De novo germline mutation in the dual specificity phosphatase 10 gene accelerates autoimmune diabetes.

Insulin-dependent or type 1 diabetes (T1D) is a polygenic autoimmune disease. In humans, more than 60 loci carrying common variants that confer disease susceptibility have been identified by genome-wide association studies, with a low individual risk contribution for most variants excepting those of the major histocompatibility complex (MHC) region (40 to 50% of risk); hence the importance of missing heritability due in part to rare variants. Nonobese diabetic (NOD) mice recapitulate major features of the human disease including genetic aspects with a key role for the MHC haplotype and a series of Idd loci. Here we mapped in NOD mice rare variants arising from genetic drift and significantly impacting disease risk. To that aim we established by selective breeding two sublines of NOD mice from our inbred NOD/Nck colony exhibiting a significant difference in T1D incidence. Whole-genome sequencing of high (H)- and low (L)-incidence sublines (NOD/NckH and NOD/NckL) revealed a limited number of subline-specific variants. Treating age of diabetes onset as a quantitative trait in automated meiotic mapping (AMM), enhanced susceptibility in NOD/NckH mice was unambiguously attributed to a recessive missense mutation of Dusp10, which encodes a dual specificity phosphatase. The causative effect of the mutation was verified by targeting Dusp10 with CRISPR-Cas9 in NOD/NckL mice, a manipulation that significantly increased disease incidence. The Dusp10 mutation resulted in islet cell down-regulation of type I interferon signature genes, which may exert protective effects against autoimmune aggression. De novo mutations akin to rare human susceptibility variants can alter the T1D phenotype.

A selective CD28 antagonist and rapamycin synergise to protect against spontaneous autoimmune diabetes in NOD mice.

AIMS/HYPOTHESIS: The CD28/B7 interaction is critical for both effector T cell activation and forkhead box P3 (FOXP3)+ regulatory T cell (Treg) generation and homeostasis, which complicates the therapeutic use of cytotoxic T lymphocyte-associated antigen 4 (CTLA-4)-immunoglobulin fusion protein (CTLA-4Ig) in autoimmunity. Here, we evaluated the impact of a simultaneous and selective blockade of the CD28 and mammalian target of rapamycin (mTOR) pathways in the NOD mouse model of type 1 diabetes. METHODS: NOD mice were treated with PEGylated anti-CD28 Fab' antibody fragments (PV1-polyethylene glycol [PEG], 10 mg/kg i.p., twice weekly), rapamycin (1 mg/kg i.p., twice weekly) or a combination of both drugs. Diabetes incidence, pancreatic islet infiltration and autoreactive T cell responses were analysed. RESULTS: We report that 4 week administration of PV1-PEG combined with rapamycin effectively controlled the progression of autoimmune diabetes in NOD mice at 10 weeks of age by reducing T cell activation and migration into the pancreas. Treatment with rapamycin alone was without effect, as was PV1-PEG monotherapy initiated at 4, 6 or 10 weeks of age. Prolonged PV1-PEG administration (for 10 weeks) accelerated diabetes development associated with impaired peripheral Treg homeostasis. This effect was not observed with the combined treatment. CONCLUSIONS/INTERPRETATION: CD28 antagonist and rapamycin treatment act in a complementary manner to limit T cell activation and infiltration of pancreatic islets and diabetes development. These data provide new perspectives for the treatment of autoimmune diabetes and support the therapeutic potential of protocols combining antagonists of CD28 (presently in clinical development) and the mTOR pathway.

Oral histone deacetylase inhibitor synergises with T cell targeted immunotherapy to preserve beta cell metabolic function and induce stable remission of new-onset autoimmune diabetes in NOD mice.

