The diagnosis of insulitis in human type 1 diabetes

Decoding the immune dance: Unraveling the interplay between beta cells and type 1 diabetes

BACKGROUND

Type 1 diabetes (T1D) is an autoimmune disease characterized by the specific destruction of insulin-producing beta cells in the pancreas by the immune system, including CD4 cells which orchestrate the attack and CD8 cells which directly destroy the beta cells, resulting in the loss of glucose homeostasis.

SCOPE OF REVIEW

This comprehensive document delves into the complex interplay between the immune system and beta cells, aiming to shed light on the mechanisms driving their destruction in T1D. Insights into the genetic predisposition, environmental triggers, and autoimmune responses provide a foundation for understanding the autoimmune attack on beta cells. From the role of viral infections as potential triggers to the inflammatory response of beta cells, an intricate puzzle starts to unfold. This exploration highlights the importance of beta cells in breaking immune tolerance and the factors contributing to their targeted destruction. Furthermore, it examines the potential role of autophagy and the impact of cytokine signaling on beta cell function and survival.

MAJOR CONCLUSIONS

This review collectively represents current research findings on T1D which offers valuable perspectives on novel therapeutic approaches for preserving beta cell mass, restoring immune tolerance, and ultimately preventing or halting the progression of T1D. By unraveling the complex dynamics between the immune system and beta cells, we inch closer to a comprehensive understanding of T1D pathogenesis, paving the way for more effective treatments and ultimately a cure.

The immunology of type 1 diabetes

Following the seminal discovery of insulin a century ago, treatment of individuals with type 1 diabetes (T1D) has been largely restricted to efforts to monitor and treat metabolic glucose dysregulation. The recent regulatory approval of the first immunotherapy that targets T cells as a means to delay the autoimmune destruction of pancreatic β-cells highlights the critical role of the immune system in disease pathogenesis and tends to pave the way for other immune-targeted interventions for T1D. Improving the efficacy of such interventions across the natural history of the disease will probably require a more detailed understanding of the immunobiology of T1D, as well as technologies to monitor residual β-cell mass and function. Here we provide an overview of the immune mechanisms that underpin the pathogenesis of T1D, with a particular emphasis on T cells.

AnnoSpat annotates cell types and quantifies cellular arrangements from spatial proteomics

Cellular composition and anatomical organization influence normal and aberrant organ functions. Emerging spatial single-cell proteomic assays such as Image Mass Cytometry (IMC) and Co-Detection by Indexing (CODEX) have facilitated the study of cellular composition and organization by enabling high-throughput measurement of cells and their localization directly in intact tissues. However, annotation of cell types and quantification of their relative localization in tissues remain challenging. To address these unmet needs for atlas-scale datasets like Human Pancreas Analysis Program (HPAP), we develop AnnoSpat (Annotator and Spatial Pattern Finder) that uses neural network and point process algorithms to automatically identify cell types and quantify cell-cell proximity relationships. Our study of data from IMC and CODEX shows the higher performance of AnnoSpat in rapid and accurate annotation of cell types compared to alternative approaches. Moreover, the application of AnnoSpat to type 1 diabetic, non-diabetic autoantibody-positive, and non-diabetic organ donor cohorts recapitulates known islet pathobiology and shows differential dynamics of pancreatic polypeptide (PP) cell abundance and CD8+ T cells infiltration in islets during type 1 diabetes progression.

Repositioning the Early Pathology of Type 1 Diabetes to the Extraislet Vasculature

Type 1 diabetes (T1D) is a prototypic T cell-mediated autoimmune disease. Because the islets of Langerhans are insulated from blood vessels by a double basement membrane and lack detectable lymphatic drainage, interactions between endocrine and circulating T cells are not permitted. Thus, we hypothesized that initiation and progression of anti-islet immunity required islet neolymphangiogenesis to allow T cell access to the islet. Combining microscopy and single cell approaches, the timing of this phenomenon in mice was situated between 5 and 8 wk of age when activated anti-insulin CD4 T cells became detectable in peripheral blood while peri-islet pathology developed. This "peri-insulitis," dominated by CD4 T cells, respected the islet basement membrane and was limited on the outside by lymphatic endothelial cells that gave it the attributes of a tertiary lymphoid structure. As in most tissues, lymphangiogenesis seemed to be secondary to local segmental endothelial inflammation at the collecting postcapillary venule. In addition to classic markers of inflammation such as CD29, V-CAM, and NOS, MHC class II molecules were expressed by nonhematopoietic cells in the same location both in mouse and human islets. This CD45- MHC class II+ cell population was capable of spontaneously presenting islet Ags to CD4 T cells. Altogether, these observations favor an alternative model for the initiation of T1D, outside of the islet, in which a vascular-associated cell appears to be an important MHC class II-expressing and -presenting cell.

Canine diabetes mellitus demonstrates multiple markers of chronic inflammation including Th40 cell increases and elevated systemic-immune inflammation index, consistent with autoimmune dysregulation

Introduction

Canine diabetes mellitus (CDM) is a relatively common endocrine disease in dogs. Many CDM clinical features resemble human type 1 diabetes mellitus (T1DM), but lack of autoimmune biomarkers makes calling the disease autoimmune controversial. Autoimmune biomarkers linking CDM and T1DM would create an alternative model for drug development impacting both human and canine disease.

Methods

We examined peripheral blood of diagnosed CDM dog patients comparing it to healthy control (HC) dogs. Dogs were recruited to a study at the Colorado State University Veterinary Teaching Hospital and blood samples collected for blood chemistry panels, complete blood counts (CBC), and immunologic analysis. Markers of disease progression such as glycated albumin (fructosamine, the canine equivalent of human HbA1c) and c-peptide were addressed.

Results

Significant differences in adaptive immune lymphocytes, innate immune macrophages/monocytes and neutrophils and differences in platelets were detected between CDM and HC based on CBC. Significant differences in serum glucose, cholesterol and the liver function enzyme alkaline phosphatase were also detected. A systemic immune inflammation index (SII) and chronic inflammation index (CII) as measures of dynamic changes in adaptive and innate cells between inflammatory and non-inflammatory conditions were created with highly significant differences between CDM and HC. Th40 cells (CD4+CD40+ T cells) that are demonstrably pathogenic in mouse T1DM and able to differentiate diabetic from non-diabetic subjects in human T1DM were significantly expanded in peripheral blood mononuclear cells.

Conclusions

Based on each clinical finding, CDM can be categorized as an autoimmune condition. The association of significantly elevated Th40 cells in CDM when compared to HC or to osteoarthritis, a chronic but non-autoimmune disease, suggests peripheral blood Th40 cell numbers as a biomarker that reflects CDM chronic inflammation. The differences in SII and CII further underscore those findings.

Insulitis in human type 1 diabetes: lessons from an enigmatic lesion

Type 1 diabetes is caused by a deficiency of insulin secretion which has been considered traditionally as the outcome of a precipitous decline in the viability of β-cells in the islets of Langerhans, brought about by autoimmune-mediated attack. Consistent with this, various classes of lymphocyte, as well as cells of the innate immune system have been found in association with islets during disease progression. However, analysis of human pancreas from subjects with type 1 diabetes has revealed that insulitis is often less intense than in equivalent animal models of the disease and can affect many fewer islets than expected, at disease onset. This is especially true in subjects developing type 1 diabetes in, or beyond, their teenage years. Such studies imply that both the phenotype and the number of immune cells present within insulitic lesions can vary among individuals in an age-dependent manner. Additionally, the influent lymphocytes are often mainly arrayed peripherally around islets rather than gaining direct access to the endocrine cell core. Thus, insulitis remains an enigmatic phenomenon in human pancreas and this review seeks to explore the current understanding of its likely role in the progression of type 1 diabetes.

The beta cell-immune cell interface in type 1 diabetes (T1D)

BACKGROUND

T1D is an autoimmune disease in which pancreatic islets of Langerhans are infiltrated by immune cells resulting in the specific destruction of insulin-producing islet beta cells. Our understanding of the factors leading to islet infiltration and the interplay of the immune cells with target beta cells is incomplete, especially in human disease. While murine models of T1D have provided crucial information for both beta cell and autoimmune cell function, the translation of successful therapies in the murine model to human disease has been a challenge.

SCOPE OF REVIEW

Here, we discuss current state of the art and consider knowledge gaps concerning the interface of the islet beta cell with immune infiltrates, with a focus on T cells. We discuss pancreatic and immune cell phenotypes and their impact on cell function in health and disease, which we deem important to investigate further to attain a more comprehensive understanding of human T1D disease etiology.

