Tolerogenic dendritic cells

Induction of a CD4+ T Regulatory Type 1 Response by Cyclooxygenase-2-Overexpressing Glioma

PGE(2), synthesized by cyclooxygenase-2 (COX-2)-overexpressing tumor, is known to contribute to cellular immune suppression in cancer patients, but the mechanism remains unclear. We report the mechanism of a CD4(+) T regulatory type 1 (Tr1) induction by CD11c(+) mature dendritic cells (DCs) that phagocytose allogeneic and autologous COX-2-overexpressing glioma. A human glioma cell line, U-87MG, and primary cultured glioblastoma cells (MG-377) overexpressed COX-2. We did not detect IL-10Ralpha expression in these gliomas, and rIL-10 did not suppress their COX-2 expression. Exposure to COX-2-overexpressing glioma induced mature DCs to overexpress IL-10 and decreased IL-12p70 production. These DCs induced a Tr1 response, which is characterized by robust secretion of IL-10 and TGF-beta with negligible IL-4 secretion by CD4(+) T cells, and an inhibitory effect on admixed lymphocytes. Peripheral CD4(+) T cell populations isolated from an MG-377 patient also predominantly demonstrated a Tr1 response against MG-377 cells. Selective COX-2 inhibition in COX-2-overexpressing gliomas at the time of phagocytic uptake by DCs abrogated this regulatory response and instead elicited Th1 activity. COX-2 stable transfectants in LN-18 (LN-18-COX2) also induced a Tr1 response. The effect of a COX-2 inhibition in LN-18-COX2 is reversible after administration of PGE(2). Taken together, robust levels of PGE(2) from COX-2-overexpressing glioma, which is unresponsive to IL-10 within the local microenvironment, may cause DCs to secrete high levels of IL-10. These results indicate that COX-2-overexpressing tumors induce a Tr1 response, which is mediated by tumor-exposed, IL-10-enhanced DCs.

Strong and durable TCR clustering at the T/dendritic cell immune synapse is not required for NFAT activation and IFN-gamma production in human CD4+ T cells

The exact function of TCR clustering and organized macromolecular patterns at the immune synapse between APCs and T lymphocytes is unclear. Using human immature or mature dendritic cells (DCs) and autologous CD4(+) effector T cells, we demonstrate that, within a given conjugate, mature DCs induce strong and long-lasting TCR clustering and protein kinase C-theta translocation in a superantigen dose-dependent manner. Moreover, mature DCs promote CD43 exclusion in a dose-independent manner. In contrast, immature DCs are less potent at inducing these molecular rearrangements. Using these models to correlate T cell functions with the frequency, the intensity, and the duration of TCR clustering, we show, in Jurkat T cells, that weak and transient TCR clustering is sufficient to promote TCR down-modulation, protein kinase C-theta translocation at the synapse, and substantial NFAT transcriptional activation. Moreover, we show, in CD4(+) T cell blasts, that strong TCR clustering is required for neither TCR down-modulation nor optimal IFN-gamma production. Together, our results demonstrate that some CD4(+) functional responses, such as cytokine production, are independent of central supramolecular activation cluster formation.

Opsonization with C1q and mannose-binding lectin targets apoptotic cells to dendritic cells

Deficiencies of early components of the classical complement pathway, particularly C1q, are strongly associated with susceptibility to systemic lupus erythematosus. Recent data link this predisposal to autoimmunity to an inappropriate clearance of apoptotic cells, which could lead to a loss of self-tolerance. In the present study, we demonstrate that opsonization of apoptotic cells with C1q and mannose-binding lectin allows and facilitates their uptake not only by macrophages but also by human immature dendritic cells (DCs). Both C1q and mannose-binding lectin enhance the uptake of apoptotic cells by DCs in a dose-dependent way. The uptake of C1q-opsonized apoptotic cells, but not nonopsonized apoptotic cells, by DCs stimulated the production of IL-6, IL-10, and TNF-alpha, without an effect on IL-12p70. We conclude that these recognition molecules of the complement system do not sequester apoptotic cells from DCs, but rather promote their uptake by immature DCs. Therefore, we propose that early complement components support safe clearance of cellular debris by facilitating phagocytosis and possibly by immunomodulatory mechanisms, thus preventing autoimmunity.

Natural antibodies sustain differentiation and maturation of human dendritic cells

The differentiation and maturation of dendritic cells (DCs) is governed by various signals in the microenvironment. Monocytes and DCs circulate in peripheral blood, which contains high levels of natural antibodies (NAbs). NAbs are germ-line-encoded and occur in the absence of deliberate immunization or microbial aggression. To assess the importance of NAbs in the milieu on DC development, we examined the status of DCs in patients with X-linked agammaglobulinemia, a disease characterized by paucity of B cells and circulating antibodies. We demonstrate that the in vitro differentiation of DCs is severely impaired in these patients, at least in part because of low levels of circulating NAbs. We identified NAbs reactive with the CD40 molecule as an important component that participates in the development of DCs. CD40-reactive NAbs restored normal phenotypes of DCs in patients. The maturation process induced by CD40-reactive NAbs was accompanied by an increased IL-10 and decreased IL-12 production. The transcription factor analysis revealed distinct signaling pathways operated by CD40-reactive NAbs compared to those by CD40 ligand. These results suggest that B cells promote bystander DC development through NAbs and the interaction between NAbs and DCs may play a role in steady-state migration of DCs.

Enhanced dendritic cell antigen capture via toll-like receptor-induced actin remodeling

Microbial products are sensed through Toll-like receptors (TLRs) and trigger a program of dendritic cell (DC) maturation that enables DCs to activate T cells. Although an accepted hallmark of this response is eventual down-regulation of DC endocytic capacity, we show that TLR ligands first acutely stimulate antigen macropinocytosis, leading to enhanced presentation on class I and class II major histocompatibility complex molecules. Simultaneously, actin-rich podosomes disappear, which suggests a coordinated redeployment of actin to fuel endocytosis. These reciprocal changes are transient and require p38 and extracellular signal-regulated kinase activation. Thus, the DC actin cytoskeleton can be rapidly mobilized in response to innate immune stimuli to enhance antigen capture and presentation.

IL-6 Regulates In Vivo Dendritic Cell Differentiation through STAT3 Activation

Dendritic cells (DCs) orchestrate immune responses according to their state of maturation. In response to infection, DCs differentiate into mature cells that initiate immune responses, while in the absence of infection, most of them remain in an immature form that induces tolerance to self Ags. Understanding what controls these opposing effects is an important goal for vaccine development and prevention of unwanted immune responses. A crucial question is what cytokine(s) regulates DC maturation in the absence of infection. In this study, we show that IL-6 plays a major role in maintaining immature DCs. IL-6 knockout (KO) mice had increased numbers of mature DCs, indicating that IL-6 blocks DC maturation in vivo. We examined this effect further in knockin mice expressing mutant versions of the IL-6 signal transducer gp130, with defective signaling through either Src homology region 2 domain-containing phosphatase 2/Gab/MAPK (gp130(F759/F759)) or STAT3 (gp130(FxxQ/FxxQ)), and combined gp130 and IL-6 defects (gp130(F759/F759)/IL-6 KO mice). Importantly, we found STAT3 activation by IL-6 was required for the suppression of LPS-induced DC maturation. In addition, STAT3 phosphorylation in DCs was regulated by IL-6 in vivo, and STAT3 was necessary for the IL-6 suppression of bone marrow-derived DC activation/maturation. DC-mediated T cell activation was enhanced in IL-6 KO mice and suppressed in gp130(F759/F759) mice. IL-6 is thus a potent regulator of DC differentiation in vivo, and IL-6-gp130-STAT3 signaling in DCs may represent a critical target for controlling T cell-mediated immune responses in vivo.