AIM/HYPOTHESIS: Combination therapy targeting the major actors involved in the immune-mediated destruction of pancreatic beta cells appears to be an indispensable approach to treat type 1 diabetes effectively. We hypothesised that the combination of an orally active pan-histone deacetylase inhibitor (HDACi: givinostat) with subtherapeutic doses of CD3 antibodies may provide ideal synergy to treat ongoing autoimmunity. METHODS: NOD mice transgenic for the human CD3ε (also known as CD3E) chain (NOD-huCD3ε) were treated for recent-onset diabetes with oral givinostat, subtherapeutic doses of humanised CD3 antibodies (otelixizumab, 50 µg/day, 5 days, i.v.) or a combination of both drugs. Disease remission, metabolic profiles and autoreactive T cell responses were analysed in treated mice. RESULTS: We demonstrated that givinostat synergised with otelixizumab to induce durable remission of diabetes in 80% of recently diabetic NOD-huCD3ε mice. Remission was obtained in only 47% of mice treated with otelixizumab alone. Oral givinostat monotherapy did not reverse established diabetes but reduced the in situ production of inflammatory cytokines (IL-1ß, IL-6, TNF-α). Importantly, the otelixizumab + givinostat combination strongly improved the metabolic status of NOD-huCD3ε mice; the mice recovered the capacity to appropriately produce insulin, control hyperglycaemia and sustain glucose tolerance. Finally, diabetes remission induced by the combination therapy was associated with a significant reduction of insulitis and autoantigen-specific CD8+ T cell responses. CONCLUSIONS/INTERPRETATION: HDACi and low-dose CD3 antibodies synergised to abrogate in situ inflammation and thereby improved pancreatic beta cell survival and metabolic function leading to long-lasting diabetes remission. These results support the therapeutic potential of protocols combining these two drugs, both in clinical development, to restore self-tolerance and insulin independence in type 1 diabetes.

Revisiting the phenotypic and genetic profiling of anergic T cells mediating long-term transplant tolerance.

PURPOSE OF REVIEW: Herein our focus will be to revisit peripheral tolerance mechanisms and in particular 'active' or 'dominant' tolerance as originally defined and mediated by regulatory CD4FoxP3 T lymphocytes (Treg) and also T-cell anergy that appears as a major mainstay to support long-term allograft survival. RECENT FINDINGS: It is at the same time interesting and rewarding that the tool that recently guided our efforts along this path is the in-vivo use of CD3 antibody, the first monoclonal introduced in the clinic (Orthoclone OKT3) about 35 years ago to treat and prevent rejection of renal allografts. Beyond their immunosuppressive activity, whenever administered judiciously, CD3 antibodies promote robust allograft tolerance through selective purging of alloreactive effectors, resetting Treg-mediated active tolerance and promoting a unique subset of anergic CD8 T cells. SUMMARY: The new findings discussed open up new perspectives from both a fundamental and a clinical point of view. In basic research, concrete molecular signaling paths are now spotted to finely dissect the conditions that lead to the establishment and maintenance of robust T-lymphocyte anergy mediating allograft tolerance. In the clinic, this may rapidly translate into novel biomarkers to be used in parallel to the ones already available, to better adapt posttransplant immunotherapy and monitor for long-term allograft acceptance.

Regulatory mechanisms of immune tolerance in type 1 diabetes and their failures.

In this brief review we propose to discuss salient data showing the importance of immune regulatory mechanisms, and in particular of Treg, for the control of pathogenic anti-ß-cell response in autoimmune diabetes. Disease progression that culminates with the massive destruction of insulin-secreting ß-cells and advent of hyperglycemia and glycosuria tightly correlates with a functional deficit in immune regulation. Better dissection of the cellular and molecular mechanisms through which the immune system normally sustains tolerance to "self", and which become defective when autoimmune aggression is overt, is the only direct and robust way to learn how to harness these effectively, so as to restore immune tolerance in patients with insulin-dependent type 1 diabetes. No doubt that regulatory T cells are a privileged mechanism underlying this self-tolerance in the periphery. The discovery of the key role of the transcription factor FoxP3, represented the cornerstone leading to the great advances in the field we are witnessing today. Type 1 diabetes is certainly one of the prototypic T cell-mediated autoimmune diseases where immune regulatory mechanisms relying on specialized subsets of T cells have been the most thoroughly analyzed from the fundamental point of view and also largely exploited in a translational therapeutic perspective.

