The nutrition-related adverse events associated with immune checkpoint inhibitor treatment for patients with non-small cell lung cancer: A systematic review.

AIMS: Immune checkpoint inhibitor therapy used for lung cancer has significantly changed response and survival rates, however, the impact on patients' nutritional status remains largely unexplored. This review aims to identify common adverse events that increase nutrition risk induced in non-small cell lung cancer patients treated with immune checkpoint inhibitor therapy and assess impact on nutritional status. METHODS: PubMed, Medline and CINAHL were systematically searched in September 2023 for randomised controlled trials comparing immune checkpoint inhibitor treatment of non-small cell lung cancer to a control group. Treatment-related adverse events that increased nutrition impact symptoms identified in the patient-generated subjective global assessment and clinical guidelines were extracted and qualitatively analysed. Risk of bias was assessed using Cochrane Risk of Bias tool 2. RESULTS: Eleven eligible randomised controlled trial studies were identified and analysed. The data demonstrated immune checkpoint inhibitor treatment was associated with a lower percentage of reported nutrition impact symptoms, for example, decreased appetite, nausea, vomiting, compared to chemotherapy treatment. Conversely, immune checkpoint inhibitor treated patients recorded a greater percentage of immune-related adverse events that alter metabolism or nutrient absorption. CONCLUSION: Non-small cell lung cancer patients treated with immune checkpoint inhibitors still experience nutrition impact symptoms but less frequently than patients treated with chemotherapy. This combined with unique nutrition-related consequences from colitis and thyroid disorders induced by immune checkpoint inhibitor therapy indicates patients should be screened, assessed and interventions implemented to improve nutrition.

Relationship between global leadership initiative on malnutrition (GLIM) defined malnutrition and survival, length of stay and post-operative complications in people with cancer: A systematic review.

BACKGROUND & AIMS: The predictive validity of the GLIM criteria for survival, length of hospital stay (LOHS) and post-operative complications among people with cancer have not been systematically reviewed. This systematic review aims to determine whether GLIM malnutrition is predictive of these outcomes, and whether the predictive validity is affected by how phenotypic and etiologic criteria are assessed. METHODS: Cohort studies published after 2018 were systematically reviewed according to PRISMA guidelines from Embase, Medline Complete and CINAHL Complete. Risk of bias and methodologic quality were assessed using the Journal of the Academy of Nutrition and Dietetics' Quality Criteria Checklist tool for Primary research. RESULTS: In total, 21 studies were included, including 28,726 participants. All studies investigated survival, where 18 reported GLIM malnutrition is associated with decreased survival. LOHS was investigated in six studies, with all finding an association between GLIM malnutrition and longer LOHS. Post-operative complications were assessed in seven studies, of which five reported GLIM malnutrition was predictive of increased post-operative complications. Methods to assess the GLIM phenotypic and etiologic criteria varied, with consistent predictive ability for survival regardless of method of assessing reduced muscle mass. However, predictive ability was more variable across different measures of inflammation and reduced intake. CONCLUSION: GLIM malnutrition was consistently predictive of worse clinical outcomes. Different measures of reduced muscle mass did not affect the predictive ability of GLIM for survival. However, variation in assessment of the etiologic criteria resulted in varying predictive ability of the GLIM diagnosis for survival.

Deficiency of the innate immune adaptor STING promotes autoreactive T cell expansion in NOD mice.

