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Objectives: Immune dysregulation contributes to the development of RA. Altered surface expression patterns of integrin adhesion receptors by immune cells is one mechanism by which this may occur. We investigated the role of β2 integrin subunits CD11a and CD11b in dendritic cell (DC) subsets of RA patients., Methods: Total β2 integrin subunit expression and its conformation ('active' vs 'inactive' state) were quantified in DC subsets from peripheral blood (PB) and SF of RA patients as well as PB from healthy controls. Ex vivo stimulation of PB DC subsets and in vitro-generated mature and tolerogenic monocyte-derived DCs (moDCs) were utilized to model the clinical findings. Integrin subunit contribution to DC function was tested by analysing clustering and adhesion, and in co-cultures to assess T cell activation., Results: A significant reduction in total and active CD11a expression in DCs in RA SF compared with PB and, conversely, a significant increase in CD11b expression was found. These findings were modelled in vitro using moDCs: tolerogenic moDCs showed higher expression of active CD11a and reduced levels of active CD11b compared with mature moDCs. Finally, blockade of CD11b impaired T cell activation in DC-T cell co-cultures., Conclusion: For the first time in RA, we show opposing expression of CD11a and CD11b in DCs in environments of inflammation (CD11alow/CD11bhigh) and steady state/tolerance (CD11ahigh/CD11blow), as well as a T cell stimulatory role for CD11b. These findings highlight DC integrins as potential novel targets for intervention in RA., (© The Author(s) 2020. Published by Oxford University Press on behalf of the British Society for Rheumatology.)

Objectives: To assess the safety of intra-articular (IA) autologous tolerogenic dendritic cells (tolDC) in patients with inflammatory arthritis and an inflamed knee; to assess the feasibility and acceptability of the approach and to assess potential effects on local and systemic disease activities., Methods: An unblinded, randomised, controlled, dose escalation Phase I trial. TolDC were differentiated from CD14+ monocytes and loaded with autologous synovial fluid as a source of autoantigens. Cohorts of three participants received 1×10 6 , 3×10 6 or 10×10 6 tolDC arthroscopically following saline irrigation of an inflamed (target) knee. Control participants received saline irrigation only. Primary outcome was flare of disease in the target knee within 5 days of treatment. Feasibility was assessed by successful tolDC manufacture and acceptability via patient questionnaire. Potential effects on disease activity were assessed by arthroscopic synovitis score, disease activity score (DAS)28 and Health Assessment Questionnaire (HAQ). Immunomodulatory effects were sought in peripheral blood., Results: There were no target knee flares within 5 days of treatment. At day 14, arthroscopic synovitis was present in all participants except for one who received 10×10 6 tolDC; a further participant in this cohort declined day 14 arthroscopy because symptoms had remitted; both remained stable throughout 91 days of observation. There were no trends in DAS28 or HAQ score or consistent immunomodulatory effects in peripheral blood. 9 of 10 manufactured products met quality control release criteria; acceptability of the protocol by participants was high., Conclusion: IA tolDC therapy appears safe, feasible and acceptable. Knee symptoms stabilised in two patients who received 10×10 6 tolDC but no systemic clinical or immunomodulatory effects were detectable., Trial Registration Number: NCT01352858., Competing Interests: Conflicts of Interest: None declared., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/.)

Tolerogenic dendritic cells (tolDC) are a new immunotherapeutic tool for the treatment of rheumatoid arthritis (RA) and other autoimmune disorders. We have established a method to generate stable tolDC by pharmacological modulation of human monocyte-derived DC. These tolDC exert potent pro-tolerogenic actions on CD4 + T cells. Lack of interleukin (IL)-12p70 production is a key immunoregulatory attribute of tolDC but does not explain their action fully. Here we show that tolDC express transforming growth factor (TGF)-β1 at both mRNA and protein levels, and that expression of this immunoregulatory cytokine is significantly higher in tolDC than in mature monocyte-derived DC. By inhibiting TGF-β1 signalling we demonstrate that tolDC regulate CD4 + T cell responses in a manner that is at least partly dependent upon this cytokine. Crucially, we also show that while there is no significant difference in expression of TGF-βRII on CD4 + T cells from RA patients and healthy controls, RA patient CD4 + T cells are measurably less responsive to TGF-β1 than healthy control CD4 + T cells [reduced TGF-β-induced mothers against decapentaplegic homologue (Smad)2/3 phosphorylation, forkhead box protein 3 (FoxP3) expression and suppression of (IFN)-γ secretion]. However, CD4 + T cells from RA patients can, nonetheless, be regulated efficiently by tolDC in a TGF-β1-dependent manner. This work is important for the design and development of future studies investigating the potential use of tolDC as a novel immunotherapy for the treatment of RA., (© 2016 British Society for Immunology.)

