More stringent conditions of plasmid DNA vaccination are required to protect grafted versus endogenous islets in nonobese diabetic mice

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.

Inducing immune tolerance: a focus on Type 1 diabetes mellitus

Tolerogenic strategies that specifically target diabetogenic immune cells in the absence of complications of immunosuppression are the desired treatment for the prevention or even reversal of Type 1 diabetes (T1D). Antigen (Ag)-based therapies must not only suppress disease-initiating diabetogenic T cells that are already activated, but, more importantly, prevent activation of naive auto-Ag-specific T cells that may become autoreactive through epitope spreading as a result of Ag liberation from damaged islet cells. Therefore, identification of auto-Ags relevant to T1D initiation and progression is critical to the design of effective Ag-specific therapies. Animal models of T1D have been successfully employed to identify potential diabetogenic Ags, and have further facilitated translation of Ag-specific tolerance strategies into human clinical trials. In this review, we highlight important advances using animal models in Ag-specific T1D immunotherapies, and the application of the preclinical findings to human subjects. We provide an up-to-date overview of the strengths and weaknesses of various tolerance-inducing strategies, including infusion of soluble Ags/peptides by various routes of delivery, genetic vaccinations, cell- and inert particle-based tolerogenic approaches, and various other strategies that target distinct tolerance-inducing pathways.

Reversal of autoimmune diabetes by restoration of antigen-specific tolerance using genetically modified Lactococcus lactis in mice

Current interventions for arresting autoimmune diabetes have yet to strike the balance between sufficient efficacy, minimal side effects, and lack of generalized immunosuppression. Introduction of antigen via the gut represents an appealing method for induction of antigen-specific tolerance. Here, we developed a strategy for tolerance restoration using mucosal delivery in mice of biologically contained Lactococcus lactis genetically modified to secrete the whole proinsulin autoantigen along with the immunomodulatory cytokine IL-10. We show that combination therapy with low-dose systemic anti-CD3 stably reverted diabetes in NOD mice and increased frequencies of local Tregs, which not only accumulated in the pancreatic islets, but also suppressed immune response in an autoantigen-specific way. Cured mice remained responsive to disease-unrelated antigens, which argues against excessive immunosuppression. Application of this therapeutic tool achieved gut mucosal delivery of a diabetes-relevant autoantigen and a biologically active immunomodulatory cytokine, IL-10, and, when combined with a low dose of systemic anti-CD3, was well tolerated and induced autoantigen-specific long-term tolerance, allowing reversal of established autoimmune diabetes. Therefore, we believe this method could be an effective treatment strategy for type 1 diabetes in humans.

Targeting of a T cell agonist peptide to lysosomes by DNA vaccination induces tolerance in the nonobese diabetic mouse

CD4 T cells are crucial effectors in the pathology of type 1 diabetes (T1D). Successful therapeutic interventions for prevention and cure of T1D in humans are still elusive. Recent research efforts have focused on the manipulation of T cells by treatment with DNA. In this paper, we studied the effects of a DNA treatment strategy designed to target antigenic peptides to the lysosomal compartment on a monospecific T cell population termed 2.5mi(+) T cells that shares reactivity with the diabetogenic T cell clone BDC-2.5 in the NOD mouse. MHC class II tetramer analysis showed that repeated administrations were necessary to expand 2.5mi(+) T cells in vivo. This expansion was independent of Ag presentation by B cells. A single peptide epitope was sufficient to induce protection against T1D, which was not due to Ag-specific T cell anergy. Typical Th2 cytokines such as IL-10 or IL-4 were undetectable in 2.5mi(+) T cells, arguing against a mechanism of immune deviation. Instead, the expanded 2.5mi(+) T cell population produced IFN-γ similar to 2.5mi(+) T cells from naive mice. Protection against T1D by DNA treatment was completely lost in NOD.CD28(-/-) mice which are largely deficient of natural regulatory T cells (Treg). Although Ag-specific Foxp3(+) Treg did not expand in response to DNA treatment, diabetes onset was delayed in Treg-reconstituted and DNA-treated NOD.SCID mice. These observations provide evidence for a Treg-mediated protective mechanism that is independent of the expansion or de novo generation of Ag-specific Treg.

Genetic vaccination for re-establishing T-cell tolerance in type 1 diabetes

Type 1 diabetes (T1D) is a T-cell mediated autoimmune disease resulting in the destruction of the insulin-secreting β cells. Currently, there is no established clinical approach to effectively suppress long-term the diabetogenic response. Genetic-based vaccination offers a general strategy to reestablish β-cell specific tolerance within the T-cell compartment. The transfer of genes encoding β-cell autoantigens, anti-inflammatory cytokines and/or immunomodulatory proteins has proven to be effective at preventing and suppressing the diabetogenic response in animal models of T1D. The current review will discuss genetic approaches to prevent and treat T1D with an emphasis on plasmid DNA- and adeno-associated virus-based vaccines.

