The Ups and Downs of Type 1 Diabetes
Von Herrath and his teams at DIDNRI and the translational diabetes center at Novo Nordisk discovered that type 1 diabetes doesn’t progress steadily but instead occurs in a nonlinear pattern physicians call relapsing/remitting. During the “pre-diabetic” and possibly asymptomatic period, T cell populations likely shift back and forth between cytotoxic and more benign players before beta cells undergo total destruction (and patients seek treatment).
This means that there is a window of time, potentially detectable, during which loss of irreplaceable pancreatic cells that could be prevented by drugs that modulate the immune response. Von Herrath’s work also hints that viral infection may accelerate disease progression, and high on his current list of suspects is human herpesvirus 6 (HVP6). Interestingly, HVP6 has also been linked to autoimmune destruction of the thyroid gland (in Hashimoto’s Disease) and to multiple sclerosis.
Ongoing Research Projects
SPECIFICITY OF PANCREATIC CD8 T CELLS IN HUMAN TYPE 1 DIABETES
A better understanding of how type 1 diabetes (T1D) develops is the first step to potentially develop new therapies capable of preventing or permanently reversing the disease. Due to the inaccessibility to human pancreatic tissue, our knowledge of the disease in humans is limited. Although mouse models have been a very useful tool for the past 30 years, humans show different islet architecture and islet cell distribution compared to rodent islets. These differences might have impacted therapeutic outcomes, which worked well in mouse models but frequently do not translate to humans, and might explain why developing efficient new therapies has been challenging.
More recently, autopsy studies of pancreas samples obtained from a limited number of individuals with T1D have challenged longstanding dogmas of how T1D develops. The Network for Pancreatic Organ donors with Diabetes (nPOD) was established with the idea of providing valuable tissues from healthy and diabetic donors in order to answer basic questions about the pathogenesis of T1D. Thanks to the nPOD program, we can study the pancreas, spleen and lymph nodes from donors with T1D in order to determine if the T cells identified in mouse models (T cells reactive against beta cell proteins or autoreactive T cells) are the same cells that destroy beta cells in human T1D and what their distribution and activation status is in the pancreas and in other tissues. I am also interested in the possible role of viral infections and whether they could make islets more accessible for these destructive, autoreactive T cells or vice versa.
CHARACTERIZATION OF BETA CELL MASS AND FUNCTION DURING THE PRE-DIABETIC PHASE
In 1986 Prof. George Eisenbarth proposed a model of disease progression that postulated a linear beta cell mass decay during the pre-diabetic phase. However, genetic factors and environmental triggers like viral infections are likely to contribute to fluctuations in beta cell mass before disease onset. Therefore, a nonlinear model depicting T1D as a “relapsing-remitting” disease has also been proposed. In addition, it has recently been shown that beta cell destruction and metabolic dysfunction are events closely associated with disease onset. Importantly, recent studies have demonstrated that during the prediabetic phase there are detectable episodes of beta cell dysfunction and killing that culminate in a peak in beta cell death before the onset of disease.
Autoantibody positive individuals might offer insight into the early events underlying diabetes development. I am investigating potential changes in beta cell mass in the pancreas of non-diabetic autoantibody positive individuals, in order to compare them to healthy, non-diabetic donors. Our findings could potentially show how beta cells change in early stages of the disease and if there is an alteration of the insulin ratio that could indicate a defect on their function.
ROLE OF HHV-6 IN THE PATHOGENESIS OF TYPE 1 DIABETES
Type 1 diabetes (T1D) is an autoimmune disease causing the destruction of insulin-producing beta cells in the pancreatic islets. Immunopathogenesis of T1D is still unknown. There are lines of evidence suggesting that both environmental factors such as viruses and genetic susceptibility play an important role in triggering the disease. However, there is still no direct link between viral infection and T1D.
