Syngeneic transfer of autoimmune diabetes from diabetic NOD mice to healthy neonates. Requirement for both L3T4+ and Lyt-2+ T cells

Grafts of supplementary thymuses injected with allogeneic pancreatic islets protect nonobese diabetic mice against diabetes

In nonobese diabetic (NOD) mice, the autoimmune attack of the beta-cells in pancreatic islets is now believed to result from abnormal thymic selection. Accordingly, grafts of thymic epithelium from NOD donors to athymic recipients promote autoimmune islet inflammation in normal strains, and intrathymic islet grafts decrease the incidence of disease in NOD animals. Two competing hypotheses of abnormal thymic selection in diabetic mice have been proposed: deficient negative selection with poor elimination of aggressive organ-specific T cells vs. deficient positive selection of protective T regulatory cells. We have now addressed these alternatives by grafting, into young NOD mice whose own thymus was left intact, newborn NOD thymuses containing allogeneic pancreatic islets. If the NOD defect represented poor negative selection, these animals would develop disease at control rates, as the generation of autoreactive T cells proceeds undisturbed in the autologous thymus. In contrast, if NOD thymuses are defective in the production of T regulatory cells, lower disease incidence is expected in the chimeras, as more protective cells can be produced in the grafted thymus. The results show a reduced incidence of diabetes in the chimeras (24%) as compared with control (72%) NOD mice, throughout adult life. We conclude that amelioration of NOD mice by intrathymic islet grafts is not caused by enhanced negative selection and suggest that autoimmune diabetes in this system is the result of inefficient generation of T regulatory cells in the thymus.

Cross-presentation in viral immunity and self-tolerance

T lymphocytes recognize peptide antigens presented by class I and class II molecules encoded by the major histocompatibility complex (MHC). Classical antigen-presentation studies showed that MHC class I molecules present peptides derived from proteins synthesized within the cell, whereas MHC class II molecules present exogenous proteins captured from the environment. Emerging evidence indicates, however, that dendritic cells have a specialized capacity to process exogenous antigens into the MHC class I pathway. This function, known as cross-presentation, provides the immune system with an important mechanism for generating immunity to viruses and tolerance to self.

Neonatal pattern of V(H) gene utilization in nonobese diabetic mice does not correlate with development of insulitis

The nonobese diabetic (NOD) mouse model is a model of human autoimmune insulin dependent diabetes, IDDM. The effector cells of the disease have been shown to be T cells, but also B cells seem to contribute. Adult NOD mice have been shown to display a bias in their utilization of immunoglobulin (Ig) variable heavy (V(H)) genes. In this study the analysis of VH gene utilization in NOD mice protected from insulitis by transgenic insertion of a major histocompatibility complex (MHC) class II E(alpha) gene, point out that the bias in V(H) gene expression is not correlated to disease development. The aberrant V(H) gene utilization pattern in mice with the NOD genetic background is instead suggested to be a consequence of a deregulation of the apoptosis inhibiting gene bcl-2. We also investigated if prolonged in vitro survival of NOD lymphocytes is correlated to disease development. The E(alpha) transgenic NOD mice were shown to display a prolonged in vitro survival of spleen T cells, similar to normal NOD mice. These results indicate that defective death mechanisms of T cells may not be primarily involved in the development of autoimmune disease in these mice. However, in contrast to results from other groups, no difference in in vitro survival could be detected for B cells from mice with NOD genetic background compared to C57BL/6 mice.

CD1-restricted NK T cells protect nonobese diabetic mice from developing diabetes

NK T cells are a unique subset of T cells that recognize lipid antigens presented by CD1d. After activation, NK T cells promptly produce large amounts of cytokines, which may modulate the upcoming immune responses. Previous studies have documented an association between decreased numbers of NK T cells and the progression of some autoimmune diseases, suggesting that NK T cells may control the development of autoimmune diseases. To investigate the role of NK T cells in autoimmune diabetes, we crossed CD1 knockout (CD1KO) mutation onto the nonobese diabetic (NOD) genetic background. We found that male CD1KO NOD mice exhibited significantly higher incidence and earlier onset of diabetes compared with the heterozygous controls. The diabetic frequencies in female mice showed a similar pattern; however, the differences were less profound between female CD1KO and control mice. Early treatment of NOD mice with alpha-galactosylceramide, a potent NK T cell activator, reduced the severity of autoimmune diabetes in a CD1-dependent manner. Our results not only suggest a protective role of CD1-restricted NK T cells in autoimmune diabetes but also reveal a causative link between the deficiency of NK T cells and the induction of insulin-dependent diabetes mellitus.

Interleukin-10 and the interleukin-10 receptor

Interleukin-10 (IL-10), first recognized for its ability to inhibit activation and effector function of T cells, monocytes, and macrophages, is a multifunctional cytokine with diverse effects on most hemopoietic cell types. The principal routine function of IL-10 appears to be to limit and ultimately terminate inflammatory responses. In addition to these activities, IL-10 regulates growth and/or differentiation of B cells, NK cells, cytotoxic and helper T cells, mast cells, granulocytes, dendritic cells, keratinocytes, and endothelial cells. IL-10 plays a key role in differentiation and function of a newly appreciated type of T cell, the T regulatory cell, which may figure prominently in control of immune responses and tolerance in vivo. Uniquely among hemopoietic cytokines, IL-10 has closely related homologs in several virus genomes, which testify to its crucial role in regulating immune and inflammatory responses. This review highlights findings that have advanced our understanding of IL-10 and its receptor, as well as its in vivo function in health and disease.

Defective CD8+ T cell peripheral tolerance in nonobese diabetic mice

Nonobese diabetic (NOD) mice develop spontaneous autoimmune diabetes that involves participation of both CD4+ and CD8+ T cells. Previous studies have demonstrated spontaneous reactivity to self-Ags within the CD4+ T cell compartment in this strain. Whether CD8+ T cells in NOD mice achieve and maintain tolerance to self-Ags has not previously been evaluated. To investigate this issue, we have assessed the extent of tolerance to a model pancreatic Ag, the hemagglutinin (HA) molecule of influenza virus, that is transgenically expressed by pancreatic islet beta cells in InsHA mice. Previous studies have demonstrated that BALB/c and B10.D2 mice that express this transgene exhibit tolerance of HA and retain only low-avidity CD8+ T cells specific for the dominant peptide epitope of HA. In this study, we present data that demonstrate a deficiency in peripheral tolerance within the CD8+ T cell repertoire of NOD-InsHA mice. CD8+ T cells can be obtained from NOD-InsHA mice that exhibit high avidity for HA, as measured by tetramer (K(d)HA) binding and dose titration analysis. Significantly, these autoreactive CD8+ T cells can cause diabetes very rapidly upon adoptive transfer into NOD-InsHA recipient mice. The data presented demonstrate a retention in the repertoire of CD8+ T cells with high avidity for islet Ags that could contribute to autoimmune diabetes in NOD mice.

