Conserved T cell receptor alpha-chain induces insulin autoantibodies

Using the T Cell Receptor as a Biomarker in Type 1 Diabetes

T cell receptors (TCRs) are unique markers that define antigen specificity for a given T cell. With the evolution of sequencing and computational analysis technologies, TCRs are now prime candidates for the development of next-generation non-cell based T cell biomarkers, which provide a surrogate measure to assess the presence of antigen-specific T cells. Type 1 diabetes (T1D), the immune-mediated form of diabetes, is a prototypical organ specific autoimmune disease in which T cells play a pivotal role in targeting pancreatic insulin-producing beta cells. While the disease is now predictable by measuring autoantibodies in the peripheral blood directed to beta cell proteins, there is an urgent need to develop T cell markers that recapitulate T cell activity in the pancreas and can be a measure of disease activity. This review focuses on the potential and challenges of developing TCR biomarkers for T1D. We summarize current knowledge about TCR repertoires and clonotypes specific for T1D and discuss challenges that are unique for autoimmune diabetes. Ultimately, the integration of large TCR datasets produced from individuals with and without T1D along with computational 'big data' analysis will facilitate the development of TCRs as potentially powerful biomarkers in the development of T1D.

Understanding Autoimmune Diabetes through the Prism of the Tri-Molecular Complex

The strongest susceptibility allele for Type 1 Diabetes (T1D) is human leukocyte antigen (HLA), which supports a central role for T cells as the drivers of autoimmunity. However, the precise mechanisms that allow thymic escape and peripheral activation of beta cell antigen-specific T cells are still largely unknown. Studies performed with the non-obese diabetic (NOD) mouse have challenged several immunological dogmas, and have made the NOD mouse a key experimental system to study the steps of immunodysregulation that lead to autoimmune diabetes. The structural similarities between the NOD I-A^g7 and HLA-DQ8 have revealed the stability of the T cell receptor (TCR)/HLA/peptide tri-molecular complex as an important parameter in the development of autoimmune T cells, as well as afforded insights into the key antigens targeted in T1D. In this review, we will provide a summary of the current understanding with regard to autoimmune T cell development, the significance of the antigens targeted in T1D, and the relationship between TCR affinity and immune regulation.

Molecular Interactions Governing Autoantigen Presentation in Type 1 Diabetes

Type 1 diabetes is a chronic autoimmune disease resulting from T cell-mediated destruction of insulin-producing beta cells within pancreatic islets. Disease incidence has increased significantly in the last two decades, especially in young children. Type 1 diabetes is now predictable in humans with the measurement of serum islet autoantibodies directed against insulin and beta cell proteins. Knowledge regarding the presentation of insulin and islet antigens to T cells has increased dramatically over the last several years. Here, we review the trimolecular complex in diabetes, which consists of a major histocompatibility molecule,self-peptide, and T cell receptor, with a focus on insulin peptide presentation to T cells. With this increased understanding of how antigens are presented to T cells comes the hope for improved therapies for type 1 diabetes prevention.

Monoclonal antibody blocking the recognition of an insulin peptide-MHC complex modulates type 1 diabetes

The primary autoantigen triggering spontaneous type 1 diabetes mellitus in nonobese diabetic (NOD) mice is insulin. The major T-cell insulin epitope lies within the amino acid 9-23 peptide of the β-chain (B:9-23). This peptide can bind within the peptide binding groove of the NOD MHC class II molecule (MHCII), IA(g7), in multiple positions or "registers." However, the majority of pathogenic CD4 T cells recognize this complex only when the insulin peptide is bound in register 3 (R3). We hypothesized that antibodies reacting specifically with R3 insulin-IA(g7) complexes would inhibit autoimmune diabetes specifically without interfering with recognition of other IA(g7)-presented antigens. To test this hypothesis, we generated a monoclonal antibody (mAb287), which selectively binds to B:9-23 and related variants when presented by IA(g7) in R3, but not other registers. The monoclonal antibody blocks binding of IA(g7)-B:10-23 R3 tetramers to cognate T cells and inhibits T-cell responses to soluble B:9-23 peptides and NOD islets. However, mAb287 has no effect on recognition of other peptides bound to IA(g7) or other MHCII molecules. Intervention with mAb287, but not irrelevant isotype matched antibody, at either early or late stages of disease development, significantly delayed diabetes onset by inhibiting infiltration by not only insulin-specific CD4 T cells, but also by CD4 and CD8 T cells of other specificities. We propose that peptide-MHC-specific monoclonal antibodies can modulate autoimmune disease without the pleiotropic effects of nonselective reagents and, thus, could be applicable to the treatment of multiple T-cell mediated autoimmune disorders.