AIMS/HYPOTHESIS: Stimulator of IFN genes (STING) is a central hub for cytosolic nucleic acid sensing and its activation results in upregulation of type I IFN production in innate immune cells. A type I IFN gene signature seen before the onset of type 1 diabetes has been suggested as a driver of disease initiation both in humans and in the NOD mouse model. A possible source of type I IFN is through activation of the STING pathway. Recent studies suggest that STING also has antiproliferative and proapoptotic functions in T cells that are independent of IFN. To investigate whether STING is involved in autoimmune diabetes, we examined the impact of genetic deletion of STING in NOD mice. METHODS: CRISPR/Cas9 gene editing was used to generate STING-deficient NOD mice. Quantitative real-time PCR was used to assess the level of type I IFN-regulated genes in islets from wild-type and STING-deficient NOD mice. The number of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)206-214-specific CD8+ T cells was determined by magnetic bead-based MHC tetramer enrichment and flow cytometry. The incidence of spontaneous diabetes and diabetes after adoptive transfer of T cells was determined. RESULTS: STING deficiency partially attenuated the type I IFN gene signature in islets but did not suppress insulitis. STING-deficient NOD mice accumulated an increased number of IGRP206-214-specific CD8+ T cells (2878 ± 642 cells in NOD.STING-/- mice and 728.8 ± 196 cells in wild-type NOD mice) in peripheral lymphoid tissue, associated with a higher incidence of spontaneous diabetes (95.5% in NOD.STING-/- mice and 86.2% in wild-type NOD mice). Splenocytes from STING-deficient mice rapidly induced diabetes after adoptive transfer into irradiated NOD recipients (median survival 75 days for NOD recipients of NOD.STING-/- mouse splenocytes and 121 days for NOD recipients of NOD mouse splenocytes). CONCLUSIONS/INTERPRETATION: Data suggest that sensing of endogenous nucleic acids through the STING pathway may be partially responsible for the type I IFN gene signature but not autoimmunity in NOD mice. Our results show that the STING pathway may play an unexpected intrinsic role in suppressing the number of diabetogenic T cells.

IL-21 regulates SOCS1 expression in autoreactive CD8+ T cells but is not required for acquisition of CTL activity in the islets of non-obese diabetic mice.

In type 1 diabetes, maturation of activated autoreactive CD8+ T cells to fully armed effector cytotoxic T lymphocytes (CTL) occurs within the islet. At present the signals required for the maturation process are poorly defined. Cytokines could potentially provide the necessary "third signal" required to generate fully mature CTL capable of killing insulin-producing ß-cells. To determine whether autoreactive CTL within islets respond to cytokines we generated non-obese diabetic (NOD) mice with a reporter for cytokine signalling. These mice express a reporter gene, hCD4, under the control of the endogenous regulatory elements for suppressor of cytokine signalling (SOCS)1, which is itself regulated by pro-inflammatory cytokines. In NOD mice, the hCD4 reporter was expressed in infiltrated islets and the expression level was positively correlated with the frequency of infiltrating CD45+ cells. SOCS1 reporter expression was induced in transferred ß-cell-specific CD8+ 8.3T cells upon migration from pancreatic draining lymph nodes into islets. To determine which cytokines induced SOCS1 promoter activity in islets, we examined hCD4 reporter expression and CTL maturation in the absence of the cytokine receptors IFNAR1 or IL-21R. We show that IFNAR1 deficiency does not confer protection from diabetes in 8.3 TCR transgenic mice, nor is IFNAR1 signalling required for SOCS1 reporter upregulation or CTL maturation in islets. In contrast, IL-21R-deficient 8.3 mice have reduced diabetes incidence and reduced SOCS1 reporter activity in islet CTLs. However IL-21R deficiency did not affect islet CD8+ T cell proliferation or expression of granzyme B or IFNγ. Together these data indicate that autoreactive CD8+ T cells respond to IL-21 and not type I IFNs in the islets of NOD mice, but neither IFNAR1 nor IL-21R are required for islet intrinsic CTL maturation.

Granzyme A Deficiency Breaks Immune Tolerance and Promotes Autoimmune Diabetes Through a Type I Interferon-Dependent Pathway.

Granzyme A is a protease implicated in the degradation of intracellular DNA. Nucleotide complexes are known triggers of systemic autoimmunity, but a role in organ-specific autoimmune disease has not been demonstrated. To investigate whether such a mechanism could be an endogenous trigger for autoimmunity, we examined the impact of granzyme A deficiency in the NOD mouse model of autoimmune diabetes. Granzyme A deficiency resulted in an increased incidence in diabetes associated with accumulation of ssDNA in immune cells and induction of an interferon response in pancreatic islets. Central tolerance to proinsulin in transgenic NOD mice was broken on a granzyme A-deficient background. We have identified a novel endogenous trigger for autoimmune diabetes and an in vivo role for granzyme A in maintaining immune tolerance.