Suppression of ongoing T cell-mediated autoimmunity by peptide-MHC class II dimer vaccination

Tissue-specific autoimmune diseases such as type 1 diabetes (T1D) are characterized by T cell-driven pathology. Administration of autoantigenic peptides provides a strategy to selectively target the pathogenic T cell response. Indeed, treatment with beta cell peptides effectively prevents T1D in NOD mice. However, the efficacy of peptide immunotherapy generally wanes as beta cell autoimmunity progresses and islet inflammation increases. With the goal of enhancing the efficacy of peptide immunotherapy, soluble (s)IA(g7)-Ig dimers covalently linked to beta cell autoantigen-derived peptides were tested for the capacity to suppress late preclinical T1D. NOD female mice with established beta cell autoimmunity were vaccinated i.v. with a short course of sIA(g7)-Ig dimers tethered to peptides derived from glutamic acid decarboxylase (GAD)65 (sIA(g7)-pGAD65). Treatment with sIA(g7)-pGAD65 dimers and the equivalent of only approximately 7 microg of native peptide effectively blocked the progression of insulitis and the development of diabetes. Furthermore, suppression of T1D was dependent on beta cell-specific IL-10-secreting CD4+ T cells, although the frequency of GAD65-specific FoxP3-expressing CD4+ T cells was also increased in sIA(g7)-pGAD65 dimer vaccinated NOD mice. These results demonstrate that MHC class II-Ig dimer vaccination is a robust approach to suppress ongoing T cell-mediated autoimmunity, and may provide a superior strategy of adjuvant-free peptide-based immunotherapy to induce immunoregulatory T cells.

Genetic-induced variations in the GAD65 T-cell repertoire governs efficacy of anti-CD3/GAD65 combination therapy in new-onset type 1 diabetes

To enhance efficacy of forthcoming type 1 diabetes (T1D) clinical trials, combination therapies (CTs) are envisaged. In this study, we showed that efficacy of a CT, using anti-CD3 antibody and glutamic acid decarboxylase of 65 kd (GAD65)-expressing plasmid, to reverse new-onset T1D was dependent upon the genetic background. Synergism between both treatments was only observed in the RIP-LCMV-GP but not in the nonobese diabetic (NOD) or RIP-LCMV-NOD models. Efficacy was associated with an expansion of bystander suppressor regulatory T cells (Tregs) recognizing the C-terminal region of GAD65 and secreting interleukin-10 (IL-10), transforming growth factor-beta (TGF-beta), and interferon-gamma (IFN-gamma). In addition, we found that frequency and epitope specificity of GAD65-reactive CD4(+) T cells during antigen priming at diabetes onset and Tregs detected after CT correlated. Consequently, NOD mice harbored significantly lower levels of GAD65-reactive CD4(+) T cells than RIP-LCMV-GP before and after treatment. Our results demonstrate that antigen-specific T cells available at treatment may differ between various major histocompatibility complex (MHC) and genetic backgrounds. These cells play a major role in shaping T-cell responses following antigen-specific immune intervention and determine whether a beneficial Tregs response is generated. Our findings hold important implications to understand and predict the success of antigen-based clinical trials, where responsiveness to immunotherapy might vary from patient to patient.

Immunotherapy for the Prevention and Treatment of Type 1 Diabetes

A major effort has been on-going to develop immunotherapies to prevent and/or treat type 1 diabetes (T1D). This autoimmune disease is characterized by the selective loss of the insulin-producing beta cells via the cumulative effects of autoantigen-specific CD4(+) and CD8(+) T cells, autoantibodies, and activated antigen-presenting cells. To be applicable in a clinical setting, immunotherapies must suppress established beta-cell autoimmunity. Preclinical studies and recent clinical findings suggest that antigen-specific and systemic-based strategies can be effective in this regard. However, either approach alone may not be sufficient to block the diabetogenic response and establish long-term protection in the clinic. In this review, we will discuss the importance of both strategies and how a combinatorial approach to treat T1D is appealing.

Parameters influencing antigen-specific immunotherapy for Type 1 diabetes

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease in which the insulin producing beta cells are destroyed. Antigen-based immunotherapy provides an approach to selectively tolerize pathogenic beta cell-specific T cells, while leaving the remainder of the immune system intact. In this article, we discuss our group's experience in defining the parameters that impact the efficacy of beta cell antigen "vaccination" for the prevention and treatment of T1D.

