Designer dendritic cells for tolerance induction: guided not misguided missiles

Bioinspired membrane-based nanomodulators for immunotherapy of autoimmune and infectious diseases

Autoimmune or infectious diseases often instigate the undesirable damages to tissues or organs to trigger immune-related diseases, which involve plenty of immune cells, pathogens and autoantibodies. Nanomedicine has a great potential in modulating immune system. Particularly, biomimetic nanomodulators can be designed for prevention, diagnosis and therapy to achieve a better targeted immunotherapy. With the development of materials science and bioengineering, a wide range of membrane-coated nanomodulators are available. Herein, we summarize recent advancements of bioinspired membrane-coated nanoplatform for systemic protection against immune-related diseases including autoimmune and infectious diseases. We also rethink the challenges or limitations in the progress of the therapeutic nanoplatform, and discuss the further application of the nanomodulators in the view of translational medicine for combating immune-related diseases.

Elevated Bioactivity of the Tolerogenic Cytokines, Interleukin-10 and Transforming Growth Factor-β, in the Blood of Acutely Malnourished Weanling Mice

The main objective of this investigation was to determine the influence of acute deficits of protein and energy on the blood levels of interleukin-10 (IL-10) and transforming growth factor-β (TGF-β), physiologically the main anti-inflammatory and tolerogenic cytokines. In four 14-day experiments, male and female C57BL/6J mice, initially 19 days old, consumed a complete purified diet either ad libitum or in restricted daily quantities, or had free access to an isocaloric purified low-protein diet. A zero-time control group (19 days old) was included. In the first two experiments, serum IL-10 levels were assessed by sandwich enzyme-linked immunosorbent assay (ELISA) and bioassay. The mean serum IL-10 bioactivities were higher (P ≤ 0.05) in both malnourished groups (low-protein and restricted intake: 15.8 and 12.2 ng/ml, respectively) than in the zero-time and age-matched control groups (6.3 and 7.3 ng/ml, respectively), whereas serum IL-10 immunoactivity was high only in the restricted intake group (e.g., second experiment: 17.0 pg/ml vs. 5.4, 3.7, and 3.1 pg/ml in the zero-time control, age-matched control and low-protein group, respectively). The third and fourth experiments centered on plasma TGF-β immunoactivity (sandwich ELISA) and bioactivity, respectively. The ELISA revealed a high mean plasma TGF-β1 level (P < 0.05) in the low-protein group only, but TGF-β bioactivity (β1 isoform, although 15% β2 in the restricted intake group) was high in both malnourished groups (8.7 and 9.3 ng/ml in the low-protein and restricted groups, respectively) relative to the age-matched control group (0.5 ng/ml). Thus, metabolically distinct weanling systems mimicking marasmus and incipient kwashiorkor both exhibit a blood cytokine profile that points to a tolerogenic microenvironment within immune response compartments. A model emerges in which malnutrition-associated immune competence, at least in advanced weight loss, centers on cytokine-mediated peripheral tolerance that reduces the risk of catabolically induced autoimmune disease, but this is at the cost of attenuated responsiveness to infectious agents.

Adoptive Transfer of Dendritic Cells Expressing Fas Ligand Modulates Intestinal Inflammation in a Model of Inflammatory Bowel Disease

Background

Inflammatory bowel diseases (IBD) are chronic relapsing inflammatory conditions of unknown cause and likely result from the loss of immunological tolerance, which leads to over-activation of the gut immune system. Gut macrophages and dendritic cells (DCs) are essential for maintaining tolerance, but can also contribute to the inflammatory response in conditions such as IBD. Current therapies for IBD are limited by high costs and unwanted toxicities and side effects. The possibility of reducing intestinal inflammation with DCs genetically engineered to over-express the apoptosis-inducing FasL (FasL-DCs) has not yet been explored.

Objective

Investigate the immunomodulatory effect of administering FasL-DCs in the rat trinitrobenzene sulfonic acid (TNBS) model of acute colitis.

Methods

Expression of FasL on DCs isolated from the mesenteric lymph nodes (MLNs) of normal and TNBS-colitis rats was determined by flow cytometry. Primary rat bone marrow DCs were transfected with rat FasL plasmid (FasL-DCs) or empty vector (EV-DCs). The effect of these DCs on T cell IFNγ secretion and apoptosis was determined by ELISPOT and flow cytometry for Annexin V, respectively. Rats received FasL-DCs or EV-DCs intraperitoneally 96 and 48 hours prior to colitis induction with TNBS. Colonic T cell and neutrophil infiltration was determined by immunohistochemistry for CD3 and myeloperoxidase activity assay, respectively. Macrophage number and phenotype was measured by double immunofluorescence for CD68 and inducible Nitric Oxide Synthase.

Results

MLN dendritic cells from normal rats expressed more FasL than those from colitic rats. Compared to EV-DCs, FasL-DCs reduced T cell IFNγ secretion and increased T cell apoptosis in vitro. Adoptive transfer of FasL-DCs decreased macroscopic and microscopic damage scores and reduced colonic T cells, neutrophils, and proinflammatory macrophages when compared to EV-DC adoptive transfer.

Conclusion

FasL-DCs are effective at treating colonic inflammation in this model of IBD and represent a possible new treatment for patients with IBD.

Human Chorionic Villous Mesenchymal Stem Cells Modify the Functions of Human Dendritic Cells, and Induce an Anti-Inflammatory Phenotype in CD1+ Dendritic Cells

BACKGROUND

Mesenchymal stem cells derived from the chorionic villi of human term placenta (pMSCs) have drawn considerable interest because of their multipotent differentiation potential and their immunomodulatory capacity. These properties are the foundation for their clinical application in the fields of stem cell transplantation and regenerative medicine. Previously, we showed that pMSCs induce an anti-inflammatory phenotype in human macrophages. In this study, we determined whether pMSCs modify the differentiation and maturation of human monocytes into dendritic cells (DCs). The consequences on dendritic function and on T cell proliferation were also investigated.

METHODS

Interleukin-4 (IL-4) and granulocyte-macrophage colony stimulating factor (GM-CSF) were used to stimulate the differentiation of monocytes into immature dendritic cells (iDCs), which were subsequently co-cultured with pMSCs. Lipopolysaccharide (LPS) was used to induce maturation of iDCs into mature dendritic cells (mDCs). Flow cytometry and enzyme-linked immunosorbent assays (ELISA) were used to quantify the effect pMSC co-culturing on DC differentiation using CD1a, a distinctive marker of DCs, as well as other molecules important in the immune functions of DCs. The phagocytic activity of iDCs co-cultured with pMSCs, and the effects of iDCs and mDC stimulation on T cell proliferation, were also investigated.

RESULTS

Monocyte differentiation into iDCs was inhibited when co-cultured with pMSCs and maturation of iDCs by LPS treatment was also prevented in the presence of pMSCs as demonstrated by reduced expression of CD1a and CD83, respectively. The inhibitory effect of pMSCs on iDC differentiation was dose dependent. In addition, pMSC co-culture with iDCs and mDCs resulted in both phenotypic and functional changes as shown by reduced expression of costimulatory molecules (CD40, CD80, CD83 and CD86) and reduced capacity to stimulate CD4(+) T cell proliferation. In addition, pMSC co-culture increased the surface expression of major histocompatibility complex (MHC-II) molecules on iDCs but decreased MHC-II expression on mDCs. Moreover, pMSC co-culture with iDCs or mDCs increased the expression of immunosuppressive molecules [B7H3, B7H4, CD273, CD274 and indoleamine-pyrrole 2,3-dioxygenase (IDO). Additionally, the secretion of IL-12 and IL-23 by iDCs and mDCs co-cultured with pMSCs was decreased. Furthermore, pMSC co-culture with mDCs decreased the secretion of IL-12 and INF-γ whilst increasing the secretion of IL-10 in a T cell proliferation experiment. Finally, pMSC co-culture with iDCs induced the phagocytic activity of iDCs.