Cognate antigen engagement on parenchymal cells stimulates CD8+ T cell proliferation in situ.

T-cell responses are initiated upon cognate presentation by professional antigen presenting cells in lymphoid tissue. T cells then migrate to inflamed tissues, but further T-cell stimulation in these parenchymal target sites is not well understood. Here we show that T-cell expansion within inflamed tissues is a distinct phase that is neither a classical primary nor classical secondary response. This response, which we term 'the mezzanine response', commences within days after initial antigen encounter, unlike the secondary response that usually occurs weeks after priming. A further distinction of this response is that T-cell proliferation is driven by parenchymal cell antigen presentation, without requiring professional antigen presenting cells, but with increased dependence on IL-2. The mezzanine response might, therefore, be a new target for inhibiting T-cell responses in allograft rejection and autoimmunity or for enhancing T-cell responses in the context of microbial or tumour immunity.

Repurposed JAK1/JAK2 Inhibitor Reverses Established Autoimmune Insulitis in NOD Mice.

Recent advances in immunotherapeutics have not yet changed the routine management of autoimmune type 1 diabetes. There is an opportunity to repurpose therapeutics used to treat other diseases to treat type 1 diabetes, especially when there is evidence for overlapping mechanisms. Janus kinase (JAK) 1/JAK2 inhibitors are in development or clinical use for indications including rheumatoid arthritis. There is good evidence for activation of the JAK1/JAK2 and signal transducer and activator of transcription (STAT) 1 pathway in human type 1 diabetes and in mouse models, especially in ß-cells. We tested the hypothesis that using these drugs to block the JAK-STAT pathway would prevent autoimmune diabetes. The JAK1/JAK2 inhibitor AZD1480 blocked the effect of cytokines on mouse and human ß-cells by inhibiting MHC class I upregulation. This prevented the direct interaction between CD8+ T cells and ß-cells, and reduced immune cell infiltration into islets. NOD mice treated with AZD1480 were protected from autoimmune diabetes, and diabetes was reversed in newly diagnosed NOD mice. This provides mechanistic groundwork for repurposing clinically approved JAK1/JAK2 inhibitors for type 1 diabetes.

Perinatal tolerance to proinsulin is sufficient to prevent autoimmune diabetes.

High-affinity self-reactive thymocytes are purged in the thymus, and residual self-reactive T cells, which are detectable in healthy subjects, are controlled by peripheral tolerance mechanisms. Breakdown in these mechanisms results in autoimmune disease, but antigen-specific therapy to augment natural mechanisms can prevent this. We aimed to determine when antigen-specific therapy is most effective. Islet autoantigens, proinsulin (PI), and islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP) were expressed in the antigen-presenting cells (APCs) of autoimmune diabetes-prone nonobese diabetic (NOD) mice in a temporally controlled manner. PI expression from gestation until weaning was sufficient to completely protect NOD mice from diabetes, insulitis, and development of insulin autoantibodies. Insulin-specific T cells were significantly diminished, were naive, and did not express IFN-γ when challenged. This long-lasting effect from a brief period of treatment suggests that autoreactive T cells are not produced subsequently. We tracked IGRP206-214-specific CD8+ T cells in NOD mice expressing IGRP in APCs. When IGRP was expressed only until weaning, IGRP206-214-specific CD8+ T cells were not detected later in life. Thus, anti-islet autoimmunity is determined during early life, and autoreactive T cells are not generated in later life. Bolstering tolerance to islet antigens in the perinatal period is sufficient to impart lasting protection from diabetes.

Rotavirus acceleration of type 1 diabetes in non-obese diabetic mice depends on type I interferon signalling.

