CD137 is expressed in a subset of Foxp3+ regulatory CD4 T cells (Tregs), but its immunoregulatory role is not fully defined. Due to alternative splicing that removes the transmembrane domain-encoding exon, CD137 exists in both membrane and soluble forms. We investigated the function of CD137 in Foxp3+ Tregs using the NOD mouse model of type 1 diabetes (T1D). Foxp3+ Treg-specific deletion of CD137 reduced circulating soluble CD137 and accelerated T1D development, driven by heightened clonal expansion and differentiation of effector T cells in pancreatic islets. CD137 deficiency in Foxp3+ Tregs reduced their frequency in islets and impaired their differentiation toward a suppressive phenotype. Restoring soluble CD137 in Foxp3+ Tregs lacking its membrane form reduced islet T cell activation and mitigated T1D acceleration without altering the accumulation of suppressive Foxp3+ Tregs. Our results indicate that both soluble and membrane forms of CD137 expressed by Foxp3+ Tregs are critical for immunoregulation, and they independently restrain T1D development.

In the non-obese diabetic (NOD) mouse model of autoimmune diabetes, interleukin (IL)-27 stimulates interferon γ (IFNγ) production by CD4 and CD8 T cells and is essential for disease development. Here, we tested the role of IL-27 in cellular communication. Single-cell RNA sequencing and T cell adoptive transfer showed that IL-27 intrinsically controlled the differentiation of islet-infiltrating CD4 T cells by driving them toward an IL-21+ Th1 phenotype. Consequently, IL-27 signaling in CD4 T cells was important for BATF and granzyme B expression in islet CD8 T effectors. BATF overexpression increased the diabetogenic potential of β cell autoreactive CD8 T cells lacking help from CD4 T cell-derived IL-21. Macrophages were the main source of IL-27 in the islets, whose expression correlated with T cell infiltration. IFNγ and CD40 signaling conferred by activated T cells induced macrophage IL-27 production. Collectively, our findings reveal a role for IL-27 in orchestrating interconnected positive feedback loops involving CD4 T cells, CD8 T cells, and macrophages in autoimmune diabetes.

Monocytes are immune regulators implicated in the pathogenesis of type 1 diabetes (T1D), an autoimmune disease that targets insulin-producing pancreatic β cells. We determined that monocytes of recent onset (RO) T1D patients and their healthy siblings express proinflammatory/cytolytic transcriptomes and hypersecrete cytokines in response to lipopolysaccharide exposure compared to unrelated healthy controls (uHCs). Flow cytometry measured elevated circulating abundances of intermediate monocytes and >2-fold more CD14 + CD16 + HLADR + KLRD1 + PRF1 + NK-like monocytes among patients with ROT1D compared to uHC. The intermediate to nonclassical monocyte ratio among ROT1D patients correlated with the decline in functional β cell mass during the first 24 months after onset. Among sibling nonprogressors, temporal decreases were measured in the intermediate to nonclassical monocyte ratio and NK-like monocyte abundances; these changes coincided with increases in activated regulatory T cells. In contrast, these monocyte populations exhibited stability among T1D progressors. This study associates heightened monocyte proinflammatory/cytolytic activity with T1D susceptibility and progression and offers insight to the age-dependent decline in T1D susceptibility.

