T cell-mediated inhibition of the transfer of autoimmune diabetes in NOD mice

Alterations in Lymphocytic Metabolism-An Emerging Hallmark of MS Pathophysiology?

Multiple sclerosis (MS) is a chronic autoimmune disease of the central nervous system (CNS) characterised by acute inflammation and subsequent neuro-axonal degeneration resulting in progressive neurological impairment. Aberrant immune system activation in the periphery and subsequent lymphocyte migration to the CNS contribute to the pathophysiology. Recent research has identified metabolic dysfunction as an additional feature of MS. It is already well known that energy deficiency in neurons caused by impaired mitochondrial oxidative phosphorylation results in ionic imbalances that trigger degenerative pathways contributing to white and grey matter atrophy. However, metabolic dysfunction in MS appears to be more widespread than the CNS. This review focuses on recent research assessing the metabolism and mitochondrial function in peripheral immune cells of MS patients and lymphocytes isolated from murine models of MS. Emerging evidence suggests that pharmacological modulation of lymphocytic metabolism may regulate their subtype differentiation and rebalance pro- and anti-inflammatory functions. As such, further understanding of MS immunometabolism may aid the identification of novel treatments to specifically target proinflammatory immune responses.

Cross-Talk of the CNS With Immune Cells and Functions in Health and Disease

The immune system's role is much more than merely recognizing self vs. non-self and involves maintaining homeostasis and integrity of the organism starting from early development to ensure proper organ function later in life. Unlike other systems, the central nervous system (CNS) is separated from the peripheral immune machinery that, for decades, has been envisioned almost entirely as detrimental to the nervous system. New research changes this view and shows that blood-borne immune cells (both adaptive and innate) can provide homeostatic support to the CNS via neuroimmune communication. Neurodegeneration is mostly viewed through the lens of the resident brain immune populations with little attention to peripheral circulation. For example, cognition declines with impairment of peripheral adaptive immunity but not with the removal of microglia. Therapeutic failures of agents targeting the neuroinflammation framework (inhibiting immune response), especially in neurodegenerative disorders, call for a reconsideration of immune response contributions. It is crucial to understand cross-talk between the CNS and the immune system in health and disease to decipher neurodestructive and neuroprotective immune mechanisms for more efficient therapeutic strategies.

Control of T Cell Responses, Tolerance and Autoimmunity by Regulatory T Cells: Current Concepts

Regulatory T cells have emerged as an important mechanism of regulating tolerance and T cell responses. CD4+ regulatory T cells can be divided into two main groups, natural regulatory T cells, which express high levels of CD25 on their cell surface and phenotypically diverse adaptive (antigen induced) regulatory T cells. Natural regulatory T cells are made in the thymus, and require strong costimulatory signals for induction and maintenance, express a transcription factor called Foxp3, and function by a largely unknown mechanism. Adaptive (antigen induced) regulatory T cells are made by sub-optimal antigenic signals in the periphery, in the presence of immunosuppressive cytokines, often in special circumstances, such as chronic viral infections or after mucosal administration of antigen, and rely on cytokines such as IL-10 and TGF-β for suppression. Regulatory T cells offer a great potential for the treatment of autoimmune diseases and during transplantation.

Mechanisms of autoimmunity in the non-obese diabetic mouse: effector/regulatory cell equilibrium during peak inflammation

Immune imbalance in autoimmune disorders such as type 1 diabetes may originate from aberrant activities of effector cells or dysfunction of suppressor cells. All possible defective mechanisms have been proposed for diabetes-prone species: (i) quantitative dominance of diabetogenic cells and decreased numbers of regulatory T cells, (ii) excessive aggression of effectors and defective function of suppressors, (iii) perturbed interaction between effector and suppressor cells, and (iv) variations in sensitivity to negative regulation. The experimental evidence available to date presents conflicting information on these mechanisms, with identification of perturbed equilibrium on the one hand and negation of critical role of each mechanism in propagation of diabetic autoimmunity on the other hand. In our analysis, there is no evidence that inherent abnormalities in numbers and function of effector and suppressor T cells are responsible for the immune imbalance responsible for propagation of type 1 diabetes as a chronic inflammatory process. Possibly, the experimental tools for investigation of these features of immune activity are still underdeveloped and lack sufficient resolution, in the presence of the extensive biological viability and functional versatility of effector and suppressor elements.

Alteration of regulatory T cells in type 1 diabetes mellitus: a comprehensive review

Type 1 diabetes mellitus (T1DM) is a T cell-mediated autoimmune disease characterized by the destruction of pancreatic β cells. Numerous studies have demonstrated the key role of CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs) in the development of T1DM. However, the changes in Treg expression and function as well as the regulation of these activities are not clearly elucidated. Most studies on the role of Tregs in T1DM were performed on peripheral blood rather than pancreas or pancreatic lymph nodes. Tissue-based studies are more difficult to perform, and there is a lack of histological data to support the role of Tregs in T1DM. In spite of this, strategies to increase Treg cell number and/or function have been viewed as potential therapeutic approaches in treating T1DM, and several clinical trials using these strategies have already emerged. Notably, many trials fail to demonstrate clinical response even when Treg treatment successfully boosts Tregs. In view of this, whether a failure of Tregs does exist and contribute to the development of T1DM and whether more Tregs would be clinically beneficial to patients should be carefully taken into consideration before applying Tregs as treatments in T1DM.

Stable activity of diabetogenic cells with age in NOD mice: dynamics of reconstitution and adoptive diabetes transfer in immunocompromised mice

The non-obese diabetic (NOD) mouse is a prevalent disease model of type 1 diabetes. Immune aberrations that cause and propagate autoimmune insulitis in these mice are being continually debated, with evidence supporting both dominance of effector cells and insufficiency of suppressor mechanisms. In this study we assessed the behaviour of NOD lymphocytes under extreme expansion conditions using adoptive transfer into immunocompromised NOD.SCID (severe combined immunodeficiency) mice. CD4(+)  CD25(+) T cells do not cause islet inflammation, whereas splenocytes and CD4(+)  CD25(-) T cells induce pancreatic inflammation and hyperglycaemia in 80-100% of the NOD.SCID recipients. Adoptively transferred effector T cells migrate to the lymphoid organs and pancreas, proliferate, are activated in the target organ in situ and initiate inflammatory insulitis. Reconstitution of all components of the CD4(+) subset emphasizes the plastic capacity of different cell types to adopt effector and suppressor phenotypes. Furthermore, similar immune profiles of diabetic and euglycaemic NOD.SCID recipients demonstrate dissociation between fractional expression of CD25 and FoxP3 and the severity of insulitis. There were no evident and consistent differences in diabetogenic activity and immune reconstituting activity of T cells from pre-diabetic (11 weeks) and new onset diabetic NOD females. Similarities in immune phenotypes and variable distribution of effector and suppressor subsets in various stages of inflammation commend caution in interpretation of quantitative and qualitative aberrations as markers of disease severity in adoptive transfer experiments.

