MHC class I-restricted determinants on the glutamic acid decarboxylase 65 molecule induce spontaneous CTL activity

Noncontiguous T cell epitopes in autoimmune diabetes: From mice to men and back again

Type 1 diabetes (T1D) is a T cell-mediated autoimmune disease that affects the insulin-producing beta cells of the pancreatic islets. The nonobese diabetic mouse is a widely studied spontaneous model of the disease that has contributed greatly to our understanding of T1D pathogenesis. This is especially true in the case of antigen discovery. Upon review of existing knowledge concerning the antigens and peptide epitopes that are recognized by T cells in this model, good concordance is observed between mouse and human antigens. A fascinating recent illustration of the contribution of the nonobese diabetic mouse in the area of epitope identification is the discovery of noncontiguous CD4+ T cell epitopes. This novel epitope class is characterized by the linkage of an insulin-derived peptide to, most commonly, a fragment of a natural cleavage product of another beta cell secretory granule constituent. These so-called hybrid insulin peptides are also recognized by T cells in patients with T1D, although the precise mechanism for their generation has yet to be defined and is the subject of active investigation. Although evidence from the tumor immunology arena documented the existence of noncontiguous CD8+ T cell epitopes, generated by proteasome-mediated peptide splicing involving transpeptidation, such CD8+ T cell epitopes were thought to be a rare immunological curiosity. However, recent advances in bioinformatics and mass spectrometry have challenged this view. These developments, coupled with the discovery of hybrid insulin peptides, have spurred a search for noncontiguous CD8+ T cell epitopes in T1D, an exciting frontier area still in its infancy.

Development of a Bioconjugate Platform for Modifying the Immune Response of Autoreactive Cytotoxic T Lymphocytes Involved in Type 1 Diabetes

Type 1 diabetes (T1D) is an autoimmune disorder characterized by autoimmune cell mediated destruction of pancreatic beta cells. Pancreatic beta cells are the only source of insulin in the body. T1D patients then have to depend on insulin injections for their lifetime. Insulin injection can modulate the blood sugar levels, but insulin has little effect on the autoimmune process. Altered peptide ligands (APL) derived from known autoantigens in T1D are able to induce tolerance in autoreactive cells in T1D animal models, but are currently unable to elicit this protection in humans. There is a need to improve immunogenicity of the APLs, as these short peptides can be easily degraded by enzymes in the blood. GAD546-554 is a dominant epitope recognized by autoreactive T cells in the nonobese diabetic (NOD) mouse model that can cause destruction of beta cells. Alanine substitution at the eighth position of GAD546-554 peptide (APL9) induced tolerance in a GAD546-554 specific cytotoxic T lymphocyte clone. To improve the antigen presentation and endosomal escape of APL9, we developed a bioconjugate platform that consists of a liposome containing a bioconjugate of APL9 and toll-like receptor 2 ligand Pam₃CysSK₄ as well as an antibody against macrophage protein F4/80. APL9 bioconjugate liposome with F4/80 antibody was able to induce tolerance in a GAD 546-554 specific clone. Diabetic NOD splenocytes pretreated with APL9 bioconjugate were also not able to transfer diabetes into prediabetic NOD recipient mice. This work is beneficial to prevent T1D as an immunotherapy strategy to render autoreactive immune cells more tolerant of beta cells.

Adoptive Transfer of mRNA-Transfected T Cells Redirected against Diabetogenic CD8 T Cells Can Prevent Diabetes

Chimeric major histocompatibility complex (MHC) molecules supplemented with T cell receptor (TCR) signaling motifs function as activation receptors and can redirect gene-modified T cells against pathogenic CD8 T cells. We have shown that β₂ microglobulin (β₂m) operates as a universal signaling component of MHC-I molecules when fused with the CD3-ζ chain. Linking the H-2K^d-binding insulin B chain peptide insulin B chain, amino acids 15-23 (InsB_15-23) to the N terminus of β₂m/CD3-ζ, redirected polyclonal CD8 T cells against pathogenic CD8 T cells in a peptide-specific manner in the non-obese diabetic (NOD) mouse. Here, we describe mRNA electroporation for delivering peptide/β₂m/CD3-ζ genes to a reporter T cell line and purified primary mouse CD8 T cells. The peptide/β₂m/CD3-ζ products paired with endogenous MHC-I chains and transmitted strong activation signals upon MHC-I cross-linking. The reporter T cell line transfected with InsB_15-23/β₂m/CD3-ζ mRNA was activated by an InsB_15-23-H-2K^d-specific CD8 T cell hybrid only when the transfected T cells expressed H-2K^d. Primary NOD CD8 T cells expressing either InsB_15-23/β₂m/CD3-ζ or islet-specific glucose-6-phosphatase catalytic subunit-related protein, amino acids 206-214 (IGRP_206-214)/β₂m/CD3-ζ killed their respective autoreactive CD8 T cell targets in vitro. Furthermore, transfer of primary CD8 T cells transfected with InsB_15-23/β₂m/CD3-ζ mRNA significantly reduced insulitis and protected NOD mice from diabetes. Our results demonstrate that mRNA encoding chimeric MHC-I receptors can redirect effector CD8 against diabetogenic CD8 T cells, offering a new approach for the treatment of type 1 diabetes.