Abstract CD137, encoded by Tnfrsf9, acts as a costimulatory molecule on activated T cells. Conversely, soluble CD137 exerts immunosuppression by binding to CD137L on T cells, inhibiting activation. In the NOD mouse model of Type 1 Diabetes (T1D), CD137 expression in Foxp3+ regulatory CD4 T cells (Tregs) inhibits T1D, but the underlying mechanism remains elusive. To investigate the role of CD137 in Treg-mediated T1D suppression, we generated Treg-specific CD137 knockout mice (NOD.Treg-Tnfrsf9-/-). While no systemic inflammation was observed, these mice developed accelerated T1D compared to wildtype control. Reduced serum-soluble CD137 in these mice indicated Tregs are its main producers. scRNA-seq revealed phenotypic alterations of Tregs isolated from pancreatic islets of NOD.Treg-Tnfrsf9-/- mice, showing lower activation and clonal expansion than wildtype counterparts. Reduced Treg activity in these mice was associated with increased frequencies of islet-activated CD8 T cell subsets and their clonal expansion. MHC class I tetramer staining revealed a higher frequency of β-cell antigen IGRP206-214 specific CD8 T cells in NOD.Treg-Tnfrsf9-/- mice. No discernible differences in the initial expansion and activation of β-cell autoreactive CD8 T cells in pancreatic lymph nodes were observed. Our results suggest CD137 expression in Tregs is critical for restraining ongoing autoimmune inflammation in islets of NOD mice but dispensable for controlling autoreactive T cells in lymphoid tissues.

IL-21 is essential for type 1 diabetes (T1D) development in the NOD mouse model. IL-21-expressing CD4 T cells are present in pancreatic islets where they contribute to T1D progression. However, little is known about their phenotype and differentiation states. To fill this gap, we generated, to our knowledge, a novel IL-21 reporter NOD strain to further characterize IL-21+ CD4 T cells in T1D. IL-21+ CD4 T cells accumulate in pancreatic islets and recognize β cell Ags. Single-cell RNA sequencing revealed that CD4 T effector cells in islets actively express IL-21 and they are highly diabetogenic despite expressing multiple inhibitory molecules, including PD-1 and LAG3. Islet IL-21+ CD4 T cells segregate into four phenotypically and transcriptionally distinct differentiation states, that is, less differentiated early effectors, T follicular helper (Tfh)-like cells, and two Th1 subsets. Trajectory analysis predicts that early effectors differentiate into both Tfh-like and terminal Th1 cells. We further demonstrated that intrinsic IL-27 signaling controls the differentiation of islet IL-21+ CD4 T cells, contributing to their helper function. Collectively, our study reveals the heterogeneity of islet-infiltrating IL-21+ CD4 T cells and indicates that both Tfh-like and Th1 subsets produce IL-21 throughout their differentiation process, highlighting the important sources of IL-21 in T1D pathogenesis.

The increasing incidence of Type 1 diabetes has coincided with the emergence of the low-fiber, high-gluten Western diet and other environmental factors linked to dysbiosis. Since Lactiplantibacillus plantarum 299 v (Lp299v) supplementation improves gut barrier function and reduces systemic inflammation, we studied its effects in spontaneously diabetic DRlyp/lyp rats provided a normal cereal diet (ND) or a gluten-free hydrolyzed casein diet (HCD). All rats provided ND developed diabetes (62.5±7.7 days); combining ND with Lp299v did not improve survival. Diabetes was delayed by HCD (72.2±9.4 days, p = .01) and further delayed by HCD+Lp299v (84.9±14.3 days, p < .001). HCD+Lp299v pups exhibited increased plasma propionate and butyrate levels, which correlated with enriched fecal Bifidobacteriaceae and Clostridiales taxa. Islet transcriptomic and histologic analyses at 40-days of age revealed that rats fed HCD expressed an autophagy profile, while those provided HCD+Lp299v expressed ER-associated protein degradation (ERAD) and antioxidative defense pathways, including Nrf2. Exposing insulinoma cells to propionate and butyrate promoted the antioxidative defense response but did not recapitulate the HCD+Lp299v islet ERAD transcriptomic profile. Here, both diet and microbiota influenced diabetes susceptibility. Moreover, Lp299v supplement modulated antioxidative defense and ER stress responses in β-cells, potentially offering a new therapeutic direction to thwart diabetes progression and preserve insulin secretion.