Gene gun-mediated DNA vaccination enhances antigen-specific immunotherapy at a late preclinical stage of type 1 diabetes in nonobese diabetic mice

Type 1 diabetes (T1D) is characterized by the T cell mediated destruction of the insulin-producing beta cells. Antigen-specific immunotherapies are used to selectively tolerize beta cell-specific pathogenic T cells either directly, or indirectly through the induction of immunoregulatory T cells. A key concern of antigen-specific immunotherapy is exacerbating autoimmunity. We compared the T cell reactivity and efficacy induced by plasmid DNA (pDNA) encoding glutamic acid decarboxylase 65 (GAD65) administered via intramuscular versus gene gun vaccination in NOD mice at a late preclinical stage of T1D. Whereas intramuscular injection of pGAD65 promoted a predominant type 1 CD4(+) T cell response and failed to suppress ongoing beta cell autoimmunity, gene gun vaccination preferentially induced IL-4 secreting CD4(+) T cells and significantly delayed the onset of diabetes. These findings demonstrate that gene gun delivery of autoantigen-encoding pDNA preferentially elicits immunoregulatory T cells and offers a safe, effective mode of pDNA vaccination for the treatment of T1D and other autoimmune diseases.

The type and frequency of immunoregulatory CD4+ T-cells govern the efficacy of antigen-specific immunotherapy in nonobese diabetic mice

Antigen-specific immunotherapy, an approach to selectively block autoimmune diabetes, generally declines in nonobese diabetic (NOD) mice as disease progresses. To define the parameters influencing the efficacy of antigen-specific immunotherapy once diabetes is established, plasmid DNA (pDNA) vaccination was used to suppress autoimmune-mediated destruction of syngeneic islet grafts in diabetic NOD recipients. pDNAs encoding a glutamic acid decarboxylase 65 (GAD65)-Ig molecule (pGAD65), interleukin (IL)-4 (pIL4), and IL-10 (pIL10) significantly delayed the onset of recurrent diabetes compared with pGAD65+pIL10-vaccinated recipients. Despite differences in efficacy, a similar frequency of GAD65-specific CD4(+) T-cells secreting IL-4, IL-10, or interferon-gamma were detected in mice treated with pGAD65+pIL4+pIL10 and pGAD65+pIL10. However, the frequency of FoxP3-expressing CD4(+)CD25(+)CD62L(hi) T-cells was increased in the renal and pancreatic lymph nodes of diabetic recipients vaccinated with pGAD65+pIL4+pIL10. These immunoregulatory CD4(+)CD25(+) T-cells (CD4(+)CD25(+) Treg) exhibited enhanced in vivo and in vitro suppressor activity that partially was transforming growth factor-beta dependent. Furthermore, duration of islet graft protection in pGAD65+pIL4+pIL10-vaccinated diabetic recipients correlated with the persistence of CD4(+)CD25(+) Treg. These data demonstrate that the frequency and maintenance of FoxP3-expressing CD4(+)CD25(+) Treg influence antigen-induced suppression of ongoing beta-cell autoimmunity in diabetic recipients.

Plasmid-based gene therapy of diabetes mellitus

Type I diabetes mellitus (T1D) is due to a loss of immune tolerance to islet antigen and thus, there is intense interest in developing therapies that can re-establish it. Tolerance is maintained by complex mechanisms that include inhibitory molecules and several types of regulatory T cells (Tr). A major historical question is whether gene therapy can be employed to generate Tr cells. This review shows that gene transfer of immunoregulatory molecules can prevent T1D and other autoimmune diseases. In our studies, non-viral gene transfer is enhanced by in vivo electroporation (EP). This technique can be used to perform DNA vaccination against islet cell antigens and when combined with appropriate immune ligands results in the generation of Tr cells and protection against T1D. In vivo EP can also be applied for non-immune therapy of diabetes. It can be used to deliver protein drugs such as glucagon-like peptide 1 (GLP-1), leptin or transforming growth factor beta (TGF-beta). These act in T1D or type II diabetes (T2D) by restoring glucose homeostasis, promoting islet cell survival and growth or improving wound healing and other complications. Furthermore, we show that in large animals EP can deliver peptide hormones, such as growth hormone releasing hormone (GHRH). We conclude that the non-viral gene therapy and EP represent a safe and efficacious approach with clinical potential.

