Transgenic insulin (B:9-23) T-cell receptor mice develop autoimmune diabetes dependent upon RAG genotype, H-2g7 homozygosity, and insulin 2 gene knockout

Aire mediates tolerance to insulin through thymic trimming of high-affinity T cell clones

Insulin is a central autoantigen in the pathogenesis of T1D, and thymic epithelial cell expression of insulin under the control of the Autoimmune Regulator (Aire) is thought to be a key component of maintaining tolerance to insulin. In spite of this general working model, direct detection of this thymic selection on insulin-specific T cells has been somewhat elusive. Here, we used a combination of highly sensitive T cell receptor transgenic models for detecting thymic selection and sorting and sequencing of Insulin-specific CD4+ T cells from Aire-deficient mice as a strategy to further define their selection. This analysis revealed a number of unique t cell receptor (TCR) clones in Aire-deficient hosts with high affinity for insulin/major histocompatibility complex (MHC) ligands. We then modeled the thymic selection of one of these clones in Aire-deficient versus wild-type hosts and found that this model clone could escape thymic negative selection in the absence of thymic Aire. Together, these results suggest that thymic expression of insulin plays a key role in trimming and removing high-affinity insulin-specific T cells from the repertoire to help promote tolerance.

A new, all-encompassing aetiology of type 1 diabetes

The aetiology of type 1 diabetes (T1D) is considered multifactorial with the contribution of the MHC on chromosome 6 being most important. Multiple factors also contribute to the aetiology of colorectal neoplasia, but the final event causing the change from normal mucosa to polyp and from polyp to cancer is due to a single somatic mutation event. Repeated formation of colorectal neoplasia within an at-risk population results in a predictable, tapering, exponential neoplasia distribution. Critical mutations driving colorectal neoplasia formation occur in mutation-prone DNA. These observations led to three hypotheses related to T1D. First, a single somatic mutation within the MHC of antigen presenting cells results in a change in phenotype from normal to T1D. Second, the distribution of additional autoimmune diseases (AAIDs) among persons with T1D adheres to a predictable, tapering, exponential distribution. And third, critical mutations driving development of T1D occur in mutation-prone DNA. To address the hypotheses in an orderly fashion, a new analytical method called genome-wide aetiology analysis (GWEA) consisting of nine steps is presented. All data required for GWEA of T1D are obtained from peer-reviewed publications or publicly available genome and proteome databases. Critical GWEA steps include AAID distribution among persons with T1D, analysis of at-risk HLA loci for mutation-prone DNA, determination of the role of non-MHC genes on GWAS, and verification of human data by cell culture or animal experiments. GWEA results show that distribution of AAID among persons with T1D adheres to a predictable, tapering, exponential distribution. A single, critical, somatic mutation within the epitope-binding groove of at-risk HLA loci alters HLA-insulin-peptide-T-cell-receptor (TCR) complex binding affinity and creates a new pathway that leads to loss of self-tolerance. The at-risk HLA loci, in particular binding pockets P1, P4 and P9, are encoded by mutation-prone DNA: GC-rich DNA sequence and somatic hypermutation hotspots. All other genes on GWAS can but do not have to amplify the new autoimmune pathway by facilitating DNA mutations, changing peptide binding affinity, reducing signal inhibition or augmenting signal intensity. Animal experiments agree with human studies. In conclusion, T1D is caused by a somatic mutation within the epitope-binding groove of an at-risk HLA gene that affects HLA-insulin-peptide-TCR complex binding affinity and initiates an autoimmune pathway. The nature of the peptide that binds to a mutated epitope-binding groove of an at-risk HLA gene determines the type of autoimmune disease that develops, that is, one at-risk HLA locus, multiple autoimmune diseases. Thus, T1D and AAIDs, and therefore common autoimmune diseases, share a similar somatic mutation-based aetiology.

HLA-DQ8 Supports Development of Insulitis Mediated by Insulin-Reactive Human TCR-Transgenic T Cells in Nonobese Diabetic Mice

In an effort to improve HLA-"humanized" mouse models for type 1 diabetes (T1D) therapy development, we previously generated directly in the NOD strain CRISPR/Cas9-mediated deletions of various combinations of murine MHC genes. These new models improved upon previously available platforms by retaining β2-microglobulin functionality in FcRn and nonclassical MHC class I formation. As proof of concept, we generated H2-Db/H2-Kd double knockout NOD mice expressing human HLA-A*0201 or HLA-B*3906 class I variants that both supported autoreactive diabetogenic CD8+ T cell responses. In this follow-up work, we now describe the creation of 10 new NOD-based mouse models expressing various combinations of HLA genes with and without chimeric transgenic human TCRs reactive to proinsulin/insulin. The new TCR-transgenic models develop differing levels of insulitis mediated by HLA-DQ8-restricted insulin-reactive T cells. Additionally, these transgenic T cells can transfer insulitis to newly developed NSG mice lacking classical murine MHC molecules, but expressing HLA-DQ8. These new models can be used to test potential therapeutics for a possible capacity to reduce islet infiltration or change the phenotype of T cells expressing type 1 diabetes patient-derived β cell autoantigen-specific TCRs.

Regulatory T cells targeting a pathogenic MHC class II: Insulin peptide epitope postpone spontaneous autoimmune diabetes

Introduction

In spontaneous type 1 diabetes (T1D) non-obese diabetic (NOD) mice, the insulin B chain peptide 9-23 (B:9-23) can bind to the MHC class II molecule (IAg7) in register 3 (R3), creating a bimolecular IAg7/InsulinB:9-23 register 3 conformational epitope (InsB:R3). Previously, we showed that the InsB:R3-specific chimeric antigen receptor (CAR), constructed using an InsB:R3-monoclonal antibody, could guide CAR-expressing CD8 T cells to migrate to the islets and pancreatic lymph nodes. Regulatory T cells (Tregs) specific for an islet antigen can broadly suppress various pathogenic immune cells in the islets and effectively halt the progression of islet destruction. Therefore, we hypothesized that InsB:R3 specific Tregs would suppress autoimmune reactivity in islets and efficiently protect against T1D.

