Antisense Oligonucleotides Down-Regulating Costimulation Confer Diabetes-Preventive Properties to Nonobese Diabetic Mouse Dendritic Cells

Antigen-specific immunotherapy via delivery of tolerogenic dendritic cells for multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system resulting from loss of immune tolerance. Many disease-modifying therapies for MS have broad immunosuppressive effects on peripheral immune cells, but this can increase risks of infection and attenuate vaccine-elicited immunity. A more targeted approach is to re-establish immune tolerance in an autoantigen-specific manner. This review discusses methods to achieve this, focusing on tolerogenic dendritic cells. Clinical trials in other autoimmune diseases also provide learnings with regards to clinical translation of this approach, including identification of autoantigen(s), selection of appropriate patients and administration route and frequency.

Emerging strategies for treating autoimmune disease with genetically modified dendritic cells

Gene editing of living cells has become a crucial tool in medical research, enabling scientists to address fundamental biological questions and develop novel strategies for disease treatment. This technology has particularly revolutionized adoptive transfer cell therapy products, leading to significant advancements in tumor treatment and offering promising outcomes in managing transplant rejection, autoimmune disorders, and inflammatory diseases. While recent clinical trials have demonstrated the safety of tolerogenic dendritic cell (TolDC) immunotherapy, concerns remain regarding its effectiveness. This review aims to discuss the application of gene editing techniques to enhance the tolerance function of dendritic cells (DCs), with a particular focus on preclinical strategies that are currently being investigated to optimize the tolerogenic phenotype and function of DCs. We explore potential approaches for in vitro generation of TolDCs and provide an overview of emerging strategies for modifying DCs. Additionally, we highlight the primary challenges hindering the clinical adoption of TolDC therapeutics and propose future research directions in this field.

Cell and biomaterial delivery strategies to induce immune tolerance

The prevalence of immune-mediated disorders, including autoimmune conditions and allergies, is steadily increasing. However, current therapeutic approaches are often non-specific and do not address the underlying pathogenic condition, often resulting in impaired immunity and a state of generalized immunosuppression. The emergence of technologies capable of selectively inhibiting aberrant immune activation in a targeted, antigen (Ag)-specific manner by exploiting the body's intrinsic tolerance pathways, all without inducing adverse side effects, holds significant promise to enhance patient outcomes. In this review, we will describe the body's natural mechanisms of central and peripheral tolerance as well as innovative delivery strategies using cells and biomaterials targeting innate and adaptive immune cells to promote Ag-specific immune tolerance. Additionally, we will discuss the challenges and future opportunities that warrant consideration as we navigate the path toward clinical implementation of tolerogenic strategies to treat immune-mediated diseases.

Advances in dendritic cell targeting nano-delivery systems for induction of immune tolerance

Dendritic cells (DCs) are the major specialized antigen-presenting cells (APCs), play a key role in initiating the body's immune response, maintain the balance of immunity. DCs can also induce immune tolerance by rendering effector T cells absent and anergy, and promoting the expansion of regulatory T cells. Induction of tolerogenic DCs has been proved to be a promising strategy for the treatment of autoimmune diseases, organ transplantation, and allergic diseases by various laboratory researches and clinical trials. The development of nano-delivery systems has led to advances in situ modulation of the tolerance phenotype of DCs. By changing the material composition, particle size, zeta-potential, and surface modification of nanoparticles, nanoparticles can be used for the therapeutic payloads targeted delivery to DCs, endowing them with great potential in the induction of immune tolerance. This paper reviews how nano-delivery systems can be modulated for targeted delivery to DCs and induce immune tolerance and reviews their potential in the treatment of autoimmune diseases, organ transplantation, and allergic diseases.

Immunomodulation by subcutaneously injected methacrylic acid-based hydrogels and tolerogenic dendritic cells in a mouse model of autoimmune diabetes

Type 1 diabetes is an autoimmune disease associated with the destruction of insulin-producing β cells. Immunotherapies are being developed to mitigate autoimmune diabetes. One promising option is the delivery of tolerogenic dendritic cells (DCs) primed with specific β-cell-associated autoantigens. These DCs can combat autoreactive cells and promote expansion of β-cell-specific regulatory immune cells, including Tregs. Tolerogenic DCs are typically injected systemically (or near target lymph nodes) in suspension, precluding control over the microenvironment surrounding tolerogenic DC interactions with the host. In this study we show that degradable, synthetic methacrylic acid (MAA)-based hydrogels are an inherently immunomodulating delivery vehicle that enhances tolerogenic DC therapy in the context of autoimmune diabetes. MAA hydrogels were found to affect the local recruitment and activation state of macrophages, DCs, T cells and other cells. Delivering tolerogenic DCs in the MAA hydrogel improved the local host response (e.g., fewer cytotoxic T cells) and enhanced peripheral Treg expansion. Non obese diabetic (NOD) mice treated with tolerogenic DCs subcutaneously injected in MAA hydrogels showed a delay in onset of autoimmune diabetes compared to control vehicles. Our findings further demonstrate the usefulness of MAA-based hydrogels as platforms for regenerative medicine in the context of type 1 diabetes.

Tolerogenic dendritic cells in type 1 diabetes: no longer a concept

Tolerogenic dendritic cells (tDC) arrest the progression of autoimmune-driven dysglycemia into clinical, insulin-requiring type 1 diabetes (T1D) and preserve a critical mass of β cells able to restore some degree of normoglycemia in new-onset clinical disease. The safety of tDC, generated ex vivo from peripheral blood leukocytes, has been demonstrated in phase I clinical studies. Accumulating evidence shows that tDC act via multiple layers of immune regulation arresting the action of pancreatic β cell-targeting effector lymphocytes. tDC share a number of phenotypes and mechanisms of action, independent of the method by which they are generated ex vivo. In the context of safety, this yields confidence that the time has come to test the best characterized tDC in phase II clinical trials in T1D, especially given that tDC are already being tested for other autoimmune conditions. The time is also now to refine purity markers and to "universalize" the methods by which tDC are generated. This review summarizes the current state of tDC therapy for T1D, presents points of intersection of the mechanisms of action that the different embodiments use to induce tolerance, and offers insights into outstanding matters to address as phase II studies are imminent. Finally, we present a proposal for co-administration and serially-alternating administration of tDC and T-regulatory cells (Tregs) as a synergistic and complementary approach to prevent and treat T1D.

Engineered Extracellular Vesicles in Treatment of Type 1 Diabetes Mellitus: A Prospective Review

Insulin replacement is an available treatment for autoimmune type 1 diabetes mellitus (T1DM). There are multiple limitations in the treatment of autoimmune diseases such as T1DM by immunosuppression using drugs and chemicals. The advent of extracellular vesicle (EV)-based therapies for the treatment of various diseases has attracted much attention to the field of bio-nanomedicine. Tolerogenic nanoparticles can induce immune tolerance, especially in autoimmune diseases. EVs can deliver cargo to specific cells without restrictions. Accordingly, EVs can be used to deliver tolerogenic nanoparticles, including iron oxide-peptide-major histocompatibility complex, polyethylene glycol-silver-2-(1'H-indole-3'-carbonyl)-thiazole-4-carboxylic acid methyl ester, and carboxylated poly (lactic-co-glycolic acid) nanoparticles coupled with or encapsulating an antigen, to effectively treat autoimmune T1DM. The present work highlights the advances in exosome-based delivery of tolerogenic nanoparticles for the treatment of autoimmune T1DM.