CONCLUSIONS

We have shown that pMSCs have an inhibitory effect on the differentiation, maturation and function of DCs, as well as on the proliferation of T cells, suggesting that pMSCs can control the immune responses at multiple levels.

A multimerized form of recombinant human CD40 ligand supports long-term activation and proliferation of B cells

BACKGROUND AIMS

CD40-activated B cells have long been studied as potent antigen-presenting cells that can potentially be used for cancer immunotherapy. Nevertheless, their use in human clinical trials has been limited by the lack of a Good Manufacturing Practice-grade soluble human CD40 ligand that is able to induce activation and proliferation of primary B cells. We describe an in vitro method to effectively generate and expand B cells through the use of a multimerized form of human recombinant CD40 ligand (rCD40L).

METHODS

Human B cells were isolated from healthy donors and cultivated with either rCD40L or on a monolayer of murine NIH3T3 cells stably expressing human CD40L (NIH3T3/tCD40L) as a widely used standard method. Morphology, expansion rate, immune phenotype and antigen presentation function were assessed.

RESULTS

B cells efficiently proliferated in response to rCD40L over 14 days of culture in comparable amounts to NIH3T3/tCD40L. B-cell division in response to CD40L was also confirmed by carboxyfluorescein succinimidyl ester dilution. Moreover, rCD40L induced on B cells upregulation of co-stimulatory molecules essential for antigen presentation. Additionally, proliferation of T cells from allogeneic healthy volunteers confirmed the immunostimulatory capacities of CD40-activated B cells.

CONCLUSIONS

We demonstrated that B cells with potent antigen presentation capacity can be generated and expanded by use of a non-xenogeneic form of CD40L that could be implemented in future human clinical settings.

CD40-activated B cells as antigen-presenting cells: the final sprint toward clinical application

Efficient antigen presentation is a prerequisite for the development of a T-cell-mediated immune response in vitro and in vivo. CD40-activated B cells (CD40B cells) are a promising alternative to dendritic cells as professional APCs for immunotherapy. CD40 activation dramatically improves antigen presentation by normal and malignant B cells, efficiently inducing naive and memory CD4(+) and CD8(+) T-cell responses. Moreover, CD40B cells do not only attract T cells by release of chemokines, but also home to secondary lymphoid organs. Furthermore, CD40B cells can be expanded exponentially over several weeks at high purity without a loss of antigen-presenting function, providing an almost unlimited source of cellular adjuvant. Vaccination with CD40B cells was shown in mice and dogs to induce a specific immune response. This article summarizes the achievements of intense research on CD40B cells over the last decade, as well as novel developments critical for a rapid translation into clinical application.

Current state of type 1 diabetes immunotherapy: incremental advances, huge leaps, or more of the same?

Thus far, none of the preclinically successful and promising immunomodulatory agents for type 1 diabetes mellitus (T1DM) has conferred stable, long-term insulin independence to diabetic patients. The majority of these immunomodulators are humanised antibodies that target immune cells or cytokines. These as well as fusion proteins and inhibitor proteins all share varying adverse event occurrence and severity. Other approaches have included intact putative autoantigens or autoantigen peptides. Considerable logistical outlays have been deployed to develop and to translate humanised antibodies targeting immune cells, cytokines, and cytokine receptors to the clinic. Very recent phase III trials with the leading agent, a humanised anti-CD3 antibody, call into question whether further development of these biologics represents a step forward or more of the same. Combination therapies of one or more of these humanised antibodies are also being considered, and they face identical, if not more serious, impediments and safety issues. This paper will highlight the preclinical successes and the excitement generated by phase II trials while offering alternative possibilities and new translational avenues that can be explored given the very recent disappointment in leading agents in more advanced clinical trials.

acDCs enhance human antigen-specific T-cell responses

Detection of human Ag-specific T cells is limited by sensitivity and blood requirements. As dendritic cells (DCs) can potently stimulate T cells, we hypothesized that their induction in PBMCs in situ could link Ag processing and presentation to Ag-specific T-cell activation. To this end, unfractionated PBMCs (fresh or frozen) or whole blood were incubated for 48 hours with protein or peptide Ag together with different DC-activating agents to rapidly and sequentially induce, pulse, and mature DCs. DC activation was therefore lined up with Ag recognition by neighboring T cells, thus telescoping the sequential steps of T-cell activation. Efficient processing of protein Ags made prior knowledge of epitopes and HLA restrictions dispensable. While reducing stimulation time, manipulation and blood requirements, in situ DC induction specifically amplified Ag-specific T-cell responses (cytokine secretion, proliferation, CD137/CD154 up-regulation, and binding of peptide-HLA multimers). IL-1β, although released by DCs, was also secreted in an Ag-specific fashion, thus providing an indirect biomarker of T-cell responses. These accelerated cocultured DC (acDC) assays offered a sensitive means with which to evaluate T-cell responses to viral and melanoma Ag vaccination, and may therefore find application for immune monitoring in viral, tumor, autoimmune, and transplantation settings.

Antigen-based immune therapeutics for type 1 diabetes: magic bullets or ordinary blanks?

The ideal drug of modern medicine is the one that achieves its therapeutic target with minimal adverse effects. Immune therapy of Type 1 diabetes (T1D) is no exception, and knowledge of the antigens targeted by pathogenic T cells offers a unique opportunity towards this goal. Different antigen formulations are being considered, such as proteins or peptides, either in their native form or modified ad hoc, DNA plasmids, and cell-based agents. Translation from mouse to human should take into account important differences, particularly in the time scale of autoimmune progression, and intervention. Critical parameters such as administration route, dosing and interval remain largely empirical and need to be further dissected. T1D staging through immune surrogate markers before and after treatment will be key in understanding therapeutic actions and to finally turn ordinary blanks into magic bullets.

Killer artificial antigen-presenting cells: the synthetic embodiment of a 'guided missile'

At present, the treatment of T-cell-dependent autoimmune diseases relies exclusively on strategies leading to nonspecific suppression of the immune systems causing a substantial reduced ability to control concomitant infections or malignancies. Furthermore, long-term treatment with most drugs is accompanied by several serious adverse effects and does not consequently result in cure of the primary immunological malfunction. By contrast, antigen-specific immunotherapy offers the potential to achieve the highest therapeutic efficiency in accordance with minimal adverse effects. Therefore, several studies have been performed utilizing antigen-presenting cells specifically engineered to deplete allo- or antigen-specific T cells ('guided missiles'). Many of these strategies take advantage of the Fas/Fas ligand signaling pathway to efficiently induce antigen-presenting cell-mediated apoptosis in targeted T cells. In this article, we discuss the advantages and shortcomings of a novel non-cell-based 'killer artificial antigen-presenting cell' strategy, developed to overcome obstacles related to current cell-based approaches for the treatment of T-cell-mediated autoimmunity.