Paired scRNA-seq and scTCR-seq reveals that diabetogenic CD8 T cells in the islets and spleens of NOD mice exhibit phenotypic and clonal heterogeneity despite restricted TCR gene usage. Expression of certain TCR genes correlates with clonal proliferation and effector phenotype. Type 1 diabetes (T1D) is an autoimmune disorder defined by CD8 T cell–mediated destruction of pancreatic β cells. We have previously shown that diabetogenic CD8 T cells in the islets of non-obese diabetic mice are phenotypically heterogeneous, but clonal heterogeneity remains relatively unexplored. Here, we use paired single-cell RNA and T-cell receptor sequencing (scRNA-seq and scTCR-seq) to characterize autoreactive CD8 T cells from the islets and spleens of non-obese diabetic mice. scTCR-seq demonstrates that CD8 T cells targeting the immunodominant β-cell epitope IGRP206-214 exhibit restricted TCR gene usage. scRNA-seq identifies six clusters of autoreactive CD8 T cells in the islets and six in the spleen, including memory and exhausted cells. Clonal overlap between IGRP206-214–reactive CD8 T cells in the islets and spleen suggests these cells may circulate between the islets and periphery. Finally, we identify correlations between TCR genes and T-cell clonal expansion and effector fate. Collectively, our work demonstrates that IGRP206-214–specific CD8 T cells are phenotypically heterogeneous but clonally restricted, raising the possibility of selectively targeting these TCR structures for therapeutic benefit.

The incidence of type 1 diabetes (T1D) has increased, coinciding with lifestyle changes that have likely altered the gut microbiota. Dysbiosis, gut barrier dysfunction, and elevated systemic inflammation consistent with microbial antigen exposure, have been associated with T1D susceptibility and progression. A 6-week, single-arm, open-label pilot trial was conducted to investigate whether daily multi-strain probiotic supplementation could reduce this familial inflammation in 25 unaffected siblings of T1D patients. Probiotic supplementation was well-tolerated as reflected by high participant adherence and no adverse events. Community alpha and beta diversity were not altered between the pre- and post-supplement stool samplings. However, LEfSe analyses identified post-supplement enrichment of the family Lachnospiraceae , producers of the anti-inflammatory short chain fatty acid butyrate. Systemic inflammation was measured by plasma-induced transcription and quantified with a gene ontology-based composite inflammatory index ( I.I. com ). Post-supplement I.I. com was significantly reduced and pathway analysis predicted inhibition of numerous inflammatory mediators and activation of IL10RA. Subjects with the greatest post-supplement reduction in I.I. com exhibited significantly lower CD4+ CD45RO+ (memory):CD4+ CD45RA+ (naïve) T-cell ratios after supplementation. Post-supplement IL-12p40, IL-13, IL-15, IL-18, CCL2, and CCL24 plasma levels were significantly reduced, while post-supplement butyrate levels trended 1.4-fold higher. Probiotic supplementation may modify T1D susceptibility and progression and warrants further study.

In type 1 diabetes (T1D) autoreactive CD8 T cells infiltrate pancreatic islets and destroy insulin-producing β cells. Progression to T1D onset is a chronic process, which suggests that the effector activity of β-cell autoreactive CD8 T cells needs to be maintained throughout the course of disease development. The mechanism that sustains diabetogenic CD8 T cell effectors during the course of T1D progression has not been completely defined. Here we used single-cell RNA sequencing to gain further insight into the phenotypic complexity of islet-infiltrating CD8 T cells in NOD mice. We identified two functionally distinct subsets of activated CD8 T cells, CD44highTCF1+CXCR6− and CD44highTCF1−CXCR6+, in islets of prediabetic NOD mice. Compared with CD44highTCF1+CXCR6− CD8 T cells, the CD44highTCF1−CXCR6+ subset expressed higher levels of inhibitory and cytotoxic molecules and was more prone to apoptosis. Adoptive cell transfer experiments revealed that CD44highTCF1+CXCR6− CD8 T cells, through continuous generation of the CD44highTCF1−CXCR6+ subset, were more capable than the latter population to promote insulitis and the development of T1D. We further showed that direct IL-27 signaling in CD8 T cells promoted the generation of terminal effectors from the CD44highTCF1+CXCR6− population. These results indicate that islet CD44highTCF1+CXCR6− CD8 T cells are a progenitor-like subset with self-renewing capacity, and, under an IL-27–controlled mechanism, they differentiate into the CD44highTCF1−CXCR6+ terminal effector population. Our study provides new insight into the sustainability of the CD8 T cell response in the pathogenesis of T1D. Key Points Functionally distinct subsets of CD8 T cells infiltrate islets in type 1 diabetes. Self-renewing islet CD44highTCF1+ CD8 T cells maintain the autoreactive response. IL-27 modulates the differentiation of islet-infiltrating CD8 T cell subsets.