Dendritic Cells and Their Immunotherapeutic Potential for Treating Type 1 Diabetes

Type 1 diabetes (T1D) results from the destruction of pancreatic beta cells through a process that is primarily mediated by T cells. Emerging evidence suggests that dendritic cells (DCs) play a crucial role in initiating and developing this debilitating disease. DCs are professional antigen-presenting cells with the ability to integrate signals arising from tissue infection or injury that present processed antigens from these sites to naïve T cells in secondary lymphoid organs, thereby triggering naïve T cells to differentiate and modulate adaptive immune responses. Recent advancements in our knowledge of the various subsets of DCs and their cellular structures and methods of orchestration over time have resulted in a better understanding of how the T cell response is shaped. DCs employ various arsenal to maintain their tolerance, including the induction of effector T cell deletion or unresponsiveness and the generation and expansion of regulatory T cell populations. Therapies that suppress the immunogenic effects of dendritic cells by blocking T cell costimulatory pathways and proinflammatory cytokine production are currently being sought. Moreover, new strategies are being developed that can regulate DC differentiation and development and harness the tolerogenic capacity of these cells. Here, in this report, we focus on recent advances in the field of DC immunology and evaluate the prospects of DC-based therapeutic strategies to treat T1D.

Antisense oligonucleotides: recent progress in the treatment of various diseases

Background

Antisense oligonucleotides are a promising novel class of therapeutic agents to treat different diseases in living things. They provide an efficient method for making target-selective agents because they change gene expression sequences. Therefore, the malfunctioning protein could be stopped, and the source of disease would be obliterated. The existing reviews of antisense oligonucleotides are focusing on discovery, development and concept. However, there is no review paper concerning the latest development of antisense oligonucleotides and their different therapeutic uses. Therefore, the present work has been targeting a comprehensive summary of newly synthesized antisense oligonucleotides and their biological activities.

Main body

Antisense oligonucleotides are different from traditional therapeutic agents that are planned to interact with mRNA and modulate protein expression through a unique mechanism of action. In the last three decades, several researchers revealed the newer antisense oligonucleotides found with a high therapeutic profile due to more selective action on the drug target and thus producing a lesser side effect and low toxicity. This review emphasizes the research work on antisense oligonucleotides and their therapeutic activities.

Short conclusion

With the support of the literature review, here we enlisted various antisense oligonucleotides that were prepared by appropriate technique and explored their pharmacological activities. To the best of our knowledge, it is the right time to consider the antisense oligonucleotides as a perfect choice of treatment for different diseases due to conceptual simplicity, more selective action, lesser side effects, low toxicity and permanent cure.

Graphical abstract

Tolerogenic Dendritic Cell-Based Approaches in Autoimmunity

Dendritic cells (DCs) dictate the outcomes of tissue-specific immune responses. In the context of autoimmune diseases, DCs instruct T cells to respond to antigens (Ags), including self-Ags, leading to organ damage, or to becoming regulatory T cells (Tregs) promoting and perpetuating immune tolerance. DCs can acquire tolerogenic properties in vitro and in vivo in response to several stimuli, a feature that opens the possibility to generate or to target DCs to restore tolerance in autoimmune settings. We present an overview of the different subsets of human DCs and of the regulatory mechanisms associated with tolerogenic (tol)DC functions. We review the role of DCs in the induction of tissue-specific autoimmunity and the current approaches exploiting tolDC-based therapies or targeting DCs in vivo for the treatment of autoimmune diseases. Finally, we discuss limitations and propose future investigations for improving the knowledge on tolDCs for future clinical assessment to revert and prevent autoimmunity. The continuous expansion of tolDC research areas will lead to improving the understanding of the role that DCs play in the development and treatment of autoimmunity.

Emerging Cellular Therapies for Anti-myeloperoxidase Vasculitis and Other Autoimmune Diseases

Anti-myeloperoxidase vasculitis (MPO-AAV) is a life-threatening autoimmune disease which causes severe inflammation of small blood vessels, mainly in the kidney. As for many other autoimmune diseases, current treatments, which consist of general immunosuppressants, are partially effective, toxic and broadly immunosuppressive, causing significant and serious adverse effects in many patients. Therefore, there is an urgent need for more targeted and less harmful therapies. Tolerogenic dendritic cells, regulatory T cells and stem cells have emerged as attractive, new and safer options for the treatment for various autoimmune diseases due to their unique and selective immunosuppressive capacity. In this review, we will discuss how these cellular therapies offer potential to become novel and safer treatments for MPO-AAV.

Regulatory Macrophages and Tolerogenic Dendritic Cells in Myeloid Regulatory Cell-Based Therapies

Myeloid regulatory cell-based therapy has been shown to be a promising cell-based medicinal approach in organ transplantation and for the treatment of autoimmune diseases, such as type 1 diabetes, rheumatoid arthritis, Crohn’s disease and multiple sclerosis. Dendritic cells (DCs) are the most efficient antigen-presenting cells and can naturally acquire tolerogenic properties through a variety of differentiation signals and stimuli. Several subtypes of DCs have been generated using additional agents, including vitamin D3, rapamycin and dexamethasone, or immunosuppressive cytokines, such as interleukin-10 (IL-10) and transforming growth factor-beta (TGF-β). These cells have been extensively studied in animals and humans to develop clinical-grade tolerogenic (tol)DCs. Regulatory macrophages (Mregs) are another type of protective myeloid cell that provide a tolerogenic environment, and have mainly been studied within the context of research on organ transplantation. This review aims to thoroughly describe the ex vivo generation of tolDCs and Mregs, their mechanism of action, as well as their therapeutic application and assessment in human clinical trials.

Current advances in using tolerogenic dendritic cells as a therapeutic alternative in the treatment of type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease characterized by the destruction of insulin-producing β-cells of the pancreatic islets by autoreactive T cells, leading to high blood glucose levels and severe long-term complications. The typical treatment indicated in T1D is exogenous insulin administration, which controls glucose levels; however, it does not stop the autoimmune process. Various strategies have been implemented aimed at stopping β-cell destruction, such as cellular therapy. Dendritic cells (DCs) as an alternative in cellular therapy have gained great interest for autoimmune disease therapy due to their plasticity to acquire immunoregulatory properties both in vivo and in vitro, performing functions such as anti-inflammatory cytokine secretion and suppression of autoreactive lymphocytes, which are dependent of their tolerogenic phenotype, displayed by features such as semimature phenotype, low surface expression of stimulatory molecules to prime T cells, as well as the elevated expression of inhibitory markers. DCs may be obtained and propagated easily in optimal amounts from peripheral blood or bone marrow precursors, such as monocytes or hematopoietic stem cells, respectively; therefore, various protocols have been established for tolerogenic (tol)DCs manufacturing for therapeutic research in the treatment of T1D. In this review, we address the current advances in the use of tolDCs for T1D therapy, encompassing protocols for their manufacturing, the data obtained from preclinical studies carried out, and the status of clinical research evaluating the safety, feasibility, and effectiveness of tolDCs.