Human herpesvirus 6 (HHV-6) is a ubiquitous pathogen of the beta-herpesvirus family. It has been proposed that HHV-6 plays a role in several autoimmune disorders such as multiple sclerosis, autoimmune connective tissue diseases, and Hashimoto’s thyroiditis. However, little is known about the involvement of HHV-6 infection in the pathogenesis of T1D. GlycoproteinB (gpB) is conserved in all herpesviruses and is known for playing a critical role during the membrane fusion and viral infection. To explore the role of HHV-6 in the pathogenesis of T1D, we obtained pancreatic tissue sections from T1D, autoantibody positive, and non-diabetic donors provided by the Network for Pancreatic Organ Donors with Diabetes (nPOD). The presence of HHV-6 gpB will be analyzed at the protein level by indirect immunofluorescence.
This study will allow us to identify the virally infected cells within the pancreas in order to define a potential mechanism of action of the virus at the cellular level. Furthermore, the correlation between gpB and MHC-I expression, a hallmark in early T1D, will be elucidated within the pancreas of the pre-diabetic and diabetic patients. Here we speculate that herpesvirus infection might be a contributing factor to T1D pathogenesis. In combination with genetic susceptibility, the strength of the cellular and humoral immune response to virus infection might contribute to autoimmunity. This study will help to determine a possible role of herpersviruses in the immunopathogenesis of T1D which can lead to preventative measures for future clinical trials.
IDO1 AND IL-6 EXPRESSION IN PANCREATIC ISLETS FROM DIABETIC SUBJECTS AS A BIOMARKER FOR T1D PATIENTS
Indoleamine 2,3-dioxygenase 1 (IDO1) is a metabolic enzyme catalyzing the conversion of tryptophan into kynurenines, whose catalytic and non-catalytic effects are involved in the regulation of immunity and in autoimmune diseases. Cytokines are a key modulator of the expression of IDO1: interferon-γ upregulates the enzyme in dendritic cells whereas interleukin 6 (IL-6) promotes proteasomal degradation of IDO1. Current data show that most of children with type 1 diabetes (T1D) have a genetic or postranslational defect in IDO1 expression and activity in peripheral blood mononuclear cells (PBMCs). Interestingly, this phenotype can be corrected by incubation of PBMCs with tocilizumab, a licensed IL-6 receptor blocker. The same drug may also control hyperglycemia in non-obese diabetic mice with overt diabetes. Therefore, a subset of individuals with T1D may gain clinical benefit in restoring IDO1 immunoregulatory mechanisms by treatment with tocilizumab.
I aim at verifying whether the phenotype identified in PBMCs may also be demonstrated in pancreata by using tissue specimens obtainable from the network of Pancreatic Organ Donors. If the results confirms our hypothesis, this study could lead to a new course of treatment in T1D.
PHENOTYPE OF PANCREATIC CD8 T CELLS IN HUMAN TYPE 1 DIABETES
Type 1 diabetes (T1D) is one of the most common chronic diseases of childhood in which insulin producing-cells are targeted by the immune system, leading to their destruction mainly by T cells, However, only limited data are available on the phenotype of the T cell implicated in the destruction process through the course of T1D.
For a long time, the study of human diabetic pancreata has been challenging due to a scarce access to the target organ. Recently, the Network for Pancreatic Organ donors with Diabetes (nPOD) was founded for the purpose of obtaining tissues from organ donors and has created a new opportunity to study the pathogenesis of T1D and better understand the local tissue environment.
This project will allows to determine the specific subsets of T cells present in pancreata from donors with T1D, pre-diabetic or control donors and provide the first detailed mapping of T cells in T1D .
IN SITU EXPRESSION OF IL-1BETA IN PANCREAS FROM DIABETIC PATIENTS
Somayeh Sabouri and Florence Anquetil
Type 1 diabetes (T1D) is an autoimmune disease that is characterized by the progressive loss of beta cells. During the last 30 years, intense efforts have been made to understand the role of cytokines in the pathogenesis of T1D. IL-1β has emerged as an interesting candidate due to its modulating effects on innate and adaptive immune responses and its role in promoting beta cell dysfunction and apoptosis in vitro.
However, recent trials using targeted IL-1 blockade in patients with T1D have failed to provide benefit and a trial in patients with Type 2 Diabetes (T2D) provided only limited benefits.