Protective Regulatory T Cell Generation in Autoimmune Diabetes by DNA Covaccination with Islet Antigens and a Selective CTLA-4 Ligand

DNA vaccination of autoimmune diabetes-prone NOD mice with unmodified target islet antigens, i.e., preproinsulin (PPIns) or glutamic acid decarboxylase 65 (GAD65), is poorly protective. However, in this study, we demonstrate protection against disease by covaccination with a mutant B7-1 molecule (B7-1wa) that binds the negative T cell regulator CTLA-4 (CD152), but not CD28. Codelivery of plasmids encoding a PPIns-GAD65 fusion construct and B7-1wa protected against both insulitis and diabetes. In vitro, the T cells of covaccinated mice had negative responses to both insulin and GAD65, and this was restored by adding blocking antibodies to transforming growth factor beta1 (TGF-beta1), suggesting a role for this cytokine. Adoptive transfer experiments revealed that DNA vaccination generated protective CD4(+) regulatory T cells (Tr) of either CD25(+) or CD25(-) phenotype. Furthermore, vaccinated mice had increased numbers of T cells with Tr-associated markers, such as CTLA-4, Foxp3, and membrane-bound TGF-beta1. Tr cells inhibited the responses of diabetogenic T cells to islet antigens, and depletion of T cells expressing membrane-bound TGF-beta1 abolished the suppressive effect. Thus, selective engagement of CTLA-4 during islet-antigen DNA vaccination induces Tr cells that protect against this autoimmune disease.

Lessons on autoimmune diabetes from animal models

T1DM (Type I diabetes mellitus) results from selective destruction of the insulin-producing beta-cells of the pancreas by the immune system, and is characterized by hyperglycaemia and vascular complications arising from suboptimal control of blood glucose levels. The discovery of animal models of T1DM in the late 1970s and early 1980s, particularly the NOD (non-obese diabetic) mouse and the BB (BioBreeding) diabetes-prone rat, had a fundamental impact on our ability to understand the genetics, aetiology and pathogenesis of this disease. NOD and BB diabetes-prone rats spontaneously develop a form of diabetes that closely resembles the human counterpart. Early studies of these animals quickly led to the realization that T1DM is caused by autoreactive T-lymphocytes and revealed that the development of T1DM is controlled by numerous polymorphic genetic elements that are scattered throughout the genome. The development of transgenic and gene-targeting technologies during the 1980s allowed the generation of models of T1DM of reduced genetic and pathogenic complexity, and a more detailed understanding of the immunogenetics of T1DM. In this review, we summarize the contribution of studies in animal models of T1DM to our current understanding of four fundamental aspects of T1DM: (i) the nature of genetic elements affording T1DM susceptibility or resistance; (ii) the mechanisms underlying the development and recruitment of pathogenic autoreactive T-cells; (iii) the identity of islet antigens that contribute to the initiation and/or progression of islet inflammation and beta-cell destruction; and (iv) the design of avenues for therapeutic intervention that are rooted in the knowledge gained from studies of animal models. Development of new animal models will ensure continued progress in these four areas.

Antigen-specific induction of regulatory T cells for type 1 diabetes therapy

Since their discovery decades ago, regulatory T (Treg) cells have prompted many investigations into their potential role in the generation or prevention of autoimmune disorders such as type 1 diabetes (T1D). Initially identified based on their ability to maintain tolerance to self-antigens in peripheral organs, Treg cells have since been efficiently induced therapeutically and shown to prevent the progression of T1D as well as other autoimmune diseases. Beneficial modification of immunity through the induction of Treg cells has been successfully achieved by antigen-based therapy as well as non-antigen-specific (systemic) treatments. In the current article, we review different strategies that have proved effective in preventing autoimmune diabetes and analyze them with respect to translation into clinical applications. Current evidence indicates that antigen-specific induction of potent regulatory mechanisms is influenced by the systemic milieu, suggesting that systemic modulation might be an essential prerequisite for antigen-based therapy and the successful maintenance or reestablishment of tolerance.

Regulatory T-cells in type 1 diabetes

Type 1 diabetes is a T-cell-mediated autoimmune disease, resulting in destruction of the insulin-producing beta cells in the pancreas. Disease progression is thought to involve the action of T-cells, particularly those producing Th1-type cytokines. Given the complexity in understanding the precise etiology of autoimmune diseases, the diversity of autoantigens, and the variability that exists between individual patients, it might be very difficult to eliminate autoaggressive T-cell responses without resorting to generalized means of immunosuppression. However, recent evidence shows that autoimmune processes are composed not only of autoaggressive T-cell responses but also of autoreactive regulatory components. Enhancing regulatory T-cell responses, therefore, has become an area of intense focus as a means of treating autoimmune diseases like type 1 diabetes. This review will concentrate on two different types of regulatory T-cells, the naturally occurring ('professional') CD4+CD25+ T-cells and antigen-induced ('adaptive') CD4+ Th2-like regulatory T-cells.