TLR5 activation in hepatocytes alleviates the functional suppression of intrahepatic CD8+ T cells

The liver is an immune-privileged organ with a tolerogenic environment for maintaining liver homeostasis. This hepatic tolerance limits the intrahepatic CD8⁺ T-cell response for eliminating infections. The tolerant microenvironment in the liver is orchestrated by liver-specific immunoregulatory cells that can be functionally regulated by pathogen-associated molecular patterns (PAMPs). Here, we report that flagellin, a key PAMP of gut bacteria, modulates the intrahepatic CD8⁺ T-cell response by activating the TLR5 signalling pathway of hepatocytes. We found that mice treated with Salmonella-derived recombinant flagellin (SF) by hydrodynamic injection had a significantly elevated IFN-γ production by the intrahepatic lymphocytes in 7 days after injection. This was correlated with a reduced immune suppressive effect of primary mouse hepatocytes (PMHs) in comparison with that of PMHs from mock-injected control mice. In vitro co-culture of SF-treated PMHs with splenocytes revealed that hepatocyte-induced immune suppression is alleviated through activation of the TLR5 but not the NLRC4 signalling pathway, leading to improved activation and function of CD8⁺ T cells during anti-CD3 stimulation or antigen-specific activation. In an acute HBV replication mouse model established by co-administration of SF together with an HBV-replicating plasmid by hydrodynamic injection, SF significantly enhanced the intrahepatic HBV-specific CD8⁺ T-cell response against HBV surface antigen. Our results clearly showed that flagellin plays a role in modulating the intrahepatic CD8⁺ T-cell response by activating the TLR5 pathway in PMHs, which suggests a potential role for gut bacteria in regulating liver immunity.

Human Tolerogenic Dendritic Cells Regulate Immune Responses through Lactate Synthesis

Cell therapy is a promising strategy for treating patients suffering from autoimmune or inflammatory diseases or receiving a transplant. Based on our preclinical studies, we have generated human autologous tolerogenic dendritic cells (ATDCs), which are being tested in a first-in-man clinical trial in kidney transplant recipients. Here, we report that ATDCs represent a unique subset of monocyte-derived cells based on phenotypic, transcriptomic, and metabolic analyses. ATDCs are characterized by their suppression of T cell proliferation and their expansion of Tregs through secreted factors. ATDCs produce high levels of lactate that shape T cell responses toward tolerance. Indeed, T cells take up ATDC-secreted lactate, leading to a decrease of their glycolysis. In vivo, ATDCs promote elevated levels of circulating lactate and delay graft-versus-host disease by reducing T cell proliferative capacity. The suppression of T cell immunity through lactate production by ATDCs is a novel mechanism that distinguishes ATDCs from other cell-based immunotherapies.

Induction of Tolerance and Immunity by Dendritic Cells: Mechanisms and Clinical Applications

Dendritic cells (DCs) are key regulators of immune responses that operate at the interface between innate and adaptive immunity, and defects in DC functions contribute to the pathogenesis of a variety of disorders. For instance, cancer evolves in the context of limited DC activity, and some autoimmune diseases are initiated by DC-dependent antigen presentation. Thus, correcting aberrant DC functions stands out as a promising therapeutic paradigm for a variety of diseases, as demonstrated by an abundant preclinical and clinical literature accumulating over the past two decades. However, the therapeutic potential of DC-targeting approaches remains to be fully exploited in the clinic. Here, we discuss the unique features of DCs that underlie the high therapeutic potential of DC-targeting strategies and critically analyze the obstacles that have prevented the full realization of this promising paradigm.

A Mathematical Model for DC Vaccine Treatment of Type I Diabetes

Type I diabetes (T1D) is an autoimmune disease that can be managed, but for which there is currently no cure. Recent discoveries, particularly in mouse models, indicate that targeted modulation of the immune response has the potential to move an individual from a diabetic to a long-term, if not permanent, healthy state. In this paper we develop a single compartment mathematical model that captures the dynamics of dendritic cells (DC and tDC), T cells (effector and regulatory), and macrophages in the development of type I diabetes. The model supports the hypothesis that differences in macrophage clearance rates play a significant role in determining whether or not an individual is likely to become diabetic subsequent to a significant immune challenge. With this model we are able to explore the effects of strengthening the anti-inflammatory component of the immune system in a vulnerable individual. Simulations indicate that there are windows of opportunity in which treatment intervention is more likely to be beneficial in protecting an individual from entering a diabetic state. This model framework can be used as a foundation for modeling future T1D treatments as they are developed.

Tolerogenic Dendritic Cells Attenuate Experimental Autoimmune Antimyeloperoxidase Glomerulonephritis

Background Because of their capacity to induce antigen-specific immunosuppression, tolerogenic dendritic cells are a promising tool for treatment of autoimmune conditions, such as GN caused by autoimmunity against myeloperoxidase (MPO).

METHODS

We sought to generate tolerogenic dendritic cells to suppress anti-MPO GN by culturing bone marrow cells with an NFκB inhibitor (BAY 11-7082) and exposing them to a pulse of MPO. After administering these MPO/BAY dendritic cells or saline to mice with established anti-MPO or anti-methylated BSA (mBSA) immunity, we assessed immune responses and GN. We also examined mechanisms of action of MPO/BAY dendritic cells.

RESULTS

MPO/BAY dendritic cells decreased anti-MPO immunity and GN without inhibiting immune responses against mBSA; they also induced IL-10-producing regulatory T cells in MPO-immunized mice without affecting IL-10⁺ CD4⁺Foxp3^- type 1 regulatory T cells or regulatory B cells. MPO/BAY dendritic cells did not inhibit anti-MPO immunity when CD4⁺Foxp3⁺ cells were depleted in vivo, showing that regulatory T cells are required for their effects. Coculture experiments with dendritic cells and CD4⁺Foxp3^- or CD4⁺Foxp3⁺ cells showed that MPO/BAY dendritic cells generate Foxp3⁺ regulatory T cells from CD4⁺Foxp3^- cells through several pathways, and induce IL-10⁺ regulatory T cells via inducible costimulator (ICOS), which was confirmed in vivo. Transfer of MPO/BAY dendritic cell-induced regulatory T cells in vivo, with or without anti-IL-10 receptor antibody, demonstrated that they suppress anti-MPO immunity and GN via IL-10.

CONCLUSIONS

MPO/BAY dendritic cells attenuate established anti-MPO autoimmunity and GN in an antigen-specific manner through ICOS-dependent induction of IL-10-expressing regulatory T cells. This suggests that autoantigen-loaded tolerogenic dendritic cells may represent a novel antigen-specific therapeutic option for anti-MPO GN.

Engineered Dendritic Cell-Directed Concurrent Activation of Multiple T cell Inhibitory Pathways Induces Robust Immune Tolerance

Inhibitory/repressor-receptors are upregulated significantly on activated T cells, and have been the molecules of attention as targets for inducing immune tolerance. Induction of effective antigen specific tolerance depends on concurrent engagement of the TCR and one or more of these inhibitory receptors. Here, we show, for the first time that dendritic cells (DCs) can be efficiently engineered to express multiple T cell inhibitory ligands, and enhanced engagement of T cell inhibitory receptors, upon antigen presentation, by these DCs can induce effective CD4+ T cell tolerance and suppress autoimmunity. Compared to control DCs, antigen presentation by DCs that ectopically express CTLA4, PD1 and BTLA selective ligands (B7.1wa, PD-L1, and HVEM-CRD1 respectively) individually (mono-ligand DCs) or in combination (multi-ligand DCs) causes an inhibition of CD4+ T cell proliferation and pro-inflammatory cytokine response, as well as increase in Foxp3+ Treg frequency and immune regulatory cytokine production. Administration of self-antigen (mouse thyroglobulin; mTg) loaded multi-ligand DCs caused hyporesponsiveness to mTg challenge, suppression of autoantibody production, and amelioration of experimental autoimmune thyroiditis. Overall, this study shows that engineered DC-directed enhanced concurrent activation of multiple T cell coinhibitory pathways is an effective way to induce self-antigen specific T cell tolerance to suppress ongoing autoimmunity.