Approaches for immunological tolerance induction to stem cell-derived cell replacement therapies

The shortage of donors for organ transplantation and also to treat degenerative diseases has led to the development of the new field of regenerative medicine. One aim of this field, in addition to in vivo induction of endogenous tissue regeneration, is to utilize stem cells as a supplementary source of cells to repair or replace tissues or organs that have ceased to function owing to ageing or autoimmunity. Embryonic stem cells hold promise in this respect because of their developmental capacity to generate all tissues within the body. More recently, the discovery of induced pluripotent stem cells, somatic cells reprogrammed to a primitive embryonic-like state by the introduction of pluripotency factors, may also act as an important cell source for cell replacement therapy. However, before cell replacement therapy can become a reality, one must consider how to overcome the potential transplant rejection of stem cell-derived products. There are several potential ways to circumvent the hurdles presented by the immune system in this setting, not least the induction of immunological tolerance in the host. In this review, we consider this and other approaches for engendering acceptance of stem cell-derived tissues.

Dendritic cell-based therapy in Type 1 diabetes mellitus

Dendritic cell (DC) immunotherapy is a clinical reality. Despite two decades of considerable data demonstrating the feasibility of using DCs to prolong transplant allograft survival and to prevent autoimmunity, only now are these cells entering clinical trials in humans. Type 1 diabetes is the first autoimmune disorder to be targeted for treatment in humans using autologous-engineered DCs. This review will highlight the role of DCs in autoimmunity and the manner in which they have been engineered to treat these disorders in rodent models, either via the induction of immune hyporesponsiveness, which may be cell- and/or antigen-specific, or indirectly by upregulation of other immune cell networks.

ADP-ribosylation controls the outcome of tolerance or enhanced priming following mucosal immunization

Accumulating evidence suggests that the dichotomy between tolerance and active IgA immunity in mucosal immune responses is regulated at the APC level. Therefore, immunomodulation of the APC could be an effective mechanism to control the two response patterns. In this study, we demonstrate that ADP-ribosylation controls the outcome of tolerance or active effector T cell immunity to an internal peptide p323-339 from OVA inserted into the cholera toxin (CT)-derived CTA1-OVA-DD adjuvant. We found that a single point mutation, CTA1R7K-OVA-DD, resulting in lack of enzymatic activity, promoted peptide-specific tolerance in TCR transgenic CD4(+) T cells following a single intranasal (i.n.) treatment. The CTA1R7K-OVA-DD-induced tolerance was strong, long-lasting, and impaired the ability of adoptively transferred naive peptide-specific CD4(+) T cells to respond to Ag-challenge, irrespective if this was given i.p or i.n. The tolerance correlated with induction of regulatory T cells of the regulatory T type 1 characterized by CD25(-)Foxp3(-)CD4(+) T cells producing IL-10. In contrast, in IL-10-deficient mice, no peptide-specific tolerance was observed, and these mice exhibited unimpaired CD4(+) T cell responsiveness to recall Ag irrespective of if they were untreated (PBS) or treated i.n. with CTA1R7K-OVA-DD. Thus, for the first time, we can provide unequivocal proof that ADP-ribosylation can control the outcome of mucosal Ag exposure from tolerance to an enhanced effector CD4(+) T cell response. The exploitation of this system for clinical treatment of autoimmune diseases is discussed.

Regulation of rat and human T-cell immune response by pharmacologically modified dendritic cells

BACKGROUND

The central function of dendritic cells (DC) in inducing and preventing immune responses makes them ideal therapeutic targets for the induction of immunologic tolerance. In a rat in vivo model, we showed that dexamethasone-treated DC (Dex-DC) induced indirect pathway-mediated regulation and that CD4+CD25+ T cells were involved in the observed effects. The aim of the present study was to investigate the mechanisms underlying the acquired immunoregulatory properties of Dex-DC in the rat and human experimental systems.

METHODS

After treatment with dexamethasone (Dex), the immunogenicity of Dex-DC was analyzed in T-cell proliferation and two-step hyporesponsiveness induction assays. After carboxyfluorescein diacetate succinimidyl ester labeling, CD4+CD25+ regulatory T-cell expansion was analyzed by flow cytometry, and cytokine secretion was measured by ELISA.

RESULTS

In this study, we demonstrate in vitro that rat Dex-DC induced selective expansion of CD4+CD25+ regulatory T cells, which were responsible for alloantigen-specific hyporesponsiveness. The induction of regulatory T-cell division by rat Dex-DC was due to secretion of interleukin (IL)-2 by DC. Similarly, in human studies, monocyte-derived Dex-DC were also poorly immunogenic, were able to induce T-cell anergy in vitro, and expand a population of T cells with regulatory functions. This was accompanied by a change in the cytokine profile in DC and T cells in favor of IL-10.

CONCLUSION

These data suggest that Dex-DC induced tolerance by different mechanisms in the two systems studied. Both rat and human Dex-DC were able to induce and expand regulatory T cells, which occurred in an IL-2 dependent manner in the rat system.

Role of Surfactant Protein A in the Innate Host Defense and Autoimmunity

Surfactant protein A (SP-A) is a lung collectin with diverse immunoregulatory activities. SP-A regulates the innate host defense by enhancing phagocytosis of pathogens and modulating the production of nitric oxide and cytokines by immune cells. Additionally, SP-A also modulates the phenotypic and functional properties of the cells of adaptive immune response such as dendritic cells (DCs) and lymphocytes. Bone marrow-derived DCs generated in the presence of SP-A fail to increase lipopolysaccharide-induced upregulation of major histocompatibility complex (MHC) class II and CD86 costimulatory molecule on DCs surface and behaves like "tolerogenic DCs". SP-A may also induce tolerance by suppressing the proliferation of activated T lymphocytes. Thus, based on immunoregulatory properties of SP-A, it may be employed as a therapeutic agent for the treatment of autoimmune disease and organ transplantation.

Thymus-homing peripheral dendritic cells constitute two of the three major subsets of dendritic cells in the steady-state thymus

Many dendritic cells (DCs) in the normal mouse thymus are generated intrathymically from common T cell/DC progenitors. However, our previous work suggested that at least 50% of thymic DCs originate independently of these progenitors. We now formally demonstrate by parabiotic, adoptive transfer, and developmental studies that two of the three major subsets of thymic DCs originate extrathymically and continually migrate to the thymus, where they occupy a finite number of microenvironmental niches. The thymus-homing DCs consisted of immature plasmacytoid DCs (pDCs) and the signal regulatory protein α–positive (Sirpα⁺) CD11b⁺ CD8α⁻ subset of conventional DCs (cDCs), both of which could take up and transport circulating antigen to the thymus. The cDCs of intrathymic origin were mostly Sirpα⁻ CD11b⁻ CD8α^hi cells. Upon arrival in the thymus, the migrant pDCs enlarged and up-regulated CD11c, major histocompatibility complex II (MHC II), and CD8α, but maintained their plasmacytoid morphology. In contrast, the migrant cDCs proliferated extensively, up-regulated CD11c, MHC II, and CD86, and expressed dendritic processes. The possible functional implications of these findings are discussed.

Mesenchymal stem cells induce mature dendritic cells into a novel Jagged-2-dependent regulatory dendritic cell population

Mesenchymal stem cells (MSCs), in addition to their multilineage differentiation, exert immunomodulatory effects on immune cells, even dendritic cells (DCs). However, whether they influence the destiny of full mature DCs (maDCs) remains controversial. Here we report that MSCs vigorously promote proliferation of maDCs, significantly reduce their expression of Ia, CD11c, CD80, CD86, and CD40 while increasing CD11b expression. Interestingly, though these phenotypes clearly suggest their skew to immature status, bacterial lipopolysaccharide (LPS) stimulation could not reverse this trend. Moreover, high endocytosic capacity, low immunogenicity, and strong immunoregulatory function of MSC-treated maDCs (MSC-DCs) were also observed. Furthermore we found that MSCs, partly via cell-cell contact, drive maDCs to differentiate into a novel Jagged-2-dependent regulatory DC population and escape their apoptotic fate. These results further support the role of MSCs in preventing rejection in organ transplantation and treatment of autoimmune disease.