MAJOR CONCLUSIONS

The last years have seen accelerated development of approaches that allow comprehensive study of human T1D. Critically, recent studies have contributed to our revised understanding that the pancreatic beta cell assumes an active role, rather than a passive position, during autoimmune disease progression. The T cell-beta cell interface is a critical axis that dictates beta cell fate and shapes autoimmune responses. This includes the state of the beta cell after processing internal and external cues (e.g., stress, inflammation, genetic risk) that that contributes to the breaking of tolerance by hyperexpression of human leukocyte antigen (HLA) class I with presentation of native and neoepitopes and secretion of chemotactic factors to attract immune cells. We anticipate that emerging insights about the molecular and cellular aspects of disease initiation and progression processes will catalyze the development of novel and innovative intervention points to provide additional therapies to individuals affected by T1D.

Enteroviral infections are not associated with type 2 diabetes

Introduction

For more than a century, enteroviral infections have been associated with autoimmunity and type 1 diabetes (T1D). Uncontrolled viral response pathways repeatedly presented during childhood highly correlate with autoimmunity and T1D. Virus responses evoke chemokines and cytokines, the "cytokine storm" circulating through the body and attack cells especially vulnerable to inflammatory destruction. Intra-islet inflammation is a major trigger of β-cell failure in both T1D and T2D. The genetic contribution of islet inflammation pathways is apparent in T1D, with several mutations in the interferon system. In contrast, in T2D, gene mutations are related to glucose homeostasis in β cells and insulin-target tissue and rarely within viral response pathways. Therefore, the current study evaluated whether enteroviral RNA can be found in the pancreas from organ donors with T2D and its association with disease progression.

Methods

Pancreases from well-characterized 29 organ donors with T2D and 15 age- and BMI-matched controls were obtained from the network for pancreatic organ donors with diabetes and were analyzed in duplicates. Single-molecule fluorescence in-situ hybridization analyses were performed using three probe sets to detect positive-strand enteroviral RNA; pancreas sections were co-stained by classical immunostaining for insulin and CD45.

Results

There was no difference in the presence or localization of enteroviral RNA in control nondiabetic and T2D pancreases; viral infiltration showed large heterogeneity in both groups ranging from 0 to 94 virus+ cells scattered throughout the pancreas, most of them in the exocrine pancreas. Very rarely, a single virus+ cell was found within islets or co-stained with CD45+ immune cells. Only one single T2D donor presented an exceptionally high number of viruses, similarly as seen previously in T1D, which correlated with a highly reduced number of β cells.

Discussion

No association of enteroviral infection in the pancreas and T2D diabetes could be found. Despite great similarities in inflammatory markers in islets in T1D and T2D, long-term enteroviral infiltration is a distinct pathological feature of T1D-associated autoimmunity and in T1D pancreases.

Islet beta-cells and intercellular adhesion molecule-1 (ICAM-1): Integrating immune responses that influence autoimmunity and graft rejection

Type 1 diabetes (T1D) develops due to autoimmune targeting of the pancreatic islet β-cells. Clinical symptoms arise from reduced insulin in circulation. The molecular events and interactions between discrete immune cell populations, infiltration of such leukocytes into pancreatic and islet tissue, and selective targeting of the islet β-cells during autoimmunity and graft rejection are not entirely understood. One protein central to antigen presentation, priming of immune cells, trafficking of leukocytes, and vital for leukocyte effector function is the intercellular adhesion molecule-1 (ICAM-1). The gene encoding ICAM-1 is transcriptionally regulated and rapidly responsive (i.e., within hours) to pro-inflammatory cytokines. ICAM-1 is a transmembrane protein that can be glycosylated; its presence on the cell surface provides co-stimulatory functions for immune cell activation and stabilization of cell-cell contacts. ICAM-1 interacts with the β2-integrins, CD11a/CD18 (LFA-1) and CD11b/CD18 (Mac-1), which are present on discrete immune cell populations. A whole-body ICAM-1 deletion protects NOD mice from diabetes onset, strongly implicating this protein in autoimmune responses. Since several different cell types express ICAM-1, its biology is fundamentally essential for various physiological and pathological outcomes. Herein, we review the role of ICAM-1 during both autoimmunity and islet graft rejection to understand the mechanism(s) leading to islet β-cell death and dysfunction that results in insufficient circulating quantities of insulin to control glucose homeostasis.

A Supportive Role of Mesenchymal Stem Cells on Insulin-Producing Langerhans Islets with a Specific Emphasis on The Secretome

Type 1 Diabetes (T1D) is a chronic autoimmune disease characterized by a gradual destruction of insulin-producing β-cells in the endocrine pancreas due to innate and specific immune responses, leading to impaired glucose homeostasis. T1D patients usually require regular insulin injections after meals to maintain normal serum glucose levels. In severe cases, pancreas or Langerhans islet transplantation can assist in reaching a sufficient β-mass to normalize glucose homeostasis. The latter procedure is limited because of low donor availability, high islet loss, and immune rejection. There is still a need to develop new technologies to improve islet survival and implantation and to keep the islets functional. Mesenchymal stem cells (MSCs) are multipotent non-hematopoietic progenitor cells with high plasticity that can support human pancreatic islet function both in vitro and in vivo and islet co-transplantation with MSCs is more effective than islet transplantation alone in attenuating diabetes progression. The beneficial effect of MSCs on islet function is due to a combined effect on angiogenesis, suppression of immune responses, and secretion of growth factors essential for islet survival and function. In this review, various aspects of MSCs related to islet function and diabetes are described.

The pathogenic "symphony" in type 1 diabetes: A disorder of the immune system, β cells, and exocrine pancreas

Type 1 diabetes (T1D) is widely considered to result from the autoimmune destruction of insulin-producing β cells. This concept has been a central tenet for decades of attempts seeking to decipher the disorder's pathogenesis and prevent/reverse the disease. Recently, this and many other disease-related notions have come under increasing question, particularly given knowledge gained from analyses of human T1D pancreas. Perhaps most crucial are findings suggesting that a collective of cellular constituents-immune, endocrine, and exocrine in origin-mechanistically coalesce to facilitate T1D. This review considers these emerging concepts, from basic science to clinical research, and identifies several key remaining knowledge voids.

Immune cell infiltration in the pancreas of type 1, type 2 and type 3c diabetes

The different types of diabetes differ in disease pathogenesis but share the impairment or loss of β-cell function leading to chronic hyperglycaemia. While immune cells are present throughout the whole pancreas in normality, their number and activation is increased in diabetes. Different patterns and composition of inflammation could be observed in type 1, type 2 and type 3c diabetes. Immune cells, pancreatic stellate cells and fibrosis were present in the islet microenvironment and could add to β-cell dysfunction and therefore development and progression of diabetes. First studies investigating the use of anti-inflammatory drugs demonstrate their ability to rescue remaining β-cell function and their potential benefit in diabetes treatment. This article provides an overview of immune cell infiltrates in different types of diabetes, highlights the knowledge of their impact on β-cell function and introduces the potential of immunomodulatory strategies.

Why does the immune system destroy pancreatic β-cells but not α-cells in type 1 diabetes?

A perplexing feature of type 1 diabetes (T1D) is that the immune system destroys pancreatic β-cells but not neighbouring α-cells, even though both β-cells and α-cells are dysfunctional. Dysfunction, however, progresses to death only for β-cells. Recent findings indicate important differences between these two cell types. First, expression of BCL2L1, a key antiapoptotic gene, is higher in α-cells than in β-cells. Second, endoplasmic reticulum (ER) stress-related genes are differentially expressed, with higher expression levels of pro-apoptotic CHOP in β-cells than in α-cells and higher expression levels of HSPA5 (which encodes the protective chaperone BiP) in α-cells than in β-cells. Third, expression of viral recognition and innate immune response genes is higher in α-cells than in β-cells, contributing to the enhanced resistance of α-cells to coxsackievirus infection. Fourth, expression of the immune-inhibitory HLA-E molecule is higher in α-cells than in β-cells. Of note, α-cells are less immunogenic than β-cells, and the CD8+ T cells invading the islets in T1D are reactive to pre-proinsulin but not to glucagon. We suggest that this finding is a result of the enhanced capacity of the α-cell to endure viral infections and ER stress, which enables them to better survive early stressors that can cause cell death and consequently amplify antigen presentation to the immune system. Moreover, the processing of the pre-proglucagon precursor in enteroendocrine cells might favour immune tolerance towards this potential self-antigen compared to pre-proinsulin.

The extent and magnitude of islet T cell infiltration as powerful tools to define the progression to type 1 diabetes

AIMS/HYPOTHESIS

Insulitis is not present in all islets, and it is elusive in humans. Although earlier studies focused on islets that fulfilled certain criteria (e.g. ≥15 CD45+ cells or ≥6 CD3+ cells), there is a fundamental lack of understanding of the infiltration dynamics in terms of its magnitude (i.e. how much) and extent (i.e. where). Here, we aimed to perform an in-depth characterisation of T cell infiltration by investigating islets with moderate (1-5 CD3+ cells) and high (≥6 CD3+ cells) infiltration in individuals with and without type 1 diabetes.