Engineering immunomodulatory biomaterials for type 1 diabetes

A cure for type 1 diabetes (T1D) would help millions of people worldwide, but remains elusive thus far. Tolerogenic vaccines and beta cell replacement therapy are complementary therapies that seek to address aberrant T1D autoimmune attack and subsequent beta cell loss. However, both approaches require some form of systematic immunosuppression, imparting risks to the patient. Biomaterials-based tools enable localized and targeted immunomodulation, and biomaterial properties can be designed and combined with immunomodulatory agents to locally instruct specific immune responses. In this Review, we discuss immunomodulatory biomaterial platforms for the development of T1D tolerogenic vaccines and beta cell replacement devices. We investigate nano- and microparticles for the delivery of tolerogenic agents and autoantigens, and as artificial antigen presenting cells, and highlight how bulk biomaterials can be used to provide immune tolerance. We examine biomaterials for drug delivery and as immunoisolation devices for cell therapy and islet transplantation, and explore synergies with other fields for the development of new T1D treatment strategies.

Optimal Tolerogenic Dendritic Cells in Type 1 Diabetes (T1D) Therapy: What Can We Learn From Non-obese Diabetic (NOD) Mouse Models?

Tolerogenic dendritic cells (tolDCs) are explored as a promising standalone or combination therapy in type 1 diabetes (T1D). The therapeutic application of tolDCs, including in human trials, has been tested also in other autoimmune diseases, however, T1D displays some unique features. In addition, unlike in several disease-induced animal models of autoimmune diseases, the prevalent animal model for T1D, the NOD mouse, develops diabetes spontaneously. This review compares evidence of various tolDCs approaches obtained from animal (mainly NOD) models of T1D with a focus on parameters of this cell-based therapy such as protocols of tolDC preparation, antigen-specific vs. unspecific approaches, doses of tolDCs and/or autoantigens, application schemes, application routes, the migration of tolDCs as well as their preventive, early pre-onset intervention or curative effects. This review also discusses perspectives of tolDC therapy and areas of preclinical research that are in need of better clarification in animal models in a quest for effective and optimal tolDC therapies of T1D in humans.

Immune checkpoints and the regulation of tolerogenicity in dendritic cells: Implications for autoimmunity and immunotherapy

The immune system is responsible for defending the host from a large variety of potential pathogens, while simultaneously avoiding immune reactivity towards self-components. Self-tolerance has to be tightly maintained throughout several central and peripheral processes; immune checkpoints are imperative for regulating the immunity/tolerance balance. Dendritic cells (DCs) are specialized cells that capture antigens, and either activate or inhibit antigen-specific T cells. Therefore, they play a key role at inducing and maintaining immune tolerance. DCs that suppress the immune response have been called tolerogenic dendritic cells (tolDCs). Given their potential as a therapy to prevent transplant rejection and autoimmune damage, several strategies are under development to generate tolDCs, in order to avoid activation and expansion of self-reactive T cells. In this article, we summarize the current knowledge relative to the main features of tolDCs, their mechanisms of action and their therapeutic use for autoimmune diseases. Based on the literature reviewed, autologous antigen-specific tolDCs might constitute a promising strategy to suppress autoreactive T cells and reduce detrimental inflammatory processes.

Downregulation of Blimp1 inhibits the maturation of bone marrow-derived dendritic cells

Modulation of differentiation of dendritic cells (DCs), which are derived from bone marrow cells, may influence their maturation and consequently regulate their ability to present antigens to alloreactive T lymphocytes. B lymphocyte‑induced maturation protein‑1 (Blimp1) is a master regulator of immunocyte differentiation, which has been investigated for its effect on DCs. In the present study, a lentivirus was used as a vector to transduce Blimp1‑short hairpin (sh)RNA into primary bone marrow cells during their differentiation to DCs. Lentiviral‑mediated Blimp1‑shRNA (lenti‑shRNA‑Blimp1) had a transduction efficiency of >60% in DC precursors. Lenti‑shRNA‑Blimp1 significantly downregulated the expression levels of Blimp1 and modulated the expression of its target proteins, including class II major histocompatibility complex (MHC) transactivator, c‑myc and interleukin‑6. Although lenti‑shRNA‑Blimp1 did not interfere with the differentiation of bone marrow cells to DCs, it inhibited DC maturation by decreasing the expression of surface MHC‑II molecules, but not the expression of MHC‑I molecules and co‑stimulatory molecules [cluster of differentiation (CD)80/CD86]. Subsequently, alloreactive T cell proliferation was alleviated and regulatory T cells were expanded in response to lenti‑shRNA‑Blimp1. A toxicity assay indicated that the morphology and proliferation of cultured DCs were mildly influenced by the lentiviral vector, indicating that the use of alternative vectors with minimal or no toxicity could be investigated in future studies. In conclusion, transduction with lenti‑shRNA‑Blimp1 modulated the maturation of DCs via MHC‑II molecule suppression and inhibited alloreactive T cell activation. The present findings supported the application of Blimp1‑based intervention as a novel approach to induce immature DCs for further immunological research.

Restoring self-tolerance in autoimmune diseases by enhancing regulatory T-cells

Self-tolerance, the state of unresponsiveness to self-tissues/antigens, is maintained through central and peripheral tolerance mechanisms, and a breach of these mechanisms leads to autoimmune diseases. Foxp3 + T-regulatory cells (Tregs) play an essential role in suppressing autoimmune response directed against self-antigens and thereby regulate self-tolerance. Natural Tregs are differentiated in the thymus on the basis of their higher TCR-affinity to self-antigens and migrate to the periphery where they maintain peripheral tolerance. In addition, extra-thymic differentiation of induced Tregs can occur in the periphery which can control abrupt immune responses under inflammatory conditions. A defect in Treg cell numbers and/or function is found to be associated with the development of autoimmune disease in several experimental models and human autoimmune diseases. Moreover, augmentation of Tregs has been shown to be beneficial in treating autoimmunity in preclinical models, and Treg based cellular therapy has shown initial promise in clinical trials. However, emerging studies have identified an unstable subpopulation of Tregs which expresses pro-inflammatory cytokines under both homeostatic and autoimmune conditions, as well as in ex vivo cultures. In addition, clinical translation of Treg cellular therapy is impeded by limitations such as lack of easier methods for selective expansion of Tregs and higher cost associated with GMP-facilities required for cell sorting, ex vivo expansion and infusion of ex vivo expanded Tregs. Here, we discuss the recent advances in molecular mechanisms regulating Treg differentiation, Foxp3 expression and lineage stability, the role of Tregs in the prevention of various autoimmune diseases, and critically review their clinical utility for treating human autoimmune diseases.

Therapies to Suppress β Cell Autoimmunity in Type 1 Diabetes

Type 1 diabetes (T1D) is an autoimmune disease that is generally considered to be T cell-driven. Accordingly, most strategies of immunotherapy for T1D prevention and treatment in the clinic have targeted the T cell compartment. To date, however, immunotherapy has had only limited clinical success. Although certain immunotherapies have promoted a protective effect, efficacy is often short-term and acquired immunity may be impacted. This has led to the consideration of combining different approaches with the goal of achieving a synergistic therapeutic response. In this review, we will discuss the status of various T1D therapeutic strategies tested in the clinic, as well as possible combinatorial approaches to restore β cell tolerance.