Identification of Candidate Tolerogenic CD8(+) T Cell Epitopes for Therapy of Type 1 Diabetes in the NOD Mouse Model

Type 1 diabetes is an autoimmune disease in which insulin-producing pancreatic islet β cells are the target of self-reactive B and T cells. T cells reactive with epitopes derived from insulin and/or IGRP are critical for the initiation and maintenance of disease, but T cells reactive with other islet antigens likely have an essential role in disease progression. We sought to identify candidate CD8(+) T cell epitopes that are pathogenic in type 1 diabetes. Proteins that elicit autoantibodies in human type 1 diabetes were analyzed by predictive algorithms for candidate epitopes. Using several different tolerizing regimes using synthetic peptides, two new predicted tolerogenic CD8(+) T cell epitopes were identified in the murine homolog of the major human islet autoantigen zinc transporter ZnT8 (aa 158-166 and 282-290) and one in a non-β cell protein, dopamine β-hydroxylase (aa 233-241). Tolerizing vaccination of NOD mice with a cDNA plasmid expressing full-length proinsulin prevented diabetes, whereas plasmids encoding ZnT8 and DβH did not. However, tolerizing vaccination of NOD mice with the proinsulin plasmid in combination with plasmids expressing ZnT8 and DβH decreased insulitis and enhanced prevention of disease compared to vaccination with the plasmid encoding proinsulin alone.

Identification of autoreactive CD8+ T cell responses targeting chromogranin A in humanized NOD mice and type 1 diabetes patients

ChgA has recently been identified as the autoantigen for diabetogenic CD4(+) T cells in NOD mice and T1D patients. However, autoreactive CD8(+) T-cell responses targeting ChgA haven't been studied yet. Here several HLA-A*0201-restricted peptides derived from mChgA and hChgA were selected by an integrated computational prediction approach, followed by an HLA-A*0201 binding assay. MChgA10-19 and mChgA(43-52) peptides, which bound well with HLA-A*0201 molecule, induced significant proliferation and IFN-γ-releasing of splenocytes from diabetic NOD.β2m(null).HHD mice. Notably, flow cytometry analysis found that mChgA(10-19) and mChgA(43-52) stimulated the production of IFN-γ, perforin, and IL-17 by splenic CD8(+) T cells of diabetic NOD.β2m(null).HHD mice. Furthermore, hChgA(10-19) and hChgA(43-52)-induced IFN-γ releasing by specific CD8(+) T cells were frequently detected in recent-onset HLA-A*0201-positive T1D patients. Thus, this study demonstrated that autoreactive CD8(+) T cells targeting ChgA were present in NOD.β2m(null).HHD mice and T1D patients, and might contribute to pathogenesis of T1D through secreting proinflammatory cytokines and cytotoxic molecules.

Impairment by sperm agglutinating factor isolated from Escherichia coli: receptor specific interactions

In an earlier work done in our laboratory, we have been able to isolate a sperm agglutinating strain of Escherichia coli from the semen sample of a male attending infertility clinic. Further, factor responsible for sperm agglutination (SAF) was isolated and purified, and, using SAF as a tool, corresponding SAF binding receptor from human spermatozoa has been purified. Characterization of SAF and SAF binding receptor using MALDI-TOF showed homology to glutamate decarboxylase and MHC class I molecule, respectively. Coincubation of SAF with spermatozoa not only resulted in spermagglutination but could also compromise other sperm parameters, namely, Mg²⁺ dependent ATPase activity and apoptosis. Intravaginal administration of SAF could lead to infertility in Balb/c mice. SAF induced impairment of sperm parameters, and infertility was observed to be due to interaction of SAF with sperm surface receptor component as, when purified receptor was introduced, receptor completely inhibited all the detrimental effects induced by SAF. From these results, it could be concluded that interaction of SAF with spermatozoa is receptor mediated.

Sercarzian immunology--In memoriam. Eli E. Sercarz, 1934-2009

During his long career as a principal investigator and educator, Eli Sercarz trained over 100 scientists. He is best known for developing hen egg white lysozyme (HEL) as a model antigen for immunologic studies. Working in his model system Eli furthered our understanding of antigen processing and immunologic tolerance. His work established important concepts of how the immune system recognizes antigenic determinants processed from whole protein antigens; specifically he developed the concepts of immunodominance and crypticity. Later in his career he focused more on autoimmunity using a variety of established animal models to develop theories on how T cells can circumvent tolerance induction and how an autoreactive immune response can evolve over time. His theory of "determinant spreading" is one of the cornerstones of our modern understanding of autoimmunity. This review covers Eli's entire scientific career outlining his many seminal discoveries.