Loss-of-function mutations of the Autoimmune Regulator (AIRE) gene results in organ-specific autoimmunity and disease Autoimmune Polyendocrinopathy type 1 (APS1)/Autoimmune Polyendocrinopathy Candidiasis Ectodermal Dystrophy (APECED). The AIRE protein is crucial in the induction of central tolerance, promoting ectopic expression of tissue-specific antigens in medullary thymic epithelial cells and enabling removal of self-reactive T-cells. AIRE expression has recently been detected in myeloid dendritic cells (DC), suggesting AIRE may have a significant role in peripheral tolerance. DC stimulation of T-cells is critical in determining the initiation or lack of an immune response, depending on the pattern of costimulation and cytokine production by DCs, defining immunogenic/inflammatory (inflDC) and tolerogenic (tolDC) DC. In AIRE-deficient patients and healthy controls, we validated the role of AIRE in the generation and function of monocyte-derived inflDC and tolDCs by determining mRNA and protein expression of AIRE and comparing activation markers (HLA-DR/DP/DQ,CD83,CD86,CD274(PDL-1),TLR-2), cytokine production (IL-12p70,IL-10,IL-6,TNF-α,IFN-γ) and T-cell stimulatory capacity (mixed lymphocyte reaction) of AIRE+ and AIRE- DCs. We show for the first time that: (1) tolDCs from healthy individuals express AIRE; (2) AIRE expression is not significantly higher in tolDC compared to inflDC; (3) tolDC can be generated from APECED patient monocytes and (4) tolDCs lacking AIRE retain the same phenotype and reduced T-cell stimulatory function. Our findings suggest that AIRE does not have a role in the induction and function of monocyte-derived tolerogenic DC in humans, but these findings do not exclude a role for AIRE in peripheral tolerance mediated by other cell types.

Objective: A population of synovial inflammatory dendritic cells (infDCs) has recently been identified in rheumatoid arthritis (RA) and is thought to be monocyte-derived. Here, we investigated the role and source of granulocyte macrophage-colony-stimulating factor (GM-CSF) in the differentiation of synovial infDC in RA., Methods: Production of GM-CSF by peripheral blood (PB) and synovial fluid (SF) CD4+ T cells was assessed by ELISA and flow cytometry. In vitro CD4+ T-cell polarisation experiments were performed with T-cell activating CD2/CD3/CD28-coated beads in the absence or presence of pro-Th1 or pro-Th17 cytokines. CD1c+ DC and CD16+ macrophage subsets were flow-sorted and analysed morphologically and functionally (T-cell stimulatory/polarising capacity)., Results: RA-SF CD4+ T cells produced abundant GM-CSF upon stimulation and significantly more than RA-SF mononuclear cells depleted of CD4+ T cells. GM-CSF-producing T cells were significantly increased in RA-SF compared with non-RA inflammatory arthritis SF, active RA PB and healthy donor PB. GM-CSF-producing CD4+ T cells were expanded by Th1-promoting but not Th17-promoting conditions. Following coculture with RA-SF CD4+ T cells, but not healthy donor PB CD4+ T cells, a subpopulation of monocytes differentiated into CD1c+ infDC; a process dependent on GM-CSF. These infDC displayed potent alloproliferative capacity and enhanced GM-CSF, interleukin-17 and interferon-γ production by CD4+ T cells. InfDC with an identical phenotype to in vitro generated cells were significantly enriched in RA-SF compared with non-RA-SF/tissue/PB., Conclusions: We demonstrate a therapeutically tractable feedback loop of GM-CSF secreted by RA synovial CD4+ T cells promoting the differentiation of infDC with potent capacity to induce GM-CSF-producing CD4+ T cells., (Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/)

The number of patients with autoimmune diseases and severe allergies and recipients of transplants increases worldwide. Currently, these patients require lifelong administration of immunomodulatory drugs. Often, these drugs are expensive and show immediate or late-occurring severe side effects. Treatment would be greatly improved by targeting the cause of autoimmunity, that is, loss of tolerance to self-antigens. Accumulating knowledge on immune mechanisms has led to the development of tolerogenic dendritic cells (tolDC), with the specific objective to restrain unwanted immune reactions in the long term. The first clinical trials with tolDC have recently been conducted and more tolDC trials are underway. Although the safety trials have been encouraging, many questions relating to tolDC, for example, cell-manufacturing protocols, administration route, amount and frequency, or mechanism of action, remain to be answered. Aiming to join efforts in translating tolDC and other tolerogenic cellular products (e.g., Tregs and macrophages) to the clinic, a European COST (European Cooperation in Science and Technology) network has been initiated-A FACTT (action to focus and accelerate cell-based tolerance-inducing therapies). A FACTT aims to minimize overlap and maximize comparison of tolDC approaches through establishment of minimum information models and consensus monitoring parameters, ensuring that progress will be in an efficient, safe, and cost-effective way.