The role of death-associated molecular patterns in the pathogenesis of systemic lupus erythematosus

This article describes apoptotic cell clearance mechanisms and discusses altered mechanisms for clearance of dying material, which represents a central pathogenic process in the development and acceleration of systemic lupus erythematosus. The article also explores ways to use this perspective for a potential direction for future treatments.

SalmonellaEscape from Antigen Presentation Can Be Overcome by Targeting Bacteria to Fcγ Receptors on Dendritic Cells

Dendritic cells (DCs) are professional APCs with the unique ability to activate naive T cells, which is required for initiation of the adaptive immune response against pathogens. Therefore, interfering with DC function would be advantageous for pathogen survival and dissemination. In this study we provide evidence suggesting that Salmonella enterica serovar typhimurium, the causative agent of typhoid disease in the mouse, interferes with DC function. Our results indicate that by avoiding lysosomal degradation, S. typhimurium impairs the ability of DCs to present bacterial Ags on MHC class I and II molecules to T cells. This process could correspond to a novel mechanism developed by this pathogen to evade adaptive immunity. In contrast, when S. typhimurium is targeted to FcgammaRs on DCs by coating bacteria with Salmonella-specific IgG, bacterial Ags are efficiently processed and presented on MHC class I and class II molecules. This enhanced Ag presentation leads to a robust activation of bacteria-specific T cells. Laser confocal microscopy experiments show that virulent S. typhimurium is rerouted to the lysosomal degradation pathway of DCs when internalized through FcgammaR. These observations are supported by electron microscopy studies demonstrating that internalized S. typhimurium shows degradation signs only when coated with IgG and captured by FcgammaRs on DCs. Therefore, our data support a potential role for bacteria-specific IgG on the augmentation of Ag processing and presentation by DCs to T cells during the immune response against intracellular bacteria.

Activation of arterial wall dendritic cells and breakdown of self-tolerance in giant cell arteritis

Giant cell arteritis (GCA) is a granulomatous and occlusive vasculitis that causes blindness, stroke, and aortic aneurysm. CD4(+) T cells are selectively activated in the adventitia of affected arteries. In human GCA artery-severe combined immunodeficiency (SCID) mouse chimeras, depletion of CD83(+) dendritic cells (DCs) abrogated vasculitis, suggesting that DCs are critical antigen-presenting cells in GCA. Healthy medium-size arteries possessed an indigenous population of DCs at the adventitia-media border. Adoptive T cell transfer into temporal artery-SCID mouse chimeras demonstrated that DCs in healthy arteries were functionally immature, but gained T cell stimulatory capacity after injection of lipopolysaccharide. In patients with polymyalgia rheumatica (PMR), a subclinical variant of GCA, adventitial DCs were mature and produced the chemokines CCL19 and CCL21, but vasculitic infiltrates were lacking. Human histocompatibility leukocyte antigen class II-matched healthy arteries, PMR arteries, and GCA arteries were coimplanted into SCID mice. Immature DCs in healthy arteries failed to stimulate T cells, but DCs in PMR arteries could attract, retain, and activate T cells that originated from the GCA lesions. We propose that in situ maturation of DCs in the adventitia is an early event in the pathogenesis of GCA. Activation of adventitial DCs initiates and maintains T cell responses in the artery and breaks tissue tolerance in the perivascular space.

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.

Update on pediatric systemic lupus erythematosus

PURPOSE OF REVIEW

The purpose of this review is to provide an update on the clinical manifestations of SLE in children. Emerging clues on the pathogenesis of the disease based on recent human studies conducted both in children and adults, will also be summarized.

RECENT FINDINGS

Pediatric Rheumatologists caring for children with SLE face many challenges. As the life expectancy of these patients improves, new recognized complications such as accelerated atherosclerosis and hypertension emerge as major causes of morbidity. However, few longitudinal studies describing the long term outcome of these children, including the impact of disease and treatment on their physical and psychological development are available. Few prospective interventional studies have been carried out to assess the efficacy of established and novel treatments in the pediatric population. Recently, basic studies aimed at understanding the immune alterations underlying this disease have been performed in children. These studies indicate an important role for interferon-alpha (IFN-alpha) in the pathogenesis of this disease and reveal an overall striking homogeneity of leukocyte gene expression profiles in children and adults with SLE. The contribution of novel gene polymorphisms to disease susceptibility and the sequential breakdown of tolerance to nuclear antigens that precedes clinical manifestations in patients with SLE are among the recent studies that are helping us understand the complex SLE puzzle.

SUMMARY

SLE continues to cause significant morbidity in the pediatric age group. A better recognition of the age-specific manifestations and long-term complications of this disease is required to improve its outcome. Understanding its unique pathogenesis will hopefully lead to the development of better, more targeted and less toxic therapies.

Breast carcinoma cell lysate-pulsed dendritic cells cross-prime MUC1-specific CD8+ T cells identified by peptide-MHC-class-I tetramers

For cancer immunotherapy the loading of dendritic cells (DCs) with whole tumor cell lysate preparations represents a simple and promising approach for presentation of tumor-associated antigens (TAAs), avoiding the disadvantages of HLA-matching and definition of TAAs. The aim of this study was to investigate whether lysate-pulsed DCs efficiently cross-prime CD8+ T cells and induce a strong T(H)1 cell response, as compared to DCs pulsed with specific peptides (FLU M1 and Melan-A/Mart-1). As a model system breast carcinoma cell lysate from either MCF-7 or MDA-MB-231 cell lines (both HLA-A*0201+) expressing the TAA MUC1 were selected. Both cell lines expressed MUC1, the epithelial mucin, which is a large molecular weight O-glycosylated protein expressed in the majority of breast, ovarian, and other epithelial malignancies and is under evaluation as a target antigen in cancer immunotherapy. We developed a simple lysate preparation method to solubilize all cell proteins without degradation. For loading of monocyte-derived dendritic cells, 100 microgmL(-1) of breast carcinoma cell lysate was used, accompanied by an adjuvant consisting of tumor necrosis factor-alpha (TNF-alpha) and prostaglandin-E2. T cells were co-cultivated with lysate or peptide pulsed DCs and were restimulated weekly. Before cultivation, and after the 3rd stimulation, tetramer frequencies for the MUC1 epitopes M1.2 and F7 as well as for the FLU M1 and Melan-A/Mart-1 epitopes were determined. After stimulation with lysate, higher frequencies for M1.2-specific T cells were observed compared with the F7 epitope. Furthermore, we found expansion factors for M1.2-specific T cells that had been stimulated with MCF-7 lysate-pulsed DCs of up to 43-fold. The analysis of typical T(H)1/T(H)2 cytokines (IFN-gamma, TNF-alpha, IL-12p70, IL-2, IL-4, IL-5, and IL-10) revealed a strong T(H)1 response. These results provide evidence for a strong T(H)1 polarization and cross-priming of MUC1-specific CD8+ T cells and demonstrate the feasibility of using lysate-pulsed dendritic cells in breast cancer immunotherapy.