METHODS

Pancreatic tissue sections from 15 non-diabetic, eight double autoantibody-positive and ten type 1 diabetic (0-2 years of disease duration) organ donors were obtained from the Network for Pancreatic Organ Donors with Diabetes, and stained for insulin, glucagon, CD3 and CD8 by immunofluorescence. T cell infiltration was quantified in a total of 8661 islets using the software QuPath. The percentage of infiltrated islets and islet T cell density were calculated. To help standardise the analysis of T cell infiltration, we used cell density data to develop a new T cell density threshold capable of differentiating non-diabetic and type 1 diabetic donors.

RESULTS

Our analysis revealed that 17.1% of islets in non-diabetic donors, 33% of islets in autoantibody-positive and 32.5% of islets in type 1 diabetic donors were infiltrated by 1 to 5 CD3+ cells. Islets infiltrated by ≥6 CD3+ cells were rare in non-diabetic donors (0.4%) but could be found in autoantibody-positive (4.5%) and type 1 diabetic donors (8.2%). CD8+ and CD8- populations followed similar patterns. Likewise, T cell density was significantly higher in the islets of autoantibody-positive donors (55.4 CD3+ cells/mm2) and type 1 diabetic donors (74.8 CD3+ cells/mm2) compared with non-diabetic individuals (17.3 CD3+ cells/mm2), which was accompanied by higher exocrine T cell density in type 1 diabetic individuals. Furthermore, we showed that the analysis of a minimum of 30 islets and the use of a reference mean value for T cell density of 30 CD3+ cells/mm2 (the 30-30 rule) can differentiate between non-diabetic and type 1 diabetic donors with high specificity and sensitivity. In addition, it can classify autoantibody-positive individuals as non-diabetic or type 1 diabetic-like.

CONCLUSIONS/INTERPRETATION

Our data indicates that the proportion of infiltrated islets and T cell density change dramatically during the course of type 1 diabetes, and these changes can be already observed in double autoantibody-positive individuals. This suggests that, as disease progresses, T cell infiltration extends throughout the pancreas, reaching the islets and exocrine compartment. While it predominantly targets insulin-containing islets, large accumulations of cells are rare. Our study fulfils the need to further understand T cell infiltration, not only after diagnosis but also in individuals with diabetes-related autoantibodies. Furthermore, the development and application of new analytical tools based on T cell infiltration, like the 30-30 rule, will allow us to correlate islet infiltration with demographic and clinical variables with the aim of identifying individuals at the very early stages of the disease.

Bi-glandular and persistent enterovirus infection and distinct changes of the pancreas in slowly progressive type 1 diabetes mellitus

In slowly progressive type 1 diabetes mellitus (SPIDDM), the pancreas shows sustained islet inflammation, pancreatitis, pancreatic acinar cell metaplasia/dysplasia (ADM), and intraepithelial neoplasia (PanIN), a precancerous lesion. The mechanisms underlying these changes remain unclear. The presence of enterovirus (EV) encoded-capsid protein 1 (VP1) and -2A protease (2A^pro) and the innate immune responses of the pancreas were studied using immunohistochemistry and in situ hybridization in 12 SPIDDM and 19 non-diabetic control pancreases. VP1, 2A^pro, and EV-RNA were detected in islets and the exocrine pancreas in all SPIDDM pancreases. Innate immune receptor, melanoma differentiation-associated gene 5 (MDA5), and interferon (IFN)-beta1 were intensified in the islets of SPIDDM patients with short disease duration. However, expressions of MDA5 and IFN-beta1were suppressed in those with longer disease duration. CD3⁺ T cell infiltration was observed in the VP1- and insulin-positive islets (insulitis) and exocrine acinar cells. CD11c⁺ dendritic cells (DCs) in islets were scarce in long-term SPIDDM. This study showed the consistent presence of EV, suggesting an association with inflammatory changes in the endocrine and exocrine pancreas in SPIDDM. Suppressed expressions of MDA5 and IFN-beta1, as well as decreased numbers of DCs in the host cells, may contribute to persistent EV infection and induction of ADM/PanIN lesions, which may potentially provide a scaffold for pancreatic neoplasms.

Inflammatory Cell Infiltration Into Islets Without PD-L1 Expression Is Associated With the Development of Immune Checkpoint Inhibitor-Related Type 1 Diabetes in Genetically Susceptible Patients

Immune checkpoint inhibitors (ICIs) could cause type 1 diabetes (T1D). However, the underlying mechanism remains unclear. We immunohistochemically analyzed pancreatic specimens from three individuals with ICI-related T1D, and their histopathological data were compared those from three patients who had received ICI therapy but did not develop T1D (non-T1D) and seven normal glucose-tolerant subjects as control subjects. All ICI-related T1D patients had susceptible HLA haplotypes. In ICI-related T1D, the β-cell area decreased and the α-cell area increased compared with non-T1D and control subjects. The number of CD3-positive cells around islets increased in ICI-related T1D and non-T1D compared with control subjects, while the number of CD68-positive cells around islets increased in ICI-related T1D compared with non-T1D and control subjects. The expression ratios of programmed death-ligand 1 (PD-L1) on islets decreased in non-T1D and almost completely disappeared in ICI-related T1D, while PD-L1 expression was observed in most cells of pancreatic islets in control subjects. This study, therefore, indicates that ICI therapy itself could reduce PD-L1 expression on islets in all subjects, which may be related to β-cell vulnerability. In addition, we showed that absence of PD-L1 expression on β-cells, genetic susceptibility, and infiltration of macrophages as well as T lymphocytes around islets might be responsible for T1D onset.

Pancreatic Pathological Changes in Murine Toxoplasmosis and Possible Association with Diabetes Mellitus

BACKGROUND

Previous studies have reported involvement of Toxoplasma gondii (T. gondii) infections in the pathogenesis of some autoimmune diseases, such as polymyositis, rheumatoid arthritis, autoimmune thyroiditis, and Crohn's disease. However, data on the association between T. gondii infections and Type 1 diabetes mellitus (T1DM) are still controversial. Therefore, in the present study, we aimed to investigate the pancreatic pathological changes in mouse models with acute and chronic toxoplasmosis and their association with T1DM.

MATERIALS AND METHODS

Three groups (10 mice each) of male Swiss Albino mice were used. One group of mice was left uninfected, whereas the second and third groups were infected with the acute virulent T. gondii RH strain and the chronic less virulent Me49 T. gondii strain, respectively. T. gondii-induced pancreatic pathological changes were evaluated by histopathological examination of pancreatic tissues. Moreover, the expression of insulin, levels of caspase-3, and the pancreatic infiltration of CD8⁺ T cells were evaluated using immunohistochemical staining.

RESULTS

Pancreatic tissues of T. gondii-infected animals showed significant pathological alterations and variable degrees of insulitis. Mice with acute toxoplasmosis exhibited marked enlargement and reduced numbers of islets of Langerhans. However, mice with chronic toxoplasmosis showed considerable reduction in size and number of islets of Langerhans. Moreover, insulin staining revealed significant reduction in β cell numbers, whereas caspase-3 staining showed induced apoptosis in islets of Langerhans of acute toxoplasmosis and chronic toxoplasmosis mice compared to uninfected mice. We detected infiltration of CD8⁺ T cells only in islets of Langerhans of mice with chronic toxoplasmosis.

CONCLUSIONS

Acute and chronic toxoplasmosis mice displayed marked pancreatic pathological changes with reduced numbers of islets of Langerhans and insulin-producing-β cells. Since damage of β cells of islets of Langerhans is associated with the development of T1DM, our findings may support a link between T. gondii infections and the development of T1DM.

Insulitis in Human Type 1 Diabetic Pancreas: From Stem Cell Grafting to Islet Organoids for a Successful Cell-Based Therapy

Type 1 diabetes (T1D) is an autoimmune disease with immune cells' islet infiltration (called "insulitis"), which leads to beta cell loss. Despite being the critical element of T1D occurrence and pathogenesis, insulitis is often present in a limited percentage of islets, also at diagnosis. Therefore, it is needed to define reproducible methods to detect insulitis and beta-cell decline, to allow accurate and early diagnosis and to monitor therapy. However, this goal is still far due to the morphological aspect of islet microvasculature, which is rather dense and rich, and is considerably rearranged during insulitis. More studies on microvasculature are required to understand if contrast-enhanced ultrasound sonography measurements of pancreatic blood-flow dynamics may provide a clinically deployable predictive marker to predict disease progression and therapeutic reversal in pre-symptomatic T1D patients. Therefore, it is needed to clarify the relation between insulitis and the dynamics of β cell loss and with coexisting mechanisms of dysfunction, according to clinical stage, as well as the micro vessels' dynamics and microvasculature reorganization. Moreover, the ideal cell-based therapy of T1D should start from an early diagnosis allowing a sufficient isolation of specific Procr+ progenitors, followed by the generation and expansion of islet organoids, which could be transplanted coupled to an immune-regulatory therapy which will permit the maintenance of pancreatic islets and an effective and long-lasting insulitis reversal.

Type 1 diabetes: what is the role of autoimmunity in β cell death?