Non-Th2 regulatory T-cell control of Th1 autoimmunity

The Th1/Th2 concept brought an attractive explanation of the active self tolerance which appears to control the onset of pathogenic autoimmunity. New data coming from various independent horizons indicate that self immunoregulation could also depend to a large extent on non-Th2 cells. Original data derived from the day-3-thymectomy model, selective T-cell lymphocytopenia and nonobese diabetic mice are discussed in an effort to analyze similarities and differences in phenotype (CD25, CD62L and CD45RB) and cytokine pattern (notably interleukin (IL)-4, IL-10 and transforming growth factor (TGF)beta) of regulatory cells involved in these models. The relationship of these cells with Th3, Tr1 and natural killer (NK) T cells are also discussed. The hypothesis is proposed that CD25 CD62L T cells mediate the physiologic regulation of self regulation whereas Th2 and Th3 cells are essentially induced following sensitization against autoantigens.

Myelin antigen-specific CD8+ T cells are encephalitogenic and produce severe disease in C57BL/6 mice

Encephalitogenic T cells that mediate experimental autoimmune encephalomyelitis (EAE) are commonly assumed to be exclusively CD4+, but formal proof is still lacking. In this study, we report that synthetic peptides 35-55 from myelin oligodendrocyte glycoprotein (pMOG(35-55)) consistently activate a high proportion of CD8+ alphabetaTCR+ T cells that are encephalitogenic in C57BL/6 (B6) mice. The encephalitogenic potential of CD8+ MOG-specific T cells was established by adoptive transfer of CD8-enriched MOG-specific T cells. These cells induced a much more severe and permanent disease than disease actively induced by immunization with pMOG(35-55). CNS lesions in pMOG(35-55) CD8+ T cell-induced EAE were progressive and more destructive. The CD8+ T cells were strongly pathogenic in syngeneic B6 and RAG-1(-/-) mice, but not in isogeneic beta2-microglobulin-deficient mice. MOG-specific CD8+ T cells could be repeatedly reisolated for up to 287 days from recipient B6 or RAG-1(-/-) mice in which disease was induced adoptively with <1 x 10(6) T cells sensitized to pMOG(35-55). It is postulated that MOG induces a relapsing and/or progressive pattern of EAE by eliciting a T cell response dominated by CD8+ autoreactive T cells. Such cells appear to have an enhanced tissue-damaging effect and persist in the animal for long periods.

In vivo blockade of the Fas-Fas ligand pathway inhibits cyclophosphamide-induced diabetes in NOD mice

There is compelling evidence to show that insulin dependent diabetes ensues from selective apoptosis of pancreatic beta-cells mediated by autoreactive T-lymphocytes. The respective implication in this phenomenon of the various apoptotic pathways driven by Fas, perforin, or tumor necrosis factor is still ill- defined. Here we took advantage of the cyclophosphamide-induced model of accelerated diabetes in NOD mice to explore the physiopathological role of the Fas-Fas Ligand pathway. A single injection of cyclophosphamide (200 mg/kg) to 7-8 week-old prediabetic NOD mice triggered diabetes within 10-15 days in 85-100% of the animals. Cyclophosphamide also induced a significant decrease in spleen T cells, that was most evident by days 6-10 after treatment, and selectively affected the CD3(+)CD62L(+)compartment that includes immunoregulatory T cells. To block the in vivo Fas-Fas ligand (Fas L) interaction we administered a biologically active recombinant fusion protein coupling mouse Fas to the Fc portion of human IgG1 (FAS-Fc). Mice treated with FAS-Fc (10 doses iv of 15 microg) starting on the day of cyclophosphamide injection up to day 22, were fully protected from disease. Unexpectedly this protective effect was not due to blockade of Fas-FasL-mediated beta-cell apoptosis but rather to the inhibition of the cyclophosphamide effect on T cells. Indeed FAS-Fc treatment prevented the drug-induced T cell depletion in general and that of immunoregulatory T cells in particular. Additionally, FAS-Fc administration limited to the phase of beta-cell destruction did not afford any protection.

Intermolecular antigen spreading occurs during the preclinical period of human type 1 diabetes

Intra- and intermolecular spreading of T cell responses to autoantigens has been implicated in the pathogenesis of autoimmune diseases. Therefore, we questioned whether T cell responses from subjects identified as at-risk (positive for autoantibody reactivity to islet proteins) for the development of type 1 diabetes, a cell-mediated autoimmune disease, would demonstrate intermolecular Ag spreading of T cell responses to islet cell proteins. Previously, we have demonstrated that by the time subjects develop type 1 diabetes, they have T cell responses to numerous islet proteins, whereas T cells from normal controls respond to a limited number of islet proteins. Initial testing of PBMC responses from 25 nondiabetic at-risk subjects demonstrated that 16 of the 25 subjects have PBMC responses to islet proteins similar to controls. Fourteen of these 16 subjects were available for follow-up. Eleven of the 14 developed T cell responses to increasing numbers of islet proteins, and 6 of these subjects developed type 1 diabetes. In the nine subjects who already demonstrated T cell Ag spreading at the initial visit, four were available for follow-up. Of these four, two had increases in T cell reactivity to islet proteins, while two maintained their initial levels of T cell reactivity. We also observed Ag spreading in autoantibody reactivity to islet proteins in nine of the 18 at-risk subjects available for follow-up. Our data strongly support the conclusion that intermolecular spreading of T cell and Ab responses to islet proteins occurs during the preclinical period of type 1 diabetes.

The regulatory role of DR4 in a spontaneous diabetes DQ8 transgenic model

MHC class II molecules are critical determinants of genetic susceptibility to human type 1 diabetes. In patients, the most common haplotype contains the DRA1*0101-DRB1*0401 (DR4) and DQA1*0301-DQB1*0302 (DQ8) loci. To assess directly the relative roles of HLA-DQ8 and DR4 for diabetes development in vivo, we generated C57BL/6 transgenic mice that lack endogenous mouse MHC class II molecules but express HLA-DQ8 and/or DR4. Neither HLA-DQ nor HLA-DR transgenic mice developed insulitis or spontaneous diabetes. However, when they were crossed to transgenic mice (C57BL/6) expressing the B7.1 costimulatory molecules on pancreatic beta cells that do not normally develop diabetes, T cells from these double transgenic mice were no longer tolerant to islet autoantigens. The majority of DQ8/RIP-B7 mice developed spontaneous diabetes, whereas only 25% of DR4/RIP-B7 mice did so. Interestingly, when DQ8 and DR4 were coexpressed (DQ8DR4/RIP-B7), only 23% of these mice developed diabetes, an incidence indistinguishable from the DR4/RIP-B7 mice. T cells from both DR4/RIP-B7 and DQ8DR4/RIP-B7 mice, unlike those from DQ8/RIP-B7 mice, exhibited a Th2-like phenotype. Thus, the expression of DR4 appeared to downregulate DQ8-restricted autoreactive T cells in DQ8DR4/RIP-B7 mice. Our data suggest that although both DQ8 and DR4 can promote spontaneous diabetes in mice with a non-autoimmune-prone genetic background, the diabetogenic effect of the DQ8 allele is much greater, whereas DR4 expression downregulates the diabetogenic effect of DQ8, perhaps by enhancing Th2-like immune responses.