Co-Stimulation-Impaired Bone Marrow-Derived Dendritic Cells Prevent Dextran Sodium Sulfate-Induced Colitis in Mice

Dendritic cells (DC) are important in the onset and severity of inflammatory bowel disease (IBD). Tolerogenic DC induce T-cells to become therapeutic Foxp3+ regulatory T-cells (Tregs). We therefore asked if experimental IBD could be prevented by administration of bone marrow-derived DC generated under conventional GM-CSF/IL-4 conditions but in the presence of a mixture of antisense DNA oligonucleotides targeting the primary transcripts of CD40, CD80, and CD86. These cell products (which we call AS-ODN BM-DC) have demonstrated tolerogenic activity in preventing type 1 diabetes and preserving beta cell mass in new-onset type 1 diabetes in the NOD mouse strain, in earlier studies. In addition to measuring efficacy in prevention of experimental IBD, we also sought to identify possible mechanism(s) of action. Weight, behavior, stool frequency, and character were observed daily for 7–10 days in experimental colitis in mice exposed to dextran sodium sulfate (DSS) following injection of the AS-ODN BM-DC. After euthanasia, the colons were processed for histology while spleen and mesenteric lymph nodes (MLNs) were made into single cells to measure Foxp3+ Treg as well as IL-10+ regulatory B-cell (Breg) population frequency by flow cytometry. AS-ODN BM-DC prevented DSS-induced colitis development. Recipients of these cells exhibited significant increases in Foxp3+ Treg and IL-10+ Breg in MLN and spleen. Histological examination of colon sections of colitis-free mice remained largely architecturally physiologic and mostly free of leukocyte infiltration when compared with DSS-treated animals. Although DSS colitis is mainly an innate immunity-driven condition, our study adds to the growing body of evidence showing that Foxp3+ Treg and IL-10 Bregs can suppress a mainly innate-driven inflammation. The already-established safety of human DC generated from monocytic progenitors in the presence of the mixture of antisense DNA targeting the primary transcripts of CD40, CD80, and CD86 in humans offers the potential to adapt them for clinical IBD therapy.

Tolerogenic Dendritic Cells in Solid Organ Transplantation: Where Do We Stand?

Over the past century, solid organ transplantation has been improved both at a surgical and postoperative level. However, despite the improvement in efficiency, safety, and survival, we are still far from obtaining full acceptance of all kinds of allograft in the absence of concomitant treatments. Today, transplanted patients are treated with immunosuppressive drugs (IS) to minimize immunological response in order to prevent graft rejection. Nevertheless, the lack of specificity of IS leads to an increase in the risk of cancer and infections. At this point, cell therapies have been shown as a novel promising resource to minimize the use of IS in transplantation. The main strength of cell therapy is the opportunity to generate allograft-specific tolerance, promoting in this way long-term allograft survival. Among several other regulatory cell types, tolerogenic monocyte-derived dendritic cells (Tol-MoDCs) appear to be an interesting candidate for cell therapy due to their ability to perform specific antigen presentation and to polarize immune response to immunotolerance. In this review, we describe the characteristics and the mechanisms of action of both human Tol-MoDCs and rodent tolerogenic bone marrow-derived DCs (Tol-BMDCs). Furthermore, studies performed in transplantation models in rodents and non-human primates corroborate the potential of Tol-BMDCs for immunoregulation. In consequence, Tol-MoDCs have been recently evaluated in sundry clinical trials in autoimmune diseases and shown to be safe. In addition to autoimmune diseases clinical trials, Tol-MoDC is currently used in the first phase I/II clinical trials in transplantation. Translation of Tol-MoDCs to clinical application in transplantation will also be discussed in this review.

Antigen Loading (e.g., Glutamic Acid Decarboxylase 65) of Tolerogenic DCs (tolDCs) Reduces Their Capacity to Prevent Diabetes in the Non-Obese Diabetes (NOD)-Severe Combined Immunodeficiency Model of Adoptive Cotransfer of Diabetes As Well As in NOD Mice

Tolerogenic DCs (tolDCs) are being researched as a promising intervention strategy also in autoimmune diseases including type 1 diabetes (T1D). T1D is a T-cell-mediated, organ-specific disease with several well-defined and rather specific autoantigens, i.e., proinsulin, insulin, glutamic acid decarboxylase 65 (GAD65), that have been used in animal as well as human intervention trials in attempts to achieve a more efficient, specific immunotherapy. In this study, we have tested tolerogenic DCs for their effectiveness to prevent adoptive transfer of diabetes by diabetogenic splenocytes into non-obese diabetes (NOD)-severe combined immunodeficiency (NOD-SCID) recipients. While i.p. application of tolDCs prepared from bone marrow of prediabetic NOD mice by vitamin D2 and dexamethasone significantly reduced diabetes transfer into the NOD-SCID females, this effect was completely abolished when tolDCs were loaded with the mouse recombinant GAD65, but also with a control protein—ovalbumin (OVA). The effect was not dependent on the presence of serum in the tolDC culture. Similar results were observed in NOD mice. Removal of possible bystander antigen-presenting cells within the diabetogenic splenocytes by negative magnetic sorting of T cells did not alter this surprising effect. Tolerogenic DCs loaded with an immunodominant mouse GAD65 peptide also displayed diminished diabetes-preventive effect. Tolerogenic DCs were characterized by surface maturation markers (CD40, CD80, CD86, MHC II) and the lipopolysaccharide stability test. Data from alloreactive T cell proliferation and cytokine induction assays (IFN-γ) did not reveal the differences observed in the diabetes incidence. Migration of tolDCs, tolDCs-GAD65 and tolDCs-OVA to spleen, mesenteric- and pancreatic lymph nodes displayed similar, mucosal pattern with highest accumulation in pancreatic lymph nodes present up to 9 days after the i.p. application. These data document that mechanisms by which tolDCs operate in vivo require much better understanding for improving efficacy of this promising cell therapy, especially in the presence of an antigen, e.g., GAD65.

Immature Dendritic Cell Therapy Confers Durable Immune Modulation in an Antigen-Dependent and Antigen-Independent Manner in Nonobese Diabetic Mice

Dendritic cell (DC) immunotherapy has been effective for prevention of type 1 diabetes (T1D) in NOD mice but fails to protect if initiated after active autoimmunity. As autoreactivity expands inter- and intramolecularly during disease progression, we investigated whether DCs unpulsed or pulsed with β cell antigenic dominant determinants (DD), subdominant determinants (SD), and ignored determinants (ID) could prevent T1D in mice with advanced insulitis. We found that diabetes was significantly delayed by DC therapy. Of interest, DCs pulsed with SD or ID appeared to provide better protection. T lymphocytes from DC-treated mice acquired spontaneous proliferating capability during in vitro culture, which could be largely eliminated by IL-2 neutralizing antibodies. This trend maintained even 29 weeks after discontinuing DC therapy and appeared antigen-independent. Furthermore, CD4+Foxp3+ T regulatory cells (Tregs) from DC-treated mice proliferated more actively in vitro compared to the controls, and Tregs from DC-treated mice showed significantly enhanced immunosuppressive activities in contrast to those from the controls. Our study demonstrates that DC therapy leads to long-lasting immunomodulatory effects in an antigen-dependent and antigen-independent manner and provides evidence for peptide-based intervention during a clinically relevant window to guide DC-based immunotherapy for autoimmune diabetes.

Harnessing the power of regulatory T-cells to control autoimmune diabetes: overview and perspective

Type 1 diabetes (T1D) is a T-cell-mediated autoimmune disease resulting in islet β-cell destruction, hypoinsulinaemia and severely altered glucose homeostasis. Although the mechanisms that initiate T1D still remain elusive, a breakdown of immune tolerance between effector T-cells (T_eff ) and regulatory T-cells (T_reg ) is considered to be the crucial component leading to autoimmunity. As such, strategies have been developed to boost the number and/or function of T_reg in the hope of specifically hampering the pathogenic T_eff activity. In this review, we will summarize the current understanding of biomarkers and functions of both forkhead box protein 3 (FoxP3)⁺ T_reg and type 1 regulatory T (Tr1) cells in health and in T1D, examine the outcome of experimental therapies in both animal models and humans via manipulation of T_reg responses and also provide an outlook on the potential of T_reg -based immunotherapies in the prevention and treatment of this disease. Discussed immunotherapies include adoptive transfer of ex-vivo expanded FoxP3⁺ T_reg , manipulation of T_reg cells via the interleukin (IL)-2/IL-2R pathway and induction of T_reg by tolerogenic peptides, tolerogenic dendritic cells or altered gut microbiota.