The current dogma of type 1 diabetes pathogenesis asserts that an autoimmune attack leads to the destruction of pancreatic β cells, with subsequent hyperglycemia. This dogma is based on islet autoantibodies emerging prior to the onset of type 1 diabetes. In this issue of the JCI, Warncke et al. report on their investigation of the development of hyperglycemia below the diabetes threshold as an early proxy of β cell demise. Surprisingly, they found that an elevation in blood glucose preceded the appearance of autoimmunity. This observation calls into question the importance of autoimmunity as the primary cause of β cell destruction and has implications for prevention and treatment in diabetes.

Exocrine and Endocrine Inflammation Increases Cellular Replication in the Pancreatic Duct Compartment in Type 1 Diabetes

Context

We recently demonstrated increased cellular proliferation in the pancreatic ductal gland (PDG) compartment of organ donors with type 1 diabetes, suggesting that PDGs may harbor progenitor cells capable of pancreatic regeneration.

Objective

We evaluated the impact of diabetes and pancreatic inflammation on PDG and interlobular duct (ILD) cellular proliferation and profiles.

Methods

Endocrine hormone expression (insulin, glucagon, somatostatin, pancreatic polypeptide) and proliferating Ki67+ cells were localized within the PDG and ILD compartments by multicolor immunohistochemistry in cross-sections from the head, body, and tail regions of pancreata from those with (n = 31) or without type 1 diabetes (n = 43). Whole-slide scanned images were analyzed using digital pathology.

Results

Type 1 diabetes donors with insulitis or histologically identified pancreatitis had increased cellular replication in the ILD and PDG compartments. Interestingly, while cellular proliferation within the pancreatic ductal tree was significantly increased in type 1 diabetes (PDG mean = 3.36%, SEM = 1.06; ILD mean = 2.78%, SEM = 0.97) vs nondiabetes(ND) subjects without pancreatic inflammation (PDG mean = 1.18%, SEM = 0.42; ILD mean = 0.74%, SEM = 0.15, P < 0.05), robust replication was also observed in ND donors with pancreatitis (PDG mean = 3.52%, SEM = 1.33; ILD mean = 2.18%, SEM = 0.54, P < 0.05). Few polyhormonal cells were present in the ILD (type 1 diabetes = 0.04 ± 0.02%; ND = 0.08 ± 0.03%, P = 0.40) or PDG compartment (type 1 diabetes = 0.02 ± 0.01%; ND = 0.08 ± 0.13%, P = 0.63).

Conclusion

These data suggest that increased pancreatic ductal cell replication is associated with sustained pancreatic inflammation; however, as replicating cells were hormone-negative, PDGs do not appear to represent a compelling endogenous source of hormone-positive endocrine cells.

A decisive bridge between innate immunity and the pathognomonic morphological characteristics of type 1 diabetes demonstrated by instillation of heat-inactivated bacteria in the pancreatic duct of rats

AIMS

Periductal inflammation and accumulation of granulocytes and monocytes in the periislet area and in the exocrine pancreas is observed within hours after instillation of heat-inactivated bacteria in the ductal compartment of the pancreas in healthy rats. The present investigation was undertaken to study how the acute inflammation developed over time.

METHODS

Immunohistochemical evaluation of the immune response triggered by instillation of heat-inactivated bacteria in the ductal compartment in rats.

RESULTS

After three weeks, the triggered inflammation had vanished and pancreases showed normal morphology. However, a distinct accumulation of both CD4+ and CD8+ T cells within and adjacent to affected islets was found in one-third of the rats instilled with heat-inactivated E. faecalis, mimicking the insulitis seen at onset of human T1D. As in T1D, this insulitis affected a minority of islets and only certain lobes of the pancreases. Notably, a fraction of the T cells expressed the CD103 antigen, mirroring the recently reported presence of tissue resident memory T cells in the insulitis in humans with recent onset T1D.

CONCLUSIONS

The results presented unravel a previously unknown interplay between innate and acquired immunity in the formation of immunopathological events indistinguishable from those described in humans with recent onset T1D.

NAG-1/GDF15 protects against streptozotocin-induced type 1 diabetes by inhibiting apoptosis, preserving beta-cell function, and suppressing inflammation in pancreatic islets

The loss of functional insulin-producing β-cells is a hallmark of type 1 diabetes mellitus (T1DM). Previously, we reported that the non-steroidal anti-inflammatory drug activated gene-1, or growth differentiation factor-15 (NAG-1/GDF15) inhibits obesity and improves insulin sensitivity in both genetic and dietary-induced obese mice. However, the regulatory role of NAG-1/GDF15 in the structure and function of β-cells and the prevention of T1DM is largely unknown. In the current study, we reported that NAG-1/GDF15 transgenic (Tg) mice are resistant to diabetogenesis induced by multiple low-dose streptozotocin (MLD-STZ) treatment. NAG-1/GDF15 overexpression significantly reduced diabetes incidence, alleviated symptoms of T1DM, and improved MLD-STZ-induced glucose intolerance and insulin resistance. Both the mass and function of pancreatic β cells were preserved in the NAG-1/GDF15 Tg mice as evidenced by significantly increased islet area and insulin production. The mechanistic study revealed that NAG-1/GDF15 significantly inhibited STZ-induced apoptosis and preserved the reduction of proliferation in the islets of the Tg mice as compared to the wild-type (WT) mice upon MLD-STZ treatment. Additionally, NAG-1/GDF15 significantly reduced both the serum and islet levels of the inflammatory cytokines (IL-1β, IL-6, and TNFα), and reduced the expression of NF-κB expression and immune cells infiltration in the islets. Collectively, these results indicate that NAG-1/GDF15 is effective in improving STZ-induced glucose intolerance, probably was mediated via suppressing inflammation, inhibiting apoptosis, and preserving β-cell mass and function.

Nanotechnology in Immunotherapy for Type 1 Diabetes: Promising Innovations and Future Advances

Diabetes is a chronic condition which affects the glucose metabolism in the body. In lieu of any clinical “cure,” the condition is managed through the administration of pharmacological aids, insulin supplements, diet restrictions, exercise, and the like. The conventional clinical prescriptions are limited by their life-long dependency and diminished potency, which in turn hinder the patient’s recovery. This necessitated an alteration in approach and has instigated several investigations into other strategies. As Type 1 diabetes (T1D) is known to be an autoimmune disorder, targeting the immune system in activation and/or suppression has shown promise in reducing beta cell loss and improving insulin levels in response to hyperglycemia. Another strategy currently being explored is the use of nanoparticles in the delivery of immunomodulators, insulin, or engineered vaccines to endogenous immune cells. Nanoparticle-assisted targeting of immune cells holds substantial potential for enhanced patient care within T1D clinical settings. Herein, we summarize the knowledge of etiology, clinical scenarios, and the current state of nanoparticle-based immunotherapeutic approaches for Type 1 diabetes. We also discuss the feasibility of translating this approach to clinical practice.

Evidence of islet CADM1-mediated immune cell interactions during human type 1 diabetes

BACKGROUND

Pathophysiology of type 1 diabetes (T1D) is illustrated by pancreatic islet infiltration of inflammatory lymphocytes, including CD8⁺ T cells; however, the molecular factors mediating their recruitment remain unknown. We hypothesized that single-cell RNA-sequencing (scRNA-Seq) analysis of immune cell populations isolated from islets of NOD mice captured gene expression dynamics providing critical insight into autoimmune diabetes pathogenesis.

METHODS

Pancreatic sections from human donors were investigated, including individuals with T1D, autoantibody-positive (aAb⁺) individuals, and individuals without diabetes who served as controls. IHC was performed to assess islet hormones and both novel and canonical immune cell markers that were identified from unbiased, state-of-the-art workflows after reanalyzing murine scRNA-Seq data sets.

RESULTS

Computational workflows identified cell adhesion molecule 1–mediated (Cadm1-mediated) homotypic binding among the most important intercellular interactions among all cell clusters, as well as Cadm1 enrichment in macrophages and DCs from pancreata of NOD mice. Immunostaining of human pancreata revealed an increased number of CADM1⁺glucagon⁺ cells adjacent to CD8⁺ T cells in sections from T1D and aAb⁺ donors compared with individuals without diabetes. Numbers of CADM1⁺CD68⁺ peri-islet myeloid cells adjacent to CD8⁺ T cells were also increased in pancreatic sections from both T1D and aAb⁺ donors compared with individuals without diabetes.

CONCLUSION

Increased detection of CADM1⁺ cells adjacent to CD8⁺ T cells in pancreatic sections of individuals with T1D and those who were aAb⁺ validated workflows and indicated CADM1-mediated intercellular contact may facilitate islet infiltration of cytotoxic T lymphocytes and serve as a potential therapeutic target for preventing T1D pathogenesis.

FUNDING

The Johns Hopkins All Children’s Foundation Institutional Research Grant Program, the National Natural Science Foundation of China (grant 82071326), and the Deutsche Forschungsgemeinschaft (grants 431549029–SFB1451, EXC2030–390661388, and 411422114-GRK2550).

