Spontaneous peripheral T-cell responses to the IA-2beta (phogrin) autoantigen in young nonobese diabetic mice

Thymus-specific serine protease, a protease that shapes the CD4 T cell repertoire

The lifespan of T cells is determined by continuous interactions of their T cell receptors (TCR) with self-peptide-MHC (self-pMHC) complexes presented by different subsets of antigen-presenting cells (APC). In the thymus, developing thymocytes are positively selected through recognition of self-pMHC presented by cortical thymic epithelial cells (cTEC). They are subsequently negatively selected by medullary thymic epithelial cells (mTEC) or thymic dendritic cells (DC) presenting self-pMHC complexes. In the periphery, the homeostasis of mature T cells is likewise controlled by the interaction of their TCR with self-pMHC complexes presented by lymph node stromal cells while they may be tolerized by DC presenting tissue-derived self-antigens. To perform these tasks, the different subsets of APC are equipped with distinct combination of antigen processing enzymes and consequently present specific repertoire of self-peptides. Here, we discuss one such antigen processing enzyme, the thymus-specific serine protease (TSSP), which is predominantly expressed by thymic stromal cells. In thymic DC and TEC, TSSP edits the repertoire of peptide presented by class II molecules and thus shapes the CD4 T cell repertoire.

Antigen presentation in the autoimmune diabetes of the NOD mouse

This paper reviews the presentation of peptides by major histocompatibility complex (MHC) class II molecules in the autoimmune diabetes of the nonobese diabetic (NOD) mouse. Islets of Langerhans contain antigen-presenting cells that capture the proteins and peptides of the beta cells' secretory granules. Peptides bound to I-A(g7), the unique MHC class II molecule of NOD mice, are presented in islets and in pancreatic lymph nodes. The various beta cell-derived peptides interact with selected CD4 T cells to cause inflammation and beta cell demise. Many autoreactive T cells are found in NOD mice, but not all have a major role in the initiation of the autoimmune process. I emphasize here the evidence pointing to insulin autoreactivity as a seminal component in the diabetogenic process.

Thymus-specific serine protease controls autoreactive CD4 T cell development and autoimmune diabetes in mice

Type 1 diabetes is a chronic autoimmune disease in which genetic predispositions affect the immune system, leading to a loss of T cell tolerance to β cells and consequent T cell-mediated destruction of insulin-producing islet cells. Genetic studies have suggested that PRSS16 is linked to a diabetes susceptibility locus of the extended HLA class I region in humans. PRSS16 encodes what we believe to be a novel protease, thymus-specific serine protease (TSSP), which shows predominant expression in thymic epithelial cells and is suspected to have a restricted role in the class II presentation pathway. Consistently, Tssp is necessary for the intrathymic selection of few class II-restricted T cell receptor specificities in B6 mice. To directly assess the role of Tssp in autoimmune diabetes, we generated Tssp-deficient (Tssp°) NOD mice. While remaining immunocompetent, Tssp° NOD mice were protected from diabetes and severe insulitis. Diabetes resistance of Tssp° NOD mice was a property of the CD4 T cell compartment that is acquired during thymic selection and correlated with an impaired selection of CD4 T cells specific for islet antigens. Hence, in the NOD mouse, Tssp is a critical regulator of diabetes development through the selection of the autoreactive CD4 T cell repertoire.

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.

On the pathogenicity of autoantigen-specific T-cell receptors

OBJECTIVE

Type 1 diabetes is mediated by T-cell entry into pancreatic islets and destruction of insulin-producing beta-cells. The relative contribution of T-cells specific for different autoantigens is largely unknown because relatively few have been assessed in vivo.

RESEARCH DESIGN AND METHODS

We generated mice possessing a monoclonal population of T-cells expressing 1 of 17 T-cell receptors (TCR) specific for either known autoantigens (GAD65, insulinoma-associated protein 2 (IA2), IA2beta/phogrin, and insulin), unknown islet antigens, or control antigens on a NOD.scid background using retroviral-mediated stem cell gene transfer and 2A-linked multicistronic retroviral vectors (referred to herein as retrogenic [Rg] mice). The TCR Rg approach provides a mechanism by which T-cells with broad phenotypic differences can be directly compared.