T-lymphocyte recognition of beta cells in type 1 diabetes: clinical perspectives

Type 1 diabetes (T1D) is an autoimmune disease characterized by the activation of lymphocytes against pancreatic β cells. Landmarks in the history of T1D were the description of insulitis and of islet cell autoantibodies, and report an association between T1D and a limited number of HLA alleles. Another step was the study of T-lymphocytes, now known to be central to the disease process of T1D whether in mice or men. In humans, T-lymphocytes, and especially CD8⁺ T-cells, are predominant in insulitis. The characterization of antigenic fragments--peptides--recognized by T-cells paves the way towards new assays for predicting T1D and its prevention using antigen- or peptide-specific immunotherapy, while avoiding side effects that may counteract the limited efficacy of immunosuppression and immunomodulation in preserving β-cells from autoimmune destruction in recent-onset T1D patients. The current need for new preclinical models for testing strategies of antigen-specific immune tolerance is also highlighted.

The preventive role of type 2 NKT cells in the development of type 1 diabetes

In the last two decades, natural killer T (NKT) cells have emerged as an important factor in preventing type 1 diabetes (T1D) when investigated in the experimental non-obese diabetic (NOD) mouse model. So far, investigations have largely focused on type 1 NKT cells with invariant T-cell receptors, whereas the role of type 2 NKT cells with diverse T-cell receptors is less well understood. However, there have been several findings which indicate that in fact type 2 NKT cells may regulate the progression of type 1 diabetes in NOD mice, including a fraction of these cells which recognize β-cell-enriched sulfatide. Therefore, the focus for this review is to present the current evidence of the effect of type 2 NKT cells on the development of T1D. In general, there is still uncertainty surrounding the mechanism of activation and function of NKT cells. Here, we present two models of the effector mechanisms, respectively, Th1/Th2 polarization and the induction of tolerogenic dendritic cells (DC). In conclusion, this review points to the importance of immunoregulation by type 2 NKT cells in preventing the development of T1D and highlights the induction of tolerogenic DC as a likely mechanism. The possible therapeutic role of type 1 and type 2 NKT cells are evaluated and future experiments concerning type 2 NKT cells and T1D are proposed.

Pancreatic islet autoimmunity

Type 1 diabetes (T1D) represents 10 to 15% of all forms of diabetes. Its incidence shows a consistent rise in all countries under survey. Evidence for autoimmunity in human T1D relies on the detection of insulitis, of islet cell antibodies, of activated β-cell-specific T lymphocytes and on the association of T1D with a restricted set of class II major histocompatibility complex (MHC) alleles. However, mechanisms that initiate the failure of immune tolerance to β-cell autoantigens remain elusive in common forms of T1D. T1D commonly develop as a multifactorial disease in which environmental factors concur with a highly multigenic background. The disease is driven by the activation of T-lymphocytes against pancreatic β-cells. Several years elapse between initial triggering of the autoimmune response to β cells, as evidenced by the appearance or islet cell autoantibodies, and the onset of clinical diabetes, defining a prediabetes stage. Active mechanisms hold back autoreactive effector T-cells in prediabetes, in particular a subset of CD4+ T-cells (T(reg)) and other regulatory T-cells, such as invariant NKT cells. There is evidence in experimental models that systemic or local infections can trigger autoimmune reactions to β-cells. However, epidemiological observations that have accumulated over years have failed to identify undisputable environmental factors that trigger T1D. Moreover, multiple environmental factors may intervene in the disease evolution and protective as weel as triggering environmental factors may be involved. Available models also indicate that local signals within the islets are required for full-blown diabetes to develop. Many autoantigens that are expressed by β-cells but also by the other endocrine islet cells and by neurons are recognized by lymphocytes along the development of T1D. The immune image of β-cells is that of native components of the β-cell membrane, as seen by B-lymphocytes, and of fragments of intracellular β-cell proteins in the form of peptides loaded onto class I MHC molecules on the β-cell surface and class I and class II molecules onto professional antigen presenting cells. Given the key role of T lymphocytes in T1D, the cartography of autoantigen-derived peptides that are presented to class I-restricted CD8(+) T-cells and class II-restricted CD4(+) T-cells is of outmost importance and is a necessary step in the development of diagnostic T-cell assays and of immunotherapy of T1D.

Regulatory T cells essential to prevent the loss of self-tolerance in murine models of erythrocyte-specific autoantibody responses

The spontaneous appearance of anti-erythrocyte autoantibodies resulting in autoimmune hemolytic anemia described in NZB mice more than 40 years ago provided a model for the study of mechanisms behind the loss of self-tolerance. We developed an in vitro model of this anti-MRBC response in which CD8(+) suppressor T cells were shown to be a controlling element. CD8(+) T cells from young NZB mice co-cultured with spleen cells from old, actively autoimmune NZB mice suppressed the anti-MRBC responses of the old mice. Eliminating the CD8(+) cells from young NZB spleen cells or even from non-autoimmune BALB/c spleen cells prior to culture removed the controlling influence of these CD8(+) cells and allowed the development of anti-MRBC-secreting cells. This review will consider the role of the CD8(+) suppressive cells in the anti-self-erythrocyte model in light of insights provided by current 'regulatory T cell' literature.

T cell recognition of autoantigens in human type 1 diabetes: clinical perspectives

Type 1 diabetes (T1D) is an autoimmune disease driven by the activation of lymphocytes against pancreatic β-cells. Among β-cell autoantigens, preproinsulin has been ascribed a key role in the T1D process. The successive steps that control the activation of autoreactive lymphocytes have been extensively studied in animal models of T1D, but remains ill defined in man. In man, T lymphocytes, especially CD8⁺ T cells, are predominant within insulitis. Developing T-cell assays in diabetes autoimmunity is, thus, a major challenge. It is expected to help defining autoantigens and epitopes that drive the disease process, to pinpoint key functional features of epitope-specific T lymphocytes along the natural history of diabetes and to pave the way towards therapeutic strategies to induce immune tolerance to β-cells. New T-cell technologies will allow defining autoreactive T-cell differentiation programs and characterizing autoimmune responses in comparison with physiologically appropriate immune responses. This may prove instrumental in the discovery of immune correlates of efficacy in clinical trials.