Rotavirus infection is associated with childhood progression to type 1 diabetes. Infection by monkey rotavirus RRV accelerates diabetes onset in non-obese diabetic (NOD) mice, which relates to regional lymph node infection and a T helper 1-specific immune response. When stimulated ex vivo with RRV, plasmacytoid dendritic cells (pDCs) from naïve NOD mice secrete type I interferon, which induces the activation of bystander lymphocytes, including islet-autoreactive T cells. This is our proposed mechanism for diabetes acceleration by rotaviruses. Here we demonstrate bystander lymphocyte activation in RRV-infected NOD mice, which showed pDC activation and strong upregulation of interferon-dependent gene expression, particularly within lymph nodes. The requirement for type I interferon signalling was analysed using NOD mice lacking a functional type I interferon receptor (NOD.IFNAR1(-/-) mice). Compared with NOD mice, NOD.IFNAR1(-/-) mice showed 8-fold higher RRV titers in lymph nodes and 3-fold higher titers of total RRV antibody in serum. However, RRV-infected NOD.IFNAR1(-/-) mice exhibited delayed pDC and lymphocyte activation, no T helper 1 bias in RRV-specific antibodies and unaltered diabetes onset when compared with uninfected controls. Thus, the type I interferon signalling induced by RRV infection is required for bystander lymphocyte activation and accelerated type 1 diabetes onset in genetically susceptible mice.

Perforin facilitates beta cell killing and regulates autoreactive CD8+ T-cell responses to antigen in mouse models of type 1 diabetes.

In type 1 diabetes, cytotoxic CD8(+) T lymphocytes (CTLs) directly interact with pancreatic beta cells through major histocompatibility complex class I. An immune synapse facilitates delivery of cytotoxic granules, comprised mainly of granzymes and perforin. Perforin deficiency protects the majority of non-obese diabetic (NOD) mice from autoimmune diabetes. Intriguingly perforin deficiency does not prevent diabetes in CD8(+) T-cell receptor transgenic NOD8.3 mice. We therefore investigated the importance of perforin-dependent killing via CTL-beta cell contact in autoimmune diabetes. Perforin-deficient CTL from NOD mice or from NOD8.3 mice were significantly less efficient at adoptive transfer of autoimmune diabetes into NODRag1(-/-) mice, confirming that perforin is essential to facilitate beta cell destruction. However, increasing the number of transferred in vitro-activated perforin-deficient 8.3 T cells reversed the phenotype and resulted in diabetes. Perforin-deficient NOD8.3 T cells were present in increased proportion in islets, and proliferated more in response to antigen in vivo indicating that perforin may regulate the activation of CTLs, possibly by controlling cytokine production. This was confirmed when we examined the requirement for direct interaction between beta cells and CD8(+) T cells in NOD8.3 mice, in which beta cells specifically lack major histocompatibility complex (MHC) class I through conditional deletion of ß2-microglobulin. Although diabetes was significantly reduced, 40% of these mice developed diabetes, indicating that NOD8.3 T cells can kill beta cells in the absence of direct interaction. Our data indicate that although perforin delivery is the main mechanism that CTL use to destroy beta cells, they can employ alternative mechanisms to induce diabetes in a perforin-independent manner.

Inhibition of AMP-Activated Protein Kinase at the Allosteric Drug-Binding Site Promotes Islet Insulin Release.

The AMP-activated protein kinase (AMPK) is a metabolic stress-sensing αßγ heterotrimer responsible for energy homeostasis. Pharmacological inhibition of AMPK is regarded as a therapeutic strategy in some disease settings including obesity and cancer; however, the broadly used direct AMPK inhibitor compound C suffers from poor selectivity. We have discovered a dihydroxyquinoline drug (MT47-100) with novel AMPK regulatory properties, being simultaneously a direct activator and inhibitor of AMPK complexes containing the ß1 or ß2 isoform, respectively. Allosteric inhibition by MT47-100 was dependent on the ß2 carbohydrate-binding module (CBM) and determined by three non-conserved CBM residues (Ile81, Phe91, Ile92), but was independent of ß2-Ser108 phosphorylation. Whereas MT47-100 regulation of total cellular AMPK activity was determined by ß1/ß2 expression ratio, MT47-100 augmented glucose-stimulated insulin secretion from isolated mouse pancreatic islets via a ß2-dependent mechanism. Our findings highlight the therapeutic potential of isoform-specific AMPK allosteric inhibitors.