Pathogenic CD4⁺ T cells recognizing an unstable peptide of insulin are directly recruited into islets bypassing local lymph nodes

In the nonobese diabetic mouse, a predominant component of the autoreactive CD4(+) T cell repertoire is directed against the B:9-23 segment of the insulin B chain. Previous studies established that the majority of insulin-reactive T cells specifically recognize a weak peptide-MHC binding register within the B:9-23 segment, that to the 12-20 register. These T cells are uniquely stimulated when the B:9-23 peptide, but not the insulin protein, is offered to antigen presenting cells (APCs). Here, we report on a T cell receptor (TCR) transgenic mouse (8F10) that offers important new insights into the biology of these unconventional T cells. Many of the 8F10 CD4(+) T cells escaped negative selection and were highly pathogenic. The T cells were directly recruited into islets of Langerhans, where they established contact with resident intra-islet APCs. Immunogenic insulin had to be presented in order for the T cells to localize and cause disease. These T cells bypassed an initial priming stage in the pancreatic lymph node thought to precede islet T cell entry. 8F10 T cells induced the production of antiinsulin antibodies and islets contained immunoglobulin (IgG) deposited on β cells and along the vessel walls.

Targeting the trimolecular complex

Class II major histocompatibility molecules (MHC) confer disease risk for multiple autoimmune disorders including type 1 diabetes. The interaction between the components of the trimolecular complex (CD4(+) T cell receptors, self-peptide, and MHC class II molecules) plays a pivotal role in autoimmune disease pathogenesis. The development of therapies targeting various components of the trimolecular complex for the prevention of type 1 diabetes is actively being pursued. This review focuses on the components of the anti-insulin trimolecular complex, registers of insulin peptide binding to 'diabetogenic' MHC class II molecules, and therapies targeting each component of the trimolecular complex.

Immunotherapy in autoimmune type 1 diabetes

Type 1 diabetes (T1D) is a chronic autoimmune disease affecting millions of people worldwide. The disease is characterized by the loss of self-tolerance to the insulin-producing β-cells in the pancreas, the destruction of β-cells, and finally the development of chronic hyperglycemia at diagnosis of T1D. Its incidence and prevalence are rising dramatically, highlighting the need for immunotherapeutic strategies able to prevent or treat the disease in a safe and specific manner. Immunotherapeutic strategies are being developed, and aim to restore immunological self-tolerance, thereby limiting unwanted immunity and β-cell destruction. Foxp3+ regulatory T (Treg) cells exert essential functions to maintain and restore immunological self-tolerance. The identification of the transcription factor Foxp3 as the specification factor for the Treg cell lineage facilitated our understanding in the biology of Treg generation and function. This review highlights the current understanding of immunotherapeutic approaches as preventative and curative measures for autoimmune T1D. It includes an overview on early immunointervention studies, which made use of general immunosuppressive agents such as cyclosporin A, followed by a discussion on newly emerging clinical trials. Besides non-antigen-specific therapies, particular attention is given to antigen-specific generation of Foxp3+ Treg cells and their potential use to limit autoimmunity such as T1D.

Treg vaccination with a strong-agonistic insulin mimetope

Foxp3(+) regulatory T (Treg) cells serve as a vital mechanism of negative regulation to maintain immunological self-tolerance thereby suppressing immune-mediated inflammation. The identification of the transcription factor Foxp3 as the specification factor for the Treg cell lineage facilitated our understanding in the biology of Treg generation and function. In the past, we carefully studied the extrathymic conversion of naive CD4(+) T cells into Foxp3(+) expressing Treg cells and found that this process is most efficient upon subimmunogenic supply of strong-agonistic T cell receptor (TCR) ligands avoiding activation of antigen-presenting and T cells. In contrast, weak-agonistic antigens fail to efficiently induce stable Foxp3(+) Treg cells irrespective of the applied dose. Here, we discuss the specific requirements for the establishment of Treg vaccination protocols to interfere with autoimmunity such as Type 1 diabetes.