Delivery of rapamycin-loaded nanoparticle down regulates ICAM-1 expression and maintains an immunosuppressive profile in human CD34+ progenitor-derived dendritic cells

Immune responses of dendritic cells (DCs) can be modulated by delivery of adjuvants to alter their maturation profile. The purpose of this study was to generate DCs from CD34(+) cells of human cord blood and characterize the effects of poly(D,L-lactic-co-glycolic acid) (PLGA)-nanoparticle encapsulated rapamycin in generating an immunosuppressive DC. Expression of ICAM-1 (intercellular adhesion molecule), a key molecule in DC-T cell interaction was increased in mature DCs in response to lipopolysaccharide (LPS). When rapamycin was encapsulated in the nanoparticle to maintain DCs in the immature state, ICAM-1 expression was down regulated. When delivered in the free form, rapamycin did not alter the expression of ICAM-1. Cytokine arrays exhibited an immunosuppressive profile of various cytokines in response to the nanoparticulate delivery of rapamycin. In addition, RT-PCR data demonstrated the presence of toll like receptor (TLR) 9 transcripts, although our DCs are myeloid in nature. In summary, our study demonstrates that DCs may be rendered immunosuppressive upon delivery of rapamycin-containing nanoparticles.

Toward a cure for type 1 diabetes mellitus: diabetes-suppressive dendritic cells and beyond

Insulin has been the gold standard therapy for diabetes since its discovery and commercial availability. It remains the only pharmacologic therapy for type 1 diabetes (T1D), an autoimmune disease in which autoreactive T cells specifically kill the insulin-producing beta cells. Nevertheless, not even molecularly produced insulin administered four or five times per day can provide a physiologic regulation able to prevent the complications that account for the morbidity and mortality of diabetic patients. Also, insulin does not eliminate the T1D hallmark: beta-cell-specific autoimmunity. In other words, insulin is not a 'cure'. A successful cure must meet the following criteria: (i) it must either replace or maintain the functional integrity of the natural, insulin-producing tissue, the endocrine islets of Langerhans' and, more specifically, the insulin-producing beta cells; (ii) it must, at least, control the autoimmunity or eliminate it altogether; and (iii) it must be easy to apply to a large number of patients. Criterion 1 has been partially realized by allogeneic islet transplantation. Criterion 2 has been partially realized using monoclonal antibodies specific for T-cell surface proteins. Criterion 3 has yet to be realized, given that most of the novel therapies are currently quasi-patient-specific. Herein, we outline the current status of non-insulin-based therapies for T1D, with a focus on cell-based immunomodulation which we propose can achieve all three criteria illustrated above.

Immunoregulatory dendritic cells to prevent and reverse new-onset Type 1 diabetes mellitus

Herein, the authors provide an overview of where dendritic cells lie in the immunopathology of autoimmune Type 1 diabetes mellitus and how dendritic cell-based therapy may be usefully translated to treat and reverse the disease. The immunopathology of Type 1 diabetes mellitus offers a number of windows at which immunotherapy can be applied to delay, stop and even reverse the autoimmune processes, especially in light of the recent antibody-based accomplishment of improvement in residual beta-cell mass function. As in almost all cell-specific inflammatory processes, dendritic cells are central regulators of diabetes onset and progression. This realisation, along with accumulating data confirming a role for dendritic cells in maintaining and inducing tolerance in multiple therapeutic settings, has prompted a line of investigation to identify the most effective embodiments of dendritic cells for diabetes immunotherapy.

Induction of peripheral tolerance by local delivery of dendritic cell progenitors to cardiac allografts in a murine heterotopic heart transplantation model

OBJECTIVE

Systemic injection of donor-derived dendritic cell (DC) progenitors is reported to prolong cardiac allograft survival in nonimmunosuppressed hosts. Our purpose was to identify whether tolerance limited to the cardiac allograft is inducible by direct delivery of DCs to the myocardium, thus diminishing the potential for systemic side effects.

METHODS

The donors were 8- to 12-week-old male B10/ H2b mice. The recipients were 8- to 12-week-old male C3H/H2k mice. For DC culture, DCs were propagated from donor bone marrow with granulocytic/macrophage colony stimulating factor (GM-CSF) (GM-CSF DCs) and/or interleukin-4 (IL-4) (GM-CSF+IL-4 DCs). The phenotypes of DCs were analyzed by flow cytometry (FACScan). For DC assay, the JAM test (a DNA fragmentation assay), the mixed lymphocyte reaction (MLR), and flow cytometry were used. For local DC delivery to the myocardium, DCs were injected retrograde into the ascending aorta, and abdominal heterotopic vascularized heart transplantation was performed. Donor heart survival was recorded.

RESULTS

JAM assays confirmed the induction of apoptosis in T cells by both DC preparations. Flow cytometry revealed that the GM-CSF DCs expressed diminished co-stimulatory molecules (B7-1 and B7-2) in comparison with the GM-CSF+IL-4 DCs. The mean survival time of cardiac allografts was 13.1 +/- 4.32 days for the controls, 35.0 +/- 25.7 days for DCs cultured with GM-CSF, and 16.9 +/- 7.30 days for DCs cultured with GM-CSF+IL-4.

CONCLUSION

Local delivery of GM-CSF DCs may induce graft tolerance and may prove to be more efficient than systemic delivery of DCs. Local delivery of GM-CSF+IL-4 DCs did not prolong cardiac graft survival, suggesting that the immune response elicited may be immunostimulatory.

Immune modulation and tolerance induction by RelB-silenced dendritic cells through RNA interference

Dendritic cells (DC), the most potent APCs, can initiate the immune response or help induce immune tolerance, depending upon their level of maturation. DC maturation is associated with activation of the NF-kappaB pathway, and the primary NF-kappaB protein involved in DC maturation is RelB, which coordinates RelA/p50-mediated DC differentiation. In this study, we show that silencing RelB using small interfering RNA results in arrest of DC maturation with reduced expression of the MHC class II, CD80, and CD86. Functionally, RelB-silenced DC inhibited MLR, and inhibitory effects on alloreactive immune responses were in an Ag-specific fashion. RelB-silenced DC also displayed strong in vivo immune regulation. An inhibited Ag-specific response was seen after immunization with keyhole limpet hemocyanin-pulsed and RelB-silenced DC, due to the expansion of T regulatory cells. Administration of donor-derived RelB-silenced DC significantly prevented allograft rejection in murine heart transplantation. This study demonstrates for the first time that transplant tolerance can be induced by means of RNA interference using in vitro-generated tolerogenic DC.

Generation of HSP60-specific regulatory T cell and effect on atherosclerosis

Although CD4(+)CD25(+) regulatory T cells are pivotal in the suppression of autoimmunity, little is known about the effect of antigen-specific regulatory T cells on the formation of atheromatous plaques. Here, we describe the induction of heat-shock protein 60 (HSP60)-specific CD4(+)CD25(high) T cells by rapamycin (RPM)-treated immature dendritic cells in vitro and explore their effect on plaques in apolipoprotein E-deficient mice. Rapamycin-treated bone marrow-derived dendritic cells (DC) were immature, expressing a low level of co-stimulation factors CD86 and CD80. Naive CD4(+) T cells expressed high levels of CD25 and forkhead box P3 (Foxp3) after incubation with rapamycin-treated and HSP60-loaded DC and displayed moderate antigen-specific, IL-10-independent inhibitory function in vitro. After adoptive transfer, HSP60-specific CD4(+)CD25(high) T cells inhibited the formation of plaques, while ovalbumin-specific cells did not. These findings suggest that RPM-treated DC can induce antigen-specific CD4(+)CD25(high) Treg cells that have inhibitory activity in vitro and prevent the development of plaques in vivo.