Induction of Systemic Tolerance in Normal but not in Transgenic Mice Through Continuous Feeding of Ovalbumin

The ingestion of most dietary protein can cause systemic tolerance, and such tolerance is easier to induce in younger than in older mice. In this study, we examined whether oral tolerance to ovalbumin (OVA) could be induced in OVA-T-cell receptor (OVA-TCR)-specific transgenic mice. Continuous feeding or gavage with OVA induced tolerance, measured as reduced antibody production, in young and aged BALB/c mice, in a dose-dependent manner, but this effect was not observed in transgenic mice. Once BALB/c mice became tolerant, this state was maintained for over 44 weeks, although the tolerant state could be reversed by adoptive cell transfer. DO11.10 mice did not become tolerant upon continuous feeding with OVA, and the adoptive transfer of naïve cells increased the levels of specific antibodies in their sera after antigenic challenge. The immunization schedule used here leads to a Th2-dependent antibody response in normal BALB/c mice. However, the same schedule induced both Th1- and Th2-antibody responses in transgenic mice. Dendritic cells (DC) from tolerant BALB/c mice were less efficient in the induction of the proliferation of cocultured T cells from both BALB/c and DO11.10 mice, as well as Th1 [interleukin (IL)-2 and interferon (IFN)-gamma] and Th2 (IL-4 and IL-10) cytokine production. The DC from DO11.10 transgenic mice were equally efficient in the induction of T-cell proliferation in both normal and transgenic mice, as well as in the induction of Th1 and Th2 cytokines, whether or not the mice consumed OVA. Transforming growth factor (TGF)-beta secretion was significantly lower in the supernatants of T cells from both normal and transgenic mice cocultured with DC from DO11.10 mice that had consumed OVA, while it was significantly higher in the presence of DC from normal tolerant mice, thus implicating TGF-beta as a regulatory cytokine in oral tolerance in the murine model.

Expression of indoleamine 2,3-dioxygenase by plasmacytoid dendritic cells in tumor-draining lymph nodes

One mechanism contributing to immunologic unresponsiveness toward tumors may be presentation of tumor antigens by tolerogenic host APCs. We show that mouse tumor-draining LNs (TDLNs) contained a subset of plasmacytoid DCs (pDCs) that constitutively expressed immunosuppressive levels of the enzyme indoleamine 2,3-dioxygenase (IDO). Despite comprising only 0.5% of LN cells, these pDCs in vitro potently suppressed T cell responses to antigens presented by the pDCs themselves and also, in a dominant fashion, suppressed T cell responses to third-party antigens presented by nonsuppressive APCs. Adoptive transfer of DCs from TDLNs into naive hosts created profound local T cell anergy, specifically toward antigens expressed by the transferred DCs. Anergy was prevented by targeted disruption of the IDO gene in the DCs or by administration of the IDO inhibitor drug 1-methyl-D-tryptophan to recipient mice. Within the population of pDCs, the majority of the functional IDO-mediated suppressor activity segregated with a novel subset of pDCs coexpressing the B-lineage marker CD19. We hypothesize that IDO-mediated suppression by pDCs in TDLNs creates a local microenvironment that is potently suppressive of host antitumor T cell responses.

Expression of indoleamine 2,3-dioxygenase by plasmacytoid dendritic cells in tumor-draining lymph nodes

One mechanism contributing to immunologic unresponsiveness toward tumors may be presentation of tumor antigens by tolerogenic host APCs. We show that mouse tumor-draining LNs (TDLNs) contained a subset of plasmacytoid DCs (pDCs) that constitutively expressed immunosuppressive levels of the enzyme indoleamine 2,3-dioxygenase (IDO). Despite comprising only 0.5% of LN cells, these pDCs in vitro potently suppressed T cell responses to antigens presented by the pDCs themselves and also, in a dominant fashion, suppressed T cell responses to third-party antigens presented by nonsuppressive APCs. Adoptive transfer of DCs from TDLNs into naive hosts created profound local T cell anergy, specifically toward antigens expressed by the transferred DCs. Anergy was prevented by targeted disruption of the IDO gene in the DCs or by administration of the IDO inhibitor drug 1-methyl-D-tryptophan to recipient mice. Within the population of pDCs, the majority of the functional IDO-mediated suppressor activity segregated with a novel subset of pDCs coexpressing the B-lineage marker CD19. We hypothesize that IDO-mediated suppression by pDCs in TDLNs creates a local microenvironment that is potently suppressive of host antitumor T cell responses.

Expression of the B7.1 costimulatory molecule on pancreatic beta cells abrogates the requirement for CD4 T cells in the development of type 1 diabetes

Although HLA-DQ8 has been implicated as a key determinant of genetic susceptibility to human type 1 diabetes, spontaneous diabetes has been observed in HLA-DQ8 transgenic mice that lack expression of murine MHC class II molecules (mII(-/-)) only when the potent costimulatory molecule, B7.1, is transgenically expressed on pancreatic beta cells. To study the contribution of HLA-DQ8 to the development of diabetes in this model, we crossed RIP-B7.1mII(-/-) mice with a set of transgenic mouse lines that differed in their HLA-DQ8 expression patterns on APC subpopulations, in particular dendritic cells and cortical thymic epithelial cells. Surprisingly, we found that even in the absence of HLA-DQ8 and CD4 T cells, a substantial fraction of the RIP-B7.1mII(-/-) mice developed diabetes. This disease process was remarkable for not only showing insulitis, but also inflammatory destruction of the exocrine pancreas with diffusely up-regulated expression of MHC class I and ICAM-1 molecules. Expression of HLA-DQ8 markedly increased the kinetics and frequency of diabetes, with the most severe disease in the lines with the highest levels of HLA-DQ8 on cortical thymic epithelial cells and the largest numbers of CD4 T cells. However, the adoptive transfer of diabetes was not HLA-DQ8-dependent and disease could be rapidly induced with purified CD8 T cells alone. Expression of B7.1 in the target tissue can thus dramatically alter the cellular and molecular requirements for the development of autoimmunity.