T-cell receptor retrogenic mice: a rapid, flexible alternative to T-cell receptor transgenic mice

The T-cell receptor (TCR) is unique in its complexity. It determines not only positive (life) and negative (death) selection in the thymus, but also mediates proliferation, anergy, differentiation, cytotoxicity and cytokine production in the periphery. Through its association with six CD3 signalling chains (εγ, δε and ζζ), the TCR is capable of recognizing an extensive variety of antigenic peptides, from both pathogens and self-antigens, and translating these interactions into multiple signalling pathways that mediate diverse T-cell developmental and functional responses. The analysis of TCR biology has been revolutionized by the development of TCR transgenic mice, which express a single clonotypic T-cell population, with diverse specificities and genetic backgrounds. However, they are time consuming to generate and characterize, limiting the analysis of large numbers of TCR over a short period of time in multiple genetic backgrounds. The recent development of TCR retrogenic technology resolves these limitations and could in time have a similarly important impact on our understanding of T-cell development and function. In this review, we will discuss the advantages and limitations of retrogenic technology compared with the generation and use of TCR transgenic mice for studying all aspects of T-cell biology.

Germline TRAV5D-4 T-cell receptor sequence targets a primary insulin peptide of NOD mice

There is accumulating evidence that autoimmunity to insulin B chain peptide, amino acids 9-23 (insulin B:9-23), is central to development of autoimmune diabetes of the NOD mouse model. We hypothesized that enhanced susceptibility to autoimmune diabetes is the result of targeting of insulin by a T-cell receptor (TCR) sequence commonly encoded in the germline. In this study, we aimed to demonstrate that a particular Vα gene TRAV5D-4 with multiple junction sequences is sufficient to induce anti-islet autoimmunity by studying retrogenic mouse lines expressing α-chains with different Vα TRAV genes. Retrogenic NOD strains expressing Vα TRAV5D-4 α-chains with many different complementarity determining region (CDR) 3 sequences, even those derived from TCRs recognizing islet-irrelevant molecules, developed anti-insulin autoimmunity. Induction of insulin autoantibodies by TRAV5D-4 α-chains was abrogated by the mutation of insulin peptide B:9-23 or that of two amino acid residues in CDR1 and 2 of the TRAV5D-4. TRAV13-1, the human ortholog of murine TRAV5D-4, was also capable of inducing in vivo anti-insulin autoimmunity when combined with different murine CDR3 sequences. Targeting primary autoantigenic peptides by simple germline-encoded TCR motifs may underlie enhanced susceptibility to the development of autoimmune diabetes.

Immunization with an insulin peptide-MHC complex to prevent type 1 diabetes of NOD mice

BACKGROUND

Mutating the insulin B:9-23 peptide prevents diabetes in NOD mice. Thus, the trimolecular complex of I-Ag7-insulin B:9-23 peptide-TCR may be essential for the development of spontaneous diabetes. Pathogenic T cells recognize the B:9-23 peptide presented by I-Ag7 in what is termed register 3, with the B22 basic amino acid (arginine) of the peptide bound in pocket 9 of I-Ag7. Our hypothesis is that immunization with an insulin B:12-22 peptide linked to I-Ag7 in register 3 (I-Ag7-B:RE#3 complex) can induce specific antibodies to the complex, block pathogenic TCRs, and thus prevent diabetes.

METHODS

We immunized young NOD mice with recombinant I-Ag7-B:RE#3 protein, in which two amino acids of the peptide were mutated to fix the peptide in register 3, and investigated the induced antibodies targeted to the peptide in register 3.

RESULTS

Specific antibodies targeting I-Ag7-B:RE#3 but not I-Ag7-HEL were identified in the sera of I-Ag7-B:RE#3 immunized mice. The sera inhibited B:9-23-induced T-cell responses in vitro. I-Ag7-B:RE#3 immunization delayed progression to diabetes (versus PBS, p=0.0005), while immunization with I-Ag7-HEL control complex did not.

CONCLUSIONS

Immunization with I-Ag7-B:RE#3 complex significantly delays the development of insulin autoantibodies and the onset of diabetes in NOD mice, which is associated with the induction of I-Ag7-B:RE#3 antibodies.