Translating Mechanism of Regulatory Action of Tolerogenic Dendritic Cells to Monitoring Endpoints in Clinical Trials

Tolerogenic dendritic cells (tolDCs) have reached patients with autoimmune and inflammatory disease, at least in clinical trials. The safety of tolDCs as intervention therapy has been established, but the capacity to modulate autoimmune response in vivo remains to be demonstrated. Studies have revealed a diversity of regulatory mechanisms that tolDCs may employ in vivo. These mechanisms differ between various types of modulated tolDC. The most often foreseen action of tolDCs is through regulatory polarization of naïve T cells or activation of existing regulatory T cells, which should ultimately diminish autoimmune inflammation. Yet, selection of a target autoantigen remains critical to expedite tissue specific tolerance induction, while measuring immune modulation incited by tolDCs in vivo provides a great challenge. We will discuss the regulatory action of different types of tolDCs and the possible methods to monitor immunological efficacy endpoints for the next generation clinical trials.

Update on Dendritic Cell-Induced Immunological and Clinical Tolerance

Dendritic cells (DCs) as highly efficient antigen-presenting cells are at the interface of innate and adaptive immunity. As such, they are key mediators of immunity and antigen-specific immune tolerance. Due to their functional specialization, research efforts have focused on the characterization of DCs subsets involved in the initiation of immunogenic responses and in the maintenance of tissue homeostasis. Tolerogenic DCs (tolDCs)-based therapies have been designed as promising strategies to prevent and control autoimmune diseases as well as allograft rejection after solid organ transplantation (SOT). Despite successful experimental studies and ongoing phase I/II clinical trials using autologous tolDCs in patients with type 1 diabetes, rheumatoid arthritis, multiple sclerosis, and in SOT recipients, additional basic research will be required to determine the optimal DC subset(s) and conditioning regimens for tolDCs-based treatments in vivo. In this review, we discuss the characteristics of human DCs and recent advances in their classification, as well as the role of DCs in immune regulation and their susceptibility to in vitro or in vivo manipulation for the development of tolerogenic therapies, with a focus on the potential of tolDCs for the treatment of autoimmune diseases and the prevention of allograft rejection after SOT.

Tolerogenic Dendritic Cells from Poorly Compensated Type 1 Diabetes Patients Have Decreased Ability To Induce Stable Antigen-Specific T Cell Hyporesponsiveness and Generation of Suppressive Regulatory T Cells

Tolerogenic dendritic cells (tolDCs) may offer an interesting intervention strategy to re-establish Ag-specific tolerance in autoimmune diseases, including type 1 diabetes (T1D). T1D results from selective destruction of insulin-producing β cells leading to hyperglycemia that, in turn, specifically affects a patient's immune system. In this study, we prepared monocyte-derived tolDCs modulated by dexamethasone and vitamin D₂ from 31 T1D patients with optimal glycemic control and 60 T1D patients with suboptimal glycemic control and assessed their tolerogenic properties in correlation with metabolic state of patients. tolDCs differentiated from both groups of patients acquired a regulatory phenotype and an anti-inflammatory profile. Interestingly, tolDCs from well-controlled patients expressed higher levels of inhibitory molecules IL-T3 and PD-L1. Additionally, glutamic acid decarboxylase (GAD)65-loaded tolDCs from well-controlled patients decreased significantly primary Th1/Th17 responses, induced stable GAD65-specific T cell hyporesponsiveness, and suppressed markedly control DC-induced GAD65-specific T cell activation compared with poorly controlled patients. The ability of tolDCs from poorly controlled patients to induce durable GAD65-specific T cell hyporesponsiveness was reversed once the control of glycemia improved. In both groups of patients, tolDCs were able to induce regulatory T cells from autologous naive CD4⁺ T cells. However, regulatory T cells from well-controlled patients had better suppressive abilities. The functionality of tolDCs was confirmed in the adoptive transfer model of NOD-SCID mice where tolDCs delayed diabetes onset. These results suggest that metabolic control of T1D affects the functional characteristics of tolDCs and subsequent effector T cell responses. Metabolic control may be relevant for refining inclusion criteria of clinical trials in the settings of T1D.

Immunomodulatory Effects of 1,25-Dihydroxyvitamin D3 on Dendritic Cells Promote Induction of T Cell Hyporesponsiveness to Myelin-Derived Antigens

While emerging evidence indicates that dendritic cells (DC) play a central role in the pathogenesis of multiple sclerosis (MS), their modulation with immunoregulatory agents provides prospect as disease-modifying therapy. Our observations reveal that 1,25-dihydroxyvitamin D₃ (1,25(OH)₂D₃) treatment of monocyte-derived DC results in a semimature phenotype and anti-inflammatory cytokine profile as compared to conventional DC, in both healthy controls and MS patients. Importantly, 1,25(OH)₂D₃-treated DC induce T cell hyporesponsiveness, as demonstrated in an allogeneic mixed leukocyte reaction. Next, following a freeze-thaw cycle, 1,25(OH)₂D₃-treated immature DC could be recovered with a 78% yield and 75% viability. Cryopreservation did not affect the expression of membrane markers by 1,25(OH)₂D₃-treated DC nor their capacity to induce T cell hyporesponsiveness. In addition, the T cell hyporesponsiveness induced by 1,25(OH)₂D₃-treated DC is antigen-specific and robust since T cells retain their capacity to respond to an unrelated antigen and do not reactivate upon rechallenge with fully mature conventional DC, respectively. These observations underline the clinical potential of tolerogenic DC (tolDC) to correct the immunological imbalance in MS. Furthermore, the feasibility to cryopreserve highly potent tolDC will, ultimately, contribute to the large-scale production and the widely applicable use of tolDC.

Insulin B chain 9-23 gene transfer to hepatocytes protects from type 1 diabetes by inducing Ag-specific FoxP3+ Tregs

Antigen (Ag)-specific tolerance in type 1 diabetes (T1D) in human has not been achieved yet. Targeting lentiviral vector (LV)-mediated gene expression to hepatocytes induces active tolerance toward the encoded Ag. The insulin B chain 9-23 (InsB9-23) is an immunodominant T cell epitope in nonobese diabetic (NOD) mice. To determine whether auto-Ag gene transfer to hepatocytes induces tolerance and control of T1D, NOD mice were treated with integrase-competent LVs (ICLVs) that selectively target the expression of InsB9-23 to hepatocytes. ICLV treatment induced InsB9-23-specific effector T cells but also FoxP3(+) regulatory T cells (Tregs), which halted islet immune cell infiltration, and protected from T1D. Moreover, ICLV treatment combined with a single suboptimal dose of anti-CD3 monoclonal antibody (mAb) is effective in T1D reversal. Splenocytes from LV.InsB9-23-treated mice, but not from LV.OVA (ovalbumin)-treated control mice, stopped diabetes development, demonstrating that protection is Ag-specific. Depletion of CD4(+)CD25(+)FoxP3(+) T cells led to diabetes progression, indicating that Ag-specific FoxP3(+) Tregs mediate protection. Integrase-defective LVs (IDLVs).InsB9-23, which alleviate the concerns for insertional mutagenesis and support transient transgene expression in hepatocytes, were also efficient in protecting from T1D. These data demonstrate that hepatocyte-targeted auto-Ag gene expression prevents and resolves T1D and that stable integration of the transgene is not required for this protection. Gene transfer to hepatocytes can be used to induce Ag-specific tolerance in autoimmune diseases.