Combining autologous dendritic cell therapy with CD3 antibodies promotes regulatory T cells and permanent islet allograft acceptance.

Cell therapy and the use of mAbs that interfere with T cell effector functions constitute promising approaches for the control of allograft rejection. In the current study, we investigated a novel approach combining administration of autologous tolerogenic dendritic cells with short-term treatment with CD3-specific Abs. Permanent acceptance of pancreatic islet allografts was achieved in mice treated with the combination therapy the day before transplantation but not in recipients treated with either therapy alone. The combination treatment induced a marked decrease in T cells infiltrating the allografts and a sustained reduction of antidonor responses. Importantly, CD4(+)Foxp3(+) regulatory T cells appeared to play a crucial role in the long-term graft acceptance. Their frequency increased significantly in the spleen, draining lymph nodes, and transplanted islets and remained elevated over the long term; they exhibited increased donor-specific suppressive functions; and their removal at the time of transplantation abrogated the therapeutic effect of the combined therapy. These results support the therapeutic potential of protocols combining autologous dendritic cells and low-dose CD3 Abs, both currently in clinical development, and that act in synergy to control allogeneic immune responses and favor graft survival in a full-mismatch situation.

Coxsackievirus infection induces direct pancreatic ß cell killing but poor antiviral CD8+ T cell responses.

Coxsackievirus B (CVB) infection of pancreatic ß cells is associated with ß cell autoimmunity and type 1 diabetes. We investigated how CVB affects human ß cells and anti-CVB T cell responses. ß cells were efficiently infected by CVB in vitro, down-regulated human leukocyte antigen (HLA) class I, and presented few, selected HLA-bound viral peptides. Circulating CD8+ T cells from CVB-seropositive individuals recognized a fraction of these peptides; only another subfraction was targeted by effector/memory T cells that expressed exhaustion marker PD-1. T cells recognizing a CVB epitope cross-reacted with ß cell antigen GAD. Infected ß cells, which formed filopodia to propagate infection, were more efficiently killed by CVB than by CVB-reactive T cells. Our in vitro and ex vivo data highlight limited CD8+ T cell responses to CVB, supporting the rationale for CVB vaccination trials for type 1 diabetes prevention. CD8+ T cells recognizing structural and nonstructural CVB epitopes provide biomarkers to differentially follow response to infection and vaccination.

Coxsackievirus and Type 1 Diabetes: Diabetogenic Mechanisms and Implications for Prevention.

The evidence for an association between coxsackievirus B (CVB) infection, pancreatic islet autoimmunity, and clinical type 1 diabetes is increasing. Results from prospective cohorts and pancreas histopathology studies have provided a compelling case. However, the demonstration of a causal relationship is missing, and is likely to remain elusive until tested in humans by avoiding exposure to this candidate viral trigger. To this end, CVB vaccines have been developed and are entering clinical trials. However, the progress made in understanding the biology of the virus and in providing tools to address the long-standing question of causality contrasts with the scarcity of information about the antiviral immune responses triggered by infection. Beta-cell death may be primarily induced by CVB itself, possibly in the context of poor immune protection, or secondarily provoked by T-cell responses against CVB-infected beta cells. The possible involvement of epitope mimicry mechanisms skewing the physiological antiviral response toward autoimmunity has also been suggested. We here review the available evidence for each of these 3 non-mutually exclusive scenarios. Understanding which ones are at play is critical to maximize the odds of success of CVB vaccination, and to develop suitable tools to monitor the efficacy of immunization and its intermingling with autoimmune onset or prevention.

Tryptophan metabolism promotes immune evasion in human pancreatic ß cells.