Platelet-rich plasma may prevent titanium-mesh exposure in alveolar ridge augmentation with anorganic bovine bone

OBJECTIVE

Bone augmentation with the titanium-mesh (Ti-mesh) technique is susceptible to a large rate of complications such as morbidity of bone graft donor site, and mesh exposure to the oral cavity. The purpose of this study was to evaluate the effectiveness of anorganic bovine bone (ABB) in alveolar bone augmentation with the Ti-mesh technique. In addition, we investigated the effect of platelet-rich plasma (PRP) in preventing mesh exposure by using it to cover the Ti-mesh.

PATIENTS AND METHODS

Patients included in the clinical trial were randomly allocated by a blinded assistant into two groups. The 30 patients recruited for this study underwent 43 alveolar bone augmentation with the Ti-mesh technique using ABB as graft material in all of them. In 15 patients, the Ti-meshes were covered with PRP (PRP group) whereas in the other 15 the Ti-meshes were not (control group). After 6 months, patients were called for clinical, radiographic, and histological evaluation, and implant placement surgery. A total of 97 implants were placed in the augmented bone and their evolution was followed up for a period of 24 months.

RESULTS

Significant differences were found between the two study groups in terms of complications and bone formation. In the control group, 28.5% of the cases suffered from mesh exposure, while in the PRP group, no exposures were registered. Radiographic analysis revealed that bone augmentation was higher in the PRP group than in the control group. Overall, 97.3% of implants placed in the control group and 100% of those placed in the PRP group were successful during the monitoring period. We suggest that the positive effect of PRP on the Ti-mesh technique is due to its capacity to improve soft tissue healing, thereby protecting the mesh and graft material secured beneath the gingival tissues.

CONCLUSIONS

Alveolar bone augmentation using ABB alone in the Ti-mesh technique is sufficient for implant rehabilitation. Besides, covering the Ti-meshes with PRP was a determining factor in avoiding mesh exposure. Ti-mesh exposure provoked significant bone loss, but in most cases it did not affect the subsequent placement of implants.

Prevention, but not cure, of autoimmune diabetes in a NOD.scid transfer model by FTY720 despite effective modulation of blood T cells

FTY720 modulates lymphocyte trafficking through blood (peripheral blood lymphocyte, PBL) and peripheral lymph nodes (PLN). Treatment with FTY720 causes retention of most blood lymphocytes in PLN. Long-term treatment can slow and/or prevent Type 1 diabetes (T1D) in the nonobese diabetic (NOD) mouse model. B and T cells are both affected by FTY720 binding to sphingosine-1-phosphate receptor 1 (S1P₁). However, little has been done to elucidate which T-cell subsets are differentially affected by FTY720 under healthy conditions, and how this affects disease pathogenesis in T1D. In healthy C57BL/6J (B6) mice, total CD4(+) and CD8(+) T-cell subsets were diminished by FTY720, but recently activated and memory subsets were spared and constituted significantly higher percentage of remaining T cells in blood. FTY720 also lowered PBL counts in NOD mice, but less severely than in B6 mice. This is consistent with a different ratio of naïve, activated, and memory cells in NOD mice compared to those in B6 mice, as well as alterations in S1P₁ and sphingosine-1-phosphate (S1P) levels in PBLs and blood of NOD mice, respectively. To address the functional consequences of PBL T-cell depletion, we studied the effects of FTY720 on disease progression in a timed adoptive transfer model of T1D. Continuous treatment with FTY720 eliminated T1D, if treatment was started before splenocyte transfer. FTY20 treatment started after disease onset slowed disease progression. The inability to fully suppress memory and effector T-cell circulation may explain why FTY720 is only partially effective in the NOD adoptive transfer model of T1D.

The PD-1 pathway in tolerance and autoimmunity

Regulatory T cells (Tregs) and the PD-1: PD-ligand (PD-L) pathway are both critical to terminating immune responses. Elimination of either can result in the breakdown of tolerance and the development of autoimmunity. The PD-1: PD-L pathway can thwart self-reactive T cells and protect against autoimmunity in many ways. In this review, we highlight how PD-1 and its ligands defend against potentially pathogenic self-reactive effector T cells by simultaneously harnessing two mechanisms of peripheral tolerance: (i) the promotion of Treg development and function and (ii) the direct inhibition of potentially pathogenic self-reactive T cells that have escaped into the periphery. Treg cells induced by the PD-1 pathway may also assist in maintaining immune homeostasis, keeping the threshold for T-cell activation high enough to safeguard against autoimmunity. PD-L1 expression on non-hematopoietic cells as well as hematopoietic cells endows PD-L1 with the capacity to promote Treg development and enhance Treg function in lymphoid organs and tissues that are targets of autoimmune attack. At sites where transforming growth factor-beta is present (e.g. sites of immune privilege or inflammation), PD-L1 may promote the de novo generation of Tregs. When considering the consequences of uncontrolled immunity, it would be therapeutically advantageous to manipulate Treg development and sustain Treg function. Thus, this review also discusses how the PD-1 pathway regulates a number of autoimmune diseases and the therapeutic potential of PD-1: PD-L modulation.

99th Dahlem conference on infection, inflammation and chronic inflammatory disorders: immune therapies of type 1 diabetes: new opportunities based on the hygiene hypothesis

Insulin-dependent (type 1) diabetes is a prototypic organ-specific autoimmune disease resulting from the selective destruction of insulin-secreting beta cells within pancreatic islets of Langerhans by an immune-mediated inflammation involving autoreactive CD4(+) and CD8(+) T lymphocytes which infiltrate pancreatic islets. Current treatment is substitutive, i.e. chronic use of exogenous insulin which, in spite of significant advances, is still associated with major constraints (multiple daily injections, risks of hypoglycaemia) and lack of effectiveness over the long term in preventing severe degenerative complications. Finding a cure for autoimmune diabetes by establishing effective immune-based therapies is a real medical health challenge, as the disease incidence increases steadily in industrialized countries. As the disease affects mainly children and young adults, any candidate immune therapy must therefore be safe and avoid a sustained depression of immune responses with the attendant problems of recurrent infection and drug toxicity. Thus, inducing or restoring immune tolerance to target autoantigens, controlling the pathogenic response while preserving the host reactivity to exogenous/unrelated antigens, appears to be the ideal approach. Our objective is to review the major progress accomplished over the last 20 years towards that aim. In addition, we would like to present another interesting possibility to access new preventive strategies based on the 'hygiene hypothesis', which proposes a causal link between the increasing incidence of autoimmune diseases, including diabetes, and the decrease of the infectious burden. The underlying rationale is to identify microbial-derived compounds mediating the protective activity of infections which could be developed therapeutically.

Immune therapy for type 1 diabetes mellitus-what is unique about anti-CD3 antibodies?