Interleukin-10 and the Interleukin-10 Receptor

Interleukin-10 (IL-10), first recognized for its ability to inhibit activation and effector function of T cells, monocytes, and macrophages, is a multifunctional cytokine with diverse effects on most hemopoietic cell types. The principal routine function of IL-10 appears to be to limit and ultimately terminate inflammatory responses. In addition to these activities, IL-10 regulates growth and/or differentiation of B cells, NK cells, cytotoxic and helper T cells, mast cells, granulocytes, dendritic cells, keratinocytes, and endothelial cells. IL-10 plays a key role in differentiation and function of a newly appreciated type of T cell, the T regulatory cell, which may figure prominently in control of immune responses and tolerance in vivo. Uniquely among hemopoietic cytokines, IL-10 has closely related homologs in several virus genomes, which testify to its crucial role in regulating immune and inflammatory responses. This review highlights findings that have advanced our understanding of IL-10 and its receptor, as well as its in vivo function in health and disease.

Cellular and molecular pathogenic mechanisms of insulin-dependent diabetes mellitus

Insulin-dependent diabetes mellitus (IDDM), also known as type 1 diabetes, is an organ-specific autoimmune disease resulting from the destruction of insulin-producing pancreatic beta cells. The hypothesis that IDDM is an autoimmune disease has been considerably strengthened by the study of animal models such as the BioBreeding (BB) rat and the nonobese diabetic (NOD) mouse, both of which spontaneously develop a diabetic syndrome similar to human IDDM. Beta cell autoantigens, macrophages, dendritic cells, B lymphocytes, and T cells have been shown to be involved in the pathogenesis of autoimmune diabetes. Among the beta cell autoantigens identified, glutamic acid decarboxylase (GAD) has been extensively studied and is the best characterized. Beta cell-specific suppression of GAD expression in NOD mice results in the prevention of IDDM. Macrophages and/or dendritic cells are the first cell types to infiltrate the pancreatic islets. Macrophages play an essential role in the development and activation of beta cell-cytotoxic T cells. B lymphocytes play a role as antigen-presenting cells, and T cells have been shown to play a critical role as final effectors that kill beta cells. Cytokines secreted by immunocytes, including macrophages and T cells, may regulate the direction of the immune response toward Th1 or Th2 as well as cytotoxic effector cell or suppressor cell dominance. Beta cells are destroyed by apoptosis through Fas-Fas ligand and TNF-TNF receptor interactions and by granzymes and perforin released from cytotoxic effector T cells. Therefore, the activated macrophages and T cells, and cytokines secreted from these immunocytes, act synergistically to destroy beta cells, resulting in the development of autoimmune IDDM.

NK T cell-induced protection against diabetes in V alpha 14-J alpha 281 transgenic nonobese diabetic mice is associated with a Th2 shift circumscribed regionally to the islets and functionally to islet autoantigen

The onset of autoimmune diabetes is related to defective immune regulation. Recent studies have shown that NK T cells are deficient in number and function in both diabetic patients and nonobese diabetic (NOD) mice. NK T cells, which are CD1d restricted, express a TCR with an invariant V alpha 14-J alpha 281 chain and rapidly produce large amounts of cytokines. V alpha 14-J alpha 281 transgenic NOD mice have increased numbers of NK T cells and are protected against diabetes onset. In this study we analyzed where and how NK T cells interfere with the development of the anti-islet autoimmune response. NK T cells, which are usually rare in lymph nodes, are abundant in pancreatic lymph nodes and are also present in islets. IL-4 mRNA levels are increased and IFN-gamma mRNA levels decreased in islets from diabetes-free V alpha 14-J alpha 281 transgenic NOD mice; the IgG1/IgG2c ratio of autoantibodies against glutamic acid decarboxylase is also increased in these mice. Treatment with IL-12 (a pro-Th1 cytokine) or anti-IL-4 Ab abolishes the diabetes protection in V alpha 14-J alpha 281 NOD mice. The protection from diabetes conferred by NK T cells is thus associated with a Th2 shift within islets directed against autoantigen such as glutamic acid decarboxylase. Our findings also demonstrate the key role of IL-4.

IL-12 plays a pathologic role at the inflammatory loci in the development of diabetes in NOD mice

Accumulating evidence suggests that CD4(+)T helper type 1 (Th1) cells play a major role in the development of insulin-dependent diabetes mellitus (IDDM) in the non-obese diabetic (NOD) mouse model. Interleukin (IL)-12 is a potent immunoregulatory molecule that is a key determinant of T-cell differentiation into Th1 cells, and has been implicated in the development of IDDM. To investigate the role of IL-12 that is locally produced by islet-infiltrating cells in the development of IDDM, we generated transgenic NOD mice in which the IL-12 p40 homodimer, a natural antagonist of IL-12, was produced exclusively in islets without affecting the levels of IL-12 p40 in the systemic circulation. We found that the incidence of diabetes was significantly reduced in these transgenic mice. These results clearly demonstrate that IL-12 locally produced by islet-infiltrating cells plays a critical role in the development of IDDM.

Identification of MHC class II-restricted peptide ligands, including a glutamic acid decarboxylase 65 sequence, that stimulate diabetogenic T cells from transgenic BDC2.5 nonobese diabetic mice

Nonobese diabetic (NOD) mice spontaneously develop insulitis and destruction of pancreatic islet beta cells similar to type 1 diabetes mellitis in humans. Insulitis also occurs in the BDC2.5 TCR transgenic line of NOD mice that express the rearranged TCR alpha- and beta-chain genes of a diabetogenic NOD CD4 T cell clone. When activated with syngeneic islet cells in culture, BDC2.5 T cells adoptively transfer disease to NOD recipients, but the identity of the islet cell Ag responsible for pathogenicity is not known. To characterize the autoantigen(s) involved, BDC2.5 T cells were used to screen a combinatorial peptide library arranged in a positional scanning format. We identified more than 100 decapeptides that stimulate these T cells at nanomolar concentrations; they are then capable of transferring disease to NOD-scid mice. Surprisingly, some of the peptides include sequences similar (8 of 10 residues) to those found within the 528-539 fragment of glutamic acid decarboxylase 65. Although this 12-mer glutamic acid decarboxylase 65 fragment is only slightly stimulatory for BDC2.5 T cells (EC(50) > 100 microM), a larger 16-mer fragment, 526-541, shows activity in the low micromolar range (EC(50) = 2.3 microM). Finally, T cells from prediabetic NOD mice respond spontaneously to these peptide analogs in culture; this finding validates them as being related to a critical autoantigen involved in the etiology of spontaneous diabetes and indicates that their further characterization is important for a better understanding of underlying disease mechanisms.

Variable effects of transgenic c-Maf on autoimmune diabetes

Autoimmune diabetes is associated with T helper 1 polarization, but protection from disease can be provided by the application of T helper 2 (Th2) cytokines. To test whether genetic manipulation of T-cells can provide protective Th2 responses, we developed transgenic mice in which T-cells express the interleukin-4-specific transcription factor c-Maf. When crossed with a transgenic model that combines a class II restricted T-cell receptor specific for influenza hemagglutinin with islet beta-cell expression of hemagglutinin, the c-Maf transgene provided significant protection from spontaneous autoimmunity but not from adoptively transferred diabetes. In a second transgenic model in which islet cells express the lymphocytic choriomeningitis virus nucleoprotein, the virus infection triggers autoimmune diabetes within a few weeks involving both CD4 and CD8 T-cells; here too transgenic c-Maf provided significant protection. Surprisingly, when the c-Maf transgene was backcrossed with the NOD model of spontaneous disease, no protection was evident. Thus, transgenic c-Maf can strongly influence autoimmune disease development in some models, but additional factors, such as background genetic differences, can influence the potency of its effect.