Structure-based selection of small molecules to alter allele-specific MHC class II antigen presentation

Class II major histocompatibility molecules are the primary susceptibility locus for many autoimmune disorders, including type 1 diabetes. Human DQ8 and I-A(g7), in the NOD mouse model of spontaneous autoimmune diabetes, confers diabetes risk by modulating presentation of specific islet peptides in the thymus and periphery. We used an in silico molecular docking program to screen a large "druglike" chemical library to define small molecules capable of occupying specific structural pockets along the I-A(g7) binding groove, with the objective of influencing presentation to T cells of the autoantigen insulin B chain peptide consisting of amino acids 9-23. In this study we show, using both murine and human cells, that small molecules can enhance or inhibit specific TCR signaling in the presence of cognate target peptides, based upon the structural pocket targeted. The influence of compounds on the TCR response was pocket dependent, with pocket 1 and 6 compounds inhibiting responses and molecules directed at pocket 9 enhancing responses to peptide. At nanomolar concentrations, the inhibitory molecules block the insulin B chain peptide consisting of amino acids 9-23, endogenous insulin, and islet-stimulated T cell responses. Glyphosine, a pocket 9 compound, enhances insulin peptide presentation to T cells at concentrations as low as 10 nM, upregulates IL-10 secretion, and prevents diabetes in NOD mice. These studies present a novel method for identifying small molecules capable of both stimulating and inhibiting T cell responses, with potentially therapeutic applications.

Specificity and detection of insulin-reactive CD4+ T cells in type 1 diabetes in the nonobese diabetic (NOD) mouse

In the nonobese diabetic (NOD) mouse model of type 1 diabetes (T1D), an insulin peptide (B:9-23) is a major target for pathogenic CD4(+) T cells. However, there is no consensus on the relative importance of the various positions or "registers" this peptide can take when bound in the groove of the NOD MHCII molecule, IA(g7). This has hindered structural studies and the tracking of the relevant T cells in vivo with fluorescent peptide-MHCII tetramers. Using mutated B:9-23 peptides and methods for trapping the peptide in particular registers, we show that most, if not all, NOD CD4(+) T cells react to B:9-23 bound in low-affinity register 3. However, these T cells can be divided into two types depending on whether their response is improved or inhibited by substituting a glycine for the B:21 glutamic acid at the p8 position of the peptide. On the basis of these findings, we constructed a set of fluorescent insulin-IA(g7) tetramers that bind to most insulin-specific T-cell clones tested. A mixture of these tetramers detected a high frequency of B:9-23-reactive CD4(+) T cells in the pancreases of prediabetic NOD mice. Our data are consistent with the idea that, within the pancreas, unique processing of insulin generates truncated peptides that lack or contain the B:21 glutamic acid. In the thymus, the absence of this type of processing combined with the low affinity of B:9-23 binding to IA(g7) in register 3 may explain the escape of insulin-specific CD4(+) T cells from the mechanisms that usually eliminate self-reactive T cells.

The anti-insulin trimolecular complex in type 1 diabetes

PURPOSE OF REVIEW

Description of the immunologic components needed for autoimmune diabetes.

RECENT FINDINGS

The major histocompatability complex (MHC) class II molecules are the primary susceptibility genes for many autoimmune diseases, including type 1 diabetes. Understanding of the structural interaction between MHC molecules, antigenic peptides, and T-cell receptors (the three components of the trimolecular complex) has increased greatly over the past several years. The components of the anti-insulin trimolecular complex and findings that insulin is a key autoantigen in type 1 diabetes are reviewed.

SUMMARY

The anti-insulin trimolecular complex is well defined in the nonobese diabetic mouse model. Insulin and specifically, the amino acid sequence 9 to 23 of the insulin B chain, represents a primary antigenic target for islet autoimmunity in the nonobese diabetic mouse model of type 1 diabetes with a specific mutation of this peptide preventing all diabetes. Initial studies suggest the human homologs of the anti-insulin trimolecular complex may be relevant in human disease.

Insulin auto-immunity: implications for the prevention of Type 1 diabetes mellitus

Mounting evidence suggests insulin is an important and potentially initiating antigen in the pathogenesis of Type 1 diabetes. High-affinity insulin antibodies are found early in disease development and appear to predict progression. Insulin is the only Type 1 diabetes auto-antigen with exclusive pancreatic expression and the only one whose gene maps to a major susceptibility locus. Preclinical studies in rodent models of immune-mediated diabetes show great promise for the possibility of preventing disease by peripheral tolerization. Translation of this evidence to clinical trials of oral, intranasal and parenteral insulin to invoke immune tolerance and prevent diabetes has not proven successful to date, but promising results in a small subset of highest-risk individuals have maintained enthusiasm for this promising prevention strategy. Currently, studies of oral and intranasal insulin are ongoing to determine the optimal dose, timing and target population for Type 1 diabetes prevention.