Methods

To test our hypothesis, we produced InsB:R3-Tregs and tested their disease-protective effects in spontaneous T1D NOD.CD28-/- mice.

Results

InsB:R3-CAR expressing Tregs secrete IL-10 dominated cytokines upon engagement with InsB:R3 antigens. A single infusion of InsB:R3 Tregs delayed the onset of T1D in 95% of treated mice, with 35% maintaining euglycemia for two healthy lifespans, readily home to the relevant target whereas control Tregs did not. Our data demonstrate that Tregs specific for MHC class II: Insulin peptide epitope (MHCII/Insulin) protect mice against T1D more efficiently than polyclonal Tregs lacking islet antigen specificity, suggesting that the MHC II/insulin-specific Treg approach is a promising immune therapy for safely preventing T1D.

A monoclonal antibody with broad specificity for the ligands of insulin B:9-23 reactive T cells prevents spontaneous type 1 diabetes in mice

Activation of T cells specific for insulin B chain amino acids 9 to 23 (B:9–23) is essential for the initiation of type 1 diabetes (T1D) in non-obese diabetic mice. We previously reported that peptide/MHC complexes containing optimized B:9–23 mimotopes can activate most insulin-reactive pathogenic T cells. A monoclonal antibody (mAb287) targeting these complexes prevented disease in 30–50% of treated animals (compared to 10% of animals given an isotype control). The incomplete protection is likely due to the relatively low affinity of the antibody for its ligand and limited specificity. Here, we report an enhanced reagent, mAb757, with improved specificity, affinity, and efficacy in modulating T1D. Importantly, mAb757 bound with nanomolar affinity to agonists of both “type A” and “type B” cells and suppressed “type B” cells more efficiently than mAb287. When given weekly starting at 4 weeks of age, mAb757 protected ~70% of treated mice from developing T1D for at least 35 weeks, while mAb287 only delayed disease in 25% of animals under the same conditions. Consistent with its higher affinity, mAb757 was also able to stain antigen-presenting cells loaded with B:9–23 mimotopes in vivo. We conclude that monoclonal antibodies that can block the presentation of pathogenic T cell receptor epitopes are viable candidates for antigen-specific immunotherapy for T1D.

Endogenous retrovirus Gag antigen and its gene variants are unique autoantigens expressed in the pancreatic islets of non-obese diabetic mice

Endogenous retrovirus (ERV) are remnants of ancient retroviruses that have been incorporated into the genome and evidence suggests that they may play a role in the etiology of T1D. We previously identified a murine leukemia retrovirus-like ERV whose Env and Gag antigens are involved in autoimmune responses in non-obese diabetic (NOD) mice. In this study, we show that the Gag antigen is present in the islet stromal cells. Although Gag gene transcripts were present, Gag protein was not detected in diabetes-resistant mice. Cloning and sequencing analysis of individual Gag genes revealed that NOD islets express Gag gene variants with complete open-reading frames (ORFs), in contrast to the diabetes-resistant mice, whose islet Gag gene transcripts are mostly non-ORFs. Importantly, the ORFs obtained from the NOD islets are extremely heterogenous, coding for various mutants that are absence in the genome. We further show that Gag antigens are stimulatory for autoreactive T cells and identified one islet-expressing Gag variant that contains an altered peptide ligand capable of inducing IFN-gamma release by the T cells. The data highlight a unique retrovirus-like factor in the islets of the NOD mouse strain, which may participate in key events triggering autoimmunity and T1D.

MHC-mismatched mixed chimerism restores peripheral tolerance of noncross-reactive autoreactive T cells in NOD mice

Mixed chimerism has shown good potential to cure some autoimmune diseases and prevent tissue rejection. It is known that MHC-mismatched but not -matched mixed chimerism effectively tolerizes autoreactive T cells, even those noncross-reactive T cells that do not directly recognize donor-type antigen presenting cells [i.e., dendritic cells (DCs)]. How this is accomplished remains unknown. These studies have shown that tolerizing peripheral residual host-type noncross-reactive autoreactive T cells requires engraftment of donor-type DCs and involves a host-type DC-mediated increase in donor-type Treg cells, which associates with restoration of tolerogenic features of host-type plasmacytoid DCs and expansion of host-type Treg cells. This study suggests a previously unrecognized tolerance network among donor- and host-type DCs and Treg cells in MHC-mismatched mixed chimeras.

Autoimmune type 1 diabetes (T1D) and other autoimmune diseases are associated with particular MHC haplotypes and expansion of autoreactive T cells. Induction of MHC-mismatched but not -matched mixed chimerism by hematopoietic cell transplantation effectively reverses autoimmunity in diabetic nonobese diabetic (NOD) mice, even those with established diabetes. As expected, MHC-mismatched mixed chimerism mediates deletion in the thymus of host-type autoreactive T cells that have T-cell receptor (TCR) recognizing (cross-reacting with) donor-type antigen presenting cells (APCs), which have come to reside in the thymus. However, how MHC-mismatched mixed chimerism tolerizes host autoreactive T cells that recognize only self-MHC–peptide complexes remains unknown. Here, using NOD.Rag1^−/−.BDC2.5 or NOD.Rag1^−/−.BDC12-4.1 mice that have only noncross-reactive transgenic autoreactive T cells, we show that induction of MHC-mismatched but not -matched mixed chimerism restores immune tolerance of peripheral noncross-reactive autoreactive T cells. MHC-mismatched mixed chimerism results in increased percentages of both donor- and host-type Foxp3⁺ Treg cells and up-regulated expression of programmed death-ligand 1 (PD-L1) by host-type plasmacytoid dendritic cells (pDCs). Furthermore, adoptive transfer experiments showed that engraftment of donor-type dendritic cells (DCs) and expansion of donor-type Treg cells are required for tolerizing the noncross-reactive autoreactive T cells in the periphery, which are in association with up-regulation of host-type DC expression of PD-L1 and increased percentage of host-type Treg cells. Thus, induction of MHC-mismatched mixed chimerism may establish a peripheral tolerogenic DC and Treg network that actively tolerizes autoreactive T cells, even those with no TCR recognition of the donor APCs.