The role of Fas-FasL in CD8+ T-cell-mediated insulin-dependent diabetes mellitus (IDDM)

In the past few years a number of studies have evaluated the contributions of different cytolytic pathways in the autoimmune destruction of pancreatic beta cells, which results in insulin-dependent (type I) diabetes mellitus. Conflicting results continue to emerge regarding the role of Fas-mediated apoptosis in beta-cell destruction. This is likely to reflect differences inherent to the model systems under investigation, as well as the pleiotropic nature of the genes that are involved in cytotoxicity. Despite these complications, it may be possible to reconcile some of these apparently conflicting results by considering that T-cell-mediated cytotoxicity can occur simultaneously by several mechanisms and that variables such as the cytokine milieu and the strength of the signal to the T cell received through the T-cell receptor complex may alter the relative contribution of each cytolytic pathway to beta-cell destruction.

The molecular specificity of insulin autoantibodies

Insulin autoantibodies (IAA) are one of several markers for Type I (autoimmune) diabetes, but alone deserve special attention. Unlike the other markers, their ligand is unique to the beta cell. IAA are the first markers to appear during the symptomless period which precedes diabetes and they are present in the vast majority of young children destined to develop diabetes. The primary and tertiary structures of insulin have been known for decades. Binding studies with insulin variants have shown epitope restriction that can distinguish Type 1 diabetes-predictive from non-predictive IAA-positive sera, thereby improving specificity for the test. With two major international Type 1 diabetes prevention trials underway, there is a pressing need to refine markers that reliably indicate the presence of, and remission from, autoimmune insulitis. The binding regions of antibodies are assembled from three multi-gene families, and some of their diversity derives from random mutation during their antigen-driven maturation. There is evidence that mature IAA derive from germline-encoded 'natural' antibodies, and that the gene segments utilised by IAA may be influenced by clinical context. Monoclonal anti-idiotypic (anti-Id) antibodies can serve as probes for antibody variable region determinants, and antibodies to the different epitopes of beef and porcine insulins have already been analysed with monoclonal reagents. Used as antibodies in a radioimmunoassay format, monoclonal anti-Ids will identify and measure autoantibody idiotopes as if they were ligands. The challenge now is to replace the conventional radiobinding assays for IAA, which only detect and titrate, with radioimmunoassays that can be standardised in absolute units. There is sufficient evidence for the existence of Type 1 diabetes-predictive IAA idiotopes to justify the development of idiotope-specific radioimmunoassays which ignore Type 1 diabetes-unrelated IAA.

IL-10 deficiency does not inhibit insulitis and accelerates cyclophosphamide-induced diabetes in the nonobese diabetic mouse

IL-10 exterts profound immunostimulatory and immunoinhibitory effects. To explore the role of IL-10 in autoimmune diabetes of nonobese diabetic (NOD) mice, we generated IL-10-deficient NOD mice. In contrast to our previous results with neutralizing antibodies to IL-10, IL-10-deficient NOD mice developed insulitis and their splenocytes readily responded to islet antigen glutamic acid decarboxylase 65. IL-10-deficient NOD mice did not develop accelerated spontaneous diabetes. On the other hand, IL-10-deficient NOD mice developed accelerated disease following cyclophosphamide (CYP) injection. These findings demonstrate that IL-10 is dispensable for autoimmune diabetes. IL-10's absence fails to accelerate endogenous diabetes but potentiates CYP-induced diabetes.

A self MHC class II beta-chain peptide prevents diabetes in nonobese diabetic mice

We explored T cell responses to the self class II MHC (I-Ag7) beta-chain-derived peptides in diabetic and prediabetic nonobese diabetic (NOD) mice. We found that one of these immunodominant epitopes of the beta-chain of I-Ag7 molecule, peptide 54-76, could regulate autoimmunity leading to diabetes in NOD mice. T cells from prediabetic young NOD mice do not respond to the peptide 54-76, but T cells from diabetic NOD mice proliferated in response to this peptide. T cells from older nondiabetic mice or mice protected from diabetes do not respond to this peptide, suggesting a role for peptide 54-76-specific T cells in pathogenesis of diabetes. We show that this peptide is naturally processed and presented by the NOD APCs to self T cells. However, the peptide-specific T cells generated after immunization of young mice regulate autoimmunity in NOD mice by blocking the diabetogenic cells in adoptive transfer experiments. The NOD mice immunized with this peptide are protected from both spontaneous and cyclophosphamide-induced insulin-dependent diabetes mellitus. Immunization of young NOD mice with this peptide elicited T cell proliferation and production of Th2-type cytokines. In addition, immunization with this peptide induced peptide-specific Abs of IgG1 isotype that recognized native I-Ag7 molecule on the cell surface and inhibited the T cell proliferative responses. These results suggest that I-Abetag7(54-76) peptide-reactive T cells are involved in the pathogenesis of diabetes. However, immunization with this peptide at young age induces regulatory cells and the peptide-specific Abs that can modulate autoimmunity in NOD mice and prevent spontaneous and induced diabetes.

Thymic and postthymic regulation of diabetogenic CD8 T cell development in TCR transgenic nonobese diabetic (NOD) mice

Natural development of diabetes in nonobese diabetic (NOD) mice requires both CD4 and CD8 T cells. Transgenic NOD mice carrying alphabeta TCR genes from a class I MHC (Kd)-restricted, pancreatic beta cell Ag-specific T cell clone develop diabetes significantly faster than nontransgenic NOD mice. In these TCR transgenic mice, a large fraction of T cells express both transgene derived and endogenous TCR beta chains. Only T cells expressing two TCR showed reactivity to the islet Ag. Development of diabetogenic T cells is inhibited in mice with no endogenous TCR expression due to the SCID mutation. These results demonstrate that the expression of two TCRs is necessary for the autoreactive diabetogenic T cells to escape thymic negative selection in the NOD mouse. Further analysis with MHC congenic NOD mice revealed that diabetes development in the class I MHC-restricted islet Ag-specific TCR transgenic mice is still dependent on the presence of the homozygosity of the NOD MHC class II I-Ag7.

High density insulin receptor-positive diabetogenic T lymphocytes in nonobese diabetic mice are memory cells

Our previous work examining the importance of insulin receptor (IR) expression on T cells has demonstrated that when T cells from nonobese diabetic mice were sorted into populations expressing a high (IR(High)) and a low (IR(Low)) density of IR, IR(High) T cells rapidly transferred insulitis and diabetes. We have further characterized IR(High) T cells. Both CD4+ and CD8+ cells were detected in the IR(High) T cell population, but IR(High) expression was detected predominantly on CD4+ cells. IRHigh T cells were polyclonal for TCR Vbeta-chain expression. By 3 color flow cytometric analysis, virtually all IR(High) T cells expressed low or negligible levels of CD62L (CD62L(Low)/-) and high levels of CD44 (CD44(High)). The lack of IL-2 receptor and transferrin receptor expression as seen previously, together with the CD62L(Low)/- CD44(High) phenotype suggests that IR(High) T cells are memory cells. However, since only about one quarter of all of the CD62L(Low)/- or CD44(High) T cells were also IR(High), the IR(High) phenotype defines a subpopulation of memory T cells that are aggressively diabetogenic.

