D status after birth modulates the risk for development of type 1 diabetes mellitus (T1DM). We previously demonstrated that the biologically active form of vitamin D, 1alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3), as well as its analogue TX527 permanently alter the morphology and T cell stimulatory function of human dendritic cells (DC). Here, we studied the mechanism of T cell modulation by 1,25(OH)2D3 or analogue treated DC. By using CFSE-labelled autoreactive T cells, we observed that T cell proliferation is hampered upon coculture with modulated DCs, i.e. T cells underwent fewer cycles of cell divisions when compared to T cells stimulated by nontreated DCs. Moreover, 1,25(OH)2D3 or analogue modulated DCs induced significantly higher numbers of early apoptotic (annexin V+/PI-) and/or late apoptotic (annexin V+/PI+) T cells. Apoptosis was selectively induced in T cells activated by modulated DC, since other T cells present in the same cultures, either resting or activated by control untreated DC, were unaffected. Thus, in vitro preconditioning of DC with 1,25(OH)2D3 or analogue yields regulatory DC that may interfere with ongoing autoimmunity in vivo without affecting T cells with other specificities.

The novel cyclophilin-binding drug sanglifehrin A specifically affects antigen uptake receptor expression and endocytic capacity of human dendritic cells

Sanglifehrin A (SFA) is a recently developed immunosuppressant that belongs to the family of immunophilin-binding ligands. SFA is a cyclophilin A-binding immunosuppressive drug with a novel, but unidentified, mechanism of action. Several reports exist about the effect of SFA on T cells, but its effect on the initiators of the immune response, i.e., dendritic cells (DCs), is relatively unknown. Therefore, we examined the effect of SFA on the differentiation and function of human monocyte-derived DCs. Unlike the well-known cyclophilin A-binding immunosuppressant cyclosporin A, which did not affect DC phenotype, differentiation of DCs in the presence of SFA resulted in CD14-CD1a DCs with normal DC morphology, viability, and a proper capacity to activate allogeneic T cells. However, DCs generated in the presence of SFA demonstrated reduced macropinocytosis and lectin-mediated endocytosis, which was in line with a decreased expression of C-type lectins, including mannose receptor, C1qRP, DC-ASGPR, and especially, DC-SIGN. In contrast, FcalphaRI (CD89) and FcgammaRII (CD32) were increased by SFA. The explicit effect of SFA on the expression of Ag uptake receptors and Ag capture by DCs makes SFA unique among immunophilin-binding immunosuppressive drugs.

Regulatory T cells and tolerogenic dendritic cells: from basic biology to clinical applications

The induction of antigen (Ag)-specific tolerance is critical for the prevention of autoimmunity and maintenance of immune homeostasis. Recently, attention has been focused on induction of active suppression by regulatory T cells (Treg cells). Also, a role for dendritic cells (DCs) in the promotion of peripheral tolerance has been demonstrated by several studies and is the subject of intensive investigation. It is currently believed that the maturation/activation state of DCs might be a control point for the induction of peripheral tolerance through modifications of the activation state of T cells. Several lines of experimental evidence suggest that unique DC subsets or discrete functional states of the DCs might be devoted to the promotion of Treg cell differentiation. The present review summarizes the emerging literature on the developmental origin and function of human Treg cells and tolerogenic/regulatory DCs. Furthermore, clinical implications of these studies for cellular therapy of immune-mediated pathologies are discussed.

Exploiting dendritic cells for cancer immunotherapy: genetic modification of dendritic cells

Dendritic cells (DCs) are pivotal regulators of immune reactivity and immune tolerance. The observation that DCs can recruit naive T cells has invigorated cancer immunology and led to the proposal of DCs as the basis for vaccines designed for the treatment of cancer. Designing effective strategies to load DCs with antigens is a challenging field of research. The successful realization of gene transfer to DCs will be highly dependent on the employed vector system. Here, we review various viral and non-viral gene transfer systems, and discuss their distinct characteristics and possible advantages and disadvantages in respect to their use in DC-based immunotherapy.