Type 1 diabetes mellitus (T1DM) is a prototypic organ-specific autoimmune disease that results from selective destruction of insulin-secreting beta-cells by immune-mediated inflammation (insulitis), that is, the infiltration of pancreatic islets by autoreactive CD4(+) and CD8(+) T lymphocytes. Current treatment is substitutive-chronic use of exogenous insulin-which, in spite of considerable advances, is still associated with constraints and lack of effectiveness over the long-term in relation to the prevention of vascular and neurological complications. Finding a cure for T1DM is an important medical health challenge, as the disease's incidence is steadily increasing in industrialized countries and projections of future prevalence are alarming. Crucially, as T1DM mainly affects children and young adults, any candidate immune therapy must be safe and avoid chronic use of immunosuppressants that promote sustained depression of immune responses. The ideal approach would, therefore, involve induction or, in the case of established T1DM, restoration of immune tolerance to target autoantigens. This Review presents, in particular, two strategies that are still in clinical development but hold great promise. These strategies are focused on the use of candidate autoantigens and anti-CD3 monoclonal antibodies.

Processing in the endoplasmic reticulum generates an epitope on the insulin A chain that stimulates diabetogenic CD8 T cell responses

RIP-B7.1 mice express the costimulator molecule B7.1 (CD80) on pancreatic beta cells and are a well-established model for studying de novo induction of diabetogenic CD8 T cells. Immunization of RIP-B7.1 mice with preproinsulin (ppins)-encoding plasmid DNA efficiently induces experimental autoimmune diabetes (EAD). EAD is associated with an influx of CD8 T cells specific for the K(b)/A(12-21) epitope into the pancreatic islets and the subsequent destruction of beta cells. In this study, we used this model to investigate how ppins-derived Ags are expressed and processed to prime diabetogenic, K(b)/A(12-21)-specific CD8 T cells. Targeting the K(b)/A(12-21) epitope, the insulin A chain, or the ppins to the endoplasmic reticulum (ER) (but not to the cytosol and/or nucleus) efficiently elicited K(b)/A(12-21)-specific CD8 T cell responses. The K(b)/A(12-21) epitope represents the COOH terminus of the ppins molecule and, hence, did not require COOH-terminal processing before binding its restriction element in the ER. However, K(b)/A(12-21)-specific CD8 T cells were also induced by COOH-terminally extended ppins-specific polypeptides expressed in the ER, indicating that the epitope position at the COOH terminus is less important for its diabetogenicity than is targeting the Ag to the ER. The K(b)/A(12-21) epitope had a low avidity for K(b) molecules. When epitopes of unrelated Ags were coprimed at the same site of Ag delivery, "strong" K(b)-restricted (but not D(b)-restricted) CD8 T cell responses led to the suppression of K(b)/A(12-21)-specific CD8 T cell priming and reduced EAD. Thus, direct expression and processing of the "weak" K(b)/A(12-21) epitope in the ER favor priming of autoreactive CD8 T cells.

Progress towards the clinical use of CD3 monoclonal antibodies in the treatment of autoimmunity

PURPOSE OF REVIEW

A major problem in the field of clinical transplantation, as well as in autoimmunity, is that conventional treatments rely on chronic immunosuppression that is not specific for the antigens involved and that increases the risk of infections and tumours. A major need and challenge is, therefore, to achieve 'operational tolerance', namely an inhibition of pathogenic responses in the absence of chronic immunosuppression.

RECENT FINDINGS

Here we review data showing that monoclonal antibodies to the CD3 complex, the signal transducing element of the T cell receptor, promote immune tolerance. This strategy has been the matter of extensive experimental studies in models of autoimmunity and has recently led to a successful clinical translation.

SUMMARY

Results from controlled trials in autoimmune insulin-dependent diabetes showed that CD3 monoclonal antibodies afford long-term effects following a short administration. The present challenge is to build on these results, first, to set the use of CD3 monoclonal antibodies as an established therapy in well selected subsets of patients with autoimmunity, and second, given the similarities of immune mechanisms underlying T cell-mediated autoimmune diseases and allograft rejection, to address if and how this therapeutic strategy could be extended to organ transplantation in the not-too-distant future.

Mechanisms Of Complete Freund's Adjuvant Protection Against Diabetes in Bb Rats: Induction Of Non-Specific Suppressor Cells

We have previously reported that a single injection of complete Freund's adjuvant (CFA) can prevent diabetes appearance in diabetes-prone (DP) BB rats. In this study, we investigated further the mechanism of CFA-induced protection from diabetes. We found that adoptive transfer of splenic cells from CFA-treated DP rats into young DP rats protected the latter from diabetes development. This suggested that CFA-induced protection from diabetes resulted from activation of regulatory (suppressor) cells. Cell mixing experiments in vitro indicated that CFA activated splenic cells with antigen-nonspecific suppressor activity (suppression of lymphoproliferative responses to lipopolysaccharide and to allogeneic splenic cells). Fractionation of splenic cells on Percoll revealed that the suppressor activity resided in low density cells relatively depleted of T-cells, B-cells, macrophages and NK cells. These results suggest that non-specific (natural) suppressor cells in CFA-treated BB rats may be responsible for suppressing autoimmune responses and preventing insulitis and diabetes development.

Role of regulatory T-cells in autoimmunity

There has been considerable historical interest in the concept of a specialist T-cell subset which suppresses over-zealous or inappropriate T-cell responses. However, it was not until the discovery that CD4(+)CD25(+) T-cells had suppressive capabilities both in vitro and in vivo that this concept regained credibility and developed into one of the most active research areas in immunology today. The notion that in healthy individuals there is a subset of T(reg)-cells (regulatory T-cells) involved in 'policing' the immune system has led to the intensive exploration of the role of this subset in disease resulting in a number of studies concluding that a quantitative or qualitative decline in T(reg)-cells is an important part of the breakdown in self-tolerance leading to the development of autoimmune diseases. Although T(reg)-cells have subsequently been widely postulated to represent a potential immunotherapy option for patients with autoimmune disease, several studies of autoimmune disorders have demonstrated high numbers of T(reg)-cells in inflamed tissue. The present review highlights the need to consider a range of other factors which may be impairing T(reg)-cell function when considering the mechanisms involved in the breakdown of self-tolerance rather than focussing on intrinsic T(reg)-cell factors.

T regulatory cells in autoimmune diabetes: past challenges, future prospects

INTRODUCTION

Accumulating evidence suggests that defective regulation is an essential underlying cause of autoimmunity. The development of type 1 diabetes in the NOD mouse strain it is a complex process that depends on a fine balance between pathogenic and regulatory pathways.