Mature myeloid dendritic cell subsets have distinct roles for activation and viability of circulating human natural killer cells

Natural killer (NK) cells are important effectors of innate immunity. In contrast to many studies of interleukin-2 (IL-2)-activated NK cells, the physiologic requirements for stimulating resting NK cells have only recently received attention. Given the emerging variety of dendritic cell (DC) types and their division of labor for stimulating immunity, we compared the capacity of monocyte-derived DCs (moDCs) with that of CD34+ hematopoietic progenitor cell (HPC)-derived dermal-interstitial DCs (DDC-IDCs) and Langerhans cells (LCs) to stimulate resting NK cells. MoDCs, and to a lesser extent CD34+ HPC-derived DDC-IDCs, directly stimulate NK-cell proliferation, CD56 up-regulation, and cytotoxicity. LCs, on the contrary, require exogenous IL-2 or IL-12 to activate NK cells, but they can maintain resting NK-cell viability and sustain NK-cell proliferation induced by moDCs. LCs do not secrete bioactive IL-12p70 but do produce significantly higher concentrations of IL-15 and IL-18 than either of the other 2 DC types. Despite secretion of IL-15, LCs lack IL-15R-alpha for surface presentation of IL-15. This together with the deficiency of IL-12p70 undermines any direct NK-cell activation by LCs. Hence, the principal myeloid DCs differ in critical ways regarding the stimulation of NK and T lymphocytes and could be used or targeted accordingly in DC-based immunotherapies.

Antinucleosome autoantibodies bind directly to cell lines in vitro and via the FcgammaRIIB receptor to B lymphocytes in vivo: a role for immune complexes in interactions between antinucleosome IgG2a and B cells of BXSB lupus mice

The initial novel observation of this study was that most B cells of male BXSB lupus mice bear surface IgG2a(b) of extrinsic origin. To define the surface antigen, we here examine three (NZBxBXSB)F1-derived IgG2a(b) monoclonal antibodies (mAbs) selected for binding to cell surfaces. Surprisingly, all three mAbs bound the nucleosome (nuc) particle, the fundamental unit of chromatin and an early target of autoimmunity in systemic lupus erythematosus. Their tentative dissociation constant (K(d)) for soluble nuc particles was approximately 7 x 10(-10) m. The mAbs bound more weakly to both H2A-H2B-DNA and H3-H4-DNA complexes, and in immunoblot they stained all four core histones. The mAbs detected a surface antigen on all cell lines examined, present on viable cells. When stripped of nuc, and in the presence of DNase I, their binding to cell lines improved. Heparin displaced the antigen from the cell surface. In vivo, the three mAbs stained B cells of several BALB/c mice clearly stronger than the isotype control; this differential staining was significantly reduced in FcgammaRIIB-deficient mice. The results indicate that the three mAbs recognize (a) planted antigen on viable cultured cells and (b) soluble autoantigen in vivo, leading to immune complexes that bind to FcgammaRIIB. Further experiments demonstrated that antinuc IgG2a could be eluted from splenocytes of a male BXSB lupus mouse. Hence, at least part of the extrinsic IgG2a(b) found on BXSB B cells may represent FcgammaRIIB-bound nuc-IgG2a(b) complexes.

Peyer's patch dendritic cells process viral antigen from apoptotic epithelial cells in the intestine of reovirus-infected mice

We explored the role of Peyer's patch (PP) dendritic cell (DC) populations in the induction of immune responses to reovirus strain type 1 Lang (T1L). Immunofluorescence staining revealed the presence of T1L structural (σ1) and nonstructural (σNS) proteins in PPs of T1L-infected mice. Cells in the follicle-associated epithelium contained both σ1 and σNS, indicating productive viral replication. In contrast, σ1, but not σNS, was detected in the subepithelial dome (SED) in association with CD11c⁺/CD8α⁻/CD11b^lo DCs, suggesting antigen uptake by these DCs in the absence of infection. Consistent with this possibility, PP DCs purified from infected mice contained σ1, but not σNS, and PP DCs from uninfected mice could not be productively infected in vitro. Furthermore, σ1 protein in the SED was associated with fragmented DNA by terminal deoxy-UTP nick-end labeling staining, activated caspase-3, and the epithelial cell protein cytokeratin, suggesting that DCs capture T1L antigen from infected apoptotic epithelial cells. Finally, PP DCs from infected mice activated T1L-primed CD4⁺ T cells in vitro. These studies show that CD8α⁻/CD11b^lo DCs in the PP SED process T1L antigen from infected apoptotic epithelial cells for presentation to CD4⁺ T cells, and therefore demonstrate the cross-presentation of virally infected cells by DCs in vivo during a natural viral infection.

A contribution of mouse dendritic cell-derived IL-2 for NK cell activation

Dendritic cells (DCs) play a predominant role in activation of natural killer (NK) cells that exert their functions against pathogen-infected and tumor cells. Here, we used a murine model to investigate the molecular mechanisms responsible for this process. Two soluble molecules produced by bacterially activated myeloid DCs are required for optimal priming of NK cells. Type I interferons (IFNs) promote the cytotoxic functions of NK cells. IL-2 is necessary both in vitro and in vivo for the efficient production of IFNγ, which has an important antimetastatic and antibacterial function. These findings provide new information about the mechanisms that mediate DC–NK cell interactions and define a novel and fundamental role for IL-2 in innate immunity.

Defective dendritic cell migration and activation of adaptive immunity in PI3Kgamma-deficient mice

Gene-targeted mice were used to evaluate the role of the gamma isoform of phosphoinositide 3-kinase (PI3Kgamma) in dendritic cell (DC) migration and induction of specific T-cell-mediated immune responses. DC obtained from PI3Kgamma-/- mice showed a reduced ability to respond to chemokines in vitro and ex vivo and to travel to draining lymph nodes under inflammatory conditions. PI3Kgamma-/- mice had a selective defect in the number of skin Langerhans cells and in lymph node CD8alpha- DC. Furthermore, PI3Kgamma-/- mice showed a defective capacity to mount contact hypersensitivity and delayed-type hypersensitivity reactions. This defect was directly related to the reduced ability of antigen-loaded DC to migrate from the periphery to draining lymph nodes. Thus, PI3Kgamma plays a nonredundant role in DC trafficking and in the activation of specific immunity. Therefore, PI3Kgamma may be considered a new target to control exaggerated immune reactions.

The HIV-1 HLA-A2-SLYNTVATL is a help-independent CTL epitope

The CTL response to the HLA-A*0201-restricted, HIV-1 p17 Gag(77-85) epitope (SLYNTVATL; SL9) has been extensively studied in patients. Although this reactivity is exceptionally prominent in chronically infected patients and inversely correlated to viral load, SL9-specific CTLs (SL9-CTLs) are rarely detected in acute infection. To explore the cellular basis for this unusual manifestation, SL9-CTLs primed ex vivo from naive circulating CD8(+) T cells of healthy, seronegative donors were generated and characterized. SL9 appeared to differ from other well-studied A*0201-restricted epitopes in several significant respects. In contrast to published reports for influenza and melanoma peptides and the HIV gag IV9 epitope studied here in parallel, SL9-CTLs were primed by immature but not mature autologous dendritic cells. Highly activated SL9-CTLs produce sufficient autocrine mediators to sustain clonal expansion and CTL differentiation for months without CD4(+) T cells or exogenous IL-2. Moreover, SL9-CTLs were sensitive to paracrine IL-2-induced apoptosis. IL-2 independence and sensitivity to paracrine IL-2 were also characteristic of SL9-CTLs immunized by dendritic cells transduced by a nonreplicating lentiviral vector encoding full-length Gag. In vitro-primed SL9-CTLs resembled those derived from patients in degeneracy of recognition and functional avidities for both SL9 and its natural mutations. Together, these data show that SL9 is a highly immunogenic, help-independent HIV epitope. The scarcity of SL9-CTLs in acute infection may result from cytokine-induced apoptosis with the intense activation of the innate immunity. In contrast, SL9-CTLs that constitutively produce autocrine help would predominate during CD4-diminished chronic infection.