Mouse and human dendritic cells (DCs) are composed of functionally specialized subsets, but precise interspecies correlation is currently incomplete. Here, we showed that murine lung and gut lamina propria CD11b+ DC populations were comprised of two subsets: FLT3- and IRF4-dependent CD24(+)CD64(-) DCs and contaminating CSF-1R-dependent CD24(-)CD64(+) macrophages. Functionally, loss of CD24(+)CD11b(+) DCs abrogated CD4+ T cell-mediated interleukin-17 (IL-17) production in steady state and after Aspergillus fumigatus challenge. Human CD1c+ DCs, the equivalent of murine CD24(+)CD11b(+) DCs, also expressed IRF4, secreted IL-23, and promoted T helper 17 cell responses. Our data revealed heterogeneity in the mouse CD11b+ DC compartment and identifed mucosal tissues IRF4-expressing DCs specialized in instructing IL-17 responses in both mouse and human. The demonstration of mouse and human DC subsets specialized in driving IL-17 responses highlights the conservation of key immune functions across species and will facilitate the translation of mouse in vivo findings to advance DC-based clinical therapies., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Dendritic cells with tolerogenic function (tolDC) have become a promising immunotherapeutic tool for reinstating immune tolerance in rheumatoid arthritis (RA) and other autoimmune diseases. The concept underpinning tolDC therapy is that it specifically targets the pathogenic autoimmune response while leaving protective immunity intact. Findings from human in-vitro and mouse in-vivo studies have been translated into the development of clinical grade tolDC for the treatment of autoimmune disorders. Recently, two tolDC trials in RA and type I diabetes have been carried out and other trials are in progress or are imminent. In this review, we provide an update on tolDC therapy, in particular in relation to the treatment of RA, and discuss the challenges and the future perspectives of this new experimental immunotherapy., (© 2012 British Society for Immunology.)

One of the therapeutic strategies under development for the treatment of rheumatoid arthritis is based on reinstating immune tolerance by vaccination with autologous dendritic cells with potent tolerogenic function. These tolerogenic dendritic cells (TolDC) can be generated ex vivo and have beneficial therapeutic effects in animal models of arthritis. Although experimental animal models have been instrumental in the development of this novel immunotherapeutic tool, several outstanding questions regarding the application of TolDC remain to be addressed. This paper reviews what has been learnt to date from studying the therapeutic potential of TolDC in animal models of arthritis and discusses issues relating to preventive versus curative effects of TolDC, the antigen specificity of TolDC therapy, the route, dose and frequency of TolDC administration and the safety of TolDC treatment. Lessons learnt from animal models will aid the design of clinical trials with TolDC.

Objective: Tolerogenic dendritic cells (DCs) are antigen-presenting cells with an immunosuppressive function. They are a promising immunotherapeutic tool for the attenuation of pathogenic T cell responses in autoimmune arthritis. The aims of this study were to determine the therapeutic action of tolerogenic DCs in a type II collagen-induced arthritis model and to investigate their effects on Th17 cells and other T cell subsets in mice with established arthritis., Methods: Tolerogenic DCs were generated by treating bone marrow-derived DCs with dexamethasone and vitamin D(3) during lipopolysaccharide-induced maturation. Mice with established arthritis received 3 intravenous injections of tolerogenic DCs, mature DCs, or saline. Arthritis severity was monitored for up to 4 weeks after treatment. Fluorescence-labeled tolerogenic DCs were used for in vivo trafficking studies. The in vivo effect of tolerogenic DCs on splenic T cell populations was determined by intracellular cytokine staining and flow cytometry., Results: Tolerogenic DCs displayed a semi-mature phenotype, produced low levels of inflammatory cytokines, and exhibited low T cell stimulatory capacity. Upon intravenous injection into arthritic mice, tolerogenic DCs migrated to the spleen, liver, lung, feet, and draining lymph nodes. Treatment of arthritic mice with type II collagen-pulsed tolerogenic DCs, but not unpulsed tolerogenic DCs or mature DCs, significantly inhibited disease severity and progression. This improvement coincided with a significant decrease in the number of Th17 cells and an increase in the number of interleukin-10-producing CD4+ T cells, whereas tolerogenic DC treatment had no detectable effect on Th1 cells or interleukin-17-producing γ/δ T cells., Conclusion: Treatment with type II collagen-pulsed tolerogenic DCs decreases the proportion of Th17 cells in arthritic mice and simultaneously reduces the severity and progression of arthritis., (Copyright © 2010 by the American College of Rheumatology.)

Objectives: Tolerogenic dendritic cells (tolDCs) constitute a promising experimental treatment for targeting autoreactive T cells in autoimmune diseases, including rheumatoid arthritis (RA). The authors' goal is to bring tolDC therapy for RA to the clinic. Here the authors address key translational issues related to the manufacturing of tolDCs from RA patients with current good manufacturing practice (cGMP)-compliant reagents, the stability of tolDCs, and the selection of suitable quality control markers., Methods: Human monocyte-derived tolDCs were established from RA patients and healthy controls (HCs) using the immunosuppressive drugs dexamethasone and vitamin D₃, and the cGMP-grade immunomodulator, monophosphoryl lipid A, in the cGMP-compliant medium, CellGroDC. The functionality of tolDCs and tolDC-modulated autologous CD4 T cells was determined by flow cytometry, [³H]thymidine incorporation and ELISA., Results: Clinical-grade tolDCs established from patients with RA exhibit a typical tolerogenic phenotype of reduced costimulatory molecules, low production of proinflammatory cytokines and impaired stimulation of autologous antigen-specific T cells, comparable to HC tolDCs. Toll-like receptor 2 (TLR-2) was highly expressed by tolDCs but not mature DCs. Furthermore, tolDCs suppressed mature DC-induced T cell proliferation, interferon γ and interleukin 17 production, and rendered T cells hyporesponsive to further stimulation. Importantly, tolDCs were phenotypically stable in the absence of immunosuppressive drugs and were refractory to further challenge with proinflammatory mediators., Conclusions: tolDCs established from patients with RA are comparable to those derived from healthy donors. TLR-2 was identified as an ideal marker for quality control of tolDCs. Potently tolerogenic and highly stable, these tolDCs are a promising cellular therapeutic for tailored immunomodulation in the treatment of RA.