DISCUSSION

We have utilized a series of transgenic and knockout mice to determine the relative importance of regulatory T cells and negative regulatory receptors on the development and progression of type 1 diabetes.

CONCLUSION

This review will focus on the origins and function of Treg in peripheral self-tolerance. We will summarize the role of Treg in preventing autoimmune diseases, with a particular focus on Type 1 Diabetes (T1D), and discuss the prospects for Treg-based therapies for autoimmune diseases.

Combined insulin B:9-23 self-peptide and polyinosinic-polycytidylic acid accelerate insulitis but inhibit development of diabetes by increasing the proportion of CD4+Foxp3+ regulatory T cells in the islets in non-obese diabetic mice

Insulin peptide B:9-23 is a major autoantigen in type 1 diabetes. Combined treatment with B:9-23 peptide and polyinosinic-polycytidylic acid (poly I:C), but neither alone, induce insulitis in normal BALB/c mice. In contrast, the combined treatment accelerated insulitis, but prevented diabetes in NOD mice. Our immunofluorescence study with anti-CD4/anti-Foxp3 revealed that the proportion of Foxp3 positive CD4(+)CD25(+) regulatory T cells (Tregs) was elevated in the islets of NOD mice treated with B:9-23 peptide and poly I:C, as compared to non-treated mice. Depletion of Tregs by anti-CD25 antibody hastened spontaneous development of diabetes in non-treated NOD mice, and abolished the protective effect of the combined treatment and conversely accelerated the onset of diabetes in the treated mice. These results indicate that poly I:C combined with B:9-23 peptide promotes infiltration of both pathogenic T cells and predominantly Tregs into the islets, thereby inhibiting progression from insulitis to overt diabetes in NOD mice.

The use of CD3-specific antibodies in autoimmune diabetes: a step toward the induction of immune tolerance in the clinic

CD3-specific monoclonal antibodies were the first rodent monoclonals introduced in clinical practice in the mid 1980s as approved immunosuppressants to prevent and treat organ allograft rejection. Since then compelling evidence has been accumulated to suggest that in addition to their immunosuppressive properties, CD3-specific antibodies can also afford inducing immune tolerance especially in the context of ongoing immune responses. Thus, they are highly effective at restoring self-tolerance in overt autoimmunity, a capacity first demonstrated in the experimental setting, which was recently transferred to the clinic with success.

Special regulatory T-cell review: Regulatory T cells and the intestinal tract--patrolling the frontier

Tolerance to self and harmless antigens is one of the central features of the immune system, and it is obtained through a combination of multiple mechanisms. Discriminating between pathogens and non-pathogenic antigens is especially important in the intestine, which constitutes the main contact surface between the body and the outside environment. Recently, the role of Foxp3+ regulatory T cells (Treg) in the establishment and maintenance of tolerance has been the focus of numerous studies. In this review, we briefly discuss the historical background leading to the identification of Foxp3+ Treg and give an overview of their role in controlling systemic and mucosal immune responses.

Adaptive TGF-beta-dependent regulatory T cells control autoimmune diabetes and are a privileged target of anti-CD3 antibody treatment

Previous results have shown that CD4(+)CD25(+) regulatory T cells (Tregs) control autoimmunity in a spontaneous model of type 1 diabetes, the nonobese diabetic (NOD) mouse. Moreover, anti-CD3 reverses diabetes in this setting by promoting Tregs that function in a TGF-beta-dependent manner. This finding contrasts with a large body of work suggesting that CD4(+)CD25(high) Tregs act in a cytokine-independent manner, thus suggesting that another type of Treg is operational in this setting. We sought to determine the basis of suppression both in untreated NOD mice and in those treated with anti-CD3. Our present results show that a subset of foxP3(+) cells present within a CD4(+)CD25(low) lymphocyte subset suppresses T cell immunity in spontaneously diabetic NOD mice in a TGF-beta-dependent manner, a functional property typical of "adaptive" regulatory T cells. This distinct Treg subset is evident in NOD, but not normal, mice, suggesting that the NOD mice may generate these adaptive Tregs in an attempt to regulate ongoing autoimmunity. Importantly, in two distinct in vivo models, these TGF-beta-dependent adaptive CD4(+)CD25(low) T cells can be induced from peripheral CD4(+)CD25(-) T lymphocytes by anti-CD3 immunotherapy which correlates with the restoration of self-tolerance.

Mapping of the murine type 1 diabetes locus Idd20 by genetic interaction

In the nonobese diabetes mouse, the murine type 1 diabetes susceptibility locus Idd20 interacts genetically with the diabetes resistance locus Idd19. Both Idds are located on distal mouse Chromosome 6, and previous studies on NOD.C3H congenic strains have shown that C3H alleles at Idd20 can suppress the disease-promoting effects of C3H alleles at Idd19 in both spontaneous and cyclophosphamide-induced diabetes. In this article we present the construction of novel congenic strains which, while maintaining the C3H alleles at Idd19, have allowed the candidate interval of Idd20 to be reduced from 4 to 1.8 cM. The analysis of these strains shows that Idd20 controls the progression of insulitis. Idd20 also increases the suppressive but not the pathogenic activity of splenocytes in diabetes transfer experiments. Our results suggest that the two Chromosome 6 susceptibility loci, Idd6 and Idd20, interact with the resistance locus Idd19 by regulating the activity of suppressor cells in the peripheral immune system.

Protection from autoimmunity: immunological indifference versus T-cell mediated suppression?

A long-held dogma was that immune tolerance could only be achieved through central deletion of potentially reactive cells at their site of origin, a concept supported by the direct demonstration of natural negative selection in bone marrow and thymus; however, it is now extensively documented that although deletion mechanisms ensure the elimination of most autoreactive cells, this purging is far from complete. There are major immune mechanisms that ensure tolerance in the periphery which are clearly non-deletional. A paper in this issue of the European Journal of Immunology demonstrates that T cell-mediated immunoregulation involving in particular the CTLA-4 signaling pathway plays a key role in controlling the pathogenic potential of fully differentiated autoreactive T cells.

Transforming growth factor-beta and T-cell-mediated immunoregulation in the control of autoimmune diabetes

It is now well-established that CD4+ regulatory T cells are instrumental in controlling immune responses both to self-antigens and to non-self-antigens. However, the precise modalities involved in their differentiation and survival, their mode of action and their antigen specificity are only partially understood. We have been particularly interested in the study of regulatory T cells controlling autoimmune insulin-dependent diabetes. Here, we provide evidence to support the phenotypic and functional diversity of regulatory T cells mediating transferable 'active' or 'dominant' peripheral tolerance in the non-obese diabetic mouse model (NOD). They include natural and adaptive regulatory T cells that are operational both in unmanipulated NOD mice and in animals undergoing treatments aimed at inducing/restoring tolerance to self-beta-cell antigens. At least in our hands, the differential cytokine-dependency appears as a major distinctive feature of regulatory T cells subsets. Among immunoregulatory cytokines, transforming growth factor-beta(TGF-beta) appeared to play a key role. Herein we discuss these results and the working hypothesis they evoke in the context of the present literature, where the role of TGF-beta-dependent T-cell-mediated immunoregulation is still debated.