MHC Class II Isotype- and Allele-Specific Attenuation of Experimental Autoimmune Encephalomyelitis

Most autoimmune diseases are associated with certain MHC class II haplotypes. Autoantigen-based specific immune therapy can lead either to beneficial or, in the context of inflammatory conditions, detrimental outcomes. Therefore, we designed a platform of peptides by combinatorial chemistry selected in a nonbiased Ag-independent approach for strong binding to the rat MHC class II isotype RT1.D(n) allelic product of the RT1(n) haplotype that is presenting autoantigen in myelin oligodendrocyte glycoprotein-induced experimental autoimmune encephalomyelitis in LEW.1N rats. Peptide p17 (Ac-FWFLDNAPL-NH(2)) was capable of suppressing the induction of and also ameliorated established experimental autoimmune encephalomyelitis. MHC class II isotype and allele specificity of the therapeutic principle were demonstrated in myelin basic protein-induced experimental autoimmune encephalomyelitis in LEW rats bearing the RT1(l) haplotype. A general immunosuppressive effect of the treatment was excluded by allogeneic heart transplantation studies. In vitro studies demonstrated the blocking effect of p17 on autoantigenic T cell responses. We thus demonstrate a rational design of strong MHC class II-binding peptides with absolute isotype and allele specificity able to compete for autoantigenic sequences presented on disease-associated MHC class II molecules.

CD40/CD154 interactions at the interface of tolerance and immunity

Development of the acquired immune response is dependent on the signaling of CD40 by its ligand, CD154. These molecules govern both the magnitude and quality of humoral- and cell-mediated immunity. A litany of studies have conclusively documented that blockade of this ligand-receptor pair can prevent, and also intervene in, the progression of antibody- and cell-mediated autoimmune diseases, and can instill long-lived allogeneic and xenogeneic graft tolerance. Many effector mechanisms of inflammation are abolished as a result of CD154 blockade, but we are now beginning to understand that CD154 blockade may, in some instances, engender long-lived, antigen-specific tolerance. In the context of transplantation tolerance, we present a hypothesis that alpha CD154 blockade is most effective at inducing long-lived allospecific tolerance if anergy and regulation can be elicited prior to the onslaught of inflammation that is induced by grafting (preemptive tolerance). This facet of alpha CD154-induced tolerance appears to co-opt the normal processes of peripheral tolerance induced by immature DCs and can be exploited to induce long-lived antigen-specific tolerance. The underlying science and the prospects for inducing long-lived antigen-specific tolerance in a model of allograft tolerance through CD154 blockade are presented and discussed.

Marked prolongation of murine cardiac allograft survival using recipient immature dendritic cells loaded with donor-derived apoptotic cells

We investigated whether recipient dendritic cells (DCs), pretreated with nuclear factor-kappaB oligodeoxyribonucleotide decoy (NF-kappaB ODN decoy) and loaded with ultraviolet B-irradiated donor apoptotic splenocytes (Apo-SCs), were able to induce murine cardiac allograft tolerance. Heterotopic vascularized heart transplantation was performed from BALB/c to C57BL/6 mice, and recipients (C57BL/6) were given one injection of recipient DCs pretreated with NF-kappaB ODN decoy and loaded with donor (BALB/c) apoptotic SCs (decoy Apo-SCs DCs) through the portal vein at 7 days, before heart transplantation in the absence of immunosuppression. The cardiac allograft survival time and the expressive levels of intragraft cytokine genes [interleukin (IL)-2, IL-10, and interferon-gamma] were evaluated. Our results indicated that injection of decoy Apo-SCs DCs significantly prolonged vascularized heart allograft survival and led to skewing of intragraft cytokine expression towards T helper 2 (IL-10). The mechanisms can be useful for therapy of allograft rejection with minimization of systemic immunosuppression.

E3 ligases in T cell anergy--turning immune responses into tolerance

Peripheral tolerance is an important strategy used by the immune system to prevent self-reactive lymphocytes from attacking host tissues. A variety of mechanisms contribute to peripheral tolerance, among them activation-induced cell death, suppression by regulatory T cells, and T cell anergy or unresponsiveness. Recent work has led to a better understanding of the cell-intrinsic program that establishes T cell anergy. A major insight is that during the induction phase of anergy, incomplete stimulation (T cell receptor stimulation without costimulation) leads via calcium influx to an altered gene expression program that includes up-regulation of several E3 ubiquitin ligases. When the anergic T cells contact antigen-presenting cells, intracellular signaling proteins are monoubiquitinated and targeted for lysosomal degradation, thus decreasing intracellular signaling and also resulting in decreased stability of the T cell-antigen-presenting cell contact. We propose a molecular program leading to T cell anergy and discuss other proteins that may play a role.

Gastrointestinal dendritic cells play a role in immunity, tolerance, and disease

Discrimination between beneficial commensal organisms and potentially harmful pathogens is a central component of the essential role that gut immune cells play in maintaining the balance between immune activation and tolerance. Antigen presenting cells (APC) are the key to this process, and the type of APC, including epithelial cells, B cells, macrophages, and dendritic cells (DC), in the gut is varied. The purpose of this review is to focus on the vast amount of data that has recently been generated on gastrointestinal dendritic cells in the context of their potential function and contribution to mucosal immunity, tolerance, and disease.

Inhibition of antigen-presenting cell functions by alcohol: implications for hepatitis C virus infection

The mechanisms of alcohol-induced immunosuppression include defects in innate and adaptive immune responses. Monocytes and dendritic cells (DCs) link innate and adaptive immune responses as they recognize viral antigens and induce antigen-specific T-cell activation. We investigated the effects of alcohol on antigen-presenting cell functions. Acute alcohol consumption by healthy volunteers (vodka, 2 ml/kg) resulted in significantly reduced antigen-presenting cell function of monocyte-derived DCs. Reduced allostimulatory capacity of DCs treated with alcohol in vitro correlated with decreased co-stimulatory molecule (B7.1 and B7.2) expression, as well as with reduced interleukin (IL)-12 and increased IL-10 concentrations, in mixed lymphocyte cultures. Dendritic cells recognize viral antigens in hepatitis C virus (HCV) infection, and HCV disease is accelerated in alcohol-dependent individuals. For patients with chronic HCV infection, we found reduced allostimulatory capacity of myeloid DCs. Furthermore, DC function was reduced by in vitro alcohol treatment of DCs obtained from HCV-infected patients, supporting the suggestion that viral factors and alcohol may interact to doubly suppress DC functions. We found that induction of maturation with lipopolysaccharide could not fully ameliorate the reduced DC allostimulatory capacity caused by alcohol treatment, HCV infection, or their combination. In addition, soluble factors in the supernatants obtained from mixed lymphocyte cultures containing alcohol-treated DCs or DCs obtained from HCV-infected patients could transfer inhibition of T-cell proliferation in cultures containing DCs obtained from healthy volunteers. Anti-IL-10 neutralizing antibody ameliorated the reduced mixed lymphocyte reaction containing DCs obtained from HCV-infected patients, whereas exogenous IL-12, but not anti-IL-10, treatment ameliorated the reduced T-cell proliferation induced by alcohol treatment of DCs obtained from healthy volunteers. Our results support the suggestion that both acute alcohol intake and in vitro alcohol treatment inhibit DC antigen-presenting cell function and support the hypothesis that viral factors interact with alcohol to reduce DC functions in HCV infection.