Type I interferons (IFNs) are required for spontaneous lacrimal gland inflammation in the nonobese diabetic (NOD) mouse model of Sjögren's disease, but the consequences of type I IFN signaling are not well-defined. Here, we use RNA sequencing to define cytokine and chemokine genes upregulated in lacrimal glands of NOD mice in a type I IFN-dependent manner. Interleukin (IL)-21 was the highest differentially expressed cytokine gene, and Il21 knockout NOD mice were relatively protected from lacrimal gland inflammation. We defined a set of chemokines upregulated early in disease including Cxcl9 and Cxcl10, which share a receptor, CXCR3. CXCR3+ T cells were enriched in lacrimal glands with a dominant proportion of CXCR3+ regulatory T cells. Together these data define the early cytokine and chemokine signals associated with type I IFN-signaling in the development of lacrimal gland inflammation in NOD mice providing insight into the role of type I IFN in autoimmunity development.

Abstract Type 1 diabetes (T1D) is an autoimmune disease characterized by destruction of the pancreatic β-cells. T1D pathogenesis has a strong genetic basis. However, in recent decades, the prevalence of high-risk HLA haplotypes among new diagnoses has declined, the age of onset has decreased, and T1D incidence has increased. These changes are consistent with increased environmental pressure and coincide with introduction of the Western diet, widespread antibiotic use and reduced breast feeding. These factors are thought to drive intestinal dysbiosis, increased gut permeability and systemic inflammation. Notably, our studies of T1D families and the BioBreeding (BB) rat have identified a peripheral inflammatory state associated with diabetes susceptibility that is consistent with microbial antigen exposure and pattern recognition receptor ligation. Lactobacillus plantarum 299v (Lp299v), a probiotic strain, is reported to increase plasma and stool levels of anti-inflammatory short chain fatty acids (SCFA) and promote IL-10 signaling in colonic derived macrophages and T-cells. Here we investigated the effect of Lp299v supplement on T1D progression and inflammatory phenotypes in diabetes prone BB DRlyp/lyp rats. Rats were weaned at 21 days onto a normal cereal diet (ND) or a gluten-free hydrolyzed casein diet (HCD), with and without daily Lp299v supplementation. All DRlyp/lyp ND rats developed T1D by day 83 (mean time to onset of 62.8+/-7.9 days). DRlyp/lyp ND+Lp299v rats exhibited an insignificant delay in T1D onset (62.6+/-6.5 days), however 8% remained diabetes-free to day 130. Providing DRlyp/lyp rats HCD prevented T1D in 17% of rats (to age 130 days) and significantly delayed onset (mean time to onset 72.8+/-7.3 days, p<0.001). Providing DRlyp/lyp rats HCD+Lp299v prevented T1D in 25% of rats and more robustly delayed onset (mean time to onset 84.9 +/-14.3 days, p<0.001). While multiplex ELISA failed to detect significantly altered plasma cytokine/chemokine levels at 40 days of life, plasma induced transcription revealed the greatest normalization of systemic inflammation in the HCD+Lp299v group. Plasma SCFA levels (propionate and butyrate, p<0.01) were elevated in the HCD+Lp299v group compared to the ND group. Global gene expression analysis of pancreatic islets was conducted at 40 days, prior to insulitis. Endoplasmic reticulum (ER) stress has been implicated in the formation of islet neoantigens that may underlie the initial loss of immune tolerance in T1D. Under one or both diets, Lp299v favorably modulated islet expression levels of pathways and transcripts related to inflammation and innate immunity (Cxcl9, Cxcl10), oxidative stress (Gsta1, Gsta4, Gstp1, Gstk1), as well as ER stress and unfolded protein response (Cirbp, Edem1, Hspa1a, Atf4). These ongoing studies add to a growing understanding that inherited susceptibility can be modulated by diet and microbiota.