An Alternative Pathway of NF-κB Activation Results in Maturation and T Cell Priming Activity of Dendritic Cells Overexpressing a Mutated IκBα

Maturation of dendritic cells (DC) is a critical step in the induction of T cell responses and depends on the activation of NF-kappaB transcription factors. Therefore, inhibition of NF-kappaB activation has been proposed as a strategy to maintain DC in an immature stage and to promote immune tolerance. Herein, we generated murine myeloid DC expressing a mutated IkappaBalpha acting as a superrepressor of the classical NF-kappaB pathway (s-rIkappaB DC) to investigate the consequences of NF-kappaB inhibition on the ability of DC to prime T cell responses. Upon in vitro LPS activation, maturation of s-rIkappaB DC was profoundly impaired as indicated by defective up-regulation of MHC class II and costimulatory molecules and reduced secretion of IL-12 p70 and TNF-alpha. In contrast, after injection, s-rIkappaB DC had the same capacity as control DC to migrate to draining lymph node and to induce Th1- and Th2-type cytokine production in a MHC class II-incompatible host mice. Likewise, s-rIkappaB DC pulsed with OVA were as efficient as control DC to induce Ag-specific T cell responses in vivo. Indeed, further in vitro experiments established that s-rIkappaB DC undergo efficient maturation upon prolonged contact with activated T cells via the alternative pathway of NF-kappaB activation triggered at least partly by lymphotoxin beta receptor ligation and involving processing of p100/RelB complexes.

Liposomal vaccines--targeting the delivery of antigen

Vaccines that can prime the adaptive immune system for a quick and effective response against a pathogen or tumor cells, require the generation of antigen (Ag)-specific memory T and B cells. The unique ability of dendritic cells (DCs) to activate naïve T cells, implies a key role for DCs in this process. The generation of tumor-specific CD8(+) cytotoxic T cells (CTLs) is dependent on both T cell stimulation with Ag (peptide-MHC-complexes) and costimulation. Interestingly, tumor cells that lack expression of T cell costimulatory molecules become highly immunogenic when transfected to express such molecules on their surface. Adoptive immunotherapy with Ag-pulsed DCs also is a strategy showing promise as a treatment for cancer. The use of such cell-based vaccines, however, is cumbersome and expensive to use clinically, and/or may carry risks due to genetic manipulations. Liposomes are particulate vesicular lipid structures that can incorporate Ag, immunomodulatory factors and targeting molecules, and hence can serve as potent vaccines. Similarly, Ag-containing plasma membrane vesicles (PMV) derived from tumor cells can be modified to incorporate a T cell costimulatory molecule to provide both TCR stimulation, and costimulation. PMVs also can be modified to contain IFN-gamma and molecules for targeting DCs, permitting delivery of both Ag and a DC maturation signal for initiating an effective immune response. Our results show that use of such agents as vaccines can induce potent anti-tumor immune responses and immunotherapeutic effects in tumor models, and provide a strategy for the development of effective vaccines and immunotherapies for cancer and infectious diseases.

Phenotypic analysis of IL-10-treated, monocyte-derived dendritic cells in patients with systemic lupus erythematosus

Dendritic cells (DC) play a dual role in the immune response, participating in its induction, and the maintenance of immune tolerance. The aim of this work was to perform a quantitative and phenotypic analysis of DC generated in vitro in the presence of IL-10 in patients with systemic lupus erythematosus (SLE). Blood samples were obtained from 10 active and untreated patients with SLE and six controls. Monocyte-derived DC were generated in vitro in the presence or absence of IL-10, and a quantitative and phenotypic analysis was performed. We found that freshly isolated monocytes from SLE patients had an increased expression of CD11b. On the other hand, the efficiency of in vitro DC generation was diminished in blood samples from SLE patients for conventional DC, but not for IL-10-treated DC. A diminished expression of HLA-DR, CD9 and CD86 was observed in conventional DC from SLE patients compared with controls. In contrast, enhanced levels of HLA-DR, CD80, CD9 and CD151 tetraspanins, FN1 (a class II MHC-tetraspanin epitope), CD85j/ILT2 and CD69 were detected in IL-10-treated DC from SLE patients. Accordingly, the phenotypic profile of IL-10-treated DC was very different in SLE and controls. However, the synthesis of IL-10 and IL-12 was similar in IL-10-treated and conventional cells in both SLE patients and controls. Our findings on the aberrant phenotype of IL-10-treated DC in SLE and their normal efficiency of in vitro generation may be important for the design of future therapies of this condition based on the administration of DC to induce immune tolerance.

MSC–DC interactions: MSC inhibit maturation and migration of BM-derived DC

BACKGROUND

Mesenchymal stromal cells (MSC) comprise one of the BM stromal cells that are known to support hematopoiesis. It has also been suggested recently that MSC display immunosuppressive capacities through inhibiting the differentiation of monocyte-derived DC. DC travel to the lymph nodes (LN) to present Ag to T cells, and CCL21 is the chemokine that plays an important role in DC migration into the T-cell area of LN. We addressed the effect of MSC on this chemotactic activity of DC, one of the typical characteristics upon maturation.

METHODS

BM cells were isolated and then cultured for generation of myeloid DC in the presence of GM-CSF and/or lipopolysaccharide with or without MSC. MSC were identified by flow cytometry of the immunologic markers and by performing colony-forming unit fibroblast assay. Migration of DC was observed with a newly developed time-lapse video microscopic technique.

RESULTS

MSC co-culture inhibited the initial differentiation of DC, as well as their maturation. The matured DC actively migrated directionally in response to CCL21, a powerful DC-attracting chemokine, whereas the MSC co-cultured DC did not.

DISCUSSION

Collectively, the findings of these experiments raise the possibility that MSC suppress the migratory function of DC and so they may serve immunoregulatory activities through the modulation of the Ag-presenting function of DC.

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

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

Suppression of Experimental Autoimmune Myasthenia Gravis by Granulocyte-Macrophage Colony-Stimulating Factor Is Associated with an Expansion of FoxP3+Regulatory T Cells

Dendritic cells (DCs) have the potential to activate or tolerize T cells in an Ag-specific manner. Although the precise mechanism that determines whether DCs exhibit tolerogenic or immunogenic functions has not been precisely elucidated, growing evidence suggests that DC function is largely dependent on differentiation status, which can be manipulated using various growth factors. In this study, we investigated the effects of mobilization of specific DC subsets-using GM-CSF and fms-like tyrosine kinase receptor 3-ligand (Flt3-L)-on the susceptibility to induction of experimental autoimmune myasthenia gravis (EAMG). We administered GM-CSF or Flt3-L to C57BL/6 mice before immunization with acetylcholine receptor (AChR) and observed the effect on the frequency and severity of EAMG development. Compared with AChR-immunized controls, mice treated with Flt3-L before immunization developed EAMG at an accelerated pace initially, but disease frequency and severity was comparable at the end of the observation period. In contrast, GM-CSF administered before immunization exerted a sustained suppressive effect against the induction of EAMG. This suppression was associated with lowered serum autoantibody levels, reduced T cell proliferative responses to AChR, and an expansion in the population of FoxP3+ regulatory T cells. These results highlight the potential of manipulating DCs to expand regulatory T cells for the control of autoimmune diseases such as MG.