Temporal relationship between immune cell influx and the expression of inducible nitric oxide synthase, interleukin-4 and interferon-gamma in pancreatic islets of NOD mice following adoptive transfer of diabetic spleen cells

Beta cell destruction in NOD mice can be accelerated by adoptive transfer of diabetic spleen cells into irradiated adult NOD mice. Here mice receiving diabetic spleen cells were examined at days 0, 7, 14, 21 and at onset of diabetes for the resulting insulitis and the number of intra-islet CD4 and CD8 cells and macrophages. The progression of insulitis and the number of intra-islet CD4 and CD8 cells and macrophages were correlated with the expression and co-localization of inducible nitric oxide synthase, interferon-gamma and interleukin-4 by dual-label light and confocal immunofluorescence microscopy. Diabetes developed in 7/8 mice by 27 days following cell transfer. The insulitis score increased slightly by day 7 but rose sharply at day 14 (p = 0.001) and was maintained until diabetes. The mean number of intra-islet CD4 and CD8 cells and macrophages showed a similar trend to the insulitis scores and were present in almost equal numbers within the islets. Immunolabelling for inducible nitric oxide synthase was observed at day 7 in only some cells of a few islets but increased sharply from day 14. It was restricted to islets with insulitis and was co-localized in selective macrophages. Weak intra-islet interleukin-4 labelling was observed at days 7 and 14 but became more pronounced at day 21 and at onset of diabetes, being present in selective CD4 cells. Intra-islet labelling for interferon-gamma was first observed at day 21, but became more intense at onset of diabetes and was co-localized in a proportion of macrophages. Both cytokines were expressed in islets with advanced insulitis. Interferon-gamma staining was also observed within endothelial cells located in the exocrine pancreas. We conclude that transfer of diabetic spleen cells results in a rapid influx of CD4 and CD8 cells and macrophages within the pancreas of recipient mice. During the period of heightened insulitis, selective immune cells begin to express inducible nitric oxide synthase and the opposing cytokines, interferon-gamma and interleukin-4. Expression of these molecules becomes more pronounced immediately prior to and during the onset of diabetes.

Protection of nonobese diabetic mice from diabetes by gene(s) closely linked to IFN-gamma receptor loci

Nonobese diabetic (NOD) mice carrying a segment of chromosome flanking the disrupted IFN-gamma receptor gene from original 129 ES cells are resistant to development of diabetes. However, extended backcrossing of this mouse line to the NOD mouse resulted in a segregation of the IFN-gammaR-deficient genotype from the diabetes-resistant phenotype. These results indicate that the protection of NOD mice from the development of diabetes is not directly linked to the defective IFN-gamma receptor gene but, rather, is influenced by the presence of a diabetes-resistant gene(s) closely linked to the IFN-gammaR loci derived from the 129 mouse strain.

Induction of diabetes in nonobese diabetic mice by Th2 T cell clones from a TCR transgenic mouse

We have produced a panel of cloned T cell lines from the BDC-2.5 TCR transgenic (Tg) mouse that exhibit a Th2 cytokine phenotype in vitro but are highly diabetogenic in vivo. Unlike an earlier report in which T cells obtained from the Tg mouse were cultured for 1 wk under Th2-promoting conditions and were found to induce disease only in NOD.scid recipients, we found that long-term T cell clones with a fixed Th2 cytokine profile can transfer disease only to young nonobese diabetic (NOD) mice and never to NOD.scid recipients. Furthermore, the mechanism by which diabetes is transferred by a Tg Th2 T cell clone differs from that of the original CD4+ Th1 BDC-2.5 T cell clone made in this laboratory. Whereas the BDC-2.5 clone rapidly causes disease in NOD.scid recipients less than 2 wk old, the Tg Th2 T cell clones can do so only when cotransferred with other diabetogenic T cells, suggesting that the Th2 T cell requires the presence of host T cells for initiation of disease.

An islet-specific CD8+ T cell hybridoma generated from non-obese diabetic mice recognizes insulin as an autoantigen

Although CD8+ T cells play a major role in beta cell destruction in insulin-dependent diabetes in the non-obese diabetic mouse, the T cell autoantigen(s) recognized by such cells remains to be identified. Therefore, an islet-reactive, CD8+ T cell line was generated from islet-infiltrating cells and hybridized by fusion with a CD8+ alphabeta TCR- BW5147 thymoma. In the presence of islets, none of the 12 CD3+ CD8+ T cell hybridomas isolated secreted IL-2/IL-4 or IFNgamma but three were islet specific, as shown by activation induced cell death. Subclone 4A7.7.15 recognized only islets expressing H-2Kd, demonstrated islet-specific inhibition of proliferation and concomitant partial arrest in the G2/M phase of the cell cycle. Further analysis using a panel of cell lines, expressing H-2Kd, and transfected with the cDNA for various putative autoantigens in type 1 diabetes showed that 4A7.7.15 recognizes insulin as an antigen.

Neonatal tumor necrosis factor alpha promotes diabetes in nonobese diabetic mice by CD154-independent antigen presentation to CD8(+) T cells

Neonatal islet-specific expression of tumor necrosis factor (TNF)-alpha in nonobese diabetic mice promotes diabetes by provoking islet-infiltrating antigen-presenting cells to present islet peptides to autoreactive T cells. Here we show that TNF-alpha promotes autoaggression of both effector CD4(+) and CD8(+) T cells. Whereas CD8(+) T cells are critical for diabetes progression, CD4(+) T cells play a lesser role. TNF-alpha-mediated diabetes development was not dependent on CD154-CD40 signals or activated CD4(+) T cells. Instead, it appears that TNF-alpha can promote cross-presentation of islet antigen to CD8(+) T cells using a unique CD40-CD154-independent pathway. These data provide new insights into the mechanisms by which inflammatory stimuli can bypass CD154-CD40 immune regulatory signals and cause activation of autoreactive T cells.