Objectives: Tumour necrosis factor alpha (TNFalpha) blockade is an effective therapy for rheumatoid arthritis (RA). The immunomodulatory effects of TNFalpha antagonists are thought to contribute to their therapeutic action. This study investigated whether anti-TNFalpha therapeutics exerted their immunoregulatory effects through modulation of dendritic cell (DC) function., Methods: Two complementary approaches were taken: in the first 'in vitro' approach monocyte-derived DC from healthy donors were matured with lipopolysaccharide and treated with TNFalpha antagonists in vitro for 48 h. In the second 'ex vivo' approach monocyte-derived DC were generated from RA patients before and 8-12 weeks into anti-TNFalpha treatment. DC were analysed for survival, phenotype, cytokine production and T-cell stimulatory capacity., Results: TNFalpha blockade during DC maturation in vitro induced approximately 40% of DC to undergo apoptosis. Importantly, the surviving DC displayed a semimature phenotype with reduced levels of HLA-DR, CD80, CD83, CD86 and CCR7, and their production of IL-10 was enhanced compared with DC matured without TNFalpha antagonists. Furthermore, anti-TNFalpha-treated DC were poor stimulators of T-cell proliferation and polarised T-cell development towards a higher IL-10/lower IFNgamma cytokine profile. Similarly, DC derived from RA patients after anti-TNFalpha treatment showed impaired upregulation of CD80 and CD86 upon lipopolysaccharide activation and displayed poor T-cell stimulatory activity., Conclusions: The data show that TNFalpha blockade has profound effects on DC function with downstream, potentially immunoregulatory, effects on T cells. These data provide an interesting new insight into the potential mechanism by which anti-TNFalpha drugs contribute to the restoration of immunoregulation in RA patients.

Dendritic cells are professional antigen-presenting cells that maintain immune tolerance to self-antigens by deleting or controlling the pathogenicity of auto-reactive T-cells. Dendritic cell-based immunotherapies show great promise for the restoration of tolerance in autoimmune disease. Dendritic cells can be modified ex vivo to induce stable tolerogenic function and be used as cellular 'vaccines' or they can be targeted in vivo with sophisticated antigen delivery systems. Tolerogenic dendritic cells induce antigen-specific T-cell tolerance in vivo and have therapeutic effects in animal models of autoimmunity. The current challenge is to bring tolerogenic dendritic cell therapy to the clinic.

Objective: Dendritic cells (DCs) are enriched in RA synovium and have been implicated in the pathogenesis of RA primarily through their ability to present autoantigen and activate T cells. However, whether DCs play an effector role in cartilage destruction is unknown. The aim of this study was to investigate whether DCs can induce collagen release from cartilage and the mechanism involved., Methods: Human monocyte-derived DCs (mDCs) were activated with CD40 ligand (CD40L) to mimic DC-T-cell interaction, and supernatants were incubated with cartilage explants. Hydroxyproline was assessed as a measure of collagen release and collagenolytic activity was measured by a bioassay using tritiated collagen. TNF-alpha in DC supernatants was measured by specific ELISA., Results: Supernatants from CD40L-activated mDCs, but not unstimulated mDCs, strongly induced the destruction of cartilage collagen. mDC supernatants did not contain collagenases but did induce collagenolytic activity in cartilage explants. Neutralization of TNF-alpha in mDC supernatants completely abolished collagenolysis., Conclusions: This study shows that mDCs, upon CD40-ligation, induce cartilage collagen degradation through an indirect mechanism via the production of TNF-alpha. Our data suggest a potential important role for mDC-derived TNF-alpha in RA, which is in line with the previously reported observations that DCs are a major source of TNF-alpha in early autoimmune lesions and that anti-TNF-alpha therapeutics effectively suppress joint damage in RA patients. We propose that DCs can act as effectors in cartilage destruction, adding a new aspect to the functional role of DCs in RA pathogenesis.