T-cell vaccination leads to suppression of intrapancreatic Th17 cells through Stat3-mediated RORγt inhibition in autoimmune diabetes

Immunization with inactivated autoreactive T cells is an effective therapeutic approach to ameliorating autoimmune diseases, while the underlying mechanisms that regulate autoreactive T cells are not completely understood. This study tested the hypothesis that T-cell vaccination (TCV) inhibits autoimmune diabetes in mice through the suppression of Th17 cells. The results showed that TCV treatment decreased hyperglycemia in type 1 diabetes (T1D) induced by multiple low-dose streptozotocin (MLD-STZ) as compared with the controls, preserved the number of healthy pancreatic islets and increased the production of insulin in the islets. Further study revealed that TCV significantly decreased the production of both interleukin (IL)-17 and IL-23 in intrapancreatic infiltrating lymphocytes (IPL) through marked inhibition of mRNA level of retinoic acid-related orphan receptor γt (RORγt) and signal transducer and activator of transcription 3 (Stat3) phosphorylation. The role of TCV-induced Th17 suppression was further validated in adoptive transfer experiments with polarized Th17 cells in sub-diabetogenic mice, which was similar to the effect of anti-IL-17 antibody treatment. Collectively our study shows that intrapancreatic Th17 cell suppression and healthy islet preservation play an important role in the treatment of T1D by TCV.

Cathepsin L inhibition prevents murine autoimmune diabetes via suppression of CD8(+) T cell activity

Background

Type 1 diabetes (T1D) is an autoimmune disease resulting from defects in central and peripheral tolerance and characterized by T cell-mediated destruction of islet β cells. To determine whether specific lysosomal proteases might influence the outcome of a T cell–mediated autoimmune response, we examined the functional significance of cathepsin inhibition on autoimmune T1D-prone non-obese diabetic (NOD) mice.

Methods and Findings

Here it was found that specific inhibition of cathepsin L affords strong protection from cyclophosphamide (CY)-induced insulitis and diabetes of NOD mice at the advanced stage of CD8⁺ T cell infiltration via inhibiting granzyme activity. It was discovered that cathepsin L inhibition prevents cytotoxic activity of CD8⁺ T cells in the pancreatic islets through controlling dipeptidyl peptidase I activity. Moreover, the gene targeting for cathepsin L with application of in vivo siRNA administration successfully prevented CY-induced diabetes of NOD mice. Finally, cathepsin L mRNA expression of peripheral CD8⁺ T cells from NOD mice developing spontaneous T1D was significantly increased compared with that from control mice.

Conclusions

Our results identified a novel function of cathepsin L as an enzyme whose activity is essential for the progression of CD8⁺ T cell-mediated autoimmune diabetes, and inhibition of cathepsin L as a powerful therapeutic strategy for autoimmune diabetes.

GAD65-Specific Cytotoxic T Lymphocytes Mediate Beta-Cell Death and Loss of Function

Autoimmunity to islet cell antigens like glutamic acid decarboxylase 65kD (GAD65) is associated with the destruction of insulin-producing beta-cells and progression to type 1 diabetes (T1D) in NOD mice and humans. T cell responses to GAD65 are detectable in the spleen of prediabetic NOD mice and in the peripheral blood of humans prior to the onset of overt hyperglycemia. Previous findings from our lab revealed that GAD65(546-554)-specific cytotoxic T lymphocytes (CTL) are present in naïve NOD mice and are able to induce islet inflammation upon adoptive transfer into NOD.scid recipients. Additionally, we found that professional antigen-presenting cells (APC) generate the p546-554 epitope from a soluble GAD65 fragment, p530-554, and from GAD65 released by injured beta-cells in vivo. Here, we report that the GAD65 fragment p546-554 is a dominant CTL-inducing epitope which is naturally processed and presented by a GAD65-expressing beta-cell line. Further, co-culture of GAD65(546-554)-specific CTL with the beta-cells leads to a reduction in insulin production and the induction of perforin-mediated cell death. Collectively, these findings support a role for the cross-presentation of GAD65 antigen in the priming and enhancement of dominant GAD65-specific CTL responses, which can directly target beta-cells that display GAD65 epitopes.

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.

Multiple roles for CD4+ T cells in anti-tumor immune responses

Our understanding of the importance of CD4+ T cells in orchestrating immune responses has grown dramatically over the past decade. This lymphocyte family consists of diverse subsets ranging from interferon-gamma (IFN-gamma)-producing T-helper 1 (Th1) cells to transforming growth factor-beta (TGF-beta)-secreting T-regulatory cells, which have opposite roles in modulating immune responses to pathogens, tumor cells, and self-antigens. This review briefly addresses the various T-cell subsets within the CD4+ T-cell family and discusses recent research efforts aimed at elucidating the nature of the 'T-cell help' that has been shown to be essential for optimal immune function. Particular attention is paid to the role of Th cells in tumor immunotherapy. We review some of our own work in the field describing how CD4+ Th cells can enhance anti-tumor cytotoxic T-lymphocyte (CTL) responses by enhancing clonal expansion at the tumor site, preventing activation-induced cell death and functioning as antigen-presenting cells for CTLs to preferentially generate immune memory cells. These unconventional roles for Th lymphocytes, which require direct cell-to-cell communication with CTLs, are clear examples of how versatile these immunoregulatory cells are.