Thus, the role of IL-1 in diabetes pathogenesis is not clear and we aim at re-evaluating the presence of IL-1β in human pancreas in a systematic manner.
TRAFFICKING AND SUPPRESSION BY REGULATORY T CELLS IN SITU DURING ONSET OF TYPE 1 DIABETES
Regulatory T cells and their actions have been extensively studied over decades in various models of autoimmunity. Harnessing the immune-regulatory properties of these cells has been the aim of many a venture on the translational end of autoimmune research. To this day, no major breakthrough has been made using these cells for cell-based therapies. In this project, we use a broad definition of “Tregs”, and investigate immune regulation performed by ‘non-conventional’ Tregs (we could also call them inducible or situation-dependent Tregs). Their function during autoimmunity is poorly understood, and detailed information on actions and true identity of these cells are lacking.
To study these events we apply both macroscopic and microscopic views on Treg trafficking and actions. Using the lab’s established method for intravital multiphoton imaging of the pancreas, high-resolved information on their behavior in the islet inflammation is gained. A whole-animal view of the trafficking and expansion of these immune cell subsets are achieved by multicolor flow cytometry in innovative fluorescent reporter strains. This two-pronged approach will enable us to get a broader picture of the immune regulation at play during type 1 diabetes.
ANTIGEN SPECIFICITY IN CD8+ T CELL INFILTRATION, KILLING, AND SUPPRESSION AT THE PANCREATIC ISLETS
Among the CD8+ cytotoxic T lymphocytes (CTL) found at inflamed islets in the pancreata of diabetic patients, very few are specific to antigens expressed in the islet. Very little is known about the activation, recruitment, or function of these non-specific cells. They are generally thought to add to islet damage through release of cytokines, but immune-suppressive effects from the presence of bystander CTLs have been described in other models.
Using well-defined antigen-driven models of type 1 diabetes, and state-of-the-art intravital multiphoton imaging, we are assessing CTL trafficking and actions. We are also mapping the phenotypes of CTLs present at islets in with regard to their expression of activation/suppression markers, and their secretome. We will also assess the islet microenvironment for metabolic and nutritional changes induced by bystander accumulation. Mapping the actions of both drivers and bystanders in type 1 diabetes is key to understanding the course of this disease. Insights into novel regulatory mechanisms during autoimmunity will increase the number of cellular tools available for modulating the autoimmune disease progression.
NEURO-IMMUNE CROSSTALK IN THE PANCREAS DURING ONSET OF TYPE 1 DIABETES
The histopathologic features of human type 1 diabetes are remarkably heterogeneous throughout the pancreas. One lobule of the organ can appear completely unaffected by the ongoing autoimmune disease, while the neighboring lobule is lacking any sign of an insulin producing beta cell. The reasons for this pattern may be several, including viral or bacterial infection, anatomical features, or neuronal influence.
In an enigmatic disease such as type 1 diabetes, we are now looking into paths less treaded upon to try to find the underlying mechanisms to the disease. Neuronal input has been shown to have great impact on immune cell function in other autoimmune disorders such as multiple sclerosis. The neuronal influence in the onset of type 1 diabetes is investigated in this project, where nerve input to the pancreas is modulated in several ways. The effect on diabetes onset and progression is followed, and possible behavioral changes in immune cell subsets are monitored by intravital multiphoton microscopy of the pancreas.
DIABETES NEURO-(AUTO)IMMUNE MODULATION
Autoreactivity to a set of self-components are present in the immune repertoire of healthy individuals, which may later develop autoimmune diseases. Type 1 Diabetes (T1D) is a prototype autoimmune disease, consequence of the insulin-producing islet ß-cells destruction by antigen-specific T-cells trafficking to the pancreas. However, neuro-immune networks may contribute to this process. Therefore, we are exploring whether nervous system antigen-reactive T-cells may modulate T1D pathogenesis. Potential dynamic cross-interference would help further understanding the layer of complexity integrating immune regulatory mechanisms governing the onset and progression of autoimmune diseases, and eventually devising novel therapeutic approaches.