Autoimmune Responses to Exosomes and Candidate Antigens Contribute to Type 1 Diabetes in Non-Obese Diabetic Mice

PURPOSE OF REVIEW

The initial autoimmune trigger of type 1 diabetes (T1D) remains unclear. In non-obese diabetic (NOD) mice, islet inflammation starts early in life, suggesting the presence of an endogenous trigger for the spontaneous autoimmune response in this T1D mouse model. In this review, we argue that abnormal release of exosomes might be the trigger of the early inflammatory and autoimmune responses in the islets.

RECENT FINDINGS

Exosomes are nano-sized membrane complexes that are secreted by cells following fusion of late endosomes and/or multivesicular bodies with the plasma membrane. They are known extracellular messengers, communicating among neighboring cells via transporting large molecules from parent cells to recipient cells. Recent evidence demonstrates that these extracellular vesicles can modulate immune responses. It has been shown that insulinoma and islet mesenchymal stem cell-released exosomes are potent immune stimuli that can induce autoreactive B and T cells. Searching for candidate antigens in the exosomes identified endogenous retrovirus (ERV) Env and Gag antigens, which are homologous to an endogenous murine leukemia retrovirus. Autoantibodies and autoreactive T cells spontaneously developed in NOD mice can react to these retroviral antigens. More importantly, expression of the retroviral antigens in the islet mesenchymal stem cells is associated with disease susceptibility, and the expression is restricted to T1D-susceptible but not resistant mouse strains. Exosomes are novel autoimmune targets, carrying autoantigens that can stimulate innate and adaptive immune responses. An abnormal or excess release of exosomes, particularly those ones containing endogenous retroviral antigens might be responsible for triggering tissue-specific inflammatory and autoimmune responses.

Ectopic Expression of Self-Antigen Drives Regulatory T Cell Development and Not Deletion of Autoimmune T Cells

Type 1 diabetes is a T cell-mediated autoimmune disease that is characterized by Ag-specific targeting and destruction of insulin-producing β cells. Although multiple studies have characterized the pathogenic potential of β cell-specific T cells, we have limited mechanistic insight into self-reactive autoimmune T cell development and their escape from negative selection in the thymus. In this study, we demonstrate that ectopic expression of insulin epitope B:9-23 (InsB_9-23) by thymic APCs is insufficient to induce deletion of high- or low-affinity InsB_9-23-reactive CD4⁺ T cells; however, we observe an increase in the proportion and number of thymic and peripheral Foxp3⁺ regulatory T cells. In contrast, the MHC stable insulin mimetope (InsB_9-23 R22E) efficiently deletes insulin-specific T cells and prevents escape of high-affinity thymocytes. Collectively, these results suggest that Ag dose and peptide-MHC complex stability can lead to multiple fates of insulin-reactive CD4⁺ T cell development and autoimmune disease outcome.

Type 1 diabetes pathogenesis is modulated by spontaneous autoimmune responses to endogenous retrovirus antigens in NOD mice

Secreted microvesicles (MVs) are potent inflammatory triggers that stimulate autoreactive B and T cells, causing Type 1 Diabetes in non-obese diabetic (NOD) mice. Proteomic analysis of purified MVs released from islet cells detected the presence of endogenous retrovirus (ERV) antigens, including Env and Gag sequences similar to the well-characterized murine leukemia retroviruses. This raises the possibility that ERV antigens may be expressed in the pancreatic islets via MV secretion. Using virus-like particles produced by co-expressing ERV Env and Gag antigens, and a recombinant gp70 Env protein, we demonstrated that NOD but not diabetes-resistant mice developed anti-Env autoantibodies that increase in titer as disease progresses. A lentiviral-based RNA interference knockdown of Gag revealed that Gag contributes to the MV-induced T-cell response, whose diabetogenic function can be demonstrated via cell-transfer into immune-deficient mice. Finally, we observed that Gag and Env are expressed in NOD islet-derived primary mesenchymal stem cells (MSCs). However, MSCs derived from the islets of diabetes-resistant mice do not express the antigens. Taken together, abnormal ERV activation and secretion of MVs may induce anti-retroviral responses to trigger autoimmunity.

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.

Beta-cell Specific Autoantibodies: Are they Just an Indicator of Type 1 Diabetes?

BACKGROUND

Autoantibodies (AAbs) against islet autoantigens (AAgs) are used for type 1 diabetes (T1D) diagnosis and prediction. Islet-specific AAbs usually appear early in life and may fluctuate in terms of number and titer sometimes for over 20 years before T1D develops. Whereas their predictive power is high for pediatric subjects with high genetic risk who rapidly progress to multiple AAb positivity, they are less reliable for children with low genetic risk, single AAb positivity and slow disease progression.

OBJECTIVE

It is unknown how AAbs develop and whether they are involved in T1D pathogenesis. So far an increase in AAb number seems to only indicate AAg spreading and progression towards clinical T1D. The goal of this review is to shed light on the possible involvement of AAbs in T1D development.

METHOD

We thoroughly review the current literature and discuss possible mechanisms of AAb development and the roles they may play in disease pathogenesis.

RESULTS

Genetic and environmental factors instigate changes at the molecular and cellular levels that promote AAb development. Although direct involvement of AAbs in T1D is less clear, autoreactive B cells are clearly involved in various immune and autoimmune responses via antigen presentation, immunoregulation and cytokine production.