Raising allo-restricted cytotoxic T lymphocytes by co-culture of murine splenocytes with autologous macrophage bearing the peptide/allo-major histococompatibility complex

Generation and adoptive transfusion of alloreactive cytotoxic T lymphocytes (CTLs) specific for tumor are expected to circumvent tumor tolerance. Here we describe a novel protocol to raise allo-restricted, peptide-specific CTLs by co-culture of murine splenocytes and autologous macrophage bearing an allogeneic H-2K molecule associated with its restricted peptide (peptide/allo-MHC). The extracellular domains of H-2K(d) were fused with constant domains of murine IgG2a heavy chain to generate a fusion protein (peptide/H-2K(d)/IgG2aFc, the dimer) consisting of divalent TCR-ligands and an IgG Fc receptor type I (FcgammaRI)-reactive moiety. The dimer is able to bind to macrophage (Mvarphi) of H-2K(k) via the interaction of the Fc part with FcgammaRI, and cause the H-2K(k) Mvarphi to be coated with the peptide/H-2K(d) complex. The results show that proliferation of CD8+ cells is enhanced and that the specific-tetramer stained CD8+ cells appear more frequently by co-culture of H-2K(k) splenocytes with the autologous Mvarphi loaded with the dimer. Furthermore, the CD8+ T cells from the co-cultural bulk exhibit an elevated cytotoxicity against a specific target (H-2K(d)-restricted, peptide-specific cytotoxicity), compared with that against the irrelevant targets. This study provides a strategy for preparation of allo-restricted, peptide-specific CTLs, which may add to our arsenal for adoptive immunotherapy to eliminate chronic virally infected or tumor cells.

CD8+ T-cells and their interaction with other cells in damage to islet beta-cells

The autoimmune attack on pancreatic beta-cells is orchestrated by a variety of cells that produce cytokines and other toxic mediators. CD8(+) T-cells work together with other lymphocytes and antigen-presenting cells to mediate this damage and have been shown in animal models to be important both in the early stages of diabetes development and in the final effector stages. Recently, there has also been much interest in studying CD8(+) T-cells that may play a role in human Type 1 diabetes and identifying their antigenic targets. The present paper will focus on the activation of CD8(+) T-cells and their interaction with other cells of the immune system and discuss the target antigens and mechanisms of damage that the CD8(+) T-cells use in the attack on the islet beta-cell.

Translational mini-review series on type 1 diabetes: Systematic analysis of T cell epitopes in autoimmune diabetes

T cell epitopes represent the molecular code words through which the adaptive immune system communicates. In the context of a T cell-mediated autoimmune disease such as type 1 diabetes, CD4 and CD8 T cell recognition of islet autoantigenic epitopes is a key step in the autoimmune cascade. Epitope recognition takes place during the generation of tolerance, during its loss as the disease process is initiated, and during epitope spreading as islet cell damage is perpetuated. Epitope recognition is also a potentially critical element in therapeutic interventions such as antigen-specific immunotherapy. T cell epitope discovery, therefore, is an important component of type 1 diabetes research, in both human and murine models. With this in mind, in this review we present a comprehensive guide to epitopes that have been identified as T cell targets in autoimmune diabetes. Targets of both CD4 and CD8 T cells are listed for human type 1 diabetes, for humanized [human leucocyte antigen (HLA)-transgenic] mouse models, and for the major spontaneous disease model, the non-obese diabetic (NOD) mouse. Importantly, for each epitope we provide an analysis of the relative stringency with which it has been identified, including whether recognition is spontaneous or induced and whether there is evidence that the epitope is generated from the native protein by natural antigen processing. This analysis provides an important resource for investigating diabetes pathogenesis, for developing antigen-specific therapies, and for developing strategies for T cell monitoring during disease development and therapeutic intervention.

Dominant CTL-inducing epitopes on GAD65 are adjacent to or overlap with dominant Th-inducing epitopes

Immune responses to GAD65 are associated with progression to T1D in NOD mice and humans. Our previous data suggested that dominant CTL-inducing and Th-inducing determinants might preferentially occur in proximal GAD65 sequences. Using a panel of 192 GAD65 peptides we discovered that four of the eight CTL-inducing peptides, including those most biologically relevant, were proximal to previously described I-A(g7)-restricted determinants that characterize natural islet autoimmunity in NOD mice. The CTL determinants 546-554 and 88-98 were presented by GAD65-expressing cells and were displayed on pancreatic LNC, along with 268-278, following beta cell damage. p546-554-specific CTL were detectable in young naive mice and transferred significant islet inflammation into NOD.scid mice. These findings demonstrate that unique regions of GAD65 may be favored during antigen processing, such that diverse dominant epitopes are produced from overlapping sequences, which can engage distinct T cell subsets. Additionally, cross-presentation may enhance GAD65-specific CTL responses in T1D.

