Insulin--a primary autoantigen in type 1 diabetes?

Pancreatic ductal cell antigens are important in the development of invasive insulitis in Non-Obese Diabetic mice

Type 1 Diabetes (T1D) is an autoimmune disease in which insulin producing beta cells of the pancreas are selectively destroyed. Glial Fibrillary Acidic Protein (GFAP) expressed in peri-islet Schwann cells (pSCs) and in the ductal cells of the pancreas is one of the candidate autoantigens for T1D. Immune responses to GFAP expressing cell types precede the islet autoimmunity in Non-Obese Diabetic (NOD) mice. By removing MHC class I from GFAP expressing cell types, we tested the role of autoantigens presented by these cell types in the development of invasive insulitis. Our findings indicate that antigens expressed by pancreatic ductal cells are important in the development of invasive insulitis in NOD mice.

Regulatory T Cell-Based Immunotherapy

CD4+CD25+ regulatory T (Treg) cells expressing the forkhead box transcription factor Foxp3 have a vital function in the maintenance of immune homeostasis and the prevention of fatal multi-organ autoimmunity throughout life. In the last decade, Foxp3+ Treg cells have raised the hope for novel cell-based therapies to achieve tolerance in clinical settings of unwanted immune responses such as autoimmunity and graft rejection. Conceptually, the antigen-specific enhancement of Treg cell function is of particular importance because such strategies will minimize the requirements for pharmaceutical immunosuppression, sparing desired protective host immune responses to infectious and malignant insults. This chapter discusses current concepts of Treg cell-based immunotherapy with particular emphasis on antigen-specific Treg cell induction from conventional CD4+ T cells to deal with organ-specific autoimmunity.

Targeted antigen delivery to DEC-205⁺ dendritic cells for tolerogenic vaccination

Dendritic cells (DCs) and Foxp3-expressing CD4⁺ regulatory T (Treg) cells play non-redundant roles in the maintenance of peripheral tolerance to self-antigens, thereby preventing fatal autoimmunity. A common hallmark of intra- and extra-thymic Treg cell lineage commitment is the induction of Foxp3 expression as a consequence of appropriate T cell receptor engagement with MHC class II:agonist ligand. It has now become increasingly clear that agonist ligand presentation by immature DCs in the steady state induces T cell tolerance by both recessive and dominant mechanisms, rather than promoting productive T helper cell responses. In this context, the ability of steady-state DCs to promote the extrathymic conversion of initially naïve CD4⁺Foxp3⁻ T cells into Foxp3⁺ Treg cells is of particular interest as it provides novel perspectives to enhance antigen-specific Treg cell function in clinical settings of unwanted immunity, such as β-cell autoimmunity.

Prevention of Type 1 Diabetes Mellitus using a Novel Vaccine

Type 1 diabetes mellitus (T1DM) affects 1 in 300 people and the incidence of the disease is rising worldwide. T1DM is caused by chronic autoimmune destruction of the insulin-producing β-cells. The exact etiology and primary auto-antigen are not yet known. The autoimmune, chronic, and progressive nature of the disease raises the possibility of intervention, preferably by slowing down or stopping the destruction of the β-cells as early as the prediabetic stage. Since the 1980s, several attempts have been made to maintain β-cell function using immunosuppressive agents, immune modulation such as plasmapheresis, cytokine therapy, or antibody treatment. These agents were not diabetes specific; the occasionally observed beneficial effect did not compensate for the often very severe side effects. According to the latest assumption, the administration of diabetes-specific auto-antigens can elicit tolerance, which can prevent the destruction of the β-cells, hopefully without serious side effects. The authors summarize current understanding of the immunology of T1DM, review the trials on prevention, and discuss their vaccination study.

Prevention of type 1 diabetes

INTRODUCTION/BACKGROUND

Type 1 diabetes is a chronic autoimmune condition characterized by destruction of insulin-producing β cells within the pancreatic islets. It is associated with considerable morbidity and mortality. Incidence levels are rising worldwide.

SOURCES OF DATA

Pubmed search (Nov 2010) using keywords: Type 1 diabetes, prevention, trials, immunotherapy.

AREAS OF AGREEMENT

The causes of disease are multifactorial with genetic and environmental factors playing a part. There is a long pre-clinical period before the onset of overt symptoms, which may be amenable to therapeutic intervention to prevent disease.

AREAS OF CONTROVERSY

The exact nature of causative environmental factors is unknown and much debated. Immunotherapeutic intervention may therefore represent the best option for disease prevention.

GROWING POINTS

Enhancement of 'regulatory' immune mechanisms currently shows the most promise as an approach to disease prevention.

AREAS TIMELY FOR DEVELOPING RESEARCH

Clinical trials of early immunotherapeutic intervention may be the answer to disease prevention.

Dendritic cell-targeted pancreatic beta-cell antigen leads to conversion of self-reactive CD4(+) T cells into regulatory T cells and promotes immunotolerance in NOD mice

Studies employing T cell receptor transgenic T cells have convincingly shown that selective delivery of non-self model antigens to DEC-205(+) dendritic cells (DCs) in the steady-state can induce Foxp3-expressing CD4(+)CD25(+) regulatory T (Treg) cells from conventional CD4(+)CD25(-)Foxp3(-) T cells. Although of considerable clinical interest, the concept of DC-targeted de novo generation of antigen-specific Treg cells has not yet been evaluated for self-antigens and self-reactive CD4(+) T cells in the non-obese diabetic (NOD) mouse model of type 1 diabetes (T1D). Here, we show in proof-of-principle experiments that targeting a mimotope peptide to the endocytic receptor DEC-205 on DCs in NOD mice induces efficient conversion of pancreatic beta-cell-reactive BDC2.5 CD4(+) T cells into long-lived Foxp3(+) Treg cells. Of note, conversion efficiency in normoglycemic and hyperglycemic mice with early diabetes onset was indistinguishable. While de novo generation of BDC2.5 Treg cells did not interfere with disease progression, anti-DEC-205-mediated targeting of whole proinsulin in prediabetic NOD mice substantially reduced the incidence of diabetes. These results suggest that promoting antigen-specific Treg cells in vivo might be a feasible approach towards cellular therapy in T1D.

Strategies to prevent type 1 diabetes

Type 1 diabetes is a chronic autoimmune condition resulting from T cell-mediated destruction of the insulin-producing cells in the islets of Langerhans. Its primary cause remains unknown, but it has been established that the clinical presentation is preceded by a long prodrome. This enables individuals at high risk of disease to be identified and offers the possibility of intervention to prevent clinical disease. Many groups are working in this field, concentrating on manipulation of environmental exposures that are potential triggers of autoimmunity and on immunomodulation strategies that aim to prevent destruction of beta-cells. Some interventions have shown promising results in early trials, but effective disease prevention remains elusive. This article reviews current progress in the field.

Mucosal exposure to antigen: cause or cure of type 1 diabetes?

The human gut offers more than 200 m2 of mucosal surface, where direct interactions between the immune system and foreign antigens take place to eliminate pathogens or induce immune tolerance toward food antigens or normal gut flora. Therefore, mucosally administered antigens can induce tolerance under certain circumstances. In autoimmune diabetes, mucosal vaccination with autoantigens elicits some efficacy in restoring tolerance in mice, but it never succeeded in humans. Furthermore, in some instances autoimmunity can be precipitated upon oral or intranasal autoantigen administration. Therefore, it is difficult to predict the effect of mucosal vaccination on autoimmunity and much effort should be put into establishing better assays to reduce the risk for possible adverse events in humans and enable a rapid and smooth translation.