Generation of Tolerogenic Dendritic Cells and Their Therapeutic Applications

Dendritic cells (DCs) are professional antigen-presenting cells (APCs) that bridge innate and adaptive immune responses, thereby leading to immune activation. DCs have been known to recognize pathogen-associated molecular patterns such as lipopolysaccharides (LPS) and nucleic acids via their pattern recognition receptors, which trigger signaling of their maturation and effector functions. Furthermore, DCs take up and process antigens as a form of peptide loaded on the major histocompatibility complex (MHC) and present them to T cells, which are responsible for the adaptive immune response. Conversely, DCs can also play a role in inducing immune suppression under specific circumstances. From this perspective, the role of DCs is related to tolerance rather than immunity. Immunologists refer to these special DCs as tolerogenic DCs (tolDCs). However, the definition of tolDCs is controversial, and there is limited information on their development and characteristics. In this review, we discuss the current concept of tolDCs, cutting-edge methods for generating tolDCs in vitro, and future applications of tolDCs, including clinical use.

Delivery of siRNAs to Dendritic Cells Using DEC205-Targeted Lipid Nanoparticles to Inhibit Immune Responses

Due to their ability to knock down the expression of any gene, siRNAs have been heralded as ideal candidates for treating a wide variety of diseases, including those involving "undruggable" targets. However, the therapeutic potential of siRNAs remains severely limited by a lack of effective delivery vehicles. Recently, lipid nanoparticles (LNPs) containing ionizable cationic lipids have been developed for hepatic siRNA delivery. However, their suitability for delivery to other cell types has not been determined. We have modified LNPs for preferential targeting to dendritic cells (DCs), central regulators of immune responses. To achieve directed delivery, we coated LNPs with a single-chain antibody (scFv; DEC-LNPs), specific to murine DEC205, which is highly expressed on distinct DC subsets. Here we show that injection of siRNAs encapsulated in DEC-LNPs are preferentially delivered to DEC205(+) DCs. Gene knockdown following uptake of DEC-LNPs containing siRNAs specific for the costimulatory molecules CD40, CD80, and CD86 dramatically decreases gene expression levels. We demonstrate the functionality of this knockdown with a mixed lymphocyte response (MLR). Overall, we report that injection of LNPs modified to restrict their uptake to a distinct cell population can confer profound gene knockdown, sufficient to inhibit powerful immune responses like the MLR.

Cell mediators of autoimmune hepatitis and their therapeutic implications

Autoimmune hepatitis is associated with interactive cell populations of the innate and adaptive immune systems, and these populations are amenable to therapeutic manipulation. The goals of this review are to describe the key cell populations implicated in autoimmune hepatitis and to identify investigational opportunities to develop cell-directed therapies for this disease. Studies cited in PubMed from 1972 to 2014 for autoimmune hepatitis, innate and adaptive immune systems, and therapeutic interventions were examined. Dendritic cells can promote immune tolerance to self-antigens, present neo-antigens that enhance the immune response, and expand the regulatory T cell population. Natural killer cells can secrete pro-inflammatory and anti-inflammatory cytokines and modulate the activity of dendritic cells and antigen-specific T lymphocytes. T helper 2 lymphocytes can inhibit the cytotoxic activities of T helper 1 lymphocytes and limit the expansion of T helper 17 lymphocytes. T helper 17 lymphocytes can promote inflammatory activity, and they can also up-regulate genes that protect against oxidative stress and hepatocyte apoptosis. Natural killer T cells can expand the regulatory T cell population; gamma delta lymphocytes can secrete interleukin-10, stimulate hepatic regeneration, and induce the apoptosis of hepatic stellate cells; and antigen-specific regulatory T cells can dampen immune cell proliferation and function. Pharmacological agents, neutralizing antibodies, and especially the adoptive transfer of antigen-specific regulatory T cells that have been freshly generated ex vivo are evolving as management strategies. The cells within the innate and adaptive immune systems are key contributors to the occurrence of autoimmune hepatitis, and they are attractive therapeutic targets.

Micro and nanoparticle drug delivery systems for preventing allotransplant rejection

Despite decades of advances in transplant immunology, tissue damage caused by acute allograft rejection remains the primary cause of morbidity and mortality in the transplant recipient. Moreover, the long-term sequelae of lifelong immunosuppression leaves patients at risk for developing a host of other deleterious conditions. Controlled drug delivery using micro- and nanoparticles (MNPs) is an effective way to deliver higher local doses of a given drug to specific tissues and cells while mitigating systemic effects. Herein, we review several descriptions of MNP immunotherapies aimed at prolonging allograft survival. We also discuss developments in the field of biomimetic drug delivery that use MNP constructs to induce and recruit our bodies' own suppressive immune cells. Finally, we comment on the regulatory pathway associated with these drug delivery systems. Collectively, it is our hope the studies described in this review will help to usher in a new era of immunotherapy in organ transplantation.

Generation of antigen-specific Foxp3+ regulatory T-cells in vivo following administration of diabetes-reversing tolerogenic microspheres does not require provision of antigen in the formulation

We have developed novel antisense oligonucleotide-formulated microspheres that can reverse hyperglycemia in newly-onset diabetic mice. Dendritic cells taking up the microspheres adopt a restrained co-stimulation ability and migrate to the pancreatic lymph nodes when injected into an abdominal region that is drained by those lymph nodes. Furthermore, we demonstrate that the absolute numbers of antigen-specific Foxp3+ T regulatory cells are increased only in the lymph nodes draining the site of administration and that these T-cells proliferate independently of antigen supply in the microspheres. Taken together, our data add to the emerging model where antigen supply may not be a requirement in "vaccines" for autoimmune disease, but the site of administration - subserved by lymph nodes draining the target organ - is in fact critical to foster the generation of antigen-specific regulatory cells. The implications of these observations on "vaccine" design for autoimmunity are discussed and summarized.

Nanoparticle-based autoimmune disease therapy

The goal of immunotherapy against autoimmunity is to block pathogenic inflammation without impairing immunity against infections and tumours. Regulatory T-cells (Tregs) play a central role in maintaining immune homeostasis, and autoimmune inflammation is frequently associated with decreased numbers and/or function of these T-cells. Therapies harnessing Tregs to treat autoimmune inflammation remain under-developed with caveats ranging from the lack of antigenic and disease specificity to the potential phenotypic and functional instability of in vitro-expanded Treg cells in vivo. Here, we review nanotechnology-based approaches designed to promote immune tolerance through various mechanisms, ranging from systemic or local suppression of antigen-presenting cells and deletion of antigen-specific T-cells, to the systemic expansion of antigen- and disease-specific Treg cells in vivo.