BIM Deficiency Protects NOD Mice From Diabetes by Diverting Thymocytes to Regulatory T Cells.

Because regulatory T-cell (Treg) development can be induced by the same agonist self-antigens that induce negative selection, perturbation of apoptosis will affect both negative selection and Treg development. But how the processes of thymocyte deletion versus Treg differentiation bifurcate and their relative importance for tolerance have not been studied in spontaneous organ-specific autoimmune disease. We addressed these questions by removing a critical mediator of thymocyte deletion, BIM, in the NOD mouse model of autoimmune diabetes. Despite substantial defects in the deletion of autoreactive thymocytes, BIM-deficient NOD (NODBim(-/-)) mice developed less insulitis and were protected from diabetes. BIM deficiency did not impair effector T-cell function; however, NODBim(-/-) mice had increased numbers of Tregs, including those specific for proinsulin, in the thymus and peripheral lymphoid tissues. Increased levels of Nur77, CD5, GITR, and phosphorylated IκB-α in thymocytes from NODBim(-/-) mice suggest that autoreactive cells receiving strong T-cell receptor signals that would normally delete them escape apoptosis and are diverted into the Treg pathway. Paradoxically, in the NOD model, reduced thymic deletion ameliorates autoimmune diabetes by increasing Tregs. Thus, modulating apoptosis may be one of the ways to increase antigen-specific Tregs and prevent autoimmune disease.

Effector-memory T cells develop in islets and report islet pathology in type 1 diabetes.

CD8(+) T cells are critical in human type 1 diabetes and in the NOD mouse. In this study, we elucidated the natural history of islet-specific glucose-6-phosphatase catalytic subunit-related protein (IGRP)-specific CD8(+) T cells in NOD diabetes using MHC-tetramer technology. IGRP206-214-specific T cells in the peripheral lymphoid tissue increased with age, and their numbers correlated with insulitis progression. IGRP206-214-specific T cells in the peripheral lymphoid tissue expressed markers of chronic Ag stimulation, and their numbers were stable after diagnosis of diabetes, consistent with their memory phenotype. IGRP206-214-specific T cells in NOD mice expand, acquire the phenotype of effector-memory T cells in the islets, and emigrate to the peripheral lymphoid tissue. Our observations suggest that enumeration of effector-memory T cells of multiple autoantigen specificities in the periphery of type 1 diabetic subjects could be a reliable reporter for progression of islet pathology.

Deficiency in type I interferon signaling prevents the early interferon-induced gene signature in pancreatic islets but not type 1 diabetes in NOD mice.

Type I interferons (IFNs) have been implicated in the initiation of islet autoimmunity and development of type 1 diabetes. To directly test their involvement, we generated NOD mice deficient in type I IFN receptors (NOD.IFNAR1(-/-)). Expression of the type I IFN-induced genes Mx1, Isg15, Ifit1, Oas1a, and Cxcr4 was detectable in NOD islets as early as 1 week of age. Of these five genes, expression of Isg15, Ifit1, Oas1a, and Mx1 peaked at 3-4 weeks of age, corresponding with an increase in Ifnα mRNA, declined at 5-6 weeks of age, and increased again at 10-14 weeks of age. Increased IFN-induced gene expression was ablated in NOD.IFNAR1(-/-) islets. Loss of Toll-like receptor 2 (TLR2) resulted in reduced islet expression of Mx1 at 2 weeks of age, but TLR2 or TLR9 deficiency did not change the expression of other IFN-induced genes in islets compared with wild-type NOD islets. We observed increased ß-cell major histocompatibility complex class I expression with age in NOD and NOD.IFNAR1(-/-) mice. NOD.IFNAR1(-/-) mice developed insulitis and diabetes at a similar rate to NOD controls. These results indicate type I IFN is produced within islets in young mice but is not essential for the initiation and progression of diabetes in NOD mice.