T cells to a dominant epitope of GAD65 express a public CDR3 motif

Non-obese diabetic (NOD) mice spontaneously develop autoimmune diabetes, and serve as a model for type 1 diabetes (T1D) and natural autoimmunity. T cell responses to the pancreatic islet antigen glutamic acid decarboxylase 65 (GAD65) can be detected in the spleens of young prediabetic NOD mice, which display a unique MHC class II molecule. Here, we report that a distinct TcR beta chain and CDR3 motif are utilized by all NOD mice in response to a dominant determinant on GAD65, establishing a public repertoire in the spontaneous autoimmunity to an important islet cell antigen. GAD65 530-543 (p530)-reactive T cells preferentially utilize the Vbeta4, Dbeta2.1 and Jbeta2.7 gene segments, with a CDR3 that is characterized by a triad of amino acids, DWG, preceded by a polar residue. In addition, we used CDR3 length spectratyping, CDR3-specific reverse transcriptase-PCR and direct TcR sequencing to show that the TcR beta chain structural patterns associated with p530-specific T cells consistently appeared in the islets of young NOD mice with insulitis, but not in the inflamed islets of streptozotocin-treated C57BL/6 mice, or in inflamed NOD salivary glands. To our knowledge, this is the first report to demonstrate that a public T cell repertoire is used in spontaneous autoimmunity to a dominant self-determinant. These findings suggest that defined clonotypes and repertoires may be preferentially selected in haplotypes predisposed to spontaneous autoimmunity.

Early autoimmune destruction of islet grafts is associated with a restricted repertoire of IGRP-specific CD8+ T cells in diabetic nonobese diabetic mice

beta cell replacement via islet or pancreas transplantation is currently the only approach to cure type 1 diabetic patients. Recurrent beta cell autoimmunity is a critical factor contributing to graft rejection along with alloreactivity. However, the specificity and dynamics of recurrent beta cell autoimmunity remain largely undefined. Accordingly, we compared the repertoire of CD8+ T cells infiltrating grafted and endogenous islets in diabetic nonobese diabetic mice. In endogenous islets, CD8+ T cells specific for an islet-specific glucose-6-phosphatase catalytic subunit-related protein derived peptide (IGRP206-214) were the most prevalent T cells. Similar CD8+ T cells dominated the early graft infiltrate but were expanded 6-fold relative to endogenous islets. Single-cell analysis of the TCR alpha and beta chains showed restricted variable gene usage by IGRP206-214-specific CD8+ T cells that was shared between the graft and endogenous islets of individual mice. However, as islet graft infiltration progressed, the number of IGRP206-214-specific CD8+ T cells decreased despite stable numbers of CD8+ T cells. These results demonstrate that recurrent beta cell autoimmunity is characterized by recruitment to the grafts and expansion of already prevalent autoimmune T cell clonotypes residing in the endogenous islets. Furthermore, depletion of IGRP206-214-specific CD8+ T cells by peptide administration delayed islet graft survival, suggesting IGRP206-214-specific CD8+ T cells play a role early in islet graft rejection but are displaced with time by other specificities, perhaps by epitope spread.

Autoimmune destruction of pancreatic beta cells

Type 1 diabetes results from the destruction of insulin-producing pancreatic beta cells by a beta cell-specific autoimmune process. Beta cell autoantigens, macrophages, dendritic cells, B lymphocytes, and T lymphocytes have been shown to be involved in the pathogenesis of autoimmune diabetes. Beta cell autoantigens are thought to be released from beta cells by cellular turnover or damage and are processed and presented to T helper cells by antigen-presenting cells. Macrophages and dendritic cells are the first cell types to infiltrate the pancreatic islets. Naive CD4+ T cells that circulate in the blood and lymphoid organs, including the pancreatic lymph nodes, may recognize major histocompatibility complex and beta cell peptides presented by dendritic cells and macrophages in the islets. These CD4+ T cells can be activated by interleukin (IL)-12 released from macrophages and dendritic cells. While this process takes place, beta cell antigen-specific CD8+ T cells are activated by IL-2 produced by the activated TH1 CD4+ T cells, differentiate into cytotoxic T cells and are recruited into the pancreatic islets. These activated TH1 CD4+ T cells and CD8+ cytotoxic T cells are involved in the destruction of beta cells. In addition, beta cells can also be damaged by granzymes and perforin released from CD8+ cytotoxic T cells and by soluble mediators such as cytokines and reactive oxygen molecules released from activated macrophages in the islets. Thus, activated macrophages, TH1 CD4+ T cells, and beta cell-cytotoxic CD8+ T cells act synergistically to destroy beta cells, resulting in autoimmune type 1 diabetes.