CONCLUSION

Our analysis suggests that understanding the mechanisms that lead to islet-specific AAb development and the diabetogenic processes that autoreactive B cells promote may uncover additional biomarkers and therapeutic targets.

Restoring Regulatory T Cells in Type 1 Diabetes

Genetic and cellular studies of type 1 diabetes in patients and in the nonobese diabetic mouse model of type 1 diabetes point to an imbalance between effector T cells and regulatory T cells (Tregs) as a driver of the disease. The imbalance may arise as a consequence of genetically encoded defects in thymic deletion of islet antigen-specific T cells, induction of islet antigen-specific thymic Tregs, unfavorable tissue environment for peripheral Treg induction, and failure of islet antigen-specific Tregs to survive in the inflamed islets secondary to insufficient IL-2 signals. These understandings are the foundation for rationalized design of new therapeutic interventions to restore the balance by selectively targeting effector T cells and boosting Tregs.

Retroviral Transduction of Bone Marrow Progenitor Cells to Generate T-cell Receptor Retrogenic Mice

T cell receptor (TCR) signaling is essential in the development and differentiation of T cells in the thymus and periphery, respectively. The vast array of TCRs proves studying a specific antigenic response difficult. Therefore, TCR transgenic mice were made to study positive and negative selection in the thymus as well as peripheral T cell activation, proliferation and tolerance. However, relatively few TCR transgenic mice have been generated specific to any given antigen. Thus, studies involving TCRs of varying affinities for the same antigenic peptide have been lacking. The generation of a new TCR transgenic line can take six or more months. Additionally, any specific backcrosses can take an additional six months. In order to allow faster generation and screening of multiple TCRs, a protocol for retroviral transduction of bone marrow was established with stoichiometric expression of the TCRα and TCRβ chains and the generation of retrogenic mice. Each retrogenic mouse is essentially a founder, virtually negating a founder effect, while the length of time to generate a TCR retrogenic is cut from six months to approximately six weeks. Here we present a rapid and flexible alternative to TCR transgenic mice that can be expressed on any chosen background with any particular TCR.

Loss of Peripheral Protection in Pancreatic Islets by Proteolysis-Driven Impairment of VTCN1 (B7-H4) Presentation Is Associated with the Development of Autoimmune Diabetes

Ag-specific activation of T cells is an essential process in the control of effector immune responses. Defects in T cell activation, particularly in the costimulation step, have been associated with many autoimmune conditions, including type 1 diabetes (T1D). Recently, we demonstrated that the phenotype of impaired negative costimulation, due to reduced levels of V-set domain-containing T cell activation inhibitor 1 (VTCN1) protein on APCs, is shared between diabetes-susceptible NOD mice and human T1D patients. In this study, we show that a similar process takes place in the target organ, as both α and β cells within pancreatic islets gradually lose their VTCN1 protein during autoimmune diabetes development despite upregulation of the VTCN1 gene. Diminishment of functional islet cells' VTCN1 is caused by the active proteolysis by metalloproteinase N-arginine dibasic convertase 1 (NRD1) and leads to the significant induction of proliferation and cytokine production by diabetogenic T cells. Inhibition of NRD1 activity, alternatively, stabilizes VTCN1 and dulls the anti-islet T cell responses. Therefore, we suggest a general endogenous mechanism of defective VTCN1 negative costimulation, which affects both lymphoid and peripheral target tissues during T1D progression and results in aggressive anti-islet T cell responses. This mechanism is tied to upregulation of NRD1 expression and likely acts in two synergistic proteolytic modes: cell-intrinsic intracellular and cell-extrinsic systemic. Our results highlight an importance of VTCN1 stabilization on cell surfaces for the restoration of altered balance of immune control during T1D.

Autoimmune Diabetes: An Overview of Experimental Models and Novel Therapeutics

Type 1 diabetes (T1D) results from a chronic and selective destruction of insulin-secreting β-cells within the islets of Langerhans of the pancreas by autoreactive CD4(+) and CD8(+) T lymphocytes. The use of animal models of T1D was instrumental for deciphering the steps of the autoimmune process leading to T1D. The non-obese diabetic (NOD) mouse and the bio-breeding (BB) rat spontaneously develop the disease similar to the human pathology in terms of the immune responses triggering autoimmune diabetes and of the genetic and environmental factors influencing disease susceptibility. The generation of genetically modified models allowed refining our understanding of the etiology and the pathogenesis of the disease. In the present review, we provide an overview of the experimental models generated and used to gain knowledge on the molecular and cellular mechanisms underlying the breakdown of self-tolerance in T1D and the progression of the autoimmune response. Immunotherapeutic interventions designed in these animal models and translated into the clinical arena in T1D patients will also be discussed.

Regulation of B lymphocyte responses to Toll-like receptor ligand binding during diabetes prevention in non-obese diabetic (NOD) mice

BACKGROUND

Interactions between genetic risk factors and the environment drive type 1 diabetes (T1D). The system of Toll-like receptors (TLR) detects these environmental triggers; however, the target cell that intermediates these interactions to drive T1D remains unknown.

METHODS

We investigated the effect of TLR pathway activation (myeloid differentiation primary response 88 [MyD88] vs TIR-domain-containing adapter-inducing interferon-β [TRIF]) on B cell subsets via flow cytometry, including their activation, survival, proliferation, and cytoskeletal mobilization. The effect of polyinosinic-polycytidylic acid (poly(I:C)) on diabetes development was addressed, including the B cell-dependent activation of diabetes-protective DX5+ cells, using genetic models and adoptive transfer.

RESULTS

B lymphocytes from non-obese diabetic (NOD) mice expressed enhanced levels of TLR-responsive proteins. Ex vivo analysis of B lymphocyte subsets demonstrated that TLR3 stimulation via TRIF deletes cells exhibiting a marginal zone phenotype, whereas MyD88-dependent ligands enhance their survival. In vivo, marginal zone B cells were activated by poly(I:C) and were unexpectedly retained in the spleen of NOD mice, in contrast with the mobilization of these cells in non-autoimmune mice, a phenotype we traced to defective actin cytoskeletal dynamics. These activated B cells mediated TLR3-induced diabetes protection.