BACKGROUND: To resist the autoimmune attack characteristic of type 1 diabetes, insulin producing pancreatic ß cells need to evade T-cell recognition. Such escape mechanisms may be conferred by low HLA class I (HLA-I) expression and upregulation of immune inhibitory molecules such as Programmed cell Death Ligand 1 (PD-L1). METHODS: The expression of PD-L1, HLA-I and CXCL10 was evaluated in the human ß cell line, ECN90, and in primary human and mouse pancreatic islets. Most genes were determined by real-time RT-PCR, flow cytometry and Western blot. Activator and inhibitor of the AKT signaling were used to modulate PD-L1 induction. Key results were validated by monitoring activity of CD8+ Jurkat T cells presenting ß cell specific T-cell receptor and transduced with reporter genes in contact culture with the human ß cell line, ECN90. FINDINGS: In this study, we identify tryptophan (TRP) as an agonist of PD-L1 induction through the AKT signaling pathway. TRP also synergistically enhanced PD-L1 expression on ß cells exposed to interferon-γ. Conversely, interferon-γ-mediated induction of HLA-I and CXCL10 genes was down-regulated upon TRP treatment. Finally, TRP and its derivatives inhibited the activation of islet-reactive CD8+ T cells by ß cells. INTERPRETATION: Collectively, our findings indicate that TRP could induce immune tolerance to ß cells by promoting their immune evasion through HLA-I downregulation and PD-L1 upregulation. FUNDING: Dutch Diabetes Research Foundation, DON Foundation, the Laboratoire d'Excellence consortium Revive (ANR-10-LABX-0073), Agence Nationale de la Recherche (ANR-19-CE15-0014-01), Fondation pour la Recherche Médicale (EQ U201903007793-EQU20193007831), Innovative Medicines InitiativeINNODIA and INNODIA HARVEST, Aides aux Jeunes Diabetiques (AJD) and Juvenile Diabetes Research Foundation Ltd (JDRF).

Interferon-α promotes neo-antigen formation and preferential HLA-B-restricted antigen presentation in pancreatic ß-cells.

Interferon (IFN)-α is the earliest cytokine signature observed in individuals at risk for type 1 diabetes (T1D), but its effect on the repertoire of HLA Class I (HLA-I)-bound peptides presented by pancreatic ß-cells is unknown. Using immunopeptidomics, we characterized the peptide/HLA-I presentation in in-vitro resting and IFN-α-exposed ß-cells. IFN-α increased HLA-I expression and peptide presentation, including neo-sequences derived from alternative mRNA splicing, post-translational modifications - notably glutathionylation - and protein cis-splicing. This antigenic landscape relied on processing by both the constitutive and immune proteasome. The resting ß-cell immunopeptidome was dominated by HLA-A-restricted ligands. However, IFN-α only marginally upregulated HLA-A and largely favored HLA-B, translating into a major increase in HLA-B-restricted peptides and into an increased activation of HLA-B-restricted vs. HLA-A-restricted CD8+ T-cells. A preferential HLA-B hyper-expression was also observed in the islets of T1D vs. non-diabetic donors, and we identified islet-infiltrating CD8+ T-cells from T1D donors reactive to HLA-B-restricted granule peptides. Thus, the inflammatory milieu of insulitis may skew the autoimmune response toward epitopes presented by HLA-B, hence recruiting a distinct T-cell repertoire that may be relevant to T1D pathogenesis.

Coxsackievirus infection induces direct pancreatic ß-cell killing but poor anti-viral CD8+ T-cell responses.

Coxsackievirus B (CVB) infection of pancreatic ß cells is associated with ß-cell autoimmunity. We investigated how CVB impacts human ß cells and anti-CVB T-cell responses. ß cells were efficiently infected by CVB in vitro, downregulated HLA Class I and presented few, selected HLA-bound viral peptides. Circulating CD8+ T cells from CVB-seropositive individuals recognized only a fraction of these peptides, and only another sub-fraction was targeted by effector/memory T cells that expressed the exhaustion marker PD-1. T cells recognizing a CVB epitope cross-reacted with the ß-cell antigen GAD. Infected ß cells, which formed filopodia to propagate infection, were more efficiently killed by CVB than by CVB-reactive T cells. Thus, our in-vitro and ex-vivo data highlight limited T-cell responses to CVB, supporting the rationale for CVB vaccination trials for type 1 diabetes prevention. CD8+ T cells recognizing structural and non-structural CVB epitopes provide biomarkers to differentially follow response to infection and vaccination.