The good turned ugly: immunopathogenic basis for diabetogenic CD8+ T cells in NOD mice

Type 1 diabetes (T1D) in both humans and nonobese diabetic (NOD) mice is a T-cell-mediated autoimmune disease in which the insulin-producing pancreatic islet beta-cells are selectively eliminated. As a result, glucose metabolism cannot be regulated unless exogenous insulin is administered. Both the CD4(+) and the CD8(+) T-cell subsets are required for T1D development. Approximately 20 years ago, an association between certain class II major histocompatibility complex (MHC) alleles and susceptibility to T1D was reported. This finding led to enormous interest in the CD4(+) T cells participating in the development of T1D, while the CD8(+) subset was relatively ignored. However, the isolation of beta-cell-autoreactive CD8(+) T-cell clones from the islets of NOD mice helped to generate interest in the pathogenic role of this subset, as has accumulating evidence that certain class I MHC alleles are additional risk factors for T1D development in humans. Three distinct diabetogenic CD8(+) T-cell populations have now been characterized in NOD mice. Here, we review recent investigations exploring their selection, activation, trafficking, and antigenic specificities. As CD8(+) T cells are suspected contributors to beta-cell demise in humans, continued exploration of these critical areas could very possibly lead to tangible benefits for T1D patients and at-risk individuals.

Active Tolerance Induction and Prevention of Autoimmune Diabetes by Immunogene Therapy Using Recombinant Adenoassociated Virus Expressing Glutamic Acid Decarboxylase 65 Peptide GAD500–585

Tolerance induction of autoreactive T cells against pancreatic beta cell-specific autoantigens such as glutamic acid decarboxylase 65 (GAD65) and insulin has been attempted as a method to prevent autoimmune diabetes. In this study, we investigate whether adenoassociated virus (AAV) gene delivery of multiple immunodominant epitopes expressing GAD(500-585) could induce potent immune tolerance and persistently suppress autoimmune diabetes in NOD mice. A single muscle injection of 7-wk-old female NOD mice with rAAV/GAD(500-585) (3 x 10(11) IU/mouse) quantitatively reduced pancreatic insulitis and efficiently prevented the development of overt type I diabetes. This prevention was marked by the inactivation of GAD(500-585)-responsive T lymphocytes, the enhanced GAD(500-585)-specific Th2 response (characterized by increased IL-4, IL-10 production, and decreased IFN-gamma production; especially elevated anti-GAD(500-585) IgG1 titer; and relatively unchanged anti-GAD(500-585) IgG2b titer), the increased secretion of TGF-beta, and the production of protective regulatory cells. Our studies also revealed that peptides 509-528, 570-585, and 554-546 in the region of GAD(500-585) played important roles in rAAV/GAD(500-585) immunization-induced immune tolerance. These data indicate that using AAV, a vector with advantage for therapeutic gene delivery, to transfer autoantigen peptide GAD(500-585), can induce immunological tolerance through active suppression of effector T cells and prevent type I diabetes in NOD mice.

Direct Cross-Priming by Th Lymphocytes Generates Memory Cytotoxic T Cell Responses

Under optimal Ag stimulation, CTL become functional effector and memory T cells. Professional APCs (pAPC) are considered essential for the activation of CTL, due to their unique capacity to provide costimulation and present exogenous Ags through MHC class I molecules. In this study, we report a novel means by which Th lymphocytes acquire and present MHC class I determinants to naive CTL. Although previous studies have looked at T cell Ag presentation to activated T cells, this study presents the first example of Ag presentation by Th cells to naive CTL. We report that activated Th cells can function as effective pAPC for CTL. Our results show that: 1) In addition to acquisition of cell surface molecules, including MHC class I/peptide complexes, from pAPC, Th cells can acquire and present MHC class I-binding peptides through TCR-MHC class II interactions with pAPC; 2) the acquired Ag can be functionally presented to CTL; and 3) Ag presentation by Th cells induces naive CTL to proliferate and preferentially differentiate into cells that phenotypically and functionally resemble central memory T cells. These findings suggest a novel role of Th cells as pAPC for the development of memory immune responses.