CONCLUSIONS

Immunotherapies must account for both B cell location and activation, and these properties may differ in autoimmune and healthy settings.

BDC12-4.1 T-cell receptor transgenic insulin-specific CD4 T cells are resistant to in vitro differentiation into functional Foxp3+ T regulatory cells

The infusion of ex vivo-expanded autologous T regulatory (Treg) cells is potentially an effective immunotherapeutic strategy against graft-versus-host disease (GvHD) and several autoimmune diseases, such as type 1 diabetes (T1D). However, in vitro differentiation of antigen-specific T cells into functional and stable Treg (iTreg) cells has proved challenging. As insulin is the major autoantigen leading to T1D, we tested the capacity of insulin-specific T-cell receptor (TCR) transgenic CD4(+) T cells of the BDC12-4.1 clone to convert into Foxp3(+) iTreg cells. We found that in vitro polarization toward Foxp3(+) iTreg was effective with a majority (>70%) of expanded cells expressing Foxp3. However, adoptive transfer of Foxp3(+) BDC12-4.1 cells did not prevent diabetes onset in immunocompetent NOD mice. Thus, in vitro polarization of insulin-specific BDC12-4.1 TCR transgenic CD4(+) T cells toward Foxp3+ cells did not provide dominant tolerance in recipient mice. These results highlight the disconnect between an in vitro acquired Foxp3(+) cell phenotype and its associated in vivo regulatory potential.

Follicular regulatory T cells control humoral autoimmunity via NFAT2-regulated CXCR5 expression

T cell–specific NFAT2 deletion results in reduced CXCR5⁺ follicular regulatory T cells, leading to uncontrolled germinal center responses and humoral autoimmunity.

Maturation of high-affinity B lymphocytes is precisely controlled during the germinal center reaction. This is dependent on CD4⁺CXCR5⁺ follicular helper T cells (T_FH) and inhibited by CD4⁺CXCR5⁺Foxp3⁺ follicular regulatory T cells (T_FR). Because NFAT2 was found to be highly expressed and activated in follicular T cells, we addressed its function herein. Unexpectedly, ablation of NFAT2 in T cells caused an augmented GC reaction upon immunization. Consistently, however, T_FR cells were clearly reduced in the follicular T cell population due to impaired homing to B cell follicles. This was T_FR-intrinsic because only in these cells NFAT2 was essential to up-regulate CXCR5. The physiological relevance for humoral (auto-)immunity was corroborated by exacerbated lupuslike disease in the presence of NFAT2-deficient T_FR cells.

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.

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.

High-throughput sequencing of islet-infiltrating memory CD4+ T cells reveals a similar pattern of TCR Vβ usage in prediabetic and diabetic NOD mice

Autoreactive memory CD4⁺ T cells play a critical role in the development of type 1 diabetes, but it is not yet known how the clonotypic composition and TCRβ repertoire of the memory CD4⁺ T cell compartment changes during the transition from prediabetes to diabetes. In this study, we used high-throughput sequencing to analyze the TCRβ repertoire of sorted islet-infiltrating memory CD4⁺CD44^high T cells in 10-week-old prediabetic and recently diabetic NOD mice. We show that most clonotypes of islet-infiltrating CD4⁺CD44^high T cells were rare, but high-frequency clonotypes were significantly more common in diabetic than in prediabetic mice. Moreover, although the CD4⁺CD44^high TCRβ repertoires were highly diverse at both stages of disease development, dominant use of TRBV1 (Vβ2), TRBV13-3 (Vβ8.1), and TRBV19 (Vβ6) was evident in both prediabetic and diabetic mice. Our findings strongly suggest that therapeutic targeting of cells specifically expressing the dominant TCRβ might reduce pancreatic infiltration in prediabetic mice and attenuate the progression to diabetes.

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.

Tolerant anti-insulin B cells are effective APCs

Autoreactive B lymphocytes that are not culled by central tolerance in the bone marrow frequently enter the peripheral repertoire in a state of functional impairment, termed anergy. These cells are recognized as a liability for autoimmunity, but their contribution to disease is not well understood. Insulin-specific 125Tg B cells support T cell-mediated type 1 diabetes in NOD mice, despite being anergic to B cell mitogens and T cell-dependent immunization. Using this model, the potential of anergic, autoreactive B cells to present Ag and activate T cells was investigated. The data show that 1) insulin is captured and rapidly internalized by 125Tg BCRs, 2) these Ag-exposed B cells are competent to activate both experienced and naive CD4(+) T cells, 3) anergic 125Tg B cells are more efficient than naive B cells at activating T cells when Ag is limiting, and 4) 125Tg B cells are competent to generate low-affinity insulin B chain epitopes necessary for activation of diabetogenic anti-insulin BDC12-4.1 T cells, indicating the pathological relevance of anergic B cells in type 1 diabetes. Thus, phenotypically tolerant B cells that are retained in the repertoire may promote autoimmunity by driving activation and expansion of autoaggressive T cells via Ag presentation.

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.

Pathogenesis of NOD diabetes is initiated by reactivity to the insulin B chain 9-23 epitope and involves functional epitope spreading

Type 1 diabetes (T1D) is mediated by destruction of pancreatic β-cells by CD4 and CD8 T cells specific for epitopes on numerous diabetogenic autoantigens resulting in loss of glucose homeostasis. Employing antigen-specific tolerance induced by i.v. administration of syngeneic splenocytes ECDI cross-linked to various diabetogenic antigens/epitopes (Ag-SP), we show that epitope spreading plays a functional role in the pathogenesis of T1D in NOD mice. Specifically, Ag-SP coupled with intact insulin, Ins B(9-23) or Ins B(15-23), but not GAD65(509-528), GAD65(524-543) or IGRP(206-214), protected 4-6 week old NOD mice from the eventual development of clinical disease; infiltration of immune cells to the pancreatic islets; and blocked the induction of DTH responses in a Treg-dependent, antigen-specific manner. However, tolerance induction in 19-21 week old NOD mice was effectively accomplished only by Ins-SP, suggesting Ins B(9-23) is a dominant initiating epitope, but autoimmune responses to insulin epitope(s) distinct from Ins B(9-23) emerge during disease progression.