Circulating platelet-neutrophil aggregates characterize the development of type 1 diabetes in humans and NOD mice

Platelet-neutrophil aggregates (PNAs) facilitate neutrophil activation and migration and could underpin the recruitment of neutrophils to the pancreas during type 1 diabetes (T1D) pathogenesis. PNAs, measured by flow cytometry, were significantly elevated in the circulation of autoantibody-positive (Aab⁺) children and new-onset T1D children, as well as in pre-T1D (at 4 weeks and 10–12 weeks) and T1D-onset NOD mice, compared with relevant controls, and PNAs were characterized by activated P-selectin⁺ platelets. PNAs were similarly increased in pre-T1D and T1D-onset NOD isolated islets/insulitis, and immunofluorescence staining revealed increased islet-associated neutrophil extracellular trap (NET) products (myeloperoxidase [MPO] and citrullinated histones [CitH3]) in NOD pancreata. In vitro, cell-free histones and NETs induced islet cell damage, which was prevented by the small polyanionic drug methyl cellobiose sulfate (mCBS) that binds to histones and neutralizes their pathological effects. Elevated circulating PNAs could, therefore, act as an innate immune and pathogenic biomarker of T1D autoimmunity. Platelet hyperreactivity within PNAs appears to represent a previously unrecognized hematological abnormality that precedes T1D onset. In summary, PNAs could contribute to the pathogenesis of T1D and potentially function as a pre-T1D diagnostic.

Immunoregulated insulitis and slow-progressing type 1 diabetes after duodenopancreatectomy

AIMS/HYPOTHESIS

We report the case of a woman who underwent a partial pancreatectomy for a serous cystadenoma when aged 56 years. She had been diagnosed with diabetes 6 years before and had Hashimoto's thyroiditis. Despite positive anti-GAD autoantibodies (GADA) and previous surgery, she was transiently weaned off long-acting insulin. Blood glucose levels remained well controlled with low-dose long-acting insulin. Insulin needs eventually increased 8 years after surgery, in conjunction with anti-zinc transporter 8 (ZnT8) seroconversion and decreasing residual C-peptide. We hypothesised that the surgical pancreas specimens and blood autoimmune T cell responses may provide correlates of this indolent clinical course.

METHODS

Beta and alpha cell area and insulitis were quantified on pancreas head tissue sections obtained at surgery. Blood T cell responses against beta cell antigens were analysed by enzyme-linked immunospot.

RESULTS

Pancreas sections displayed reduced beta cell and normal alpha cell area (0.27% and 0.85% of section area, respectively). High-grade insulitis was observed, mostly in insulin-containing islets, with a peri-insulitis pattern enriched in T cells positive for regulatory forkhead box protein 3 (FOXP3). In vitro challenge with beta cell antigens of circulating T cells collected 4 and 9 years after surgery revealed dominant and persistent IL-10 responses; IFN-γ responses increasing at 9 years, after anti-ZnT8 seroconversion, was observed.

CONCLUSIONS/INTERPRETATION

Despite persistent GADA and the histopathological finding of insulitis and decreased beta cell area 6 years after diabetes diagnosis, glycaemic control was maintained with low-dose insulin up to 8 years after surgery. Regulated T cell responses towards beta cell antigens and FOXP3-positive peri-insulitis suggest spontaneous long-term regulation of islet autoimmunity after substantial beta cell loss, and eventual autoimmune progression upon anti-ZnT8 seroconversion.

Expression of CD47 in the pancreatic β-cells of people with recent-onset type 1 diabetes varies according to disease endotype

AIMS

We are studying the dialogue between β-cells and the immune system in type 1 diabetes and have identified a cell surface receptor, signal regulatory protein-alpha (SIRPα) as an important component in the regulation of β-cell survival. SIRPα interacts with another protein, CD47, to mediate signalling. In the present work, we have studied the expression and role of CD47 in human islet cells in type 1 diabetes.

METHODS

Clonal EndoC-βH1 cells were employed for functional studies. Cells were exposed to pro-inflammatory cytokines and their viability monitored by flow cytometry after staining with propidium iodide. Targeted knockdown of CD47 or SIRPα was achieved with small interference RNA molecules and the expression of relevant proteins studied by Western blotting or immunocytochemistry. Human pancreas sections were selected from the Exeter Archival Diabetes Biobank and used to examine the expression of CD47 by immunofluorescence labelling. Image analysis was employed to quantify expression.

RESULTS

CD47 is abundantly expressed in both α and β cells in human pancreas. In type 1 diabetes, the levels of CD47 are increased in α cells across all age groups, whereas the expression in β-cells varies according to disease endotype. Knockdown of either CD47 or SIRPα in EndoC-βH1 cells resulted in a loss of viability.

CONCLUSIONS

We conclude that the CD47 plays a previously unrecognised role in the regulation of β-cell viability. This system is dysregulated in type 1 diabetes suggesting that it may be targeted therapeutically to slow disease progression.

Substance Use Affects Type 1 Diabetes Pancreas Pathology: Implications for Future Studies

Access to human pancreas samples from organ donors has greatly advanced our understanding of type 1 diabetes pathogenesis; however, previous studies have shown that donors have a high rate of substance use, and its impact on pancreatic histopathology in this disease is not well described. One-hundred-thirty-one type 1 diabetes and 111 control organ donor pancreata from persons 12-89 years of age (mean 29.8 ± 15.5 years) within the Network for Pancreatic Organ donors with Diabetes (nPOD) were examined for insulin positivity, insulitis, amyloid staining, acute and chronic pancreatitis, and chronic exocrine changes (acinar atrophy, fibrosis, fatty infiltration, or periductal fibrosis); findings were compared by history of substance use. A secondary analysis compared exocrine pancreatic histopathologic findings in type 1 diabetes versus control organ donors regardless of substance use history. We observed a high but congruent rate of substance use in type 1 diabetes and control organ donors (66.4% and 64% respectively). Among donors with type 1 diabetes (but not controls), islet amyloid (OR 9.96 [1.22, 81.29]) and acute pancreatitis (OR 3.2 [1.06, 9.63]) were more common in alcohol users while chronic exocrine changes (OR 8.86 [1.13, 69.31]) were more common in cocaine users. Substance use impacted the pancreata of donors with type 1 diabetes more than controls. Overall, despite similar rates of substance use, acute pancreatitis (15.3% versus 4.5%, p=0.0061), chronic pancreatitis (29.8% versus 9.9%, p=0.0001), and chronic exocrine changes (73.3% versus 36.9%, p<0.0001) were more common in type 1 diabetes donors than controls. Alcohol and/or cocaine use in type 1 diabetes organ donors increases exocrine pancreas pathology and islet amyloid deposition but does not affect insulitis or insulin positivity. Exocrine pathology in type 1 diabetes donors is common, and further study of the pathophysiology of these changes is needed.

The β-cell glucose toxicity hypothesis: Attractive but difficult to prove

β cells in the hyperglycemic environment of diabetes have marked changes in phenotype and function that are largely reversible if glucose levels can be returned to normal. A leading hypothesis is that these changes are caused by the elevated glucose levels leading to the concept of glucose toxicity. Support for the glucose toxicity hypothesis is largely circumstantial, but little progress has been made in defining the responsible mechanisms. Then questions emerge that are difficult to answer. In the very earliest stages of diabetes development, there is a dramatic loss of glucose-induced first-phase insulin release (FPIR) with only trivial elevations of blood glucose levels. A related question is how impaired insulin action on target tissues such as liver, muscle and fat can cause increased insulin secretion. The existence of a sophisticated feedback mechanism between insulin secretion and insulin action on peripheral tissues driven by glucose has been postulated, but it has been difficult to measure increases in blood glucose levels that might have been expected. These complexities force us to challenge the simplicity of the glucose toxicity hypothesis and feedback mechanisms. It may turn out that glucose is somehow driving all of these changes, but we must develop new questions and experimental approaches to test the hypothesis.

The Human Islet: Mini-Organ With Mega-Impact

This review focuses on the human pancreatic islet-including its structure, cell composition, development, function, and dysfunction. After providing a historical timeline of key discoveries about human islets over the past century, we describe new research approaches and technologies that are being used to study human islets and how these are providing insight into human islet physiology and pathophysiology. We also describe changes or adaptations in human islets in response to physiologic challenges such as pregnancy, aging, and insulin resistance and discuss islet changes in human diabetes of many forms. We outline current and future interventions being developed to protect, restore, or replace human islets. The review also highlights unresolved questions about human islets and proposes areas where additional research on human islets is needed.

Peripheral autoreactive CD8 T-cell frequencies are too variable to be a reliable predictor of disease progression of human type 1 diabetes

Objectives

The detection of a peripheral immune cell signature that specifically reflects autoimmunity in type 1 diabetes would enable the prediction and staging of disease on an individual basis. However, defining such a signature is technically challenging. Reliable interpretation of immune cell‐related biomarkers depends on their inherent variability and, to understand this variability, longitudinal analyses are required.