In vivo evidence for the contribution of human histocompatibility leukocyte antigen (HLA)-DQ molecules to the development of diabetes

Although DQA1*0301/DQB1*0302 is the human histocompatibility leukocyte antigen (HLA) class II gene most commonly associated with human type 1 diabetes, direct in vivo experimental evidence for its diabetogenic role is lacking. Therefore, we generated C57BL/6 transgenic mice that bear this molecule and do not express mouse major histocompatibility complex (MHC) class II molecules (DQ8(+)/mII(-)). They did not develop insulitis or spontaneous diabetes. However, when DQ8(+)/mII(-) mice were bred with C57BL/6 mice expressing costimulatory molecule B7-1 on beta cells (which normally do not develop diabetes), 81% of the DQ8(+)/mII(-)/B7-1(+) mice developed spontaneous diabetes. The diabetes was accompanied by severe insulitis composed of both T cells (CD4(+) and CD8(+)) and B cells. T cells from the diabetic mice secreted large amounts of interferon gamma, but not interleukin 4, in response to DQ8(+) islets and the putative islet autoantigens, insulin and glutamic acid decarboxylase (GAD). Diabetes could also be adoptively transferred to irradiated nondiabetic DQ8(+)/mII(-)/B7-1(+) mice. In striking contrast, none of the transgenic mice in which the diabetes protective allele (DQA1*0103/DQB1*0601, DQ6 for short) was substituted for mouse MHC class II molecules but remained for the expression of B7-1 on pancreatic beta cells (DQ6(+)/mII(-)/B7-1(+)) developed diabetes. Only 7% of DQ(-)/mII(-)/B7-1(+) mice developed diabetes at an older age, and none of the DQ(-)/mII(+)/B7-1(+) mice or DQ8(+)/mII(+)/B7-1(+) mice developed diabetes. In conclusion, substitution of HLA-DQA1*0301/DQB1*0302, but not HLA-DQA1*0103/DQB1*0601, for murine MHC class II provokes autoimmune diabetes in non-diabetes-prone rat insulin promoter (RIP).B7-1 C57BL/6 mice. Our data provide direct in vivo evidence for the diabetogenic effect of this human MHC class II molecule and a unique "humanized" animal model of spontaneous diabetes.

Superantigens: mechanisms by which they may induce, exacerbate and control autoimmune diseases

Superantigens are polypeptide molecules produced by a broad range of infectious microorganisms which elicit excessive and toxic T-cell responses in mammalian hosts. In light of this property and the fact that autoimmune diseases are frequently the sequelae of microbial infections, it has been suggested that superantigens may be etiologic agents of autoreactive immunological responses resulting in initiation, exacerbation or relapse of autoimmune diseases. This article relates the biology of superantigens to possible mechanisms by which they may exert these activities and reviews the evidence for their roles in various human and animal models of autoimmune disease. Finally, a mechanism of active suppression by superantigen-activated CD4+ T-cells that could be exploited for therapy as well as prophylaxis of human autoimmune diseases is proposed.

Role of Inflammatory Infiltrate in Activation and Effector Function of Cloned Islet Reactive Nonobese Diabetic CD8+ T Cells: Involvement of a Nitric Oxide-Dependent Pathway

To investigate how CD8+ T cells interact with β cells and local inflammatory cells in islets, we have isolated CD8+ T cell clones from nonobese diabetic (NOD) spleen that recognize and destroy both islets and the NOD insulinoma cell line NIT-1. The clones destroyed NOD islets with pre-existing inflammation better than islets without signs of inflammation. Islets from NOD-scid mice were destroyed only poorly, but that could be improved by adding IL-7 to the assay. Anti-IFN-γ Abs inhibited destruction of infiltrated islets. Single islets were effective stimulators of IFN-γ production by cloned CD8+ T cells, which varied &gt;50-fold depending on the degree of islet infiltration. This effect of the islet mononuclear infiltrate could be mimicked by adding spleen cells to NIT-1 cells, which augmented IFN-γ production above the level stimulated by NIT-1 cells alone. The enhancing effect of spleen cells could be attributed to their macrophage subpopulation and was not MHC restricted, although recognition of islet Ag by cloned CD8+ T cells and subsequent islet destruction was restricted to islets expressing H-2Db molecules. An inhibitor of inducible NO synthase inhibited destruction of inflamed islets by cloned CD8+ T cells. We propose that macrophages in inflamed islets provide a form of bystander costimulation of β cell-specific CD8+ T cells. CD8+ T cells respond to Ag and costimulation by producing IFN-γ that activates macrophages. Activated macrophages facilitate islet destruction by CD8+ T cells through a NO synthesis-dependent pathway.

Apoptotic and effector pathways in autoimmunity

Programmed cell death is an important anti-autoimmune mechanism used to delete autoreactive lymphocytes and to limit the spread both of viral infections and of tissue damage caused by immune responses. However, in autoimmune diseases, activation of programmed cell death by effector mechanisms that are similar to the normal immune response leads to augmented destruction of the targeted tissues.

Anti-CD43 Monoclonal Antibody L11 Blocks Migration of T Cells to Inflamed Pancreatic Islets and Prevents Development of Diabetes in Nonobese Diabetic Mice

Nonobese diabetic mice are a well-known model for human insulin-dependent diabetes mellitus. These mice develop autoimmune-mediated inflammation of the pancreatic islets, followed by destruction of the insulin-producing β cells and development of diabetes. Nonobese diabetic mice also have salivary gland inflammation, and serve as a model for human Sjogren’s syndrome. T cells are a prominent component of the inflammatory infiltrate in these sites, and T cell recruitment from the blood is thought to be essential for the initiation and maintenance of pathologic tissue damage. A unique mAb to murine CD43, L11, has recently been shown to block the migration of T cells from blood into organized lymphoid tissues. Here we demonstrate that L11 significantly inhibits T cell migration from blood into inflamed islets and salivary glands. Treatment of nonobese diabetic mice with L11 from 1 to 4 or 8 to 12 wk of age led to significant protection against the development of diabetes. Moreover, protection was long-lived, with decreased incidence of diabetes even months after cessation of Ab administration. When treatment was started at 1 wk of age, L11 inhibited the development of inflammation in pancreatic islets and salivary glands. L11 treatment had no long-term effect on numbers or phenotypes of peripheral lymphocytes. These data indicate that anti-CD43 Abs that block T cell migration may be useful agents for the prevention or treatment of autoimmune diseases including insulin-dependent diabetes mellitus and Sjogren’s syndrome.

Comparing the Relative Role of Perforin/Granzyme Versus Fas/Fas Ligand Cytotoxic Pathways in CD8+ T Cell-Mediated Insulin-Dependent Diabetes Mellitus

CD8+ cytotoxic T cells play a critical role in initiating insulin-dependent diabetes mellitus. The relative contribution of each of the major cytotoxic pathways, perforin/granzyme and Fas/Fas ligand (FasL), in the induction of autoimmune diabetes remains controversial. To evaluate the role of each lytic pathway in β cell lysis and induction of diabetes, we have used a transgenic mouse model in which β cells expressing the influenza virus hemagglutinin (HA) are destroyed by HA-specific CD8+ T cells from clone-4 TCR-transgenic mice. Upon adoptive transfer of CD8+ T cells from perforin-deficient clone-4 TCR mice, there was a 30-fold increase in the number of T cells required to induce diabetes. In contrast, elimination of the Fas/FasL pathway of cytotoxicity had little consequence. When both pathways of cytolysis were eliminated, mice did not become diabetic. Using a model of spontaneous diabetes, which occurs in double transgenic neonates that express both clone-4 TCR and Ins-HA transgenes, mice deficient in either the perforin or FasL/Fas lytic pathway become diabetic soon after birth. This indicates that, in the neonate, large numbers of autoreactive CD8+ T cells can lead to destruction of islet β cells by either pathway.