Manipulating dendritic cell biology for the active immunotherapy of cancer

Dendritic cells (DCs) are specialized antigen-presenting cells (APCs) that have an unequaled capacity to initiate primary immune responses, including tolerogenic responses. Because of the importance of DCs in the induction and control of immunity, an understanding of their biology is central to the development of potent immunotherapies for cancer, chronic infections, autoimmune disease, and induction of transplantation tolerance. This review discusses recent advances in DC research and the application of this knowledge toward new strategies for the clinical manipulation of DCs for cancer immunotherapy.

Cellular Immunotherapy with Dendritic Cells in Cancer: Current Status

Dendritic cells (DCs) are specialized antigen-presenting cells whose immunogenicity leads to the induction of antigen-specific immune responses. DCs can easily be generated ex vivo from peripheral blood monocytes or bone marrow/circulating hematopoietic stem cells cultured in the presence of cytokine cocktails. DCs have been used in numerous clinical trials to induce antitumor immune responses in cancer patients. The studies carried out to date have demonstrated that DCs pulsed with tumor antigens can be safely administered, and this approach produces antigen-specific immune responses. Clinical responses have been observed in a minority of patients. It is likely that either heavy medical pretreatment or the presence of large tumor burdens (or both) is among the causes that impair the benefits of vaccination. Hence, the use of DCs should be considered in earlier stages of disease such as the adjuvant setting. Prospective applications of DCs extend to their use in allogeneic adoptive immunotherapy to specifically target the graft versus tumor reaction. DCs continue to hold promise for cellular immunotherapy, and further investigation is required to determine the clinical settings in which patients will most benefit from the use of this cellular immune adjuvant.

The Regulatory Role of Dendritic Cells in the Immune Response

Dendritic cells (DCs) are key regulators of immune reactions. They control early innate responses, regulate long-lasting adaptive immunity and contribute to the maintenance of self-tolerance. DCs continuously monitor the environment through a multifaceted innate antigen receptor repertoire and, in response to perturbations, start a complex genetic reprogramming that leads to a complete activation of innate and, then, adaptive immune responses. This review discusses how DCs become efficient activators of NK and, subsequently, T cells following a microbial encounter.

Autoimmunity through cytokine-induced dendritic cell activation

We propose a model where autoimmunity can be viewed as a dynamic system driven by opposite vectors IFN-alpha/beta and TNF. These cytokines drive differentiation of distinct types of DCs, TNF-DCs, or IFN-DCs, which present different antigens leading to distinct autoimmune responses. When balanced, both cytokines synergize in protective immunity. When one of the cytokines prevails, autoimmunity occurs, Type I interferons (IFN-alpha/beta) playing a major role in systemic lupus erythematosus (SLE) and TNF playing a major role in rheumatoid arthritis. This model complements the Type 1/Type 2 paradigm. Therefore, immunity can be viewed as a dynamic system driven by two sets of opposite vectors: IFN-alpha/beta/TNF and IFN-gamma/IL-4.

Immature Dendritic Cells (DCs) Use Chemokines and Intercellular Adhesion Molecule (ICAM)-1, But Not DC-Specific ICAM-3-Grabbing Nonintegrin, to Stimulate CD4+ T Cells in the Absence of Exogenous Antigen

Dendritic cells (DCs) possess a number of unique features that distinguish them from other APCs. One such feature is their ability to trigger Ag-independent responses in T cells. Previous studies have focused on mature DCs, but the prevalence of this phenomenon in the resting-state immature DCs has never been considered. In this study, we show that, in the absence of Ag, human immature DCs trigger multiple responses in autologous primary CD4+ T cells, namely, increased motility, small Ca2+ transients, and up-regulation of CD69. These responses are particularly marked in CD4+ memory T cells. By using several experimental approaches, we found that DC-specific ICAM-3-grabbing nonintegrin plays no role in the induction of T cell responses, whereas ICAM-1/LFA-1 interactions are required. In addition, DC-produced chemokines contribute to the Ag-independent T cell stimulatory ability of DCs, because pertussis toxin-treated T cells exhibit diminished responses to immature DCs. More particularly, CCL17 and CCL22, which are constitutively produced by immature DCs, mediate both T cell polarization and attraction. Thus, immature DCs owe part of their outstanding Ag-independent T cell stimulatory ability to chemokines and ICAM-1, but not DC-specific ICAM-3-grabbing nonintegrin.

Poly-beta amino ester-containing microparticles enhance the activity of nonviral genetic vaccines

Current nonviral genetic vaccine systems are less effective than viral vaccines, particularly in cancer systems where epitopes can be weakly immunogenic and antigen-presenting cell processing and presentation to T cells is down-regulated. A promising nonviral delivery method for genetic vaccines involves microencapsulation of antigen-encoding DNA, because such particles protect plasmid payloads and target them to phagocytic antigen-presenting cells. However, conventional microparticle formulations composed of poly lactic-co-glycolic acid take too long to release encapsulated payload and fail to induce high levels of target gene expression. Here, we describe a microparticle-based DNA delivery system composed of a degradable, pH-sensitive poly-beta amino ester and poly lactic-co-glycolic acid. These formulations generate an increase of 3-5 orders of magnitude in transfection efficiency and are potent activators of dendritic cells in vitro. When used as vaccines in vivo, these microparticle formulations, unlike conventional formulations, induce antigen-specific rejection of transplanted syngenic tumor cells.

Requirement of dying cells and environmental adjuvants for the induction of autoimmunity

OBJECTIVE

Cells commonly die without eliciting autoimmunity. However, dying cells are a potential initiating stimulus for systemic lupus erythematosus (SLE). Our goal was to verify whether immune adjuvants influence the autoimmunity induction that ensues following in vivo injection of dying cells.

METHODS

Mice were immunized with apoptotic thymocytes in the presence of artificial moieties, such as Freund's incomplete adjuvant (IFA), or natural adjuvants, such as dendritic cells (DCs). Renal involvement and the development of autoantibodies were monitored.

RESULTS

Apoptotic cells failed to induce clinical disease or to sustain production of autoantibodies in (NZB x NZW)F(1) mice. In contrast, autoimmunity developed in the presence of IFA or DCs. The characteristics of the adjuvant influenced the array of autoantibodies, the kinetics of their development, and the severity of the disease. DCs were required for induction of anti-beta(2)-glycoprotein I IgG. Adjuvants alone did not elicit disease.