RESULTS

Neither GAD- nor IA2-specific TCRs mediated T-cell islet infiltration or diabetes even though T-cells developed in these Rg mice and responded to their cognate epitope. IA2beta/phogrin and insulin-specific Rg T-cells produced variable levels of insulitis, with one TCR producing delayed diabetes. Three TCRs specific for unknown islet antigens produced a hierarchy of insulitogenic and diabetogenic potential (BDC-2.5 > NY4.1 > BDC-6.9), while a fourth (BDC-10.1) mediated dramatically accelerated disease, with all mice diabetic by day 33, well before full T-cell reconstitution (days 42-56). Remarkably, as few as 1,000 BDC-10.1 Rg T-cells caused rapid diabetes following adoptive transfer into NOD.scid mice. CONCLUSIONS; Our data show that relatively few autoantigen-specific TCRs can mediate islet infiltration and beta-cell destruction on their own and that autoreactivity does not necessarily imply pathogenicity.

Are other protein tyrosine phosphatases than PTPN22 associated with autoimmunity?

The discovery that a single amino acid substitution in the PTPN22 protein tyrosine phosphatase can predispose to so many autoimmune diseases (see chapters 2 and 3), even when present in a single copy, raises many questions regarding the broader significance of this observation. Is there something unique about PTPN22 or are genetic variants of other protein tyrosine phosphatases likely also associated with autoimmune disease? If so, will polymorphisms in other phosphatases be found in the same spectrum of diseases? Are protein tyrosine phosphatases like PTPN22 good drug targets for the treatment of human autoimmunity? In this review, I offer some basis for thinking about these questions.

Initial results of screening of nondiabetic organ donors for expression of islet autoantibodies

CONTEXT

Type 1A diabetes is characterized by a long prodromal phase during which autoantibodies to islet antigens are present. Nevertheless, we lack data on the pancreatic pathology of subjects who are positive for islet autoantibodies (to islet autoantigens GAD65, insulin, and ICA512).

OBJECTIVE

In this manuscript, we describe a novel strategy in obtaining pancreata and pancreatic lymph nodes from islet autoantibody-positive organ donors that involves careful coordination among the laboratory and the organ donor provider organization.

DESIGN

We developed a rapid screening protocol for islet autoantibodies measurement of organ donors to allow identification of positive subjects before organ harvesting. In this way we were able to obtain pancreata and pancreatic lymph nodes from subjects with and without islet autoimmunity.

SETTING

The organ donors used in this study were obtained from the general community.

SUBJECTS

The population studied consisted of 112 organ donors (age range 1 month to 86 yr, mean age 39 yr).

MAIN OUTCOME MEASURE

The main outcome measure of this study consisted of evaluating the pancreatic histology and identify T cells autoreactive for islet antigens in the pancreatic lymph nodes.

RESULTS

To date we have identified three positive subjects and obtained the pancreas for histological evaluation from one of the autoantibody-positive donors who expressed ICA512 autoantibodies. Although this subject did not exhibit insulitis, lymphocytes derived from pancreatic lymph nodes reacted to the islet antigen phogrin.

CONCLUSION

In summary, these results indicate that it is possible to screen organ donors in real time for antiislet antibodies, characterize pancreatic histology, and obtain viable T cells for immunological studies.

Pathogenic T-cell clones in autoimmune diabetes: more lessons from the NOD mouse

T-cell clones that can efficiently transfer diabetes to prediabetic nonobese diabetic (NOD) mice provide a powerful approach to dissecting the autoimmune disease process and for investigating immunoregulation. Diabetogenic T-cell clones carried in culture allow for detailed analysis of T-cell effector function and in vivo activity, and thus the contribution of a single clonotype to pathogenesis can be studied. As T cells comprising most or all of the repertoire in T-cell receptor transgenic (TCR-Tg) mice, diabetogenic T-cell clones have led to new variations on the NOD mouse model of autoimmune disease. T-cell clones are being used to screen peptide libraries and proteomic arrays to identify the autoantigens that drive these clones in vivo and to extend our knowledge of the processes that give rise to these antigens. With the identification of peptide agonists and natural ligands, the development of MHC-peptide multimers has been possible. These reagents can track T cells in vivo and thus provide new approaches for disease diagnosis and therapy as well as a versatile set of tools for basic research on how T cells contribute to autoimmune disease.