Individual nonobese diabetic mice exhibit unique patterns of CD8+ T cell reactivity to three islet antigens, including the newly identified widely expressed dystrophia myotonica kinase

Spontaneous autoimmune diabetes development in NOD mice requires both CD8(+) and CD4(+) T cells. Three pathogenic CD8(+) T cell populations (represented by the G9C8, 8.3, and AI4 clones) have been described. Although the Ags for G9C8 and 8.3 are known to be insulin and islet-specific glucose-6-phosphatase catalytic subunit-related protein, respectively, only mimotope peptides had previously been identified for AI4. In this study, we used peptide/MHC tetramers to detect and quantify these three pathogenic populations among beta cell-reactive T cells cultured from islets of individual NOD mice. Even within age-matched groups, each individual mouse exhibited a unique distribution of beta cell-reactive CD8(+) T cells, both in terms of the number of tetramer-staining populations and the relative proportion of each population in the islet infiltrate. Thus, the inflammatory process in each individual follows its own distinctive course. Screening of a combinatorial peptide library in positional scanning format led to the identification of a peptide derived from dystrophia myotonica kinase (DMK) that is recognized by AI4-like T cells. Importantly, the antigenic peptide is naturally processed and presented by DMK-transfected cells. DMK is a widely expressed protein that is nonetheless the target of a beta cell-specific autoimmune response.

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.

Requirement for Both H-2Db and H-2Kd for the Induction of Diabetes by the Promiscuous CD8+ T Cell Clonotype AI4

The NOD mouse is a model for autoimmune type 1 diabetes in humans. CD8(+) T cells are essential for the destruction of the insulin-producing pancreatic beta cells characterizing this disease. AI4 is a pathogenic CD8(+) T cell clone, isolated from the islets of a 5-wk-old female NOD mouse, which is capable of mediating overt diabetes in the absence of CD4(+) T cell help. Recent studies using MHC-congenic NOD mice revealed marked promiscuity of the AI4 TCR, as the selection of this clonotype can be influenced by multiple MHC molecules, including some class II variants. The present work was designed, in part, to determine whether similar promiscuity also characterizes the effector function of mature AI4 CTL. Using splenocyte and bone marrow disease transfer models and in vitro islet-killing assays, we report that efficient recognition and destruction of beta cells by AI4 requires the beta cells to simultaneously express both H-2D(b) and H-2K(d) class I MHC molecules. The ability of the AI4 TCR to interact with both H-2D(b) and H-2K(d) was confirmed using recombinant peptide libraries. This approach also allowed us to define a mimotope peptide recognized by AI4 in an H-2D(b)-restricted manner. Using ELISPOT and mimotope/H-2D(b) tetramer analyses, we demonstrate for the first time that AI4 represents a readily detectable T cell population in the islet infiltrates of prediabetic NOD mice. Our identification of a ligand for AI4-like T cells will facilitate further characterization and manipulation of this pathogenic and promiscuous T cell population.

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.

Expression of Activated Notch3 in Transgenic Mice Enhances Generation of T Regulatory Cells and Protects against Experimental Autoimmune Diabetes

Thymic-derived dysregulated tolerance has been suggested to occur in type 1 diabetes via impaired generation of CD4(+)CD25(+) T regulatory cells, leading to autoimmune beta cell destruction. In this study, we demonstrate that Notch3 expression is a characteristic feature of CD4(+)CD25(+) cells. Furthermore, streptozotocin-induced autoimmune diabetes fails to develop in transgenic mice carrying the constitutively active intracellular domain of Notch3 in thymocytes and T cells. The failure to develop the disease is associated with an increase of CD4(+)CD25(+) T regulatory cells, accumulating in lymphoid organs, in pancreas infiltrates and paralleled by increased expression of IL-4 and IL-10. Accordingly, CD4(+) T cells from Notch3-transgenic mice inhibit the development of hyperglycemia and insulitis when injected into streptozotocin-treated wild-type mice and display in vitro suppressive activity. These observations, therefore, suggest that Notch3-mediated events regulate the expansion and function of T regulatory cells, leading to protection from experimental autoimmune diabetes and identify the Notch pathway as a potential target for therapeutic intervention in type 1 diabetes.

Normal incidence of diabetes in NOD mice tolerant to glutamic acid decarboxylase

Experiments in nonobese diabetic (NOD) mice that lacked expression of glutamic acid decarboxylase (GAD) in beta cells have suggested that GAD represents an autoantigen essential for initiating and maintaining the diabetogenic immune response. Several attempts of inducing GAD-specific recessive tolerance to support this hypothesis have failed. Here we report on successful tolerance induction by expressing a modified form of GAD under control of the invariant chain promoter resulting in efficient epitope display. In spite of specific tolerance insulitis and diabetes occurred with normal kinetics indicating that GAD is not an essential autoantigen in the pathogenesis of diabetes.