Minute defects in the expression of MHC E molecules lead to impaired protection from autoimmunity in NOD mice

The E complex of the major histocompatibility complex (MHC) can prevent the spontaneous development of diabetes in nonobese diabetic (NOD) mice transgenic for the Ea gene. None of three promoter-mutated Ea constructs with Ea expression directed to different subsets of immunocompetent cells exerts full protection in NOD mice. The promoter-mutated constructs are all capable of mediating intrathymic elimination of I-E-restricted T cells. Thus, thymic negative selection is not responsible for the protective effect but a more complex effect is likely. Here we show that combinations of two or three different mutated Ea constructs do not protect against intra-islet insulitis either. We also show that spleen cells from protected animals are sufficient to protect NOD mice in adoptive transfer experiments. The only detectable expression defects in splenic cells or cells influencing the repertoire of splenic cells are in the B-cell compartment. Furthermore, in three construct combinations, the differences to wild-type expression are extremely small. Thus, we conclude that even minute disturbances of the E expression pattern might reduce the protection of NOD mice from insulitis.

IL-2 Receptor-Targeted Cytolytic IL-2/Fc Fusion Protein Treatment Blocks Diabetogenic Autoimmunity in Nonobese Diabetic Mice

High affinity IL-2R5 is present on recently activated but not on resting or memory T cells. Selective targeting of T cells bearing high affinity IL-2R is an attractive therapy for many T cell-dependent cytopathic disease processes. A variety of rodent mAbs directed against the α-chain of the IL-2R, as well as IL-2 fusion toxins, have been used in animals and humans to achieve selective immunosuppression. Here we report on the development of a novel IL-2R targeting agent, a cytolytic chimeric IL-2/Fc fusion protein. This immunoligand binds specifically and with high affinity to IL-2R and is structurally capable of recruiting host Ab-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity activities. The Ig component ensures an extended circulating t1/2 of 25 h following systemic administration. To subsequently explore the mechanisms of the antidiabetogenic effects of IL-2/Fc, we have mutated the FcR binding and complement C1q binding (Fc−/−) domains of the Fc fragment to render the Fc unable to direct Ab-dependent cell-mediated cytotoxicity and complement-dependent cytotoxicity activities. In a model of passive transfer of diabetes in nonobese diabetic mice, lytic IL-2/Fc, but not nonlytic IL-2/Fc−/−, exhibited striking antidiabetogenic effects. Together with the negligible potential of IL-2/Fc for immunogenicity, this finding forecasts that cytolytic IL-2/Fc may offer a new therapeutic approach for selective targeting of auto and alloimmune T cells.

T cell reactivity to human insulinoma cell line (CM) antigens in patients with type 1 diabetes

Autoimmune (type 1) diabetes mellitus results from a progressive destruction of insulin secreting beta cells operated by T lymphocytes in pancreatic islets. Circulating autoreactive T cells to specific beta cell antigens are detected in patients with type 1 diabetes. To date, several beta cell autoantigens have been identified in this disease (GAD, IA-2, 38kD secretory protein, insulin, ICA69 etc.), however, it is possible that also other unidentified self molecules contribute to trigger beta cell autoimmunity. In this study we used the human insulinoma cell line CM as source of beta cell antigens to detect reactive T lymphocytes in patients with type 1 diabetes mellitus. This cell line has been previously shown to express a number of recognized beta cell antigens. Since the expression of several beta cell antigens is affected by glucose stimulation we tested two preparations of CM cells cultured under different conditions containing low (0.8 mM) and high glucose concentration (11 mM). T cell proliferation was measured using cells from 32 patients with type 1 diabetes (19 of recent onset and 13 at 3 to 22 months from diagnosis) and 27 age-matched control subjects. A significant increase in T cell proliferation to CM cells grown in high glucose conditions (11 mM) (p < 0.05) was found in type 1 diabetic patients compared to controls. No significant differences were observed when using CM cells cultured at the low glucose concentration. Furthermore, the response to both extracts of CM cells was independent of disease duration (p = 0.6 for both CM cells cultured at 0.8 and 11 mM glucose). These data indicate that T cell reactivity to homogenates of CM cells is detectable in patients with type 1 diabetes and suggest that this human insulinoma cell line is an interesting potential source of beta cell material for immunological studies of autoimmune diabetes.

Prevalent CD8(+) T cell response against one peptide/MHC complex in autoimmune diabetes

Spontaneous autoimmune diabetes in nonobese diabetic (NOD) mice is the result of a CD4(+) and CD8(+) T cell-dependent autoimmune process directed against the pancreatic beta cells. CD8(+) T cells play a critical role in the initiation and progression of diabetes, but the specificity and diversity of their antigenic repertoire remain unknown. Here, we define the structure of a peptide mimotope that elicits the proliferation, cytokine secretion, differentiation, and cytotoxicity of a diabetogenic H-2K(d)-restricted CD8(+) T cell specificity (NY8.3) that uses a T cell receptor alpha (TCRalpha) rearrangement frequently expressed by CD8(+) T cells propagated from the earliest insulitic lesions of NOD mice (Valpha17-Jalpha42 elements, often joined by the N-region sequence M-R-D/E). Stimulation of splenic CD8(+) T cells from single-chain 8. 3-TCRbeta-transgenic NOD mice with this mimotope leads to preferential expansion of T cells bearing an endogenously derived TCRalpha chain identical to the one used by their islet-associated CD8(+) T cells, which is also identical to the 8.3-TCRalpha sequence. Cytotoxicity assays using islet-derived CD8(+) T cell clones from nontransgenic NOD mice as effectors and peptide-pulsed H-2K(d)-transfected RMA-S cells as targets indicate that nearly half of the CD8(+) T cells recruited to islets in NOD mice specifically recognize the same peptide/H-2K(d) complex. This work demonstrates that beta cell-reactive CD8(+) T cells mount a prevalent response against a single peptide/MHC complex and provides one peptide ligand for CD8(+) T cells in autoimmune diabetes.

Establishment of an embryonic stem (ES) cell line derived from a non-obese diabetic (NOD) mouse: in vivo differentiation into lymphocytes and potential for germ line transmission

A non-obese diabetic (NOD) mouse-derived embryonic stem (ES) cell line has been stably maintained in an undifferentiated state with a characteristic ES cell-like morphology, expressing the stem cell marker alkaline phosphatase, and displaying a normal diploid karyotype. After injecting the NOD-ES cells into blastocysts, chimeric mice were obtained. Small but significant numbers of lymphocytes expressed the NOD-derived MHC allele. When a chimeric mouse was mated with C57BL/6 mice, an agouti mouse was obtained, having the NOD-derived H-2 I-A(beta)g7 haplotype. Thus, an NOD-ES cell line which can differentiate into lymphocytes with potential for germ line transmission was successfully established.