Suppression of Th1-mediated autoimmunity by embryonic stem cell-derived dendritic cells

We herein demonstrate the immune-regulatory effect of embryonic stem cell-derived dendritic cells (ES-DCs) using two models of autoimmune disease, namely non-obese diabetic (NOD) mice and experimental autoimmune encephalomyelitis (EAE). Treatment of pre-diabetic NOD mice with ES-DCs exerted almost complete suppression of diabetes development during the observation period for more than 40 weeks. The prevention of diabetes by ES-DCs was accompanied with significant reduction of insulitis and decreased number of Th1 and Th17 cells in the spleen. Development of EAE was also inhibited by the treatment with ES-DCs, and the therapeutic effect was obtained even if ES-DCs were administrated after the onset of clinical symptoms. Treatment of EAE-induced mice with ES-DCs reduced the infiltration of inflammatory cells into the spinal cord and suppressed the T cell response to the myelin antigen. Importantly, the ES-DC treatment did not affect T cell response to an exogenous antigen. As the mechanisms underlying the reduction of the number of infiltrating Th1 cells, we observed the inhibition of differentiation and proliferation of Th1 cells by ES-DCs. Furthermore, the expression of VLA-4α on Th1 cells was significantly inhibited by ES-DCs. Considering the recent advances in human induced pluripotent stem cell-related technologies, these results suggest a clinical application for pluripotent stem cell-derived dendritic cells as a therapy for T cell-mediated autoimmune diseases.

Targeting dendritic cell function during systemic autoimmunity to restore tolerance

Systemic autoimmune diseases can damage nearly every tissue or cell type of the body. Although a great deal of progress has been made in understanding the pathogenesis of autoimmune diseases, current therapies have not been improved, remain unspecific and are associated with significant side effects. Because dendritic cells (DCs) play a major role in promoting immune tolerance against self-antigens (self-Ags), current efforts are focusing at generating new therapies based on the transfer of tolerogenic DCs (tolDCs) during autoimmunity. However, the feasibility of this approach during systemic autoimmunity has yet to be evaluated. TolDCs may ameliorate autoimmunity mainly by restoring T cell tolerance and, thus, indirectly modulating autoantibody development. In vitro induction of tolDCs loaded with immunodominant self-Ags and subsequent cell transfer to patients would be a specific new therapy that will avoid systemic immunosuppression. Herein, we review recent approaches evaluating the potential of tolDCs for the treatment of systemic autoimmune disorders.

Tolerogenic dendritic cells induce antigen-specific hyporesponsiveness in insulin- and glutamic acid decarboxylase 65-autoreactive T lymphocytes from type 1 diabetic patients

Tolerogenic dendritic cells (tDC) constitute a promising therapy for autoimmune diseases, since they can anergize T lymphocytes recognizing self-antigens. Patients with type 1 diabetes mellitus (T1D) have autoreactive T cells against pancreatic islet antigens (insulin, glutamic acid decarboxylase 65 -GAD65-). We aimed to determine the ability of tDC derived from T1D patients to inactivate their insulin- and GAD65-reactive T cells. CD14+ monocytes and CD4+CD45RA- effector/memory lymphocytes were isolated from 25 patients. Monocyte-derived DC were generated in the absence (control, cDC) or presence of IL-10 and TGF-β1 (tDC), and loaded with insulin or GAD65. DC were cultured with T lymphocytes (primary culture), and cell proliferation and cytokine secretion were determined. These lymphocytes were rechallenged with insulin-, GAD65- or candidin-pulsed cDC (secondary culture) to assess whether tDC rendered T cells hyporesponsive to further stimulation. In the primary cultures, tDC induced significant lower lymphocyte proliferation and IL-2 and IFN-γ secretion than cDC; in contrast, tDC induced higher IL-10 production. Lymphocytes from 60% of patients proliferated specifically against insulin or GAD65 (group 1), whereas 40% did not (group 2). Most patients from group 1 had controlled glycemia. The secondary cultures showed tolerance induction to insulin or GAD65 in 14 and 10 patients, respectively. A high percentage of these patients (70-80%) belonged to group 1. Importantly, tDC induced antigen-specific T-cell hyporesponsiveness, since the responses against unrelated antigens were unaffected. These results suggest that tDC therapy against multiple antigens might be useful in a subset of T1D patients.

The role of dendritic cells in tissue-specific autoimmunity

In this review, we explore the role of dendritic cell subsets in the development of tissue-specific autoimmune diseases. From the increasing list of dendritic cell subclasses, it is becoming clear that we are only at the beginning of understanding the role of these antigen presenting cells in mediating autoimmunity. Emerging research areas for the study of dendritic cell involvement in the onset and inhibition of tissue-specific autoimmunity are presented. Further, we compare tissue specific to systemic autoimmunity to demonstrate how development of dendritic cell-based therapies may be broadly applicable to both classes of autoimmunity. Continued development of these research areas will lead us closer to clinical assessment of novel immunosuppressive therapy for the reversal and prevention of tissue-specific autoimmunity. Through description of dendritic cell functions in the modulation of tissue-specific autoimmunity, we hope to stimulate a greater appreciation and understanding of the role dendritic cells play in the development and treatment of autoimmunity.

1,25-Dihydroxyvitamin D3 promotes tolerogenic dendritic cells with functional migratory properties in NOD mice

The biologically active form of vitamin D, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], is able to promote the generation of tolerogenic mature dendritic cells (mDCs) with an impaired ability to activate autoreactive T cells. These cells could represent a reliable tool for the promotion or restoration of Ag-specific tolerance through vaccination strategies, for example in type 1 diabetes patients. However, successful transfer of 1,25(OH)2D3-treated mDCs (1,25D3-mDCs) depends on the capacity of 1,25(OH)2D3 to imprint a similar tolerogenic profile in cells derived from diabetes-prone donors as from diabetes-resistant donors. In this study, we examined the impact of 1,25(OH)2D3 on the function and phenotype of mDCs originating from healthy (C57BL/6) and diabetes-prone (NOD) mice. We show that 1,25(OH)2D3 is able to imprint a phenotypic tolerogenic profile on DCs derived from both mouse strains. Both NOD- and C57BL/6-derived 1,25D3-mDCs decreased the proliferation and activation of autoreactive T cells in vitro, despite strain differences in the regulation of cytokine/chemokine expression. In addition, 1,25D3-mDCs from diabetes-prone mice expanded CD25(+)Foxp3(+) regulatory T cells and induced intracellular IL-10 production by T cells in vitro. Furthermore, 1,25D3-mDCs exhibited an intact functional migratory capacity in vivo that favors homing to the liver and pancreas of adult NOD mice. More importantly, when cotransferred with activated CD4(+) T cells into NOD.SCID recipients, 1,25D3-mDCs potently dampened the proliferation of autoreactive donor T cells in the pancreatic draining lymph nodes. Altogether, these results argue for the potential of 1,25D3-mDCs to restore Ag-specific immune tolerance and arrest autoimmune disease progression in vivo.

Characterization of Bone Marrow-Derived Dendritic Cells Developed in Serum-Free Media and their Ability to Prevent Type 1 Diabetes in Nonobese Diabetic Mice

Dendritic cells (DC) have been investigated as a cell-based therapy for Type 1 Diabetes (T1D). BM-DC expanded ex vivo with GM-CSF and IL-4 is typically cultured with fetal bovine serum (FBS). The effect of FBS on NOD BM-DC has not been extensively studied. In the present study we compare BM-DC generated in serum-free culture media (X-VIVO20; FBS−) with BM-DC generated in media containing 10% FBS (RPMI1640/10%FBS; FBS+). We show that FBS− BM-DC display a phenotype and cytokine-producing profile distinct from FBS+ BMDC. Additionally, compared to FBS+ BM-DC, we show evidence of an altered T_h cell response induced by FBS− BM-DC. Finally, we demonstrate that only FBS− BM-DC prevent the onset of T1D and induce increased levels of CD4⁺Foxp3⁺ regulatory T cells as well as a long-lasting β cell-specific T cell response. This study indicates that serum-free media generates a more tolerogenic BM-DC capable of preventing T1D in the NOD mice.