Proinflammatory cytokines contribute to development and function of regulatory T cells in type 1 diabetes.

Type 1 diabetes is caused by immune-mediated loss of pancreatic beta cells. It has been proposed that inflammatory cytokines play a role in killing beta cells. Expression of interleukin (IL)-1 and tumor necrosis factor (TNF-α) has been detected in islets from patients with type 1 diabetes, and these cytokines can induce beta cell death in vitro. We produced nonobese diabetic (NOD) mice lacking receptors for these cytokines. Islets from mice lacking IL-1RI or TNFR1 were killed when transplanted into wild-type NOD mice, suggesting that cytokine action on beta cells is not required for killing. Mice lacking TNFR1 did not develop diabetes, and mice lacking IL-1R had delayed onset of diabetes, indicating a role for these cytokines in disease development. TNFR1-deficient mice had an increased number of CD4(+) CD25(+) FoxP3(+) regulatory T cells with enhanced suppressive capacity. IL-1 was produced at higher levels in NOD mice and resulted in dilution of suppressor function of CD4(+) CD25(+) FoxP3(+) regulatory T cells. Our data suggest that blocking inflammatory cytokines may increase the capacity of the immune system to suppress type 1 diabetes through regulatory T cells.

Granzyme B is dispensable in the development of diabetes in non-obese diabetic mice.

Pancreatic beta cell destruction in type 1 diabetes is mediated by cytotoxic CD8(+) T lymphoctyes (CTL). Granzyme B is an effector molecule used by CTL to kill target cells. We previously showed that granzyme B-deficient allogeneic CTL inefficiently killed pancreatic islets in vitro. We generated granzyme B-deficient non-obese diabetic (NOD) mice to test whether granzyme B is an important effector molecule in spontaneous type 1 diabetes. Granzyme B-deficient islet antigen-specific CD8(+) T cells had impaired homing into islets of young mice. Insulitis was reduced in granzyme B-deficient mice at 70 days of age (insulitis score 0.043±0.019 in granzyme B-deficient versus 0.139±0.034 in wild-type NOD mice p<0.05), but was similar to wild-type at 100 and 150 days of age. We observed a reduced frequency of CD3(+)CD8(+) T cells in the islets and peripheral lymphoid tissues of granzyme B-deficient mice (p<0.005 and p<0.0001 respectively), but there was no difference in cell proportions in the thymus. Antigen-specific CTL developed normally in granzyme B-deficient mice, and were able to kill NOD islet target cells as efficiently as wild-type CTL in vitro. The incidence of spontaneous diabetes in granzyme B-deficient mice was the same as wild-type NOD mice. We observed a delayed onset of diabetes in granzyme B-deficient CD8-dependent NOD8.3 mice (median onset 102.5 days in granzyme B-deficient versus 57.50 days in wild-type NOD8.3 mice), which may be due to the delayed onset of insulitis or inefficient priming at an earlier age in this accelerated model of diabetes. Our data indicate that granzyme B is dispensable for beta cell destruction in type 1 diabetes, but is required for efficient early activation of CTL.

Intra-islet proliferation of cytotoxic T lymphocytes contributes to insulitis progression.

Infiltration of pancreatic islets by immune cells, termed insulitis, increases progressively once it begins and leads to clinical type 1 diabetes. But even after diagnosis some islets remain unaffected and infiltration is patchy rather than uniform. Traffic of autoreactive T cells into the pancreas is likely to contribute to insulitis progression but it could also depend on T-cell proliferation within islets. This study utilizes transgenic NOD mice to assess the relative contributions of these two mechanisms. Progression of insulitis in NOD8.3 TCR transgenic mice was mildly reduced by inhibition of T-cell migration with the drug FTY720. In FTY720-treated mice, reduced beta cell MHC class I expression prevented progression of insulitis both within affected islets and to previously unaffected islets. CTL proliferation was significantly reduced in islets with reduced or absent beta cell expression of MHC class I protein. This indicates that intra-islet proliferation, apparently dependent on beta cell antigen presentation, in addition to recruitment, is a significant factor in progression of insulitis.