Personalized Immunotherapies for Type 1 Diabetes: Who, What, When, and How?

Our understanding of the immunopathological features of type 1 diabetes (T1D) has greatly improved over the past two decades and has shed light on disease heterogeneity dictated by multiple immune, metabolic, and clinical parameters. This may explain the limited effects of immunotherapies tested so far to durably revert or prevent T1D, for which life-long insulin replacement remains the only therapeutic option. In the era of omics and precision medicine, offering personalized treatment could contribute to turning this tide. Here, we discuss how to structure the selection of the right patient at the right time for the right treatment. This individualized therapeutic approach involves enrolling patients at a defined disease stage depending on the target and mode of action of the selected drug, and better stratifying patients based on their T1D endotype, reflecting intrinsic disease aggressiveness and immune context. To this end, biomarker screening will be critical, not only to help stratify patients and disease stage, but also to select the best predicted responders ahead of treatment and at early time points during clinical trials. This strategy could contribute to increase therapeutic efficacy, notably through the selection of drugs with complementary effects, and to further develop precision multi-hit medicine.

Pancreatic Islet Cells Response to IFNγ Relies on Their Spatial Location within an Islet.

Type 1 diabetes (T1D) is an auto-immune disease characterized by the progressive destruction of insulin-producing pancreatic beta cells. While beta cells are the target of the immune attack, the other islet endocrine cells, namely the alpha and delta cells, can also be affected by the inflammatory milieu. Here, using a flow cytometry-based strategy, we compared the impact of IFNγ, one of the main cytokines involved in T1D, on the three endocrine cell subsets isolated from C57BL/6 mouse islets. RNA-seq analyses revealed that alpha and delta cells exposed in vitro to IFNγ display a transcriptomic profile very similar to that of beta cells, with an increased expression of inflammation key genes such as MHC class I molecules, the CXCL10 chemokine and the programmed death-ligand 1 (PD-L1), three hallmarks of IFNγ signaling. Interestingly, at low IFNγ concentration, we observed two beta cell populations (responders and non-responders) based on PD-L1 protein expression. Our data indicate that this differential sensitivity relies on the location of the cells within the islet rather than on the existence of two different beta cells subsets. The same findings were corroborated by the in vivo analysis of pancreatic islets from the non-obese diabetic mouse model of T1D, showing more intense PD-L1 staining on endocrine cells close to immune infiltrate. Collectively, our work demonstrates that alpha and delta cells are as sensitive as beta cells to IFNγ, and suggests a gradual diffusion of the cytokine into an islet. These observations provide novel insights into the in situ inflammatory processes occurring in T1D progression.

Regulation of T-Cell Immune Responses by Pro-Resolving Lipid Mediators.

Both the initiation and the resolution of inflammatory responses are governed by the sequential activation, migration, and control/suppression of immune cells at the site of injury. Bioactive lipids play a major role in the fine-tuning of this dynamic process in a timely manner. During inflammation and its resolution, polymorphonuclear cells (PMNs) and macrophages switch from producing pro-inflammatory prostaglandins and leukotrienes to specialized pro-resolving lipid mediators (SPMs), namely, lipoxins, resolvins, protectins, and maresins, which are operative at the local level to limit further inflammation and tissue injury and restore homeostasis. Accumulating evidences expand now the role and actions of these lipid mediators from innate to adaptive immunity. In particular, SPMs have been shown to contribute to the control of chronic inflammation, and alterations in their production and/or function have been associated with the persistence of several pathological conditions, including autoimmunity, in human and experimental models. In this review, we focus on the impact of pro-resolving lipids on T cells through their ability to modulate T-cell responses. In particular, the effects of the different families of SPMs to restrain effector T-cell functions while promoting regulatory T cells will be reviewed, along with the underlying mechanisms. Furthermore, the emerging concept of SPMs as new biological markers for disease diagnostic and progression and as putative therapeutic tools to regulate the development and magnitude of inflammatory and autoimmune diseases is discussed.

Oral Fc-Coupled Preproinsulin Achieves Systemic and Thymic Delivery Through the Neonatal Fc Receptor and Partially Delays Autoimmune Diabetes.