Recent advances in genetic analyses have significantly refined human type 1 diabetes (T1D) associated loci. The goal of such effort is to identify the causal genes and have a complete understanding of the molecular pathways that independently or interactively influence cellular processes leading to the destruction of insulin producing pancreatic β cells. UBASH3A has been suggested as the underlying gene for a human T1D associated region on chromosome 21. To further evaluate the role of UBASH3A in T1D, we targeted Ubash3a in NOD mice using zinc-finger nuclease mediated mutagenesis. In both 10-week-old females and males, significantly more advanced insulitis was observed in UBASH3A-deficient than in wild-type NOD mice. Consistently, UBASH3A-deficient NOD mice developed accelerated T1D in both sexes, which was associated with increased accumulation of β-cell autoreactive T cells in the spleen and pancreatic lymph node. Adoptive transfer of splenic T cells into NOD.Rag1-/- mice demonstrated that UBASH3A deficiency in T cells was sufficient to promote T1D development. Our results provide strong evidence to further support a role of UBASH3A in T1D. In addition to T1D, UBASH3A deficiency also promoted salivary gland inflammation in females, demonstrating its broad impact on autoimmunity.

CD137 modulates type 1 diabetes (T1D) progression in NOD mice. We previously showed that CD137 expression in CD4 T cells inhibits T1D, but its expression in CD8 T cells promotes disease development by intrinsically enhancing the accumulation of beta-cell-autoreactive CD8 T cells. CD137 is expressed on a subset of FOXP3(+) regulatory CD4 T cells (Tregs), and CD137(+) Tregs are the main source of soluble CD137. Soluble CD137 suppresses T cells in vitro by binding to the CD137 ligand (CD137L) upregulated on activated T cells. To further study how the opposing functions of CD137 are regulated, we successfully targeted Tnfsf9 (encoding CD137L) in NOD mice using the CRISPR/Cas9 system (designated NOD.Tnfsf9(-/-)). Relative to wild-type NOD mice, T1D development in the NOD.Tnfsf9(-/-) strain was significantly delayed, and mice developed less insulitis and had reduced frequencies of beta-cell-autoreactive CD8 T cells. Bone marrow chimera experiments showed that CD137L-deficient hematopoietic cells were able to confer T1D resistance. Adoptive T cell transfer experiments showed that CD137L deficiency on myeloid APCs was associated with T1D suppression. Conversely, lack of CD137L on T cells enhanced their diabetogenic activity. Furthermore, neither CD137 nor CD137L was required for the development and homeostasis of FOXP3(+) Tregs. However, CD137 was critical for the in vivo T1D-suppressive activity of FOXP3(+) Tregs, suggesting that the interaction between CD137 and CD137L regulates their function. Collectively, our results provide new insights into the complex roles of CD137-CD137L interaction in T1D.

Immune-mediated destruction of insulin-producing beta cells causes type 1 diabetes (T1D). However, how beta cells participate in their own destruction during the disease process is poorly understood. Here, we report that modulating the unfolded protein response (UPR) in beta cells of non-obese diabetic (NOD) mice by deleting the UPR sensor IRE1 alpha prior to insulitis induced a transient dedifferentiation of beta cells, resulting in substantially reduced islet immune cell infiltration and beta cell apoptosis. Single-cell and whole-islet transcriptomics analyses of immature beta cells revealed remarkably diminished expression of beta cell autoantigens and MHC class I components, and upregulation of immune inhibitory markers. IRE1 alpha-deficient mice exhibited significantly fewer cytotoxic CD8 T cells in their pancreata, and adoptive transfer of their total T cells did not induce diabetes in Rag1(-/-) mice. Our results indicate that inducing beta cell dedifferentiation, prior to insulitis, allows these cells to escape immune-mediated destruction and may be used as a novel preventive strategy for T1 D in high-risk individuals.