Following the fate of one insulin-reactive CD4 T cell: conversion into Teffs and Tregs in the periphery controls diabetes in NOD mice

In diabetic patients and susceptible mice, insulin is a targeted autoantigen. Insulin B chain 9-23 (B:9-23) autoreactive CD4 T cells are key for initiating autoimmune diabetes in NOD mice; however, little is known regarding their origin and function. To this end, B:9-23-specific, BDC12-4.1 T-cell receptor (TCR) transgenic (Tg) mice were studied, of which, despite expressing a single TCR on the recombination activating gene-deficient background, only a fraction develops diabetes in an asynchronous manner. BDC12-4.1 CD4 T cells convert into effector (Teff) and Foxp3(+)-expressing adaptive regulatory T cells (aTregs) soon after leaving the thymus as a result of antigen recognition and homeostatic proliferation. The generation of aTreg causes the heterogeneous diabetes onset, since crossing onto the scurfy (Foxp3) mutation, BDC12-4.1 TCR Tg mice develop accelerated and fully penetrant diabetes. Similarly, adoptive transfer and bone marrow transplantation experiments showed differential diabetes kinetics based on Foxp3(+) aTreg's presence in the BDC12-4.1 donors. A single-specificity, insulin-reactive TCR escapes thymic deletion and simultaneously converts into aTreg and Teff, establishing an equilibrium that determines diabetes penetrance. These results are of particular importance for understanding disease pathogenesis. They suggest that once central tolerance is bypassed, autoreactive cells arriving in the periphery do not by default follow solely a pathogenic fate upon activation.

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.

Insulin as a key autoantigen in the development of type 1 diabetes

Type 1 diabetes is a T-cell-mediated autoimmune disease against pancreatic beta cells. T cells target various antigens such as insulin, chromogranin A, glutamic acid decarboxylase and islet-specific glucose-6-phosphatase catalytic subunit-related protein. Elimination of insulin dramatically prevents diabetes in the non-obese diabetic (NOD) mouse model and response to insulin occurs prior to that to other antigens. These findings suggest that insulin is a target antigen at the early stage of the disease and is likely to be essential to cause anti-islet autoimmunity in NOD mice. In this review, we discuss whether insulin is truly essential and is only the single essential autoantigen for NOD mice and potentially for man. Although the ultimate principle is still being addressed, it is certain that T-cell response to insulin is a major check point to develop type 1 diabetes in NOD mice. Given multiple similarities between diabetes of NOD mice and man, targeting insulin and insulin-reactive T cells may provide opportunities to develop robust immunotherapies.

Beyond the hormone: insulin as an autoimmune target in type 1 diabetes

Insulin is not only the hormone produced by pancreatic β-cells but also a key target antigen of the autoimmune islet destruction leading to type 1 diabetes. Despite cultural biases between the fields of endocrinology and immunology, these two facets should not be regarded separately, but rather harmonized in a unifying picture of diabetes pathogenesis. There is increasing evidence suggesting that metabolic factors (β-cell dysfunction, insulin resistance) and immunological components (inflammation and β-cell-directed adaptive immune responses) may synergize toward islet destruction, with insulin standing at the crossroad of these pathways. This concept further calls for a revision of the classical dichotomy between type 1 and type 2 diabetes because metabolic and immune mechanisms may both contribute to different extents to the development of different forms of diabetes. After providing a background on the mechanisms of β-cell autoimmunity, we will explain the role of insulin and its precursors as target antigens expressed not only by β-cells but also in the thymus. Available knowledge on the autoimmune antibody and T-cell responses against insulin will be summarized. A unifying scheme will be proposed to show how different aspects of insulin biology may lead to β-cell destruction and may be therapeutically exploited. We will argue about possible reasons why insulin remains the mainstay of metabolic control in type 1 diabetes but has so far failed to prevent or halt β-cell autoimmunity as an immune modulatory reagent.

Prevention of type 1 diabetes in mice by tolerogenic vaccination with a strong agonist insulin mimetope

Subimmunogenic vaccination with an agonist mimetope of insulin converts naive T cells into regulatory T cells and prevents type 1 diabetes in NOD mice.

Type 1 diabetes (T1D) results from the destruction of insulin-secreting pancreatic β cells by autoreactive T cells. Insulin is an essential target of the autoimmune attack. Insulin epitopes recognized by diabetogenic T cell clones bind poorly to the class II I-A^g7 molecules of nonobese diabetic (NOD) mice, which results in weak agonistic activity of the peptide MHC complex. Here, we describe a strongly agonistic insulin mimetope that effectively converts naive T cells into Foxp3⁺ regulatory T cells in vivo, thereby completely preventing T1D in NOD mice. In contrast, natural insulin epitopes are ineffective. Subimmunogenic vaccination with strongly agonistic insulin mimetopes might represent a novel strategy to prevent T1D in humans at risk for the disease.

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

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

[Antitumor effects of raddeanin A on S180, H22 and U14 cell xenografts in mice]

BACKGROUND & OBJECTIVE

Raddeanin A, a triterpenoid saponin from Anemone raddeana Regel, has good antitumor activity in vitro. This study was to investigate its antitumor effects on tumor cell xenografts in mice.