Immature Dendritic Cells Suppress Collagen-Induced Arthritis by In Vivo Expansion of CD49b+ Regulatory T Cells

Dendritic cells (DCs) are specialized APCs with an important role in the initiation and regulation of immune responses. Immature DCs (iDCs) reportedly mediate tolerance in the absence of maturation/inflammatory stimuli, presumably by the induction of regulatory T cells. In this study, we show for the first time that repetitive iDC injections trigger the expansion of a novel regulatory population with high immunomodulatory properties, able to protect mice from collagen-induced arthritis. These regulatory T cells are characterized by the expression of the CD49b molecule and correspond to a CD4+ alpha-galactosylceramide/CD1d-nonrestricted T cell population producing IL-10. Adoptive transfer of < 10(5) TCRbeta+ CD49b+ cells isolated from the liver of iDCs-vaccinated mice, conferred a complete protection against arthritis. This protection was associated with an attenuation of the B and T cell response associated with a local secretion of IL-10. Thus, together these data demonstrate that iDCs can expand and activate a novel regulatory population of CD49b+ T cells, with high immunosuppressive potential able to mediate protection against a systemic autoimmune disease.

Intravenous immunoglobulin and dendritic cells

Intravenous immunoglobulin (IVIg) has increasingly been used for the treatment of autoimmune and systemic inflammatory diseases, and in supportive therapy of immunodeficient patients. Available clinical and experimental evidence suggests, however, that a wide spectrum of immune-mediated conditions could benefit from IVIg, including acute and chronic/relapsing diseases and autoimmune diseases mediated by pathogenic autoantibodies or by autoaggressive T-cells. Dendritic cells (DCs) are professional antigen-presenting cells and because of their capacity to stimulate naïve T-cells, they play a central role in the initiation of primary immune responses. Several immunomodulatory agents have been shown to inhibit DC activation. Recently, we examined the effects of IVIg on differentiation, maturation, and functions of DCs. We demonstrate that DCs are one of the targets for the immunomodulatory effects of IVIg.

Fas-ligand-expressing adenovirus-transfected dendritic cells decrease allergen-specific T cells and airway inflammation in a murine model of asthma

T cells expressing a type-2 T helper profile of cytokines (Th2 cells) have been demonstrated to play an important role in the initiation and progression of allergic asthma, and it is well known that Fas ligand (FasL) induces apoptosis when bound to its receptor, Fas. In the present study, we examined the possibility of modulating asthma manifestations by dendritic cells (DCs) genetically engineered to express FasL (DC-FasL), which could deliver a death signal to T cells in an antigen-specific manner. The delivery of DC-FasL into ovalbumin (OVA)-immunized allergic mice decreased the airway hyper-responsiveness (AHR). Moreover, we established a mouse model of airway inflammation by using an adoptive transfer of Th2 cells derived from ovalbumin T cell receptor transgenic mice to study the effect of DC-FasL on airway reactivity. The administration of DC-FasL in Th2-cell-induced allergic mice had significantly decreased AHR, airway inflammation, and IL-4, IL-5 and IL-13 production. Furthermore, the numbers of OVA-specific T cells were decreased in the lung of mice receiving DC-FasL. These results demonstrate that FasL-expressing dendritic cells might be applied for the modulation of allergic responses.

Roles of dendritic cells and regulatory T cells in autoantigen-induced murine immune tolerance model

AIM: To investigate the important roles of dendritic cells (DC) and CD4⁺CD25⁺ regulatory T cells in immune prevention against insulin dependent diabetes (IDDM) by autoantigen insulin administration.

METHODS: The model of IDDM was established by intraperitoneal injection of low-dose streptozotocin (STZ) 40 mg/kg per day for 5 consecutive days in Balb/c mice. The bovine insulin (100 μg) in incomplete Freund's adjuvant (IFA, emulsified 1∶1) was given subcutaneously to the mice weekly for 4 wk. The blood glucose was examined once a week and all the mice were killed after 5 wk. Pancreas tissues were collected for histopathological examination. DC precursor cells from bone marrow and lymphocytes from spleen were isolated. The phenotype of DC and CD4⁺ CD25⁺ regulatory T cells were analyzed by fluorescence activated cell sorter (FACS). DC-stimulated proliferation of lymphacytes was determined by allo-mixed lymphocyte reaction (aMLR).

RESULTS: The level of blood glucose was decreased significantly after insulin injection in comparison with that in the model control group (13.79 ± 2.71 mmol/L vs 20.98 ± 1.43 mmol/L, P < 0.05). Fewer lymphocytes infiltration was observed and pancreatic histological structure was intact. The surface marker CD11c on DC from bone marrow was decreased markedly in IDDM mice (26.4%) than that in normal mice (47.5%). DC differentiated abnormally, and the capacity of stimulating proliferation of allogeneic T cell was weakened as compared with that of normal mice (1.47 ± 0.01 vs 2.93 ± 0.01, P < 0.01, and 1.32 ± 0.01 vs 2.94 ± 0.02, P < 0.01, at DC/T ratios of 1∶10 and 1∶20, respectively). The percentage of CD4⁺CD25⁺ T cells were decreased to 1.43%, while it was 5.09% in normal mice. In contrast, blood glucose in mice given insulin subcutaneously was well controlled, and the amount of DC with CD11c was increased (50% approximately); the expression of CD86 and MHC-Ⅱ was low (26.6% and 28.8%, respectively) and MLR showed that DC capacity in stimulating T cell proliferation was lower than those from the normal mice, but higher than those from IDDM model mice (2.30 ± 0.06 and 2.17 ± 0.02, at DC/T ratios of 1∶10 and 1∶20, respectively); the percentage of CD4⁺CD25⁺ T cells from spleen was enhanced to 7.15%.

CONCLUSION: Subcutaneous administration of insulin can confer protection to mice against IDDM induced by STZ. The immune protection of autoantigen may be associated with the establishment of immune tolerance by improving the function of abnormal DC and promoting the production of CD4⁺CD25⁺ T cells in vivo.

The PD-1-PD-L pathway in immunological tolerance

Since the first observation of spontaneous autoimmune diseases in programmed cell death 1 (PD-1) knockout mice, PD-1 has been postulated to have essential roles in the regulation of autoimmunity but the precise mechanism was largely unknown. Recent studies clearly demonstrated that PD-1 has dual roles in immunological tolerance: induction and maintenance of peripheral tolerance. PD-1 ligands (PD-Ls) on antigen-presenting cells have been shown to switch off autoreactive T cells and induce peripheral tolerance, whereas those on parenchymal cells prevent tissue destruction by suppressing effector T cells to maintain tolerance. In addition, PD-1 and other immuno-inhibitory receptors have been shown to collaborate in the regulation of tolerance. Here, we review recent studies on the role of PD-1 in immunological tolerance and discuss possible clinical applications of PD-1 manipulation.

CD4+ regulatory T cells: mechanisms of induction and effector function

The main subsets of CD4+ regulatory T (Tr) cells are the CD4+ CD25+ Tr cells and the type 1 regulatory (Tr1) cells. Both subsets are essential for the maintenance of peripheral tolerance. CD4+ CD25+ Tr cells control immune homeostasis (e.g., in autoimmunity) mainly by cell contact-dependent interactions. In contrast, Tr1 cells regulate immune responses in transplantation, allergy, and autoimmune diseases, via an IL-10- and TGF-beta-dependent mechanism. Identification of the mechanisms responsible for the induction of the different Tr subsets in vivo is a matter of intense investigation. Studies on dendritic cells (DC), performed in the last years by several groups, have significantly contributed to clarify this point. Indeed, it is now clear that the role of DCs is not only to sense danger, but also to tolerize the immune system to antigens (Ags) encountered in the absence of maturation/inflammatory stimuli. Therefore, if a naïve T cell encounters the antigen on immature DCs (iDCs), it differentiates into a Tr cell rather than an effector T cell. A better understanding of the mechanisms underlying the induction and functions of Tr cells in controlling the immune system is critical in view of a future cellular therapy to modulate immune-mediated pathologies.