Molecular targeting of islet autoantigens

Type 1 diabetes of man and animal models results from immune-mediated specific beta cell destruction. Multiple islet antigens are targets of autoimmunity and most of these are not beta cell specific. Immune responses to insulin appear to be essential for the development of diabetes of the NOD mouse. In this review, we will emphasize the unusual manner in which selected autoantigenic peptides (particularly the recently discovered target of BDC2.5 T cells [chromagranin A]) are presented and recognized by autoreactive CD4(+) T cell receptors. We hypothesize that "unusual" structural interactions of specific trimolecular complexes (MHC class II, peptide, and T cell receptors) are fundamental to the escape from the thymus of autoreactive T cells able to cause type 1 diabetes.

Genetics, pathogenesis and clinical interventions in type 1 diabetes

Type 1 diabetes is an autoimmune disorder afflicting millions of people worldwide. Once diagnosed, patients require lifelong insulin treatment and can experience numerous disease-associated complications. The last decade has seen tremendous advances in elucidating the causes and treatment of the disease based on extensive research both in rodent models of spontaneous diabetes and in humans. Integrating these advances has led to the recognition that the balance between regulatory and effector T cells determines disease risk, timing of disease activation, and disease tempo. Here we describe current progress, the challenges ahead and the new interventions that are being tested to address the unmet need for preventative or curative therapies.

Banting Lecture 2009: An unfinished journey: molecular pathogenesis to prevention of type 1A diabetes

The Banting Medal for Scientific Achievement Award is the American Diabetes Association's highest scientific award and honors an individual who has made significant, long-term contributions to the understanding of diabetes, its treatment, and/or prevention. The award is named after Nobel Prize winner Sir Frederick Banting, who codiscovered insulin treatment for diabetes.

Dr. Eisenbarth received the American Diabetes Association's Banting Medal for Scientific Achievement at the Association's 69th Scientific Sessions, June 5–9, 2009, in New Orleans, Louisiana. He presented the Banting Lecture, An Unfinished Journey—Type 1 Diabetes—Molecular Pathogenesis to Prevention , on Sunday, June 7, 2009.

Gamma delta T cell receptors confer autonomous responsiveness to the insulin-peptide B:9-23

The range and physical qualities of molecules that act as ligands for the gammadelta T cell receptors (TCRs) remain uncertain. Processed insulin is recognized by alphabeta T cells, which mediate diabetes in non-obese diabetic (NOD) mice. Here, we present evidence that gammadelta T cells in these mice recognize processed insulin as well. Hybridomas generated from NOD spleen and pancreatic lymph nodes included clones expressing gammadelta TCRs that responded specifically to purified islets of Langerhans and to an insulin peptide, but not to intact insulin. The gammadelta TCRs associated with this type of response are diverse, but a cloned gammadelta TCR was sufficient to transfer the response. The response to the insulin peptide was autonomous as demonstrated by stimulating single responder cells in isolation. This study reveals a novel specificity for gammadelta TCRs, and raises the possibility that gammadelta T cells become involved in islet-specific autoimmunity.

Analysis of T cell receptor beta chains that combine with dominant conserved TRAV5D-4*04 anti-insulin B:9-23 alpha chains

OBJECTIVE

The objective of this study was to define the spectrum of TCR beta chains permissive for T cells with alpha chains containing the conserved TRAV5D-4*04 sequence to target the insulin B:9-23 peptide, a major epitope for initiation of diabetes in the NOD mouse.

MATERIALS AND METHODS

We produced T cell hybridomas from mice with single T cell receptors (BDC12-4.1 TCR alpha(+)beta(+) double transgenic mice and BDC12-4.4 TCR alpha(+)beta(+) double retrogenic mice) or from mice with only the corresponding alpha chains transgene or retrogene and multiple endogenous TCR beta chains.

RESULTS

Hybridomas with the complete BDC12-4.1 and BDC12-4.4 T cell receptors, despite having markedly different TCR beta chains, responded to similar B:9-23 peptides. Approximately 1% of the hybridomas from mice with the fixed TRAV5D-4*04 alpha chains and multiple endogenous beta chains responded to B:9-23 peptides while the majority of hybridomas with different beta chains did not respond. There was no apparent conservation of TCR beta chain sequences in the responding hybridomas.

CONCLUSIONS

Approximately 1% of hybridomas utilizing different TCR beta chains paired with the conserved TRAV5D-4*04 containing alpha chains respond to insulin peptide B:9-23. Therefore, TCR beta chain sequences make an important contribution to insulin B:9-23 peptide recognition but multiple beta chain sequences are permissive for recognition.