Human genetic studies implicate interleukin-27 (IL-27) in the pathogenesis of type 1 diabetes (T1D), but the underlying mechanisms remain largely unexplored. To further define the role of IL-27 in T1D, we generated non-obese diabetic (NOD) mice deficient in IL-27 or IL-27R alpha. In contrast to wild-type NOD mice, both NOD.II27(-/-) and NOD.II27ra(-/-) strains are completely resistant to T1D. IL-27 from myeloid cells and IL-27 signaling in T cells are critical for T1D development. IL-27 directly alters the balance of regulatory T cells (Tregs) and T helper 1 (Th1) cells in pancreatic islets, which in turn modulates the diabetogenic activity of CD8 T cells. IL-27 also directly enhances the effector function of CD8 T cells within pancreatic islets. In addition to T1D, IL-27 signaling in T cells is also required for lacrimal and salivary gland inflammation in NOD mice. Our study reveals that IL-27 contributes to autoimmunity in NOD mice through multiple mechanisms and provides substantial evidence to support its pathogenic role in human T1D.

The gene encoding the co-stimulatory molecule CD137 is located within the Idd9.3 T1D susceptibility locus and contributes to diabetes progression in NOD mice. We have previously shown that CD137 expression in T cells has dual functions: CD4+CD137+ T cells inhibited T1D development while CD8+CD137+ T cells showed potent diabetogenecity. The protective function of CD137 in CD4+T cells is likely due to the significant amounts of soluble CD137 (sCD137) produced by Foxp3+ Tregs. sCD137 is an alternatively spliced form of CD137 lacking the transmembrane encoding exon. Treating NOD mice with recombinant sCD137 prevents T1D development. We aim to study the impact of CD137 ligand on the expression of sCD137. We used CRISPR/Cas9 to generate a strain of NOD depleted of CD137L (NOD.Tnfsf9−/−). Development of T1D was repressed in the newly generated strain. Deficiency of CD137L was associated with increased levels of serum sCD137. CD137-deficient-T cells contributed significantly to the elevated serum levels of sCD137. Ligand-deficient-Treg cells produced higher levels of sCD137 proteins compared to wild-type Tregs. Moreover, we detected increased levels of sCD137 transcripts in Tregs lacking the expression of CD137L. We direct our efforts to uncover the molecular mechanisms involved in the regulatory role of CD137L influencing the expression of sCD137.

Abstract T cells infiltrate pancreatic islets and directly mediate the destruction of insulin-producing β cells during the development of type 1 diabetes (T1D). However, islet-infiltrating T cell differentiation states and functional diversity have not been completely defined. We used unbiased single-cell RNA sequencing analyses to define the phenotypic complexity of islet-infiltrating T cells in non-obese diabetic (NOD) mice. In the CD4 T cell compartment, we identified naïve, memory, and regulatory T cells, as well as multiple Il21 expressing effector subsets positive for markers indicative of Th1 and Tfh cells. In the CD8 T cell compartment, we identified naïve cells and two activated subsets defined by Slamf6 or Cxcr6 expression, respectively resembling the self-renewing progenitor cells and terminally differentiated effectors found during chronic lymphocytic choriomeningitis virus (LCMV) infection. Single-cell regulatory network inference and clustering (SCENIC) analysis revealed that regulon activity of several transcription factors with known roles in effector CD8 T cell function including Batf were turned on in the Slamf6+ and Cxcr6+ cells. Previous studies have shown that IL-21 induced BATF expression in CD8 T cells is critical to sustain their effector function against chronic LCMV infection. Similarly, we found lower BATF expression in activated islet CD8 T cells from NOD. Il21+/− compared to NOD mice. We further demonstrated that overexpression of BATF in β cell autoreactive CD8 T cells eliminated their need for IL-21 to cause T1D. Our results reveal phenotypically diverse and novel islet-infiltrating T cell subsets and suggest a model in which the IL-21-BATF pathway is critical for the diabetogenic activity of CD8 T cells.