Role of Naturally Arising Regulatory T Cells in Hematopoietic Cell Transplantation

Naturally arising CD4(+)CD25(+) regulatory T cells (Tregs) have the potential to suppress aberrant immune responses and to regulate peripheral T-cell homeostasis. In murine models of bone marrow transplantation, Tregs promote donor bone marrow engraftment and decrease the incidence and severity of graft-versus-host-disease without abrogating the beneficial graft-versus-tumor immunologic effect. These findings, in concert with observations that Tregs in mice and humans share phenotypic and functional characteristics, have led to active investigations into the use of these cells to decrease complications associated with human hematopoietic cell transplantation. Early human studies suggest that an imbalance of Tregs and effector T cells may contribute to the development of graft-versus-host-disease. However, the mechanisms of immunoregulation, in particular the allorecognition properties of Tregs, their effects on and interaction with other immune cells, and their sites of suppressive activity, are not well understood. In this review, we discuss the current knowledge of Treg biology and the potential therapeutic strategies and barriers of Treg immunotherapy in human hematopoietic cell transplantation.

Resetting the functional capacity of regulatory T cells: a novel immunotherapeutic strategy to promote immune tolerance

Over the last few years, there has been a re-emergence of the concept of suppressor/regulatory T cells among the central players of immune mechanisms controlling a wide variety of immune responses from physiological autoreactivity (i.e., response to self-antigens) to responses to transplants, tumours and infectious antigens. Regulatory T cells are diverse in their phenotypes, antigen specificity, mode of action and immunopathological relevance. This review briefly summarises studies from the authors' group showing that specialised subsets of regulatory T cells are instrumental in the control of autoimmune diseases and more specifically of Type 1 diabetes. In addition, this review will provide evidence supporting the notion that CD3-specific monoclonal antibodies are representatives of a new category of immunotherapeutic agents that possess the unique capacity to promote immunological tolerance (an antigen-specific unresponsiveness in the absence of long-term generalised immunosuppression) through their ability to induce immunoregulatory T cells.

Breakpoints in immunoregulation required for Th1 cells to induce diabetes

We describe a novel TCR-transgenic mouse line, TCR7, where MHC class II-restricted, CD4+ T cells are specific for the subdominant H-2b epitope (HEL74-88) of hen egg lysozyme (HEL), and displayed an increased frequency in the thymus and in peripheral lymphoid compartments over that seen in non-transgenic littermate controls. CD4+ T cells responded vigorously to HEL or HEL74-88 epitope presented on APC and could develop into Th1 or Th2 cells under appropriate conditions. Adoptive transfer of TCR7 Ly5.1 T cells into Ly5.2 rat insulin promoter (RIP)-HEL transgenic recipient hosts did not lead to expansion of these cells or result in islet infiltration, although these TCR7 cells could expand upon transfer into mice expressing high levels of HEL in the serum. Islet cell infiltration only occurred when the TCR7 cells had been polarized to either a Th1 or Th2 phenotype prior to transfer, which led to insulitis. Progression from insulitis to autoimmune diabetes only occurred in these recipients when Th1 but not Th2 TCR7 cells were transferred and CTLA-4 signaling was simultaneously blocked. These findings show that regulatory pathways such as CTLA-4 can hold in check already differentiated autoreactive effector Th1 cells, to inhibit the transition from tolerance to autoimmune diabetes.

Deficiency in NOD antigen-presenting cell function may be responsible for suboptimal CD4+CD25+ T-cell-mediated regulation and type 1 diabetes development in NOD mice

Various defects in antigen-presenting cells (APCs) and T-cells, including regulatory cells, have been associated with type 1 diabetes development in NOD mice. CD4(+)CD25(+) regulatory cells play a crucial role in controlling various autoimmune diseases, and a deficiency in their number or function could be involved in disease development. The current study shows that NOD mice had fewer CD4(+)CD25(+) regulatory cells, which expressed normal levels of glucocorticoid-induced tumor necrosis factor receptor and cytotoxic T-lymphocyte-associated antigen-4. We have also found that NOD CD4(+)CD25(+) cells regulate poorly in vitro after stimulation with anti-CD3 and NOD APCs in comparison with B6 CD4(+)CD25(+) cells stimulated with B6 APCs. Surprisingly, stimulation of NOD CD4(+)CD25(+) cells with B6 APCs restored regulation, whereas with the reciprocal combination, NOD APCs failed to activate B6 CD4(+)CD25(+) cells properly. Interestingly, APCs from disease-free (>30 weeks of age), but not diabetic, NOD mice were able to activate CD4(+)CD25(+) regulatory function in vitro and apparently in vivo because only spleens of disease-free NOD mice contained potent CD4(+)CD25(+) regulatory cells that prevented disease development when transferred into young NOD recipients. These data suggest that the failure of NOD APCs to activate CD4(+)CD25(+) regulatory cells may play an important role in controlling type 1 diabetes development in NOD mice.

Increasing donor chimerism and inducing tolerance to islet allografts by post-transplant donor lymphocyte infusion

Inducing donor chimerism is the most consistently successful approach to achieve transplant tolerance. We found that a low level of donor chimerism, which was induced by a relatively non-toxic approach, induced donor-specific tolerance to islet allografts in chemically induced diabetic mice. However, a similar level of donor chimerism could not protect donor islet allografts in non-obese diabetic (NOD) mice that spontaneously developed autoimmune diabetes. Rejection of donor islet allografts in diabetic NOD mice with a low level of donor chimerism was mediated by recurrent autoimmunity. We used post-transplant donor lymphocyte infusion (DLI) to increase donor chimerism and to induce tolerance to islet allografts. DLI significantly increased donor chimerism and promoted donor-specific tolerance to islet allografts in diabetic NOD mice. Self-tolerance to islet autoantigens was restored and restoring self-tolerance is mediated by immunoregulation. Thus, our data showed that adoptive immunotherapy with post-transplant DLI after establishing a low level of donor chimerism as a platform enhances donor chimerism, induces donor-specific tolerance to islet allografts and restores self-tolerance in the setting of autoimmune diabetes. Our data also showed that central tolerance is not sufficient to induce tolerance and peripheral tolerance through immunoregulation for restoring self-tolerance is required in the setting of autoimmune diabetes.