Disabling an integral CTL epitope allows suppression of autoimmune diabetes by intranasal proinsulin peptide

Insulin is a major target of the autoimmune response associated with destruction of pancreatic beta cells in type 1 diabetes. A peptide that spans the junction of the insulin B chain and the connecting (C) peptide in proinsulin has been reported to stimulate T cells from humans at risk for type 1 diabetes and autoimmune diabetes-prone NOD mice. Here we show that proinsulin B24-C36 peptide binds to I-A(g7), the MHC class II molecule of the NOD mouse, and, after intranasal administration, induces regulatory CD4(+) T cells that, in the absence of CD8(+) T cells, block the adoptive transfer of diabetes. Curiously, however, intranasal B24-C36 did not inhibit development of spontaneous diabetes in treated mice. We then determined that B24-C36, and its core sequence B25-C34, bind to K(d), the NOD mouse MHC class I molecule, and elicit CD8(+) CTLs. When the CD8(+) T lymphocyte epitope was truncated at the C34 valine anchor residue for binding to K(d), the residual CD4(+) T cell epitope, B24-C32/33, significantly inhibited diabetes development after a single intranasal dose. This study identifies a novel CTL epitope in proinsulin and demonstrates that the therapeutic potential of a "tolerogenic" autoantigen peptide can be compromised by the presence of an integral CTL epitope.

Celiac disease association with CD8+ T cell responses: identification of a novel gliadin-derived HLA-A2-restricted epitope

One of the diagnostic hallmarks of the histological lesions associated with celiac disease is the extensive infiltration of the small intestinal epithelium by CD8(+) T cells of unknown Ag specificity. In this study, we report recognition of the gliadin-derived peptide (A-gliadin 123-132) by CD8(+) T lymphocytes from celiac patients. A-gliadin 123-132-specific IFN-gamma production and cytotoxic activity were detected in PBMCs derived from patients on gluten-free diet, but not from either celiac patients on gluten-containing diet or healthy controls. In contrast, A-gliadin 123-132-specific cells were isolated from small intestine biopsies of patients on either gluten-free or gluten-containing diets. Short-term T cell lines derived from the small intestinal mucosa and specific for the 123-132 epitope recognized human APC pulsed with either whole recombinant alpha-gliadin or a partial pepsin-trypsin gliadin digest. Finally, we speculate on a possible mechanism leading to processing and presentation of class I-restricted gliadin-derived epitopes in celiac disease patients.

Accelerated diabetes in rat insulin promoter-tumor necrosis factor-alpha transgenic nonobese diabetic mice lacking major histocompatibility class II molecules

The major predisposing genetic component in type 1 diabetes maps to the major histocompatibility complex locus in both mice and humans. To verify the HLA class II association with disease pathogenesis, we adopted the transgenic approach. Expression of HLA-DQ8, the molecule showing the strongest association with human type 1 diabetes, in the diabetes-predisposing milieu of NOD mice in the absence of the endogenous class II molecule I-A(g7) did not render susceptibility to type 1 diabetes. To study if providing a local proinflammatory environment would lead to diabetes in these mice, Abeta(o).NOD.DQ8 were bred with C57BL/6 mice expressing tumor necrosis factor (TNF)-alpha in the beta-cells of the islets of Langerhans. Surprisingly, although diabetes was evident in the F1 intercross expressing rat insulin promoter (RIP)-TNF, offspring lacking either endogenous or transgenic class II molecules developed accelerated diabetes with high frequency in both sexes. Moreover, expression of any functional class II molecule seemed to confer significant protection from diabetes in this model. Thus, neonatal expression of TNF-alpha in an islet-specific manner bypassed the requirement of CD4(+) T-cells and resulted in diabetes that could be mediated by CD8(+) T-cells. We also show for the first time that diabetes in NOD.RIP-TNF mice can occur independent of inheritance of NOD-derived idd1.

Memory CD8(+) T cells undergo peripheral tolerance

Memory T cells differ from naive T cells in that they respond more rapidly and in greater numbers. In addition, memory T cells are generally believed to be less susceptible to tolerance induction than naive T cells. In this study, we show that this is not the case. Using two different methods of tolerance induction, peptide-induced tolerance and crosstolerance, we present evidence that memory CD8(+) T cells are as susceptible to tolerance as naive cells. These results have a direct impact on manipulating T cell responses to self-antigens in order to improve immunotherapy of cancer and autoimmune diseases.

Investigation of antigen delivery route in vivo and imune-boosting effects mediated by pH-sensitive liposomes encapsulated with K(b)-restricted CTL epitope

Using fluorescein isothiocyanate (FITC)-conjugated H-2K(b) CTL epitope (SIINFEKL) as a model system, we investigated the antigen delivery route by pH-sensitive liposomes in vivo. Fluorescence was initially detected in lymph nodes at 3 h after immunization, and its intensity reached a peak value in superticial inguinal lymph node at 9 h. No trace could be detected in spleen even with prolonged monitoring for up to 24 h. These results strongly suggest that the presentation of CTL-peptide antigen vehicled by pH-sensitive liposomes exclusively occurs in lymph nodes. In mice immunized with the H-2K(b) CTL epitope encapsulated pH-sensitive liposomes, peptide-specific CTL response was detected at day 3. The response was strongly augmented by the second immunization and persisted up to at least 45 days. These results suggest that pH-sensitive liposome formula functions as a potential adjuvant of peptide antigens and is useful for the induction of antigen specific CTLsv in vivo.