Background: It is understood that chronic allograft failure occurs as a result of alloimmune and non-alloimmune injury. Dendritic cells (DC) are thought to be crucial in regulating (allo)immune airway damage and interactions with epithelial cells are likely. Studies in human lung transplantation are limited, however, and the available literature on DC is inconsistent. This study focused on the ex vivo influence of primary bronchial epithelial cells derived from lung allografts on DC differentiation., Methods: Epithelial cell conditioned media (ECCM) were added to monocytes differentiating into DC under the influence of interleukin-4 and granulocyte macrophage-colony stimulating factor. The resultant cells were compared with DC cultured without ECCM and with monocyte-derived macrophages. Expression of typical DC (eg, CD1a) and macrophage (eg, CD14) markers was assessed by flow cytometry. Phenotypical assessments were complemented by functional studies of mannose receptor-mediated phagocytosis (FITC-dextran uptake) and antigen-presenting capability (mixed lymphocyte reactions)., Results: Cells exposed to ECCM expressed significantly lower levels of CD1a than unexposed DC. CD14 expression and phagocytic function were increased. ECCM cultured cells also expressed lower levels of T cell co-stimulatory molecules, secreted an anti-inflammatory cytokine profile and had significantly reduced antigen-presenting capability., Conclusion: Using phenotypic and functional approaches, this study has shown that ECCM from lung allografts drives the production of macrophage-like cells from monocytes rather than DC. The data suggest that epithelial cells may restrain airway DC and potential alloimmunity. It is unclear whether the observed effect is specifically seen in lung transplant recipients or is a general property of bronchial epithelial cells. This may reflect a homeostatic inter-relationship between airway epithelial and DC populations relevant both to lung allografts and the lung more generally.

Autoimmune pathologies are caused by a breakdown in self-tolerance. Tolerogenic dendritic cells (tolDC) are a promising immunotherapeutic tool for restoring self-tolerance in an antigen-specific manner. Studies about tolDC have focused largely on generating stable maturation-resistant DC, but few have fully addressed questions about the antigen-presenting and migratory capacities of these cells, prerequisites for successful immunotherapy. Here, we investigated whether human tolDC, generated with dexamethasone and the active form of vitamin D3, maintained their tolerogenic function upon activation with LPS (LPS-tolDC), while acquiring the ability to present exogenous autoantigen and to migrate in response to the CCR7 ligand CCL19. LPS activation led to important changes in the tolDC phenotype and function. LPS-tolDC, but not tolDC, expressed the chemokine receptor CCR7 and migrated in response to CCL19. Furthermore, LPS-tolDC were superior to tolDC in their ability to present type II collagen, a candidate autoantigen in rheumatoid arthritis. tolDC and LPS-tolDC had low stimulatory capacity for allogeneic, naïve T cells and skewed T cell polarization toward an anti-inflammatory phenotype, although LPS-tolDC induced significantly higher levels of IL-10 production by T cells. Our finding that LPS activation is essential for inducing migratory and antigen-presenting activity in tolDC is important for optimizing their therapeutic potential.

Promising immunotherapeutic tools for T cell-mediated pathologies are alternatively activated dendritic cells (aaDC), which exert their effect through the regulation and tolerization of T cells. As naïve and memory T cells have different susceptibilities to tolerogenic signals, it is important to understand the modulatory effects of aaDC on these T cell subsets. We have examined regulation of naïve and memory CD4+ T cells by human aaDC generated with dexamethasone, the active form of vitamin D3, 1alpha,25-dihydroxyvitamin D3, and LPS. Although aaDC induced low, primary, allogeneic responses by naïve and memory T cells, aaDC regulated the differentiation of these T cell subsets in a distinct manner. Naïve T cells primed by aaDC retained a strong, proliferative capacity upon restimulation but were skewed toward a low IFN-gamma/high IL-10 cytokine profile. In contrast, memory T cells primed by aaDC became hyporesponsive in terms of proliferation and cytokine production. Induction of anergy in memory T cells by aaDC was not a result of the presence of CD25hi regulatory T cells and could be partially reversed by IL-2. Both T cell subsets acquired regulatory activity and inhibited primary CD4 and CD8 responses. Addition of exogenous IL-12p70 during T cell priming by aaDC prevented anergy induction in memory T cells and cytokine polarization in naïve T cells, indicating that the lack of IL-12p70 is a key feature of aaDC. Our finding that aaDC differentially regulate naïve and memory T cells is important for understanding and maximizing the therapeutic potential of aaDC.

Background: Extracorporeal Photopheresis (ECP) has been shown to be an effective treatment of graft-versus-host disease, solid organ graft rejection, and other T-cell-mediated diseases. The mechanisms of action of ECP include lymphocyte apoptosis, cytokine modulation, and the induction of regulatory T cells. It has been suggested that dendritic cells (DCs) are more resistant to ECP-induced apoptosis and might be directly modulated by ECP. We tested this hypothesis using in vitro Psoralen/UVA (PUVA) treatment as an in vitro model of ECP., Methods: Monocyte-derived DCs (mo-DCs) were treated with 8-methoxypsoralen /UVA and analyzed for surface molecule expression, apoptosis markers, endocytosis, and migratory and immunostimulatory capacity. Mo-DC phenotype and cytokine secretion was tested after CD40L stimulation. Naive T cells stimulated with PUVA-treated mo-DCs were tested for Th1/Th2 cytokine secretion and associated chemokine receptor patterns., Results: DCs underwent apoptosis after in vitro PUVA and in vivo ECP. In vitro, the induction of apoptosis was preceded by partial maturation of immature mo-DCs. PUVA-treated immature mo-DCs also exhibited enhanced migratory and immunostimulatory capacity. However, mo-DCs stimulation through CD40 ligation was abrogated and interleukin (IL)-12 secretion was abolished 24 hr after PUVA treatment. PUVA-treated mo-DCs skewed naive T cells toward a Th2 response as defined by increased IL-4, IL-10, and IL-13 and decreased interferon-gamma levels, and the expression of the Th2-associated chemokine receptors CCR4 and CCR10. The observed Th2 shift was partially reversed by exogenous IL-12., Conclusion: These data suggest that direct modulation of DC function as well as apoptosis contribute to the immunoregulatory effects of ECP.