METHODS

The inhibitory effects of raddeanin A on the proliferation of human nasopharyngeal carcinoma KB cells and ovarian cancer SKOV3 cells were measured by MTT assay. The inhibitory effects of raddeanin A injection on the growth of sarcoma S180, liver cancer H22 and cervical carcinoma U14 cell xenografts in mice and the effect of raddeanin A lavage on the growth of S180 cell xenografts were measured. The acute toxicity of raddeanin A was also measured.

RESULTS

The 50% inhibition concentration (IC(50)) of raddeanin A was 4.64 microg/mL for KB cells and 1.40 microg/mL for SKOV3 cells. When injected with raddeanin A at a dose of 4.5 mg/kg, the growth inhibition rates of S180, H22 and U14 cell xenografts were 60.5%, 36.2% and 61.8%, respectively. When lavaged with raddeanin A at a dose of 200 mg/kg, the growth inhibition rate of S180 cell xenografts was 64.7%. The median lethal dose (LD50) of raddeanin A lavage was 1.1 g/kg and that of raddeanin A injection was 16.1 mg/kg.

CONCLUSION

Raddeanin A has good antitumor activity both in vitro and in vivo, and would be a potential antitumor medicine.

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.

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.

Unique autoreactive T cells recognize insulin peptides generated within the islets of Langerhans in autoimmune diabetes

In addition to the genetic framework, there are two other critical requirements for the development of tissue-specific autoimmune disease. First, autoreactive T cells need to escape thymic negative selection. Second, they need to find suitable conditions for autoantigen presentation and activation in the target tissue. We show here that these two conditions are fulfilled in diabetic mice of the nonobese diabetic (NOD) strain. A set of autoreactive CD4(+) T cells specific for an insulin peptide, with the noteworthy feature of not recognizing the insulin protein when processed by antigen-presenting cells (APCs), escaped thymic control, participated in diabetes and caused disease. Moreover, APCs in close contact with beta cells in the islets of Langerhans bore vesicles with the antigenic insulin peptides and activated peptide-specific T cells. Our findings may be relevant for other cases of endocrine autoimmunity.

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.

Insulin2 gene (Ins2) transcription by NOD bone marrow-derived cells does not influence autoimmune diabetes development in NOD-Ins2 knockout mice

Insulin is a critical autoantigen for the development of autoimmune diabetes in non-obese diabetic (NOD) mice. About 80% of NOD females and 30-40% of NOD males develop diabetes. However, Insulin2 (Ins2) knockout NOD mice develop autoimmune diabetes with complete penetrance in both sexes, at an earlier age, and have stronger autoimmune responses to insulin. The severe diabetes phenotype observed in NOD-Ins2-/- mice suggests that lack of Ins2 expression in the thymus may compromise immunological tolerance to insulin. Insulin is a prototypical tissue specific antigen (TSA) for which tolerance is dependent on expression in thymus and peripheral lymphoid tissues. TSA are naturally expressed by medullary thymic epithelial cells (mTEC), stromal cells in peripheral lymphoid tissues and bone marrow (BM)-derived cells, mainly CD11c(+) dendritic cells. The natural expression of TSA by mTEC and stromal cells has been shown to contribute to self-tolerance. However, it is unclear whether this also applies to BM-derived cells naturally expressing TSA. To address this question, we created BM chimeras and investigated whether reintroducing Ins2 expression solely by NOD BM-derived cells delays diabetes development in NOD-Ins2-/- mice. On follow-up, NOD-Ins2-/- mice receiving Ins2-expressing NOD BM cells developed diabetes at similar rates of those receiving NOD-Ins2-/- BM cells. Diabetes developed in 64% of NOD recipients transplanted with NOD BM and in 47% of NOD mice transplanted with NOD-Ins2-/- BM (P = ns). Thus, NOD-Ins2-/- BM did not worsen diabetes in NOD recipients and Ins2 expression by NOD BM-derived cells did not delay diabetes development in NOD-Ins2-/- mice.

Activation of insulin-reactive CD8 T-cells for development of autoimmune diabetes

OBJECTIVE

We have previously reported a highly diabetogenic CD8 T-cell clone, G9C8, in the nonobese diabetic (NOD) mouse, specific to low-avidity insulin peptide B15-23, and cells responsive to this antigen are among the earliest islet infiltrates. We aimed to study the selection, activation, and development of the diabetogenic capacity of these insulin-reactive T-cells.

RESEARCH DESIGN AND METHODS

We generated a T-cell receptor (TCR) transgenic mouse expressing the cloned TCR Valpha18/Vbeta6 receptor of the G9C8 insulin-reactive CD8 T-cell clone. The mice were crossed to TCRCalpha-/- mice so that the majority of the T-cells expressed the clonotypic TCR, and the phenotype and function of the cells was investigated.

RESULTS

There was good selection of CD8 T-cells with a predominance of CD8 single-positive thymocytes, in spite of thymic insulin expression. Peripheral lymph node T-cells had a naïve phenotype (CD44lo, CD62Lhi) and proliferated to insulin B15-23 peptide and to insulin. These cells produced interferon-gamma and tumor necrosis factor-alpha in response to insulin peptide and were cytotoxic to insulin peptide-coated targets. In vivo, the TCR transgenic mice developed insulitis but not spontaneous diabetes. However, the mice developed diabetes on immunization, and the activated transgenic T-cells were able to transfer diabetes to immunodeficient NOD.scid mice.

CONCLUSIONS

Autoimmune CD8 T-cells responding to a low-affinity insulin B-chain peptide escape from thymic negative selection and require activation in vivo to cause diabetes.

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.