Pathogenesis of type 1 diabetes (T1D) involves various interactions between genetic and environmental factors. The gene encoding the co-stimulatory molecule CD137 is located within the Idd9.3 T1D susceptibility locus and contributes to diabetes progression in NOD mice. We have previously shown that CD137 expression in T cells has dual functions: CD4+CD137+ T cells negatively regulate T1D development while CD8+CD137+ T cells showed potent diabetogenecity. The protective function of CD137 in CD4+ T cells is likely due to the significant amounts of soluble CD137 (CD137) produced by Foxp3+ Tregs. The interaction between CD137 and its ligand (CD137L) induces two signaling pathways, forward one driven by CD137 and the reverse signaling mediated by CD137L, both of which modulate T cell function. Here, we study the impact of CD137L deficiency on T1D to gain further insight into disease pathogenesis. We successfully generated a mouse strain with the NOD background and knockout of the gene encoding CD137L ( Tnfsf9 ) using CRISPR/Cas9 technology. Relative to wild type NOD, Tnfsf9 -/- mice showed significant delay in T1D development, less islet-infiltrating autoreactive CD8 T cells, reduced high-avidity IGRP autoreactive CD8 T cells in the spleen and pancreatic lymph node, and less inflamed islets. Interestingly, we detect significant increase in serum levels of sCD137. Furthermore, we could not detect differences in CD137+ Treg populations between NOD and Tnfsf9 -/- mice. In bone marrow transfer experiments, CD137L deficiency in either hosts or donors was able to suppress T1D development. Tnfsf9 -/- and wild type T cells showed similar capacity to induce T1D in NOD.Rag1-/- recipients. We are working on identifying the cellular source of increased sCD137 and the mechanism behind this elevation. We direct our efforts to understand how CD137-CD137L interaction can modulate T1D pathogenesis and how to translate the data from NOD mouse to understand the pathogenesis of human diabetes. Disclosure B. Foda: None. M.H. Forsberg: None. A.E. Ciecko: None. K.W. Mueller: None. A. Geurts: None. Y. Chen: None.

Human genome wide association studies have identified a 0.73 Mb region on chromosome 16 significantly linked to the development of type 1 diabetes (T1D) and IL27 is proposed to be the causal gene. IL27 encodes the p28 subunit of the heterodimeric cytokine interleukin 27 (IL-27). Human eQTL studies suggest a disease promoting role for IL-27 in the pathogenesis of T1D. However, the function of IL-27 in T1D has not been completely defined. The focus of this study was to test the role of IL-27 in the progression of T1D using the NOD mouse model. We generated NOD mice deficient in IL-27 or IL-27 receptor (IL-27Rα). In sharp contrast to wildtype NOD mice, both NOD.Il27−/− and NOD.Il27ra−/− strains were completely protected from T1D. Additionally, histological examination of pancreatic sections revealed that both NOD.Il27−/− and NOD.Il27ra−/− mice had significantly less insulitis compared to the wildtype NOD control. Furthermore, IL-27 production by myeloid antigen presenting cells was sufficient to drive T1D progression. Adoptive transfer of IL-27 deficient T cells into NOD.Rag1−/− recipients resulted in diabetes development indicating that IL-27 deficient mice still harbor diabetogenic T cells. However, NOD.Rag1−/− recipients of IL-27Rα deficient T cells did not develop diabetes demonstrating that direct IL-27 signaling is essential for their diabetogenic activity. We further demonstrated that direct IL-27 signaling promoted the accumulation of CD8 T cells and altered CD4 T cell subsets (reducing Foxp3+ but increasing T-BET+ frequency) in pancreatic islets. Our observations reveal that IL-27 signaling in T cells is required for diabetes development in the NOD mouse and provide additional evidence to support its potential role in human T1D.