Using the principle of functional polarization of dendritic cells (DCs), we have developed a novel protocol to generate human DCs combining the three features critical for the induction of type-1 immunity: (a) fully mature status; (b) responsiveness to secondary lymphoid organ chemokines; and (c) high interleukin-12p70 (IL-12p70)-producing ability. We show that IFN-alpha and polyinosinic:polycytidylic acid (p-I:C) synergize with the "classical" type-1-polarizing cytokine cocktail [tumor necrosis factor alpha (TNFalpha)/IL-1beta/IFNgamma], allowing for serum-free generation of fully mature type-1-polarized DCs (DC1). Such "alpha-type-1-polarized DC(s)" (alphaDC1) show high migratory responses to the CCR7 ligand, 6C-kine but produce much higher levels of IL-12p70 as compared to TNFalpha/IL-1beta/IL-6/prostaglandin E2 (PGE2)-matured DCs (sDC), the current "gold standard" in DC-based cancer vaccination. A single round of in vitro sensitization with alphaDC1 (versus sDCs) induces up to 40-fold higher numbers of long-lived CTLs against melanoma-associated antigens: MART-1, gp100, and tyrosinase. Serum-free generation of alphaDC1 allows, for the first time, the clinical application of DCs that combine the key three features important for their efficacy as anticancer vaccines.

Type I IFNs (IFN-alphabeta) constitute a family of cytokines that have important antiviral and immunoregulatory properties and have been successfully used in the treatment of a wide variety of diseases. There are 12 functional human IFN-alpha subtypes and one IFN-beta subtype that signal through the common cell surface IFN-alphabetaR. To date, virtually no information is available on the specificity of IFN-alpha responses in immune cells. In this study, Janus kinase/STAT signaling and transcriptional responses to selected IFN-alpha subtypes in human T cells and dendritic cells were analyzed. Evidence for IFN-alpha subtype and cell type specificity was found. Also, differences between kinetics of expression of IFN-stimulated genes (ISGs) and in the requirements of individual ISGs for additional signaling pathways were observed. In particular, IFN-gamma-inducible protein-10 (IP-10), a key chemokine in Th1-type inflammatory diseases, was differentially regulated. In dendritic cells, it was highly induced by IFN-alpha2 and IFN-alpha21 but much less efficiently by IFN-alpha1. It was only marginally induced by these subtypes in T cells. In marked contrast to other ISGs analyzed, optimum induction of IP-10 was dependent on activation of p38 kinase(s). The observed variations (subtype-, cell type-, and ISG-related differentials) provide further insight into the complexity and plasticity of the IFN-alphabeta response. Furthermore, the novel observation that IFN-alpha1 poorly induces IP-10 is potentially of clinical importance, because this subtype may be more beneficial in cases where Th1-mediated side effects (e.g., exacerbation of autoimmune diseases) are not desirable.

The central effector cells in the pathogenesis of atopic allergic diseases are type 2 T helper (Th2) cells, which display an aberrant cytokine profile dominated by type 2 cytokines. Initial reports from mouse studies indicated that established and committed Th2 cells are stable and unsusceptible to modulation. However, there is a growing awareness that in humans, established effector Th2 cells are more flexible and can be reverted to predominant Th1 phenotypes. In fact, the Th1-driving cytokine interleukin (IL)-12 is the crucial factor in this respect. IL-12 is mainly produced by dendritic cells (DC), which can be primed for high or low IL-12 production, depending on inflammatory and/or microbial signals they encounter during their residence in the peripheral tissues. Accordingly, both the regulation of and the priming for IL-12 production in DC form ideal targets for therapeutic intervention. The development of new therapies for atopic allergy now focuses on local IL-12-promoting substances to target both the development of new Th2 cells and the persistent population of established allergen-specific Th2 cells., (Copyright 2001 S. Karger AG, Basel)