An indirect role for NK cells in a CD4(+) T-cell-dependent mouse model of type I diabetes.

CD8(+) T cells kill pancreatic ß-cells in a cell-cell contact-dependent mechanism in the non-obese diabetic mouse. CD4(+) T lymphocytes are also able to kill pancreatic ß-cells, but they do not directly contact ß-cells and may use another cell type as the actual cytotoxic cell. Natural killer (NK) cells could have this role but it is uncertain whether they are cytotoxic towards ß-cells. Therefore, the requirement for NK cells in ß-cell destruction in the CD4-dependent T-cell antigen receptor transgenic NOD4.1 mice was examined. NK cells failed to kill ß-cells in vitro, even in the absence of major histocompatibility complex class I. We observed only 9.7±1.1% of islet infiltrating NK cells from NOD4.1 mice expressing the degranulation marker CD107a. Diabetogenic CD4(+) T cells transferred disease to NODscid.IL2Rγ(-/-) mice lacking NK cells, indicating that NK cells do not contribute to ß-cell death in vitro or in vivo. However, depletion of NK cells reduced diabetes incidence in NOD4.1 mice, suggesting that NK cells may help to maintain the right environment for cytotoxicity of effector cells.

Complete diabetes protection despite delayed thymic tolerance in NOD8.3 TCR transgenic mice due to antigen-induced extrathymic deletion of T cells.

Prevention of autoimmunity requires the elimination of self-reactive T cells during their development in the thymus and maturation in the periphery. Transgenic NOD mice that overexpress islet-specific glucose 6 phosphatase catalytic subunit-related protein (IGRP) in antigen-presenting cells (NOD-IGRP mice) have no IGRP-specific T cells. To study the relative contribution of central and peripheral tolerance mechanisms to deletion of antigen-specific T cells, we crossed NOD-IGRP mice to highly diabetogenic IGRP206-214 T-cell receptor transgenic mice (NOD8.3 mice) and studied the frequency and function of IGRP-specific T cells in the thymus and periphery. Peripheral tolerance was extremely efficient and completely protected NOD-IGRP/NOD8.3 mice from diabetes. Peripheral tolerance was characterized by activation of T cells in peripheral lymphoid tissue where IGRP was expressed followed by activation-induced cell death. Thymectomy showed that thymic output of IGRP-specific transgenic T cells compensated for peripheral deletion to maintain peripheral T-cell numbers. Central tolerance was undetectable until 10 weeks and complete by 15 weeks. These in vivo data indicate that peripheral tolerance alone can protect NOD8.3 mice from autoimmune diabetes and that profound changes in T-cell repertoire can follow subtle changes in thymic antigen presentation.

Pathogenic mechanisms in type 1 diabetes: the islet is both target and driver of disease.

Recent advances in our understanding of the pathogenesis of type 1 diabetes have occurred in all steps of the disease. This review outlines the pathogenic mechanisms utilized by the immune system to mediate destruction of the pancreatic beta-cells. The autoimmune response against beta-cells appears to begin in the pancreatic lymph node where T cells, which have escaped negative selection in the thymus, first meet beta-cell antigens presented by dendritic cells. Proinsulin is an important antigen in early diabetes. T cells migrate to the islets via the circulation and establish insulitis initially around the islets. T cells within insulitis are specific for islet antigens rather than bystanders. Pathogenic CD4⁺ T cells may recognize peptides from proinsulin which are produced locally within the islet. CD8⁺ T cells differentiate into effector T cells in islets and then kill beta-cells, primarily via the perforin-granzyme pathway. Cytokines do not appear to be important cytotoxic molecules in vivo. Maturation of the immune response within the islet is now understood to contribute to diabetes, and highlights the islet as both driver and target of the disease. The majority of our knowledge of these pathogenic processes is derived from the NOD mouse model, although some processes are mirrored in the human disease. However, more work is required to translate the data from the NOD mouse to our understanding of human diabetes pathogenesis. New technology, especially MHC tetramers and modern imaging, will enhance our understanding of the pathogenic mechanisms.