CONCLUSION

A "two-hit" signal composed of autoantigens and adjuvants initiates systemic autoimmunity. Moreover, environmental signals at the site of clearance of dead cells shape the features and the severity of the autoimmune disease. Strategies aimed at preventing the accumulation of dying cells and at modulating endogenous adjuvants may be beneficial for the treatment of SLE.

Toll-like receptor 9-dependent and -independent dendritic cell activation by chromatin-immunoglobulin G complexes

Dendritic cell (DC) activation by nucleic acid-containing immunoglobulin (Ig)G complexes has been implicated in systemic lupus erythematosus (SLE) pathogenesis. However, the mechanisms responsible for activation and subsequent disease induction are not completely understood. Here we show that murine DCs are much more effectively activated by immune complexes that contain IgG bound to chromatin than by immune complexes that contain foreign protein. Activation by these chromatin immune complexes occurs by two distinct pathways. One pathway involves dual engagement of the Fc receptor FcgammaRIII and Toll-like receptor (TLR)9, whereas the other is TLR9 independent. Furthermore, there is a characteristic cytokine profile elicited by the chromatin immune complexes that distinguishes this response from that of conventional TLR ligands, notably the induction of BAFF and the lack of induction of interleukin 12. The data establish a critical role for self-antigen in DC activation and explain how the innate immune system might drive the adaptive immune response in SLE.

Pattern of cytokine responses to gram-positive and gram-negative commensal bacteria is profoundly changed when monocytes differentiate into dendritic cells

The normal gastrointestinal bacterial flora is crucial for the maturation of acquired immunity via effects on antigen-presenting cells (APCs). Here we investigated how two types of APCs, monocytes and dendritic cells (DCs), react to different bacterial strains typical of the commensal intestinal microflora. Purified human monocytes and monocyte-derived DCs were stimulated with UV-inactivated gram-positive (Lactobacillus plantarum and Bifidobacterium adolescentis) and gram-negative (Escherichia coli and Veillonella parvula) bacterial strains. Monocytes produced higher levels of interleukin 12p70 (IL-12p70) and tumor necrosis factor (TNF), as detected by an enzyme-linked immunosorbent assay, in response to L. plantarum than in response to E. coli and V. parvula. In contrast, DCs secreted large amounts of IL-12p70, TNF, IL-6, and IL-10 in response to E. coli and V. parvula but were practically unresponsive to L. plantarum and B. adolescentis. The lack of a response to the gram-positive strains correlated with lower surface expression of Toll-like receptor 2 (TLR2) on DCs than on monocytes. The surface expression of TLR4 on DCs was undetectable when it was analyzed by flow cytometry, but blocking this receptor decreased the TNF production in response to V. parvula, indicating that TLR4 is expressed at a low density on DCs. Gamma interferon increased the expression of TLR4 on DCs and also potentiated the cytokine response to the gram-negative strains. Our results indicate that when monocytes differentiate into DCs, their ability to respond to different commensal bacteria dramatically changes, and they become unresponsive to probiotic gram-positive bacteria. These results may have important implications for the abilities of different groups of commensal bacteria to regulate mucosal and systemic immunity.

Restored immune response to an MHC-II-Restricted antigen in tumor-bearing hosts after elimination of regulatory T cells

BACKGROUND/PURPOSE

Pediatric sarcomas have a poor prognosis, recur frequently, and are not effectively treated by currently available therapy. Immunotherapy is a promising treatment modality; however, to be successful, immune tolerance must be overcome. CD4+CD25+ T cells are immunosuppressive. The authors hypothesize that immune tolerance may be overcome by eliminating the regulatory CD4+CD25+ T cells, which are induced by tumor.

METHODS

A murine fibrosarcoma (MF), which expresses an MHC-II-restricted tumor antigen (mL26), was injected subcutaneously. CD4+ T cells were isolated and CD25+ population examined. Monoclonal antibody was used to deplete CD25+ T cells. Proliferation to mL26 was used to determine CD4+ T cell response to tumor-associated antigen (TAA).

RESULTS

Depletion of CD25+ cells prevented tumor establishment. Tumor-infiltrating CD25+ T cells, which made up 48% of CD4+ T cells in tumors, suppressed proliferation in allogeneic mixed lymphocyte reactions. Draining lymph node cells from tumor-bearing (TB) mice did not proliferate in response to mL26, whereas those from naive mice responded vigorously. Depletion of CD25+ cells before immunization restored response to mL26 in TB mice.

CONCLUSIONS

CD4+CD25+ T cells induced by MF facilitate tumor establishment and maintain immune tolerance. Depletion of CD4+CD25+ T cells may be an effective means for reversing tumor tolerance and enhancing cancer vaccines.

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.

Prevention of murine acute graft-versus-host disease by recipient-derived TGFβ1-treated dendritic cells

Acute graft-versus-host disease (GVHD) remains the major barrier to allogeneic bone marrow transplantation (allo-BMT). Evidence has accumulated that transforming growth factor beta1-treated dendritic cells (TGFbeta-DC), deficient in surface costimulatory molecules, inhibit alloantigen-specific T-cell responses and induce graft hyporeactivity. To analyze the effect of TGFbeta-DC on GVHD after allo-BMT, 5.0 x 10(6) recipient-derived TGFbeta-DC were injected into C57BL/6 (H-2b) with bone marrow-splenocyte grafts from major histocompatibility complex (MHC) disparate BALB/c mice (H-2d). Survival analysis showed TGFbeta-DC cotransplantation resulted in significant prolongation of allograft survival, namely a mean survival time (MST) of 44.3 +/- 4.5 days, versus the untreated MST of 9.5 +/- 0.6 days (P < .01). However, mature DC aggravated the GVHD with an MST of 6.6 +/- 0.6 days (P < .01). In addition, the third-party C3H-derived TGFbeta-DC did not enhance the survival rate (MST = 9.7 +/- 0.5 days). Furthermore, serum IFN-gamma, IL-12, and IL-18 levels in TGFbeta-DC cotransplanted mice were reduced compared with untreated BMT hosts, while serum IL-10 levels were not changed. These results suggest that TGFbeta-DC cotransplantation may attenuate the severity of GVHD after BMT.

Modulating vaccine responses with dendritic cells and Toll-like receptors

The immune system is ignorant or even unresponsive to most foreign proteins that are injected in a soluble, deaggregated form, but when injected together with an immune-stimulating agent (i.e. an adjuvant, such as CpG-rich DNA), these foreign proteins can generate robust immunity and long-lived memory to the antigen. In fact, the nature of the adjuvant is what determines the particular type of immune response that follows, which may be biased towards cytotoxic T-cell responses, antibody responses, particular classes of T-helper responses, or antibody isotypes. Clearly, the ability of a vaccine to skew the response toward a particular type is of paramount importance, because different pathogens require distinct types of protective immunities. Therefore, the quest to manipulate the immune system to generate optimally effective immunity against different pathogens can justifiably be considered the 'grand challenge' of modern immunology. Central to this issue is a rare but widely distributed network of cells known as dendritic cells (DCs). DCs, which have been called 'Nature's adjuvants,' express pathogen recognition receptors, such as the Toll-like receptors (TLRs) and C-type lectins, which enable them to sense and respond to microbes or vaccines. Research in the last decade has demonstrated a fundamental role for DCs in initiating and controlling the quality and strength of the immune response. As such, DCs and TLRs represent attractive immune modulatory targets for vaccinologists. The present review provides a summary of emerging themes in the biology DCs and TLRs, with a particular focus on relevance for vaccine development.