Methods

We performed a longitudinal observational study in which 40 individuals with elevated genetic risk of type 1 diabetes and persistent islet autoantibodies provided a blood sample every 4–6 weeks for > 1 year.

Results

Peripheral immune cell composition (T cells, NK cells and monocytes) was assessed using well‐validated flow cytometry panels and demonstrated that, while non‐antigen‐specific immune cell subsets were stable over time, autoantigen‐reactive T‐cell frequencies were highly variable in and between individuals. Neither the frequency nor phenotype of non‐antigen‐specific subsets or autoreactive CD8⁺ T cells associated with clinical onset of T1D.

Conclusion

The findings from the Type 1 Diabetes Longitudinal BIomarker Trial underscore the inherent challenge of evaluating changes in peripheral immune cell populations as surrogates of organ‐specific disease activity. The variability of peripheral antigen‐specific T cells precludes their use as a prognostic marker and clearly demonstrates that a reliable prognostic cell signature remains elusive.

Identification and characterisation of tertiary lymphoid organs in human type 1 diabetes

AIMS/HYPOTHESIS

We and others previously reported the presence of tertiary lymphoid organs (TLOs) in the pancreas of NOD mice, where they play a role in the development of type 1 diabetes. Our aims here are to investigate whether TLOs are present in the pancreas of individuals with type 1 diabetes and to characterise their distinctive features, in comparison with TLOs present in NOD mouse pancreases, in order to interpret their functional significance.

METHODS

Using immunofluorescence confocal microscopy, we examined the extracellular matrix (ECM) and cellular constituents of pancreatic TLOs from individuals with ongoing islet autoimmunity in three distinct clinical settings of type 1 diabetes: at risk of diabetes; at/after diagnosis; and in the transplanted pancreas with recurrent diabetes. Comparisons were made with TLOs from 14-week-old NOD mice, which contain islets exhibiting mild to heavy leucocyte infiltration. We determined the frequency of the TLOs in human type 1diabetes with insulitis and investigated the presence of TLOs in relation to age of onset, disease duration and disease severity.

RESULTS

TLOs were identified in preclinical and clinical settings of human type 1 diabetes. The main characteristics of these TLOs, including the cellular and ECM composition of reticular fibres (RFs), the presence of high endothelial venules and immune cell subtypes detected, were similar to those observed for TLOs from NOD mouse pancreases. Among 21 donors with clinical type 1 diabetes who exhibited insulitis, 12 had TLOs and had developed disease at younger age compared with those lacking TLOs. Compartmentalised TLOs with distinct T cell and B cell zones were detected in donors with short disease duration. Overall, TLOs were mainly associated with insulin-containing islets and their frequency decreased with increasing severity of beta cell loss. Parallel studies in NOD mice further revealed some differences in so far as regulatory T cells were essentially absent from human pancreatic TLOs and CCL21 was not associated with RFs.

CONCLUSIONS/INTERPRETATION

We demonstrate a novel feature of pancreas pathology in type 1 diabetes. TLOs represent a potential site of autoreactive effector T cell generation in islet autoimmunity and our data from mouse and human tissues suggest that they disappear once the destructive process has run its course. Thus, TLOs may be important for type 1 diabetes progression.

T cell transgressions: Tales of T cell form and function in diverse disease states

Insights into T cell form, function, and dysfunction are rapidly evolving. T cells have remarkably varied effector functions including protecting the host from infection, activating cells of the innate immune system, releasing cytokines and chemokines, and heavily contributing to immunological memory. Under healthy conditions, T cells orchestrate a finely tuned attack on invading pathogens while minimizing damage to the host. The dark side of T cells is that they also exhibit autoreactivity and inflict harm to host cells, creating autoimmunity. The mechanisms of T cell autoreactivity are complex and dynamic. Emerging research is elucidating the mechanisms leading T cells to become autoreactive and how such responses cause or contribute to diverse disease states, both peripherally and within the central nervous system. This review provides foundational information on T cell development, differentiation, and functions. Key T cell subtypes, cytokines that create their effector roles, and sex differences are highlighted. Pathological T cell contributions to diverse peripheral and central disease states, arising from errors in reactivity, are highlighted, with a focus on multiple sclerosis, rheumatoid arthritis, osteoarthritis, neuropathic pain, and type 1 diabetes.

Means, Motive, and Opportunity: Do Non-Islet-Reactive Infiltrating T Cells Contribute to Autoimmunity in Type 1 Diabetes?

In human type 1 diabetes and animal models of the disease, a diverse assortment of immune cells infiltrates the pancreatic islets. CD8⁺ T cells are well represented within infiltrates and HLA multimer staining of pancreas sections provides clear evidence that islet epitope reactive T cells are present within autoimmune lesions. These bona fide effectors have been a key research focus because these cells represent an intellectually attractive culprit for β cell destruction. However, T cell receptors are highly diverse in human insulitis. This suggests correspondingly broad antigen specificity, which includes a majority of T cells for which there is no evidence of islet-specific reactivity. The presence of “non-cognate” T cells in insulitis raises suspicion that their role could be beyond that of an innocent bystander. In this perspective, we consider the potential pathogenic contribution of non-islet-reactive T cells. Our intellectual framework will be that of a criminal investigation. Having arraigned islet-specific CD8⁺ T cells for the murder of pancreatic β cells, we then turn our attention to the non-target immune cells present in human insulitis and consider the possible regulatory, benign, or effector roles that they may play in disease. Considering available evidence, we overview the case that can be made that non-islet-reactive infiltrating T cells should be suspected as co-conspirators or accessories to the crime and suggest some possible routes forward for reaching a better understanding of their role in disease.

Whole-Slide Image Analysis of Human Pancreas Samples to Elucidate the Immunopathogenesis of Type 1 Diabetes Using the QuPath Software

Type 1 diabetes is a chronic disease of the pancreas characterized by the loss of insulin-producing beta cells. Access to human pancreas samples for research purposes has been historically limited, restricting pathological analyses to animal models. However, intrinsic differences between animals and humans have made clinical translation very challenging. Recently, human pancreas samples have become available through several biobanks worldwide, and this has opened numerous opportunities for scientific discovery. In addition, the use of new imaging technologies has unraveled many mysteries of the human pancreas not merely in the presence of disease, but also in physiological conditions. Nowadays, multiplex immunofluorescence protocols as well as sophisticated image analysis tools can be employed. Here, we described the use of QuPath—an open-source platform for image analysis—for the investigation of human pancreas samples. We demonstrate that QuPath can be adequately used to analyze whole-slide images with the aim of identifying the islets of Langerhans and define their cellular composition as well as other basic morphological characteristics. In addition, we show that QuPath can identify immune cell populations in the exocrine tissue and islets of Langerhans, accurately localizing and quantifying immune infiltrates in the pancreas. Therefore, we present a tool and analysis pipeline that allows for the accurate characterization of the human pancreas, enabling the study of the anatomical and physiological changes underlying pancreatic diseases such as type 1 diabetes. The standardization and implementation of these analysis tools is of critical importance to understand disease pathogenesis, and may be informative for the design of new therapies aimed at preserving beta cell function and halting the inflammation caused by the immune attack.

Type 1 diabetes mellitus: much progress, many opportunities

As part of the centennial celebration of insulin's discovery, this review summarizes the current understanding of the genetics, pathogenesis, treatment, and outcomes in type 1 diabetes (T1D). T1D results from an autoimmune response that leads to destruction of the β cells in the pancreatic islet and requires lifelong insulin therapy. While much has been learned about T1D, it is now clear that there is considerable heterogeneity in T1D with regard to genetics, pathology, response to immune-based therapies, clinical course, and susceptibility to diabetes-related complications. This Review highlights knowledge gaps and opportunities to improve the understanding of T1D pathogenesis and outlines emerging therapies to treat or prevent T1D and reduce the burden of T1D.

Coordinated interactions between endothelial cells and macrophages in the islet microenvironment promote β cell regeneration

Endogenous β cell regeneration could alleviate diabetes, but proliferative stimuli within the islet microenvironment are incompletely understood. We previously found that β cell recovery following hypervascularization-induced β cell loss involves interactions with endothelial cells (ECs) and macrophages (MΦs). Here we show that proliferative ECs modulate MΦ infiltration and phenotype during β cell loss, and recruited MΦs are essential for β cell recovery. Furthermore, VEGFR2 inactivation in quiescent ECs accelerates islet vascular regression during β cell recovery and leads to increased β cell proliferation without changes in MΦ phenotype or number. Transcriptome analysis of β cells, ECs, and MΦs reveals that β cell proliferation coincides with elevated expression of extracellular matrix remodeling molecules and growth factors likely driving activation of proliferative signaling pathways in β cells. Collectively, these findings suggest a new β cell regeneration paradigm whereby coordinated interactions between intra-islet MΦs, ECs, and extracellular matrix mediate β cell self-renewal.