Optimal clearance of the various pathogen types encountered by the human body requires the selective activation of particular cellular and/or humoral immune responses. The orchestration of the types of effector responses is directed by Th cells through the production of type 1 (Th1 cell-associated) and type 2 (Th2 cell-associated) cytokines. The way in which the Th cell cytokine profile is matched to the type of invading pathogen, and why these profiles sometimes derail and lead to disease, is not well understood. Here, we will discuss the concept that antigen-presenting cells (APC) provide Th cells not only with antigen and costimulatory signals, but also with a polarizing signal (signal 3). This signal can be mediated by many APC-derived factors, but IL-12 and PGE2 seem to be of major importance. The Th2-biased responses in atopic allergy appeared to be associated with monocytes with a decreased IL-12/PGE2 ratio and, consequently, with the down-regulation of type 1 cytokine production in Th cells. As for Th cells, APC can be functionialy polarized. In vitro experiments with monocyte-derived dendritic cells (DC) showed that the presence of IFN-gamma during activation of immature DC primes for mature DC with the ability of high IL-12 production and, consequently, a Th1-driving capacity (APC1 or DC1). In contrast, PGE2 primes for a low IL-12 production ability and a Th2-driving capacity (APC2 or DC2). These findings suggest that pathogens provoke either Th1- or Th2-cell development by inducing the production of a certain pattern of inflammatory DC-polarizing mediators (e.g. IFN-gamma and PGE2) at the site of infection. The type of immune polarization will not only depend on the type of pathogen, but also varies with the type of infected tissue, i.e. that different tissues produce different mediators in response to the same pathogen. In the case of atopic allergy, this concept implies that the Th2-cell bias may be related to low levels of cross-regulatory infections, to Th1 cell-inducing pathogens, or to an aberrant function of stromal cells in peripheral tissues.

Activation of immature CD83- dendritic cells (DC) in peripheral tissues induces their maturation and migration to lymph nodes. Activated DC become potent stimulators of Th cells and efficient inducers of Th1- and Th2-type cytokine production. This study analyzes the ability of human monocyte-derived CD1a+ DC at different stages of IL-1 beta and TNF-alpha-induced maturation to produce the major Th1-driving factor IL-12. DC at the early stages of maturation (2 and 4 h) produced elevated amounts of IL-12 p70 during interaction with CD40 ligand-bearing Th cells or, after stimulation with the T cell-replacing factors, soluble CD40 ligand and IFN-gamma. The ability to produce IL-12 was strongly down-regulated at later time points, 12 h after the induction of DC maturation, and in fully mature CD83+ cells, at 48 h. In contrast, the ability of mature DC to produce IL-6 was preserved or even enhanced, indicating their intact responsiveness to CD40 triggering. A reduced IL-12-producing capacity of mature DC resulted mainly from their impaired responsiveness to IFN-gamma, a cofactor in CD40-induced IL-12 p70 production. This correlated with reduced expression of IFN-gamma R (CD119) by mature DC. In addition, while immature DC produced IL-12 and IL-6 after stimulation with LPS or Staphylococcus aureus Cowan I strain, mature DC became unresponsive to these bacterial stimuli. Together with the previously described ability of IL-10 and PGE2 to stably down-regulate the ability to produce IL-12 in maturing, but not in fully mature, DC, the current data indicate a general resistance of mature DC to IL-12-modulating factors.

IL-12 is a key cytokine in the development of Th1 responses. IL-12 production by antigen-presenting cells (APC) can be induced by the interaction between CD40 on the APC and CD40 ligand (CD40L) expressed on T cells after activation. Our previous study indicated that in dendritic cells (DC), the only APC that can activate naive T(h) cells efficiently, the mere CD40 engagement is insufficient to induce IL-12 production. The aim of the present study was to dissect the conditions for efficient IL-12 production by DC further. Using populations of naive and memory Th cells, recombinant CD40L, neutralizing and blocking antibodies, and by determining IFN-gamma production and CD40L expression levels, we here show that T cell-induced IL-12 production by DC results from the action of two signals, mediated by CD40L and IFN-gamma, and that the inability of naive T(h) cells to induce IL-12 production resides in their inability to produce IFN-(gamma). Other factors than CD40L and IFN-gamma can provide the required signals for IL-12 production by DC, as either factor could be replaced by lipopolysaccharide (LPS). The two-signal requirement proved unique for the production of IL-12, since either CD40 engagement or LPS was sufficient for the efficient production of tumor necrosis factor-alpha, IL-8 and the p40 subunit of IL-12, and may be considered as a safety mechanism for optimal control of potentially harmful T(h)1 responses.

Activation of immature dendritic cells (DC) in peripheral tissues induces their migration to lymph nodes and their maturation into CD83+ DC, which are able to prime naive T cells. The inflammatory cytokines IL-1beta and TNF-alpha induce mature DC, which can secrete IL-12 and promote the development of Th0/Th1-biased cells. DC maturation factors with a Th2-promoting function have not been described. Here we show that PGE2, although it does not induce final DC maturation by itself, synergizes with IL-1beta and TNF-alpha, and allows their effectiveness at 100-fold lower concentrations. While being phenotypically identical with the DC matured in the presence of high concentrations of IL-1beta and TNF-alpha alone, DC matured in the additional presence of PGE2 show impaired IL-12 production and bias naive Th cell development toward the Th2. The ability of DC to produce IL-12 is also suppressed by IL-10, which in contrast to PGE2, inhibits their maturation. The differences in the ability to produce IL-12, established during the final DC maturation, are stable after the removal of modulatory factors. Importantly, fully mature DC become unsusceptible to PGE2 and IL-10. This indicates that the levels of IL-12 production in vivo, in mature DC interacting with Th cells within the lymph nodes, are mainly predetermined at the stage of immature DC in peripheral tissues. These data imply that the character of pathogen-induced local inflammatory reaction can "instruct" local DC to initiate Th1 or Th2-biased responses.