Tolerogenic vaccinations using beta-cell antigens are attractive for type 1 diabetes prevention, but clinical trials have been disappointing. This is probably due to the late timing of intervention, when multiple auto-antibodies are already present. We therefore devised a strategy to introduce the initiating antigen preproinsulin (PPI) during neonatal life, when autoimmunity is still silent and central tolerance mechanisms, which remain therapeutically unexploited, are more active. This strategy employs an oral administration of PPI-Fc, i.e. PPI fused with an IgG Fc to bind the intestinal neonatal Fc receptor (FcRn) that physiologically delivers maternal antibodies to the offspring during breastfeeding. Neonatal oral PPI-Fc vaccination did not prevent diabetes development in PPI T-cell receptor-transgenic G9C8.NOD mice. However, PPI-Fc was efficiently transferred through the intestinal epithelium in an Fc- and FcRn-dependent manner, was taken up by antigen presenting cells, and reached the spleen and thymus. Although not statistically significant, neonatal oral PPI-Fc vaccination delayed diabetes onset in polyclonal Ins2-/-.NOD mice that spontaneously develop accelerated diabetes. Thus, this strategy shows promise in terms of systemic and thymic antigen delivery via the intestinal FcRn pathway, but the current PPI-Fc formulation/regimen requires further improvements to achieve diabetes prevention.

Peptidylarginine Deiminase Inhibition Prevents Diabetes Development in NOD Mice.

Protein citrullination plays a role in several autoimmune diseases. Its involvement in murine and human type 1 diabetes has recently been recognized through the discovery of antibodies and T-cell reactivity against citrullinated peptides. In the current study, we demonstrate that systemic inhibition of peptidylarginine deiminases (PADs), the enzymes mediating citrullination, through BB-Cl-amidine treatment, prevents diabetes development in NOD mice. This prevention was associated with reduced levels of citrullination in the pancreas, decreased circulating autoantibody titers against citrullinated glucose-regulated protein 78, and reduced spontaneous neutrophil extracellular trap formation of bone marrow-derived neutrophils. Moreover, BB-Cl-amidine treatment induced a shift from Th1 to Th2 cytokines in the serum and an increase in the frequency of regulatory T cells in the blood and spleen. In the pancreas, BB-Cl-amidine treatment preserved insulin production and was associated with a less destructive immune infiltrate characterized by reduced frequencies of effector memory CD4+ T cells and a modest reduction in the frequency of interferon-γ-producing CD4+ and CD8+ T cells. Our results point to a role of citrullination in the pathogenesis of autoimmune diabetes, with PAD inhibition leading to disease prevention through modulation of immune pathways. These findings provide insight in the potential of PAD inhibition for treating autoimmune diseases like type 1 diabetes.

CD8+ T Cells Variably Recognize Native Versus Citrullinated GRP78 Epitopes in Type 1 Diabetes.

In type 1 diabetes, autoimmune ß-cell destruction may be favored by neoantigens harboring posttranslational modifications (PTMs) such as citrullination. We studied the recognition of native and citrullinated glucose-regulated protein (GRP)78 peptides by CD8+ T cells. Citrullination modulated T-cell recognition and, to a lesser extent, HLA-A2 binding. GRP78-reactive CD8+ T cells circulated at similar frequencies in healthy donors and donors with type 1 diabetes and preferentially recognized either native or citrullinated versions, without cross-reactivity. Rather, the preference for native GRP78 epitopes was associated with CD8+ T cells cross-reactive with bacterial mimotopes. In the pancreas, a dominant GRP78 peptide was instead preferentially recognized when citrullinated. To further clarify these recognition patterns, we considered the possibility of citrullination in the thymus. Citrullinating peptidylarginine deiminase (Padi) enzymes were expressed in murine and human medullary epithelial cells (mTECs), with citrullinated proteins detected in murine mTECs. However, Padi2 and Padi4 expression was diminished in mature mTECs from NOD mice versus C57BL/6 mice. We conclude that, on one hand, the CD8+ T cell preference for native GRP78 peptides may be shaped by cross-reactivity with bacterial mimotopes. On the other hand, PTMs may not invariably favor loss of tolerance because thymic citrullination, although impaired in NOD mice, may drive deletion of citrulline-reactive T cells.