Insulin Receptor-Expressing T Cells Appear in Individuals at Risk for Type 1 Diabetes and Can Move into the Pancreas in C57BL/6 Transgenic Mice

Insulin receptor (IR) expression on the T cell surface can indicate an activated state; however, the IR is also chemotactic, enabling T cells with high IR expression to physically move toward insulin. In humans with type 1 diabetes (T1D) and the NOD mouse model, a T cell-mediated autoimmune destruction of insulin-producing pancreatic β cells occurs. In previous work, when purified IR⁺ and IR^- T cells were sorted from diabetic NOD mice and transferred into irradiated nondiabetic NOD mice, only those that received IR⁺ T cells developed insulitis and diabetes. In this study, peripheral blood samples from individuals with T1D (new onset to 14 y of duration), relatives at high-risk for T1D, defined by positivity for islet autoantibodies, and healthy controls were examined for frequency of IR⁺ T cells. High-risk individuals had significantly higher numbers of IR⁺ T cells as compared with those with T1D (p < 0.01) and controls (p < 0.001); however, the percentage of IR⁺ T cells in circulation did not differ significantly between T1D and control subjects. With the hypothesis that IR⁺ T cells traffic to the pancreas in T1D, we developed a (to our knowledge) novel mouse model exhibiting a FLAG-tagged mouse IR on T cells on the C57BL/6 background, which is not susceptible to developing T1D. Interestingly, these C57BL/6-CD3FLAGmIR/mfm mice showed evidence of increased IR⁺ T cell trafficking into the islets compared with C57BL/6 controls (p < 0.001). This transgenic animal model provides a (to our knowledge) novel platform for investigating the influence of IR expression on T cell trafficking and the development of insulitis.

Insulitis in the pancreas of non-diabetic organ donors under age 25 years with multiple circulating autoantibodies against islet cell antigens

Autoantibodies against islet cell antigens are routinely used to identify subjects at increased risk of symptomatic type 1 diabetes, but their relation to the intra-islet pathogenetic process that leads to positivity for these markers is poorly understood. We screened 556 non-diabetic organ donors (3 months to 24 years) for five different autoantibodies and found positivity in 27 subjects, 25 single- and two double autoantibody-positive donors. Histopathological screening of pancreatic tissue samples showed lesion characteristic for recent-onset type 1 diabetes in the two organ donors with a high-risk profile, due to their positivity for multiple autoantibodies and HLA-inferred risk. Inflammatory infiltrates (insulitis) were found in a small fraction of islets (<5%) and consisted predominantly of CD3+CD8+ T-cells. Islets with insulitis were found in close proximity to islets devoid of insulin-positivity; such pseudo-atrophic islets were present in multiple small foci scattered throughout the pancreatic tissue or were found to be distributed with a lobular pattern. Relative beta cell area in both single and multiple autoantibody-positive donors was comparable to that in autoantibody-negative controls. In conclusion, in organ donors under age 25 years, insulitis and pseudo-atrophic islets were restricted to multiple autoantibody-positive individuals allegedly at high risk of developing symptomatic type 1 diabetes, in line with reports in older age groups. These observations may give further insight into the early pathogenetic events that may culminate in clinically overt disease.

Presumption of guilt for T cells in type 1 diabetes: lead culprits or partners in crime depending on age of onset?

Available evidence provides arguments both for and against a primary pathogenic role for T cells in human type 1 diabetes. Genetic susceptibility linked to HLA Class II lends strong support. Histopathology documents HLA Class I hyperexpression and islet infiltrates dominated by CD8+ T cells. While both hallmarks are near absent in autoantibody-positive donors, the variable insulitis and residual beta cells of recent-onset donors suggests the existence of a younger-onset endotype with more aggressive autoimmunity and an older-onset endotype with more vulnerable beta cells. Functional arguments from ex vivo and in vitro human studies and in vivo 'humanised' mouse models are instead neutral or against a T cell role. Clinical support is provided by the appearance of islet autoantibodies before disease onset. The faster C-peptide loss and superior benefits of immunotherapies in individuals with younger-onset type 1 diabetes reinforce the view of age-related endotypes. Clarifying the relative role of T cells will require technical advances in the identification of their target antigens, in their detection and phenotyping in the blood and pancreas, and in the study of the T cell/beta cell crosstalk. Critical steps toward this goal include the understanding of the link with environmental triggers, the description of T cell changes along the natural history of disease, and their relationship with age and the 'benign' islet autoimmunity of healthy individuals. Graphical abstract.

Oligonucleotide IMT504 Improves Glucose Metabolism and Controls Immune Cell Mediators in Female Diabetic NOD Mice

Type 1 diabetes occurs as a consequence of progressive autoimmune destruction of beta cells. A potential treatment for this disease should address the immune attack on beta cells and their preservation/regeneration. The objective of this study was to elucidate whether the immunomodulatory synthetic oligonucleotide IMT504 was able to ameliorate diabetes in NOD mice and to provide further understanding of its mechanism of action. We found that IMT504 restores glucose homeostasis in a diabetes mouse model similar to human type 1 diabetes, by regulating expression of immune modulatory factors and improving beta cell function. IMT504 treatment markedly improved fasting glycemia, insulinemia, and homeostatic model assessment of beta cell function (HOMA-Beta cell) index. Moreover, this treatment increased islet number and decreased apoptosis, insulitis, and CD45⁺ pancreas-infiltrating leukocytes. In a long-term treatment, we observed improvement of glucose metabolism up to 9 days after IMT504 cessation and increased survival after 15 days of the last IMT504 injection. We postulate that interleukin (IL)-12B (p40), possibly acting as a homodimer, and Galectin-3 (Gal-3) may function as mediators of this immunomodulatory action. Overall, these results validate the therapeutic activity of IMT504 as a promising drug for type 1 diabetes and suggest possible downstream mediators of its immunomodulatory effect.

Histological validation of a type 1 diabetes clinical diagnostic model for classification of diabetes

AIMS

Misclassification of diabetes is common due to an overlap in the clinical features of type 1 and type 2 diabetes. Combined diagnostic models incorporating clinical and biomarker information have recently been developed that can aid classification, but they have not been validated using pancreatic pathology. We evaluated a clinical diagnostic model against histologically defined type 1 diabetes.

METHODS

We classified cases from the Network for Pancreatic Organ donors with Diabetes (nPOD) biobank as type 1 (n = 111) or non-type 1 (n = 42) diabetes using histopathology. Type 1 diabetes was defined by lobular loss of insulin-containing islets along with multiple insulin-deficient islets. We assessed the discriminative performance of previously described type 1 diabetes diagnostic models, based on clinical features (age at diagnosis, BMI) and biomarker data [autoantibodies, type 1 diabetes genetic risk score (T1D-GRS)], and singular features for identifying type 1 diabetes by the area under the curve of the receiver operator characteristic (AUC-ROC).

RESULTS

Diagnostic models validated well against histologically defined type 1 diabetes. The model combining clinical features, islet autoantibodies and T1D-GRS was strongly discriminative of type 1 diabetes, and performed better than clinical features alone (AUC-ROC 0.97 vs. 0.95; P = 0.03). Histological classification of type 1 diabetes was concordant with serum C-peptide [median < 17 pmol/l (limit of detection) vs. 1037 pmol/l in non-type 1 diabetes; P < 0.0001].

CONCLUSIONS

Our study provides robust histological evidence that a clinical diagnostic model, combining clinical features and biomarkers, could improve diabetes classification. Our study also provides reassurance that a C-peptide-based definition of type 1 diabetes is an appropriate surrogate outcome that can be used in large clinical studies where histological definition is impossible. Parts of this study were presented in abstract form at the Network for Pancreatic Organ Donors Conference, Florida, USA, 19-22 February 2019 and Diabetes UK Professional Conference, Liverpool, UK, 6-8 March 2019.

Loss of sympathetic innervation to islets of Langerhans in canine diabetes and pancreatitis is not associated with insulitis

Canine diabetes mellitus (DM) affects 0.6% of the canine population and yet, its etiology is poorly understood. Most affected dogs are diagnosed as adults and are insulin-dependent. We compared pan-leukocyte and sympathetic innervation markers in pancreatic islets of adult dogs with spontaneous DM (sDM), spontaneous pancreatitis (sPanc), both (sDMPanc), toxin-induced DM (iDM) and controls. We found evidence of decreased islet sympathetic innervation but no significant infiltration of islets with leukocytes in all disease groups. We show that loss of sympathetic innervation is ongoing in canine DM and does not necessarily precede it. We further found selective loss of islet-associated beta cells in dogs with sDM and sDMPanc, suggesting that collateral damage from inflammation in the exocrine pancreas is not a likely cause of DM in these dogs. The cause of this selective loss of beta cells needs to be further elucidated but overall, our findings are not supportive of an autoimmune process as a cause of sDM in adult dogs. The loss of sympathetic innervation in sPanc in dogs that do not suffer from DM links the disease in the exocrine pancreas to a pathological process in the endocrine pancreas, suggesting pancreatitis might be a potential precursor to DM.