Diabetes incidence is unaltered in glutamate decarboxylase 65-specific TCR retrogenic nonobese diabetic mice: generation by retroviral-mediated stem cell gene transfer

TCR transgenic mice are valuable tools for dissecting the role of autoantigen-specific T cells in the pathogenesis of type 1 diabetes but are time-consuming to generate and backcross onto congenic strains. To circumvent these limitations, we developed a new approach to rapidly generate mice expressing TCR using retroviral-mediated stem cell gene transfer and a novel picornavirus-like 2A peptide to link the TCR alpha- and beta-chains in a single retroviral vector. We refer to these as retrogenic (Rg) mice to avoid confusion with conventional transgenic mice. Our approach was validated by demonstrating that Rg nonobese diabetic (NOD)-scid mice expressing the diabetogenic TCRs, BDC2.5 and 4.1, generate clonotype-positive T cells and develop diabetes. We then expressed three TCR specific for either glutamate decarboxylase (GAD) 206-220 or GAD 524-538 or for hen egg lysozyme 11-25 as a control in NOD, NOD-scid, and B6.H2(g7) mice. Although T cells from these TCR Rg mice responded to their respective Ag in vitro, the GAD-specific T cells exhibited a naive, resting phenotype in vivo. However, T cells from Rg mice challenged with Ag in vivo became activated and developed into memory cells. Neither of the GAD-reactive TCR accelerated or protected mice from diabetes, nor did activated T cells transfer or protect against diabetes in NOD-scid recipients, suggesting that GAD may not be a primary target for diabetogenic T cells. Generation of autoantigen-specific TCR Rg mice represents a powerful approach for the analysis of a wide variety of autoantigens.

A comprehensive guide to antibody and T-cell responses in type 1 diabetes

Type 1 diabetes (T1D) is an organ-specific autoimmune disease in which the insulin-producing beta cells in the pancreatic islets are selectively eliminated. T cells specific for beta-cell antigens are the mediators of this precise cellular destruction. However, antibodies to beta-cell proteins are also generated and may be used for predicting disease in at-risk populations. Over the past two decades, numerous beta-cell proteins and lipids have been implicated as autoantigens in patients or in non-obese diabetic (NOD) mice, a well-studied animal model of T1D. Here, we present a review of these antigens, accompanied by their T-cell epitopes, where known, and a discussion of our current understanding of why particular self-proteins become disease-inciting antigens. Although two dozen beta-cell antigens have been identified to date, few of these have been confirmed to be recognized by pathogenic T cells early in the disease process. Further identification and characterization of initiating beta-cell antigens targeted by pathogenic T cells should be a priority for future studies.

T-cell epitopes in type 1 diabetes

Type 1 diabetes (TID) results from T-cell-mediated destruction of pancreatic b cells in genetically predisposed individuals. Autoreactive CD4(+) T helper cells and CD8(+) cytotoxic T lymphocytes (CTLs) recognize b-cell-derived peptides in the context of major histocompatibility complex class II and I molecules, respectively, in a process that terminates in b-cell death. Many peptide epitopes derived from b-cell proteins have been described for both humans and the nonobese diabetic (NOD) mouse, but their relative importance in disease pathogenesis is unclear. The significance of identifying key b-cell epitopes is underscored by a study showing that in the NOD mouse monitoring of a single population of b-cell-specific CTLs in the peripheral blood using a high-avidity analogue of the endogenous peptide may be used to accurately predict diabetes occurrence. Future studies focused on the discovery of immunodominant b-cell epitopes and their high-avidity analogues should have considerable implications for prediction and immunotherapy of TID.