Dendritic cells (DC) are important initiators of specific primary immune responses because they are the only APC that can efficiently activate naive Th cells. DC have the capacity to produce interleukin-12 (IL-12), a cytokine that plays a pivotal role in the development of Th1-mediated cellular immune responses. The present study focuses on the conditions under which human DC produce bioactive IL-12 p70 and, consequently, direct the development of naive T helper (Th) cells toward the Th1 phenotype. Bacteria or bacterial compounds such as Staphylococcus aureus Cowan strain I (SAC) or lipopolysaccharide (LPS) induced substantial IL-12 levels in DC, which could be further upregulated by interferon-gamma (IFN-gamma), whereas induction of IL-12 production via CD40 ligation required IFN-gamma as an obligatory, complementary signal. Also, activated naive Th cells were poor inducers of IL-12 production, unless exogenous IFN-gamma was present, whereas activated memory Th cells were effective inducers of IL-12 production and did not require exogenous IFN-gamma. Next, the cytokine profiles of matured Th cells that were primed by DC under different conditions were examined. DC promoted the development of naive Th cells into memory Th0 cells that produced both the type 1 cytokine IFN-gamma and the type 2 cytokine IL-4. In contrast, after activation with SAC, DC efficiently directed the development of Th1 cells through the release of IL-12. An APC-independent Th cell maturation model, using either recombinant IL-12 or supernatants of SAC-activated DC and neutralizing anti-IL-12 antibodies, confirmed that DC-derived IL-12 was the major Th1 skewing factor. Together, these data indicate that the contact between DC and naive Th cells during the initiation of specific immune responses does not result in the efficient induction of IL-12 production and that, consequently, exogenous IL-12-inducing factors are required to promote primary Th1-mediated cellular immune responses.

We studied to what extent the presence of an inflammatory mediator PGE2, during the development of dendritic cells (DC) affects their subsequent ability to induce Th1- and Th2-type cytokines in maturing naive Th cells. PGE2 (10(-9)-10(-6) M) did not alter the morphology or the expression of class II MHC and costimulatory molecules on DC obtained from monocytes in the presence of granulocyte-macrophage CSF and IL-4, although at concentrations above 10(-8) M, PGE2 prevented the acquisition of CD1a marker. Both control DC and DC maturing in the presence of PGE2 (PGE2-DC) were potent stimulators of naive Th cells. In contrast to control DC, which produced high amounts of IL-12 and trace amounts of IL-10, PGE2-DC produced no IL-12 and high amounts of IL-10 when stimulated in the absence of PGE2. This distinct cytokine profile of PGE2-DC was stable for at least 48 h of additional culture in the absence of PGE2. Control DC induced the development of Th0-like cells from superantigen-activated naive Th cells, whereas PGE2-DC promoted the development of Th cells that produced high amounts of IL-4 and IL-5. Experiments using IL-12-neutralizing Abs or rIL-12 indicated a crucial role of IL-12 deficiency in the induction of type 2 cytokine profiles. These findings suggest that elevated levels of PGE2 promote type 2 Th responses by stably impairing the ability of maturing DC to produce IL-12. Since type 2 Th responses are protective in several Th1-related autoimmune disorders, PGE2-DC may be considered for use in immunotherapy.

In order to investigate the impact of an inflammatory mediator PGE2 on the functions of maturing DC we used an in vitro model of DC generation from peripheral blood monocytes. Addition of PGE2 (10(-9) M-10(-6) M) to the cultures performed in the presence of GM-CSF and IL-4 did not alter the morphology nor high levels of expression of class II MHC and co-stimulatory molecules on arising DC, although at concentrations above 10(-8) M, the acquisition of CD1a was selectively prevented. Control DC and the DC maturing in the presence of PGE2 (PGE2-DC) induced a similar proliferation of naive Th cells. Control DC produced high amounts of IL-12, and only trace amounts of IL-10, whereas PGE2-DC produced no IL-12 and high levels of IL-10, when stimulated after the removal of PGE2. The deficient IL-12 production by PGE2-DC was observed after stimulation both in the absence and in the presence of IFN gamma, and was not compensated during further 48 h culture in the absence of PGE2. Compared to control DC, PGE2-DC induced development of Th cells secreting elevated amounts of IL-4 and IL-5, from naive precursors. These data indicate that elevated tissue levels of PGE2 may promote type 2 Th responses by impairing the ability of locally maturing DC to produce IL-12. Since Th2 responses mediate protection in Th1-related autoimmune disorders, the use of PGE2-DC in immunotherapy of such disorders may be considered.