Amino acid-modified calcitonin immunization induces tumor epitope-specific immunity in a transgenic mouse model for medullary thyroid carcinoma

Up to now, no relevant tumor antigen has been identified in medullary thyroid carcinoma (MTC). The aim of the present study was to prove the concept of an immunization with an amino acid-modified calcitonin (CT) for the treatment of MTC in a transgenic mouse model. Amino acid-modified (human) CT has been chosen for vaccination because of its higher binding affinity to the murine H2-Kb-MHC molecule. Mice were immunized over 6 months with monthly injections of amino acid-modified CT-pulsed dendritic cells. For enumeration of tumor epitope-specific CD8+ cytotoxic T cells, tetramer analyses were performed. CT peptide-treated mice revealed a mean 0.73 +/- 0.45 and 0.91 +/- 0.59% positive cells, depending on the two tetramers tested, whereas no increase was seen in control protein-immunized mice (0.08-0.12% tetramer-positive cells). Importantly, the subset of CT-specific CD8+ T cells also showed a high expression of interferon-gamma. In line with these results, CT-immunized mice also showed an intratumor infiltration with CD8+ T lymphocytes. Importantly, we also found a diminished tumor outgrowth of -57% and a decrease of the serum CT levels (2.0 +/- 0.1 pg/ml) compared with control protein-immunized Ret/Cal mice (3.0 +/- 0.4 pg/ml). In summary, we show that amino acid-modified CT is recognized from the immune system leading to a specific antitumor immune response and a diminished tumor outgrowth in transgenic MTC mice. The results are of potential importance because they might be applicable to patients with metastatic spread of a MTC.

Conserved T cell receptor alpha-chain induces insulin autoantibodies

A fundamental question is what are the molecular determinants that lead to spontaneous preferential targeting of specific autoantigens in autoimmune diseases, such as the insulin B:9-23 peptide sequence in type 1 diabetes. Anti-insulin B:9-23 T cell clones isolated from prediabetic NOD islets have a conserved Valpha-segment/Jalpha-segment, but no conservation of the alpha-chain N region and no conservation of the Vbeta-chain. Here, we show that the conserved T cell receptor alpha-chain generates insulin autoantibodies when transgenically or retrogenically introduced into mice without its corresponding Vbeta. We suggest that a major part of the mystery as to why islet autoimmunity develops relates to recognition of a primary insulin peptide by a conserved alpha chain T cell receptor.

Cutting edge: Immunosuppressant as adjuvant for tolerogenic immunization

Vaccination for autoimmune and alloimmune diseases has long been an attractive idea. Yet, there is no suitable adjuvant to forcefully steer the immune response toward tolerance. In this study we show that dexamethasone, a potent glucocorticoid immunosuppressant, can function as a tolerogenic adjuvant when applied together with peptide immunogen. BALB/c mice with pre-established delayed-type hypersensitivity to hen OVA were immunized with an OVA-derived, MHC II-restricted peptide (OVA(323-339)) in the presence of dexamethasone. The treatment caused long-term desensitization in treated animals to hen OVA via a dexamethasone-dependent tolerogenic mechanism that blocks maturation of dendritic cells and expands OVA(323-339)-specific CD4(+)CD25(+)Foxp3(+) regulatory T cells in vivo. Similar treatment of NOD mice using dexamethasone and an insulin-derived, MHC II-restricted peptide (B:9-23) prevented predisposed spontaneous diabetes. Remarkably, in both models, dexamethasone-augmented immunization induced long-term persistent, Ag-specific regulatory T cells responsive to recall Ags. These results reveal for the first time the potential usefulness of immunosuppressants as tolerogenic adjuvants.

Disruption of the homeostatic balance between autoaggressive (CD4+CD40+) and regulatory (CD4+CD25+FoxP3+) T cells promotes diabetes

Although regulatory T cells (Tregs) are well described, identifying autoaggressive effector T cells has proven more difficult. However, we identified CD4loCD40+ (Th40) cells as being necessary and sufficient for diabetes in the NOD mouse model. Importantly, these cells are present in pancreata of prediabetic and diabetic NOD mice, and Th40 cells but not CD4+CD40(-) T cells transfer progressive insulitis and diabetes to NOD.scid recipients. Nonobese-resistant (NOR) mice have the identical T cell developmental background as NOD mice, yet they are diabetes-resistant. The seminal issue is how NOR mice remain tolerant to diabetogenic self-antigens. We show here that autoaggressive T cells develop in NOR mice and are confined to the Th40 subset. However, NOR mice maintain Treg numbers equivalent to their Th40 numbers. NOD mice have statistically equal numbers of CD4+CD25+forkhead box P3+intrinsic Tregs compared with NOR or nonautoimmune BALB/c mice, and NOD Tregs are equally as suppressive as NOR Tregs. A critical difference is that NOD mice develop expanded numbers of Th40 cells. We suggest that a determinant factor for autoimmunity includes the Th40:Treg ratio. Mechanistically, NOD Th40 cells have low susceptibility to Fas-induced cell death and unlike cells from NOR and BALB/c mice, have predominantly low Fas expression. CD40 engagement of Th40 cells induces Fas expression but further confers resistance to Fas-mediated cell death in NOD mice. A second fundamental difference is that NOD Th40 cells undergo much more rapid homeostatic expansion than Th40 cells from NOR mice.

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.

Real-time imaging of the pancreas during development of diabetes

Type 1 diabetes (T1D) is the most common autoimmune disease affecting almost 20 million people worldwide. T1D is thought to be caused by autoaggressive T cells infiltrating pancreatic islets and destroying insulin-producing beta cells. Because insulin therapy, the current treatment for T1D, does not protect against all late complications and because life expectancy is affected, researchers are searching for preventive or curative approaches that block or prevent immune-mediated islet destruction. However, the precise in vivo events that take place in islets during T1D development remain unknown. During the past decade, 2-photon microscopy (2PM) has emerged as a new technique to assess cell-cell interactions in real-time and at high resolution in vivo. This technique has been demonstrated recently to be a promising tool to study the progressive development of T1D pathogenesis at the cellular level. In this review, we propose a new surgical and immunological approach so that 2PM can be utilized to monitor the duration that effector cells reside within an islet, determine the number of effector cells needed for elimination of beta cells, and follow the fate of beta cells when regulatory cells are present. Understanding the cellular dynamics during T1D development is critical for the rational design of immunotherapies.