The natural killer T lymphocyte: a player in the complex regulation of autoimmune diabetes in non-obese diabetic mice

Manipulation of the immune response to specifically prevent autoaggression requires an understanding of the complex interactions that occur during the pathogenesis of autoimmunity. Much attention has been paid to conventional T lymphocytes recognizing peptide antigens presented by classical major histocompatibility complex (MHC) class I and II molecules, as key players in the destructive autoreactive process. A pivotal role for different types of regulatory T lymphocytes in modulating the development of disease is also well established. Lately, CD1d-restricted natural killer T (NKT) lymphocytes have been the subject of intense investigation because of their ability to regulate a diversity of immune responses. The non-classical antigen presenting molecule CD1d presents lipids and glycolipids to this highly specialized subset of T lymphocytes found in both humans and mice. From experimental models of autoimmunity, evidence is accumulating that NKT cells can protect from disease. One of the best studied is the murine type 1 diabetes model, the non-obese diabetic (NOD) mouse. While the NKT cell population was first recognized to be deficient in NOD mice, augmenting NKT cell activity has been shown to suppress the development of autoimmune disease in this strain. The mechanism by which CD1d-restricted T cells exert this function is still described incompletely, but investigations in NOD mice are starting to unravel specific effects of NKT cell regulation. This review focuses on the role of CD1d-restricted NKT cells in the control of autoimmune diabetes.

Gene therapy for type 1 diabetes

The most intensively studied autoimmune disorder, type 1 diabetes mellitus (DM1), has attracted perhaps the greatest interest for gene-based therapeutic and prophylactic interventions. The final clinical manifestation of this immunologically and genetically complex disease, the absence of insulin, is the major starting point for almost all the gene therapy modalities attempted to date. Insulin replacement by transplantation of islets of Langerhans or surrogate beta cells is the obvious choice, but the allogeneic nature of the transplants activates potent antidonor immunoreactivity necessitating gene and cell-based immunosuppressive strategies as an alternative to the toxic pharmacologic immunosuppressives indicated for classic solid organ transplants. Accumulating knowledge of the cellular mechanisms involved in onset, however, have yielded promising tolerance induction prophylactic approaches using genes and cells. Despite the early successes in a number of animal models, the true test of efficacy in humans remains to be demonstrated.

Regulatory T cells in the control of autoimmune diabetes: the case of the NOD mouse

Over the last few years, there has been a revival of the concept of suppressor/regulatory T cells being central players in the control of various immune responses, including autoimmune responses and immune response to transplants, tumors, and infectious agents. It appears that regulatory T cells are diverse in their phenotypes, antigen specificity, and modes of action. Here we summarize studies from various groups, including our own, demonstrating that specialized subsets of regulatory T cells are pivotal in the control of autoimmune diabetes as well shown by the compelling evidence accumulated using the non-obese diabetic (NOD) mouse model. We also provide a discussion of the evidence showing that some biological products (such as CD3-specific monoclonal antibodies) are representatives of a new category of immunotherapeutic agents endowed with unique capacities to promote immunological tolerance (an antigen-specific unresponsiveness in the absence of long-term generalized immunosuppression) through their ability to induce immunoregulatory T cells.

The NOD mouse: a model of immune dysregulation

Autoimmunity is a complex process that likely results from the summation of multiple defective tolerance mechanisms. The NOD mouse strain is an excellent model of autoimmune disease and an important tool for dissecting tolerance mechanisms. The strength of this mouse strain is that it develops spontaneous autoimmune diabetes, which shares many similarities to autoimmune or type 1a diabetes (T1D) in human subjects, including the presence of pancreas-specific autoantibodies, autoreactive CD4+ and CD8+ T cells, and genetic linkage to disease syntenic to that found in humans. During the past ten years, investigators have used a wide variety of tools to study these mice, including immunological reagents and transgenic and knockout strains; these tools have tremendously enhanced the study of the fundamental disease mechanisms. In addition, investigators have recently developed a number of therapeutic interventions in this animal model that have now been translated into human therapies. In this review, we summarize many of the important features of disease development and progression in the NOD strain, emphasizing the role of central and peripheral tolerance mechanisms that affect diabetes in these mice. The information gained from this highly relevant model of human disease will lead to potential therapies that may alter the development of the disease and its progression in patients with T1D.

Autoimmune diabetes onset results from qualitative rather than quantitative age-dependent changes in pathogenic T-cells

Diabetogenic T-cells can be detected in pre-diabetic nonobese diabetic (NOD) mice after transfer in NOD-SCID recipients. Here we demonstrate that 6-week-old pre-diabetic NOD mice, >2 months before disease onset, already harbor pathogenic T-cells in equal numbers to overtly diabetic animals. The delay in diabetes appearance is explained by the presence of regulatory CD4+ CD25+ T-cells that control diabetogenic effectors and that are, in our hands, transforming growth factor (TGF)-beta-dependent. Our present results suggest, however, that diabetes onset is only partly explained by a decline in this regulatory T-cell activity. Another major factor appears to be the progressive resistance of diabetogenic cells to TGF-beta-dependent mediated inhibition. We propose that progression to overt disease correlates with the pathogenic T-cell's escape from TGF-beta-dependent T-cell-mediated regulation.

Inflammatory bowel disease: dysfunction of GALT and gut bacterial flora (I)

Gut-associated lymphoid tissue (GALT) is the largest lymphoid organ in the body. This is not surprising considering the huge load of antigens (Ags) from food and commensal bacteria with which it interacts on a daily basis. Gut-associated lymphoid tissue has to recognise and allow the transfer of beneficial Ags whilst concurrently dealing with and successfully removing putative and overtly harmful Ags. This distinctive biological feature of GALT is believed to be crucial to good health. Deregulation or dysfunction of GALT is thought to predispose to inflammatory bowel diseases (IBD) such as ulcerative colitis and Crohn's disease. The exact mechanism(s) underlying the pathogenesis of IBD is (are) poorly understood and the immunological defects in GALT are poorly documented. Advances in immunology have highlighted the importance of dendritic cells (DCs), which are the key Ag presenting cells in tissues and lymphoid compartments. Their crucial role in GALT, in health and disease is discussed in this review. Interaction of DCs with T cells in the gut produces a subset of T lymphocytes, which have immunosuppressive function. Inappropriate Ag uptake and presentation to naïve T cells in mesenteric lymph nodes may lead to T cell tolerance in GALT. These various complex factors in the gut are discussed and their possible relevance to IBD evaluated.