Cell-based immunotherapy with suppressor CD8+ T cells in rheumatoid arthritis

The chronic persistence of rheumatoid synovitis, an inflammation driven by activated T cells, macrophages, and fibroblasts causing irreversible joint damage, suggests a failure in physiologic mechanisms that down-regulate and terminate chronic immune responses. In vitro CD8(+)CD28(-)CD56(+) T cells tolerize APCs, prevent the priming of naive CD4(+) T cells, and suppress memory CD4(+) T cell responses. Therefore, we generated CD8(+)CD28(-)CD56(+) T cell clones from synovial tissues, expanded them in vitro, and adoptively transferred them into NOD-SCID mice engrafted with synovial tissues from patients with rheumatoid arthritis. Adoptively transferred CD8(+)CD28(-)CD56(+) T cells displayed strong anti-inflammatory activity. They inhibited production of IFN-gamma, TNF-alpha, and chemokines in autologous and HLA class I-matched heterologous synovitis. Down-regulation of costimulatory ligands CD80 and CD86 on synovial fibroblasts was identified as one mechanism of immunosuppression. We propose that rheumatoid synovitis can be suppressed by cell-based immunotherapy with immunoregulatory CD8(+) T cells.

Limitations of CD95 ligand-transduced killer dendritic cells to prevent graft rejections

As an attempt to experimentally induce antigen (Ag)-specific immunosuppression, we have previously created CD95 ligand (CD95L)-transduced dendritic cells (DC), which delivered apoptotic, but not activation, signals to CD4+ T cells in vitro in an Ag-dependent manner. We have also demonstrated that CD95L-transduced DC (termed killer DC) injected into syngeneic animals suppressed delayed-type hypersensitivity responses to an administered Ag. Based on these findings, we tested whether the injection of killer DC derived from A/J mice (H-2a) into allogeneic BALB/c recipients (H-2d) could prolong the survival of A/J-derived skin grafts by depleting A/J-reactive effector T cells. This attempt has not been successful. In this study, we elucidate the reasons for this failure, especially in terms of in vitro effects of killer DC on in vivo primed alloreactive T cells. We show that killer DC (i) failed to induce the proliferation of naive alloreactive T cells in a CD95/CD95L-dependent fashion, (ii) inhibited the proliferation of in vivo primed alloreactive T cells, (iii) killed relatively small fractions (up to 30%) of these T cells in vitro in a CD95/CD95L-dependent fashion and (iv) significantly, but incompletely, inhibited the generation of cytotoxic T-lymphocyte activities against A/J determinants. Thus, killer DC have significant, but modest, capacities to suppress in vitro alloimmune responses, which may not be sufficient to prolong the survival of alloskin grafts in a stringent allograft model. This study suggests that the current format of killer DC technology requires more modifications for its clinical application to prevent graft rejection.

Unexpected effects of viral interleukin-10-secreting dendritic cells in vivo: preferential inhibition of TH2 responses

Viral interleukin (IL)-10 (vIL-10) has been widely described as an immunoregulatory cytokine that does not possess the T-cell costimulatory activities of cellular IL-10; it was therefore believed to be a more potent tolerogenic mediator. The immunosuppressive properties of this cytokine are partly attributed to its capacity to render dendritic cells (DCs) unable to undergo full maturation and to activate T cells. We reported here that myeloid DCs retrovirally transduced with vIL-10 had an impaired production of IL-12 and a decreased expression of MHC class II molecules but had minor defects in costimulatory molecule expression and no alteration on CCR5 and CCR7 expression. In mixed leukocyte reaction, vIL-10-transduced C57BL/6 bm12 (MHC class II mismatch) DCs had a reduced capacity to stimulate C57BL/6 wild-type CD4+ T-cell proliferation. We show that bm12 vIL-10-transduced DC administration in CD8-/- C57BL/6 mice promoted IFN-gamma production, down-regulated TH2-type cytokine production, and did not induce skin graft tolerance. These findings suggest that vIL-10-transduced DC may surprisingly facilitate Th1-type inflammatory responses in vivo.

Transforming Growth Factor β1–Modified Donor Cell Transfusion Induced Allo-Heart Tolerance

The therapeutic value of the transforming growth factor beta 1 (TGF-beta1) in transplantation has been reported; however, cell-mediated gene therapy using TGF-beta1 is not a widespread application in organ transplantation. This study was performed to evaluate whether TGF-beta1-modified donor spleen cell-specific transfusion could induce tolerogenicity and prolong allograft survival in rat heterotopic heart transplantation. Stable TGF-beta1-transduced spleen cells were established. Wistar rat splenic T-cell responses to donor spleen cells that received TGF-beta1-transduced were severely impaired. Survival of Sprague-Dawley cardiac allografts in Wistar rats given TGF-beta1-modified donor spleen cells (5 x 10(6), 7 days before transplantation), was extended modestly but significantly. Liposome transduction of donor spleen cells to overexpress TGF-beta1 is associated with marked impairment of their T-cell allostimulatory activity but only modest prolongation of allo-heart survival.

IL-10-producing T regulatory type 1 cells and oral tolerance

Oral tolerance is mediated by multiple mechanisms such as anergy and/or active suppression of antigen-specific effector T cells by T regulatory (Tr) cells. Among the CD4(+) Tr cells, T regulatory type 1 cells (Tr1) have been shown to downmodulate immune responses through production of the immunosuppressive cytokines IL-10 and TGF-beta. Human Tr1 cells can be induced to differentiate in vitro by IL-10 1 IFN-alpha or after stimulation by immature dendritic cells (DCs) or DCs rendered tolerogenic by exposure to immunomodulatory compounds. Murine Tr1 cells can be induced to differentiate in vitro by activating naive CD4(+) T cells in the presence of high doses of IL-10. Several protocols for induction of oral tolerance, including oral administration of the antigen with IL-10, have been shown to induce antigen-specific Tr1 cells that suppress undesired immune responses toward self-antigens, allergens, and food antigens. Overall, these data demonstrate that IL-10-producing Tr1 cells play a central role in the induction of oral as well as systemic tolerance.

Human mesenchymal stem cells inhibit differentiation and function of monocyte-derived dendritic cells

Mesenchymal stem cells (MSCs), in addition to their multilineage differentiation, have a direct immunosuppressive effect on T-cell proliferation in vitro. However, it is unclear whether they also modulate the immune system by acting on the very first step. In this investigation, we addressed the effects of human MSCs on the differentiation, maturation, and function of dendritic cells (DCs) derived from CD14+ monocytes in vitro. Upon induction with granulocyte-macrophage colony-stimulating factor (GM-CSF) plus interleukin-4 (IL-4), MSC coculture could strongly inhibit the initial differentiation of monocytes to DCs, but this effect is reversible. In particular, such suppression could be recapitulated with no intercellular contact at a higher MSC/monocyte ratio (1:10). Furthermore, mature DCs treated with MSCs were significantly reduced in the expression of CD83, suggesting their skew to immature status. Meanwhile, decreased expression of presentation molecules (HLA-DR and CD1a) and costimulatory molecules (CD80 and CD86) and down-regulated IL-12 secretion were also observed. In consistence, the allostimulatory ability of MSC-treated mature DCs on allogeneic T cells was impaired. In conclusion, our data suggested for the first time that human MSCs could suppress monocyte differentiation into DCs, the most potent antigen-presenting cells (APCs), thus indicating the versatile regulation of MSCs on the ultimate specific immune response.