Transfer of dendritic cells (DC) ex vivo stimulated with interferon-gamma (IFN-gamma) down-modulates autoimmune diabetes in non-obese diabetic (NOD) mice

The NOD mouse has been used to explore the many features of insulin-dependent diabetes mellitus (IDDM) that is caused by the destruction of insulin-producing beta cells in the islets of Langerhans of the pancreas. Self-reactive T cells have been considered to mediate IDDM in the NOD mouse, and antigen-presenting cells like DC and macrophages are expected to be involved in the processes from their role in generating regulatory or effector T cells. The present study shows that transfer of IFN-gamma-stimulated DC of the NOD or ICR mouse into the NOD mouse did not accelerate IDDM onset but afforded long-lasting protection against clinical and histological signs of IDDM in the recipient mice. The anti-diabetogenic ability was unique to IFN-gamma-stimulated DC when compared with unstimulated DC. A considerable proportion of the injected IFN-gamma-stimulated DC was demonstrated to migrate into the pancreas and its associated lymphoid tissues, suggesting the DC exert their anti-diabetogenic effects there. These findings suggest that development of autoimmune diabetes in the NOD mouse is under the control of DC, and that IDDM onset could be controlled by appropriately manipulating DC systems in vivo, which may open the gate for the therapeutic application of ex vivo-conditioned DC to human IDDM.

Antigen presentation pathways for immunity to islet transplants. Relevance to immunoisolation

Tremendous advances have been made over the past several years in the development of diverse biocompatible materials and structural designs for the implantation of immunoisolated cells and tissues. This area of bioengineering has clear application to insulin-dependent diabetes for which the implantation of micro- or macroencapsulated pancreatic islets or surrogate beta cells has great potential therapeutic benefit. This discussion concentrates on three antigen-specific immunologic processes that impede the application of islet transplantation as a therapy for insulin-dependent diabetes: (1) Allograft immunity, (2) Xenograft immunity, and (3) Autoimmune pathogenesis of Type I diabetes. Special emphasis is placed on the potential impact of these immune pathways on immunoisolated tissues.

Islet mass plays a critical role in initiation, but not progression, of the diabetogenic process in NOD mice

Pancreatectomy (90%) at a preinsulitis age (7 weeks) protects NOD mice from diabetes while pancreatectomy at a mid-insulitis age (13 weeks) has no such protective effect. The present study examined the effects of islet transplantation in pancreatectomized diabetes-free NOD mice. Transplantation of syngeneic NOD islets as well as allogeneic C3H/He and C57BL/6 islets 3 weeks after pancreatectomy-induced spontaneous diabetes whereas transplantation of xenogeneic Sprague-Dawley rat islets or allogeneic C3H/He skin failed to induce diabetes, demonstrating that the diabetogenic antigen(s) of NOD islets is also expressed by islets of diabetes-resistant mouse strains but not by xenogeneic rat islets. Removal of NOD islet grafts by nephrectomy 7-14 days after transplantation had no effect on the subsequent chronic development of diabetes, while graft removal 3 days after transplantation completely abolished the diabetogenic effect of islet transplantation. Thus, activation of the diabetogenic response by islet isografting takes less than 7 days and the continuous presence of a large islet mass is not required for progression to diabetes. While islet transplantation at 10 and 15 weeks of age caused diabetes, delayed islet transplantation at 23 and 35 weeks of age failed to induce diabetes in pancreatectomized diabetes-free NOD mice, suggesting that initiation of the diabetogenic autoimmune process must take place within a certain window of time. The pancreatectomy/islet transplantation model is excellent for studying the immunological events surrounding activation and progression of the diabetogenic autoimmune process and for identifying the diabetogenic islet antigen(s).

A conformationally-constrained MHC class II I-Ag7-derived peptide protects NOD mice from the development of diabetes

Allele-specific peptide vaccination against disease-associated MHC class II molecules is a promising new strategy for modulating self-antigen presentation to autoreactive T cells in autoimmune diseases. To evaluate the potential of this approach for treatment of insulin-dependent diabetes mellitus (IDDM), we have designed a cyclic peptide vaccine, DiavaX, from the third hypervariable region of the beta-chain of the NOD mouse MHC class II I-Ag7. NOD mice were treated at 5 and 9 weeks of age with 100 microg DiavaX emulsified in alum, a control peptide in alum, or alum alone. At the end of the study, 87% of alum treated mice had developed diabetes, compared with only 28% of DiavaX-treated mice. None of the control peptides, including a linear I-Ag7, a scrambled cyclic I-Ag7, or an analogous cyclic I-Aspeptide, reduced the incidence of diabetes, demonstrating that the protective effect of DiavaX is conformationally dependent and both allele- and sequence-specific. DiavaX treatment did not cause any general immune suppression, but did induce peptide-specific antibodies and memory T cells. DiavaX-induced protection from diabetes was associated with the maintenance of a non-destructive islet-associated autoimmune response. These data indicate that a conformationally constrained peptide from the disease-associated MHC represents a potential vaccine candidate for the prevention of clinical IDDM.

Role of autoreactive CD8+ T cells in organ-specific autoimmune diseases: insight from transgenic mouse models

There is now convincing evidence that autoreactive CD8+ T cells can contribute to the pathogenesis of organ-specific autoimmune diseases. In the non-obese diabetic mouse, there is direct evidence that beta-islet cell-specific CD8+ cytotoxic T cells have a pathogenic effect. In human diseases such as autoimmune diabetes and multiple sclerosis, indirect evidence also suggests a role for CD8+ T cells in tissue damage, although their antigen specificity is unknown. Transgenic mouse models as well as the use of knockout mice have been instrumental in the identification of the role of autoreactive CD8+ T cells. Spontaneous models of CD8+ T-cell-mediated autoimmunity generated through transgenesis should help delineate the effector mechanisms leading to tissue destruction. The study of autoreactive CD8+ T cells and the characterization of their antigenic specificity should help unravel the pathophysiology of organ-specific autoimmune diseases, help identify exacerbating foreign antigens, and allow the design of antigen-specific immunotherapy targeting the pathogenic autoreactive T cells.

Role of dendritic cells in the induction and maintenance of autoimmune diseases

Autoimmune diseases are characterised by the loss of tolerance against self-determinants, activation of autoreactive lymphocytes and pathological damage to single or multiple organs. The mechanisms by which autoimmune responses are triggered and activation of autoreactive lymphocytes is initiated and maintained are not yet fully understood. Translocation of previously immunologically ignored antigens from the periphery to secondary lymphoid organs is probably a key step in the initiation of autoimmunity. Antigen transport and primary sensitisation of T lymphocytes is mainly mediated by dendritic cells which reside in peripheral non-lymphoid tissues and maintain a continuous gradient of antigens towards secondary lymphoid tissues. In the transgenic rat insulin promoter-glycoprotein model of autoimmune diabetes, dendritic cell (DC)-mediated antigen transport initiates an autoimmune response against a pancreatic neoself-antigen. Dose and timing of antigen delivery by DC and turnover of antigenic peptides presented by DC are the main parameters regulating the outcome of autoimmune diabetes in this model system. An important sequel of continued antigenic stimulation via DC is the formation of lymphoid structures in the pancreas. Thus, appropriate and repeated activation of cytotoxic T lymphocytes by DC, in concert with local inflammatory processes leading to formation of organised lymphoid tissue in the target organ, is likely to be crucial in the development of destructive autoimmunity. Therapeutic intervention to selectively manipulate antigen transport by dendritic cells or to influence antigen presentation may prove beneficial for the treatment of autoimmune diseases. Furthermore, the capacity of DC to induce potent antiself responses might have implications for the use of DC presenting self-antigens in treatment of established tumours.