New generation CD3 monoclonal antibodies: are we ready to have them back in clinical transplantation?

PURPOSE OF REVIEW: The continuing problem of late graft loss and immunosuppressive drug toxicity forces us to explore new treatments for the induction of transplant tolerance. Monoclonal antibodies targeting molecules implicated in lymphocyte activation, in particular CD3/TCR, constitute a promising strategy. RECENT FINDINGS: Promising results were obtained from the use of antibodies targeting CD3/TCR, coreceptors or costimulatory pathways as tolerance-promoting tools in experimental transplantation. These antibodies do not uniformly depress the immune system but act in an antigen-specific manner by preferentially targeting effector T cells while preserving regulatory T cells. However, translation to the clinic proved to be more difficult than expected. New generation CD3 antibodies, currently used in phase II/III trials in autoimmunity, constitute a promising approach as, beside their immunosuppressive effect, they also express potent tolerogenic capacities. Importantly, CD3 therapy is effective especially when applied in primed hosts, highlighting the importance of the therapeutic window for tolerance induction. SUMMARY: Further investigations are required for adapting to the clinic monoclonal antibodies as substitutes for current immunosuppression. Our aim is to show that development of new therapeutic strategies/molecules may come from transversal-type research, in particular from experience in autoimmunity, as immune responses leading to autoimmunity and graft rejection involve similar pathways.

Peptides Derived From Insulin Granule Proteins Are Targeted by CD8+ T Cells Across MHC Class I Restrictions in Humans and NOD Mice.

The antigenic peptides processed by ß-cells and presented through surface HLA class I molecules are poorly characterized. Each HLA variant (e.g., the most common being HLA-A2 and HLA-A3) carries some peptide-binding specificity. Hence, features that, despite these specificities, remain shared across variants may reveal factors favoring ß-cell immunogenicity. Building on our previous description of the HLA-A2/A3 peptidome of ß-cells, we analyzed the HLA-A3-restricted peptides targeted by circulating CD8+ T cells. Several peptides were recognized by CD8+ T cells within a narrow frequency (1-50/106), which was similar in donors with and without type 1 diabetes and harbored variable effector/memory fractions. These epitopes could be classified as conventional peptides or neoepitopes, generated either via peptide cis-splicing or mRNA splicing (e.g., secretogranin-5 [SCG5]-009). As reported for HLA-A2-restricted peptides, several epitopes originated from ß-cell granule proteins (e.g., SCG3, SCG5, and urocortin-3). Similarly, H-2Kd-restricted CD8+ T cells recognizing the murine orthologs of SCG5, urocortin-3, and proconvertase-2 infiltrated the islets of NOD mice and transferred diabetes into NOD/scid recipients. The finding of granule proteins targeted in both humans and NOD mice supports their disease relevance and identifies the insulin granule as a rich source of epitopes, possibly reflecting its impaired processing in type 1 diabetes.

Proinsulin: a unique autoantigen triggering autoimmune diabetes.

In healthy individuals the immune system does not react aggressively toward host cells, a phenomenon defined as self tolerance. If self tolerance is broken autoimmune disease can develop, during which autoreactive lymphocytes are directed to a variety of autoantigenic epitopes. However, researchers have yet to determine whether immune responses to multiple autoantigens develop independently of each other or are the result of the response "spreading" from one autoantigen to another. In a study of NOD mice in this issue of the JCI, Krishnamurthy et al. show that the autoreactive T cell response to the autoantigen proinsulin lies upstream of that to islet-specific glucose-6-phosphatase catalytic subunit-related protein, suggesting that the pathogenic autoimmune response to proinsulin subsequently spreads to other antigens (see the related article beginning on page 3258). These data support the current view that this pancreatic beta cell hormone is the first autoantigen targeted by the immune response in autoimmune diabetes.