Expression of C‐type lectin receptors by subsets of dendritic cells in human skin

C-type lectins are cell surface receptors that recognize carbohydrate structures which are often part of microbial pathogens. Several of these molecules are expressed on dendritic cells and are involved in antigen uptake. Expression of C-type lectins on dendritic cells of the human skin, i.e. Langerhans cells of the epidermis and dermal dendritic cells, has been incompletely studied to date. We therefore investigated C-type lectins in situ and on dendritic cells obtained by migration from skin explants by immunofluorescence and flow cytometry. Emphasis was laid on expression patterns of DEC-205/CD205 and BDCA-2, a marker for plasmacytoid dendritic cells. Langerhans cells in situ expressed low levels of DEC-205. Expression was upregulated upon maturation in skin explant organ culture. Most dermal dendritic cells were found to be positive for DEC-205 and DC-SIGN/CD209. Few BDCA-2-expressing cells were found in most skin samples. They were located in small groups in the dermis close beneath the basement membrane. The vast majority of all types of dendritic cells in normal human skin was of immature phenotype, i.e. did not express DC-LAMP/CD208. It is concluded that normal appearing human skin harbors different subsets of dendritic cells including few scattered BDCA-2-expressing cells, presumably plasmacytoid dendritic cells, expressing variable sets of C-type lectin receptors. This may critically contribute to the capacity of the skin immune system to flexibly respond to the world of microbial pathogens.

Reduced T-cell and dendritic cell function is related to cyclooxygenase-2 overexpression and prostaglandin E2 secretion in patients with breast cancer

BACKGROUND

In several neoplastic diseases, including breast cancer, immunosuppression correlates with disease stage, progression, and outcome. Thus, thorough analysis of immune parameters in breast cancer patients may be beneficial in designing effective anticancer immune-based therapies.

METHODS

We investigated dendritic cell and T-cell function in breast cancer patients at various stages of the disease and in age-matched controls. We also evaluated cyclooxygenase-2 (COX-2) expression and prostaglandin E2 (PGE2) levels within the tumor milieu and in the circulation.

RESULTS

T cells from cancer patients showed decreased proliferation in response to CD3 antibody stimulation. Analysis of T-cell helper type 1 and 2 cytokines revealed reduced levels of interferon-gamma, tumor necrosis factor-alpha, interleukin (IL)-12, and IL-2 and increased levels of IL-10 and IL-4. Dendritic cells from these patients showed significantly reduced expression of co-stimulatory molecules (B7 and CD40) and demonstrated reduced phagocytic ability, reduced antigen presentation to T cells, and reduced ability to mature in response to lipopolysaccharide. Data revealed increased synthesis of PGE2, an immune suppressor, along with increased expression of COX-2, a key regulator of PGE2 synthesis.

CONCLUSIONS

COX-2-induced PGE2 may contribute to immunosuppression and may directly block antitumor immunity while promoting tumor growth, providing us with the rationale for using COX-2 inhibition combined with immunotherapy.

A Signal through OX40 (CD134) Allows Anergic, Autoreactive T Cells to Acquire Effector Cell Functions

To study mechanisms of peripheral self-tolerance, we injected small numbers of naive CD4(+) TCR-transgenic T cells into mice expressing the MHC/peptide ligand under the control of an MHC class II promoter. The donor T cells expand rapidly to very large numbers, acquire memory markers, and go out into tissues, but the animals remain healthy, and the accumulated T cells are profoundly anergic to restimulation with Ag in vitro. Provision of a costimulatory signal by coinjection of an agonist Ab to OX40 (CD134), a TNFR family member expressed on activated CD4 T cells, results in death of the mice within 12 days. TCR-transgenic T cells recovered at 5 days from anti-OX40-treated mice have a unique phenotype: they remain unresponsive to Ag in vitro, but they are larger, more granular, and strongly IL-2R positive. Some spontaneously secrete IFN-gamma directly ex vivo, and the majority make IFN-gamma in response to PMA and ionomycin. Although they are anergic by conventional tests requiring Ag recognition, they respond vigorously to cytokines, proliferating in response to IL-2, and secreting IFN-gamma when TCR signaling is bypassed with IL-12 and IL-18. We conclude that the costimulatory signal through OX40 allows otherwise harmless, proliferating, autoreactive T cells to acquire effector cell functions. The ability of these T cells to respond to cytokines by synthesizing additional inflammatory cytokines without a TCR signal may drive the fatal pathogenic process in vivo.

A Bcl-2-dependent molecular timer regulates the lifespan and immunogenicity of dendritic cells

The lifespan of antigen-bearing dendritic cells (DCs) is determined by signals from pathogens and T cells. These signals regulate DC survival by modulating expression of Bcl-2 family proteins. Toll-like receptors and T cell costimulatory molecules both trigger a DC survival pathway that is dependent on Bcl-x(L). However, Toll-like receptors uniquely increase expression of Bim and trigger cell death by a pathway that is blocked by Bcl-2. This pathway serves as a molecular 'timer' that sets the lifespan of DCs and regulates the magnitude of T cell responses in vivo. Thus, signals derived from the innate and acquired immune systems control DC lifespan and immunogenicity by distinct molecular mechanisms.

Production of donor T cells is critical for induction of donor-specific tolerance and maintenance of chimerism

Nonmyeloablative conditioning has significantly reduced the morbidity associated with bone marrow transplantation. The donor hemopoietic cell lineage(s) responsible for the induction and maintenance of tolerance in nonmyeloablatively conditioned recipients is not defined. In the present studies we evaluated which hemopoietic stem cell-derived components are critical to the induction of tolerance in a total body irradiation-based model. Recipient B10 mice were pretreated with mAbs and transplanted with allogeneic B10.BR bone marrow after conditioning with 100-300 cGy total body irradiation. The proportion of recipients engrafting increased in a dose-dependent fashion. All chimeric recipients exhibited multilineage donor cell production. However, induction of tolerance correlated strictly with early production of donor T cells. The chimeras without donor T cells rejected donor skin grafts and demonstrated strong antidonor reactivity in vitro, while possessing high levels of donor chimerism. These animals lost chimerism within 8 mo. Differentiation into T cells was aborted at a prethymic stage in recipients that did not produce donor T cells. Moreover, donor Ag-driven clonal deletion of recipient T cells occurred only in chimeras with donor T cells. These results demonstrate that donor T cell production is critical in the induction of transplantation tolerance and the maintenance of durable chimerism. In addition, donor T cell production directly correlates with the deletion of potentially alloreactive cells.