Satisfaction (not) guaranteed: re-evaluating the use of animal models of type 1 diabetes

Without a doubt, rodent models have been instrumental in describing pathways that lead to pancreatic beta-cell destruction, evaluating potential causes of type 1 diabetes and providing proof-of-principle for the potential of immune-based interventions. However, despite more than two decades of productive research, we are still yet to define an initiating autoantigen for the human disease, to determine the precise mechanisms of beta-cell destruction in humans and to design interventions that prevent or cure type 1 diabetes. In this Perspective article, we propose that a major philosophical change would benefit this field, a proposition that is based on evaluation of situations in which rodent models have provided useful guidance and in which they have led to disappointments.

CD4+ Tregs and immune control

Recent years have seen Tregs become a popular subject of immunological research. Abundant experimental data have now confirmed that naturally occurring CD25+CD4+ Tregs in particular play a key role in the maintenance of self tolerance, with their dysfunction leading to severe or even fatal immunopathology. The sphere of influence of Tregs is now known to extend well beyond just the maintenance of immunological tolerance and to impinge on a host of clinically important areas from cancer to infectious diseases. The identification of specific molecular markers in both human and murine immune systems has enabled the unprecedented investigation of these cells and should prove key to ultimately unlocking their clinical potential.

CD4+ Tregs and immune control

Recent years have seen Tregs become a popular subject of immunological research. Abundant experimental data have now confirmed that naturally occurring CD25+CD4+ Tregs in particular play a key role in the maintenance of self tolerance, with their dysfunction leading to severe or even fatal immunopathology. The sphere of influence of Tregs is now known to extend well beyond just the maintenance of immunological tolerance and to impinge on a host of clinically important areas from cancer to infectious diseases. The identification of specific molecular markers in both human and murine immune systems has enabled the unprecedented investigation of these cells and should prove key to ultimately unlocking their clinical potential.

Prevention of diabetes in nonobese diabetic mice mediated by CD1d-restricted nonclassical NKT cells

A role for regulatory lymphocytes has been demonstrated in the pathogenesis of type 1 diabetes in the NOD mouse but the nature of these cells is debated. CD1d-restricted NKT lymphocytes have been implicated in this process. Previous reports of reduced diabetes incidence in NOD mice in which the numbers of NKT cells are artificially increased have been attributed to the enhanced production of IL-4 by these cells and a role for classical NKT cells, using the Valpha14-Jalpha18 rearrangement. We now show that overexpression in NOD mice of CD1d-restricted TCR Valpha3.2(+)Vbeta9(+) NKT cells producing high levels of IFN-gamma but low amounts of IL-4 leads to prevention of type 1 diabetes, demonstrating a role for nonclassical CD1d-restricted NKT cells in the regulation of autoimmune diabetes.

DNA vaccination encoding glutamic acid decarboxylase can enhance insulitis and diabetes in correlation with a specific Th2/3 CD4 T cell response in non-obese diabetic mice

DNA vaccination encoding beta cell autoantigens has been shown very recently to prevent type I diabetes in non-obese diabetic (NOD) mice. However, DNA vaccination encoding microbial or reporter antigens is known to induce specific long-lasting CD4 Th1 and strong cytolytic CD8 T cell responses. As this immune phenotype is associated strongly with beta cell destruction leading to diabetes, we have chosen to study the effects of plasmids encoding glutamic acid decarboxylase (GAD), a crucial beta cell autoantigen, in female NOD mice that developed a 'moderate' diabetes incidence. In the present study, 3-week-old female NOD mice were vaccinated twice in tibialis muscles with plasmid-DNA encoding 65-kDa GAD or betagalactosidase. In GAD-DNA immunized mice, diabetes cumulative incidence (P < 3.10(-3)) and insulitis (P < 7.10(-3)) increased significantly. Simultaneously, DNA immunization induced GAD-specific CD4 T cells secreting interleukin (IL)-4 (P < 0.05) and transforming growth factor (TGF)-beta (P = 0.03). These cells were detected in spleen and in pancreatic lymph nodes. Furthermore, vaccination produced high amounts of Th2 cytokine-related IgG1 (P < 3.10(-3)) and TGF-beta-related IgG2b to GAD (P = 0.015). Surprisingly, diabetes onset was correlated positively with Th2-related GAD-specific IgG1 (P < 10(-4)) and TGF-beta-related IgG2b (P < 3.10(-3)). Moreover, pancreatic lesions resembled Th2-related allergic inflammation. These results indicate, for the first time, that GAD-DNA vaccination could increase insulitis and diabetes in NOD mice. In addition, our study suggests that Th2/3 cells may have potentiated beta cell injury.

Recessive tolerance to preproinsulin 2 reduces but does not abolish type 1 diabetes

Although autoimmune diseases can be initiated by immunization with a single antigen, it is not clear whether a single self antigen is essential for the initiation and, perhaps, the perpetuation of spontaneous autoimmunity. Some studies have suggested that insulin may represent an essential autoantigen in type 1 diabetes. Here we show that unlike tolerance to glutamic acid decarboxylase, tolerance to transgenically overexpressed preproinsulin 2 substantially reduced the onset and severity of type 1 diabetes in nonobese diabetic mice. However, some mice still developed type 1 diabetes, suggesting that insulin is a key, but not absolutely essential, autoantigen. The results are consistent with the idea that the human IDDM2 locus controls susceptibility to type 1 diabetes by regulating intrathymic preproinsulin expression.

Regulatory T cells and type 1 diabetes

A resurgent interest in T cells with regulatory activity has prompted many recent investigations into their potential role in pathogenesis and prevention of type 1 diabetes. While some studies have suggested that regulatory T cells participate in the preservation of active tolerance to autoantigens, findings obtained in multiple animal models for type 1 diabetes have documented the therapeutic induction of protective regulatory T cells. A review of the proposed mechanisms operative in regulatory T cell-mediated diabetes prevention indicates a common theme of localized regulatory T cell activation and subsequent suppression of pathogenic T cell trafficking, differentiation, and/or effector function. However, adaptation of experimental protocols for regulatory T cell induction to clinical applications faces several challenges. Immunization with self-antigens carries obvious risks especially in the face of multiple variables that can affect generation, trafficking, and regulatory activity of autoantigen-specific T cells. We also emphasize that the frequent use of lymphopenic recipients of adoptively transferred pathogenic and regulatory T cells constitutes a potentially confounding variable that further complicates translation into clinical settings. The therapeutic induction of regulatory T cells in prediabetic individuals carries great potential but is currently limited by the risks associated with deliberate generation of autoimmune responses that may exacerbate rather than ameliorate the autoimmune process. However, in vitro amplification and autologous regulatory T cell therapy might soon become a clinical reality.