Organisation of the human pancreas in health and in diabetes

For much of the last century, our knowledge regarding the pancreas in type 1 and type 2 diabetes was largely derived from autopsy studies of individuals with these disorders or investigations utilising rodent models of either disease. While many important insights emanated from these efforts, the mode for investigation has increasingly seen change due to the availability of transplant-quality organ-donor tissues, improvements in pancreatic imaging, advances in metabolic assessments of living patients, genetic analyses, technological advances for laboratory investigation and more. As a result, many long-standing notions regarding the role for and the changes that occur in the pancreas in individuals with these disorders have come under question, while, at the same time, new issues (e.g., beta cell persistence, disease heterogeneity, exocrine contributions) have arisen. In this article, we will consider the vital role of the pancreas in human health and physiology, including discussion of its anatomical features and dual (exocrine and endocrine) functions. Specifically, we convey changes that occur in the pancreas of those with either type 1 or type 2 diabetes, with careful attention to the facets that may contribute to the pathogenesis of either disorder. Finally, we discuss the emerging unknowns with the belief that understanding the role of the pancreas in type 1 and type 2 diabetes will lead to improvements in disease diagnosis, understanding of disease heterogeneity and optimisation of treatments at a personalised level. Graphical abstract.

Protective effects of acarbose against insulitis in multiple low-dose streptozotocin-induced diabetic mice

AIMS

The development of type 1 diabetes is associated with inflammatory lesion of the pancreatic islets, known as insulitis. In this study, we focused on the protective effects of acarbose against insulitis in streptozotocin (STZ)-induced diabetic mice and the underlying mechanisms.

MAIN METHODS

The mouse models were established via intraperitoneal injection of multiple low-dose STZ. Blood glucose level and body weight were measured. The severity of insulitis and inflammatory parameters in pancreatic tissues were evaluated. Insulin levels in pancreas and serum were also assessed. In vitro, MIN6 β cells were exposed to pro-inflammatory cytokines to assess the protective effects of acarbose. Cell function and apoptosis were evaluated.

KEY FINDINGS

We found that acarbose administration by gavage reduced the severity of insulitis and improved insulin levels in the experimental diabetic mice. ELISA revealed decreased levels of the inflammatory response markers IL-1β and TNF-α in mouse pancreatic tissues following acarbose treatment. In vitro, acarbose increased cell viability, decreased cell apoptosis, and improved GSIS in MIN6 β cells exposed to pro-inflammatory cytokines. In addition, caspase-3 level and p-p53/p53 ratio in β cells were reduced by acarbose treatment.

SIGNIFICANCE

Taken together, these results revealed a novel function of acarbose in attenuating insulitis. The protective effects of acarbose elicited in vitro and in vivo were shown to be mediated, at least in part, through its anti-inflammatory action.

Insulitis and lymphoid structures in the islets of Langerhans of a 66-year-old patient with long-standing type 1 diabetes

Insulitis is a characteristic inflammatory lesion consisting of immune cell infiltrates around and within the pancreatic islets of patients with recent-onset type 1 diabetes (T1D). The infiltration is typically mild, both in terms of the number of infiltrating cells and the number of islets affected. Here, we present an unusual histopathological case study of a 66-year-old female patient with long-standing T1D, insulitis, and islet-associated lymphoid tissue. Most islets in the head of the pancreas of this patient were insulin-deficient, whereas the islets in the tail appeared normal. Insulitis was present in 0.84% of the insulin-containing islets and three islets had large lymphocytic infiltrates resembling tertiary lymphoid structures (TLS). Of note, this is the first description of potential TLS in the endocrine pancreas of a patient with T1D. Their association with a marked residual beta cell mass is of interest and may hint at new insights into disease progression and regulation of autoimmunity.

Secretory Functions of Macrophages in the Human Pancreatic Islet Are Regulated by Endogenous Purinergic Signaling

Endocrine cells of the pancreatic islet interact with their microenvironment to maintain tissue homeostasis. Communication with local macrophages is particularly important in this context, but the homeostatic functions of human islet macrophages are not known. In this study, we show that the human islet contains macrophages in perivascular regions that are the main local source of the anti-inflammatory cytokine interleukin-10 (IL-10) and the metalloproteinase MMP9. Macrophage production and secretion of these homeostatic factors are controlled by endogenous purinergic signals. In obese and diabetic states, macrophage expression of purinergic receptors MMP9 and IL-10 is reduced. We propose that in those states, exacerbated β-cell activity due to increased insulin demand and increased cell death produce high levels of ATP that downregulate purinergic receptor expression. Loss of ATP sensing in macrophages may reduce their secretory capacity.

Pancreas Pathology of Latent Autoimmune Diabetes in Adults (LADA) in Patients and in a LADA Rat Model Compared With Type 1 Diabetes

Approximately 10% of patients with type 2 diabetes suffer from latent autoimmune diabetes in adults (LADA). This study provides a systematic assessment of the pathology of the endocrine pancreas of patients with LADA and for comparison in a first rat model mimicking the characteristics of patients with LADA. Islets in human and rat pancreases were analyzed by immunohistochemistry for immune cell infiltrate composition, by in situ RT-PCR and quantitative real-time PCR of laser microdissected islets for gene expression of proinflammatory cytokines, the proliferation marker proliferating cell nuclear antigen (PCNA), the anti-inflammatory cytokine interleukin (IL) 10, and the apoptosis markers caspase 3 and TUNEL as well as insulin. Human and rat LADA pancreases showed differences in areas of the pancreas with respect to immune cell infiltration and a changed ratio between the number of macrophages and CD8 T cells toward macrophages in the islet infiltrate. Gene expression analyses revealed a changed ratio due to an increase of IL-1β and a decrease of tumor necrosis factor-α. IL-10, PCNA, and insulin expression were increased in the LADA situation, whereas caspase 3 gene expression was reduced. The analyses into the underlying pathology in human as well as rat LADA pancreases provided identical results, allowing the conclusion that LADA is a milder form of autoimmune diabetes in patients of an advanced age.

Hyaluronan deposition in islets may precede and direct the location of islet immune-cell infiltrates

AIMS/HYPOTHESIS

Substantial deposition of the extracellular matrix component hyaluronan (HA) is characteristic of insulitis in overt type 1 diabetes. We investigated whether HA accumulation is detectable in islets early in disease pathogenesis and how this affects the development of insulitis and beta cell mass.

METHODS

Pancreas tissue from 15 non-diabetic organ donors who were positive for islet autoantibodies (aAbs) and from 14 similarly aged aAb^- control donors were examined for the amount of islet HA staining and the presence of insulitis. The kinetics of HA deposition in islets, along with the onset and progression of insulitis and changes in beta cell mass, were investigated in BioBreeding DRLyp/Lyp rats (a model of spontaneous autoimmune diabetes) from 40 days of age until diabetes onset.

RESULTS

Abundant islet HA deposits were observed in pancreas tissues from n = 3 single- and n = 4 double-aAb⁺ donors (aAb⁺HA^high). In these seven tissues, the HA-stained areas in islets measured 1000 ± 240 μm² (mean ± SEM) and were fourfold larger than those from aAb^- control tissues. The aAb⁺HA^high tissues also had a greater prevalence of islets that were highly rich in HA (21% of the islets in these tissues contained the largest HA-stained areas [>2000 μm²] vs less than 1% in tissues from aAb^- control donors). The amount of HA staining in islets was associated with the number of aAbs (i.e. single- or double-aAb positivity) but not with HLA genotype or changes in beta cell mass. Among the seven aAb⁺HA^high tissues, three from single- and one from double-aAb⁺ donors did not show any islet immune-cell infiltrates, indicating that HA accumulates in aAb⁺ donors independently of insulitis. The three aAb⁺HA^high tissues that exhibited insulitis had the largest HA-stained areas and, in these tissues, islet-infiltrating immune cells co-localised with the most prominent HA deposits (i.e. with HA-stained areas >2000 μm²). Accumulation of HA in islets was evident prior to insulitis in 7-8-week-old presymptomatic DRLyp/Lyp rats, in which the islet HA-stained area measured 2370 ± 170 μm² (mean ± SEM), which was threefold larger than in 6-week-old rats. This initial islet HA deposition was not concurrent with beta cell loss. Insulitis was first detected in 9-10-week-old rats, in which the HA-stained areas were 4980 ± 500 μm². At this age, the rats also exhibited a 44% reduction in beta cell mass. Further enlargement of the HA-positive areas (mean ± SEM: 7220 ± 880 μm²) was associated with invasive insulitis. HA deposits remained abundant in the islets of rats with destructive insulitis, which had lost 85% of their beta cells.

CONCLUSIONS/INTERPRETATION

This study indicates that HA deposition in islets occurs early in type 1 diabetes and prior to insulitis, and points to a potential role of HA in triggering islet immune-cell infiltration and the promotion of insulitis.