Differentiation of Tr1 cells by immature dendritic cells requires IL-10 but not CD25+CD4+ Tr cells

Dendritic cells (DCs) are specialized antigen-presenting cells that monitor the antigenic environment and activate naive T cells. The role of DCs is not only to sense danger but also to tolerize the immune system to antigens encountered in the absence of maturation/inflammatory stimuli. Indeed, if a naive T cell encounters its antigen on immature DCs (iDCs), it may differentiate into a T-regulatory (Tr) rather than a T-effector cell. However, little is known about the mechanisms by which iDCs differentiate Tr cells. We developed a standardized and highly reproducible protocol to differentiate Tr cells by repetitive exposure of naive peripheral blood CD4+ T cells to allogeneic iDCs. The resultant Tr cells are phenotypically and functionally identical to type 1 Tr (Tr1) cells because their generation requires production of IL-10 by iDCs, and they suppress T-cell responses through an interleukin-10 (IL-10)– and a transforming growth factor β (TGF-β)–dependent mechanism. In addition, Tr1 cells induced by iDCs do not require the presence of CD4+CD25+ Tr cells for their generation, nor do they express high constitutive levels of CD25 or the transcription factor FoxP3. Thus, iDCs can drive the differentiation of Tr1 cells and can be used to generate large numbers of alloantigen-specific Tr1 cells for clinical use as a cellular therapy to restore peripheral tolerance.

TGF-beta1 treated murine dendritic cells are maturation resistant and down-regulate Toll-like receptor 4 expression

OBJECTIVE

To explore the effects of transforming growth factor beta1 (TGF-beta1) on dendritic cells (DC).

METHODS

Murine bone marrow cells were cultured with GM-CSF and TGF-beta1 to develop TGF-beta1-treated DC (TGFbeta-DC). Then they were stimulated by lipopolysaccharide (LPS). Their phenotypes were assessed by flow cytometry (FCM). The allogeneic stimulating capacity of DC was measured by mixed lymphocyte reaction (MLR) using BrdU ELISA method and IL-12p70 protein was detected by ELISA. The expression of Toll-like receptor 4 (TLR4) was analyzed by semi quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and FCM.

RESULTS

Compared to immature DC (imDC) cultured by GM-CSF alone, the TGFbeta-DC express lower CD80, CD86, I-Ab and CD40. The TGFbeta-DC were resistant to maturation with LPS. Maturation resistance was evident from a failure to up-regulate co-stimulatory molecules (CMs), to stimulate larger T cells proliferation and to enhance secretion of IL-12p70. We also found that TGF-beta1 could down-regulate TLR4 expression on TGFbeta-DC.

CONCLUSION

TGFbeta-DC are resistant to maturation stimulus (LPS) and might have some correlation with the down-modulation of TLR4 expression.

Biodegradable nanoparticle mediated antigen delivery to human cord blood derived dendritic cells for induction of primary T cell responses

Dendritic cells (DCs) in the peripheral tissues act as sentinels of the immune system. They detect and capture pathogens entering the body and present their antigens to T cells to trigger responses directed towards elimination of the pathogen. The induction of peripheral tolerance against self and certain foreign antigens is also believed to be mediated through DCs. The outcome of any immune response is largely controlled by the microenvironment of antigen capture, processing and presentation by DCs. The "context" of antigen delivery to DCs will directly influence the microenvironment of antigen presentation and hence the regulation of immune responses. We report here preliminary investigations describing the formulation of a pharmaceutically acceptable, biodegradable, and strategic nanoparticulate delivery system, and its application for efficient antigen loading of DCs to achieve antigen specific T cell activation. "Pathogen-mimicking" nanoparticles capable of interacting with DCs were fabricated by incorporating monophosphoryl lipid A (MPLA; toll-like receptor (TLR) 4 ligand) or CpG ODN (seq #2006; TLR9 ligand) in biodegradable copolymer, poly(D,L,-lactic-co-glycolic acid) (PLGA). The uptake of PLGA nanoparticles by human umbilical cord blood derived DCs (DCs propagated from CD34 progenitors) was conclusively demonstrated by scanning electron microscopy (SEM), fluorescence activated cell sorting (FACS) and confocal laser scanning microscopy (CLSM). Cell phenotype at day 12 of cultures was determined as immature DC using specific cell surface markers, i.e. CD11c (approximately 90%), MHC-II (approximately 70%), CD86 (approximately 20%), CD83 (approximately 5%), CD80 (approximately 40%), CD40 (approximately 40%), and CCR7 (approximately 5%). Tetanus toxoid (TT), a model antigen, was encapsulated in nanoparticles along with an immunomodulator, i.e. either MPLA or CpG ODN. DCs pulsed with various antigen formulations were co-cultured with autologous naïve T cells at various cell ratios (DC: T cells were 1:5-20). The DCs pulsed with TT and MPLA together in nanoparticles induced significantly higher T cell proliferation (P<0.05) as compared to when DCs pulsed with TT and MPLA in solution were employed. A similar trend was observed when CpG ODN was used instead of MPLA in the TT nanoparticles. This strategy of antigen delivery to DCs was then tested with a cancer vaccine candidate, a MUC1 lipopeptide. The T cell proliferation observed in the presence of nanoparticulate MUC1 and MPLA pulsed-DCs was much higher than DCs pulsed with soluble antigen (P<0.0005). These results indicate that PLGA nanoparticles mimicking certain features of pathogens are efficient delivery systems for targeting vaccine antigens to DCs and activation of potent T cell responses.

Protective potential of experimental autoimmune myasthenia gravis in Lewis rats by IL-10-modified dendritic cells

Dendritic cells (DC) are usually regarded as antigen-presenting cells (APC) involved in T cell activation, but DC also directly or indirectly affect B cell function, antibody synthesis and isotype switch. In this study, we explore potential of DC-based immunotherapy in ongoing experimental autoimmune myasthenia gravis (EAMG) in Lewis rats, which is mediated by anti-acetylcholine receptor (AChR) antibodies. Spleen DC were isolated from onset of Lewis rat EAMG on day 39 post immunization (p.i.), exposed in vitro to IL-10 and then injected intraperitoneally into ongoing EAMG Lewis rats at dose of 1 x 10(6) cells/rat on day 5 p.i. with AChR + complete Freund's adjuvant. IL-10-modified DC resulted in lower clinical scores, less body weight loss, lower numbers of anti-AChR IgG antibody-secreting cells and lower affinity of anti-AChR antibodies in rats receiving IL-10-modified DC, accompanied with lower expression of CD80 and CD86 and lower lymphocyte proliferation among lymph node mononuclear cells compared with control EAMG rats. Lower levels of IL-10 and IFN-gamma were also found in the supernatants of AChR-stimulated lymph node MNC culture in rats receiving IL-10-modified DC. These results demonstrate that IL-10-modified DC induced hypo-responsiveness by down-regulating co-stimulatory molecules, and reduced production of anti-AChR antibodies possibly by inhibiting IL-10 production. Importantly, this procedure that autologous DC from EAMG were adopted to treat ongoing EAMG is more close to clinical trial in human, encouraging future evaluation in human myasthenia gravis.