Interference with islet-specific homing of autoreactive T cells: an emerging therapeutic strategy for type 1 diabetes

Integrin Regulated Autoimmune Disorders: Understanding the Role of Mechanical Force in Autoimmunity

The pathophysiology of autoimmune disorders is multifactorial, where immune cell migration, adhesion, and lymphocyte activation play crucial roles in its progression. These immune processes are majorly regulated by adhesion molecules at cell–extracellular matrix (ECM) and cell–cell junctions. Integrin, a transmembrane focal adhesion protein, plays an indispensable role in these immune cell mechanisms. Notably, integrin is regulated by mechanical force and exhibit bidirectional force transmission from both the ECM and cytosol, regulating the immune processes. Recently, integrin mechanosensitivity has been reported in different immune cell processes; however, the underlying mechanics of these integrin-mediated mechanical processes in autoimmunity still remains elusive. In this review, we have discussed how integrin-mediated mechanotransduction could be a linchpin factor in the causation and progression of autoimmune disorders. We have provided an insight into how tissue stiffness exhibits a positive correlation with the autoimmune diseases’ prevalence. This provides a plausible connection between mechanical load and autoimmunity. Overall, gaining insight into the role of mechanical force in diverse immune cell processes and their dysregulation during autoimmune disorders will open a new horizon to understand this physiological anomaly.

Extracellular microparticles derived from hepatic progenitor cells deliver a death signal to hepatoma-initiating cells

The malignant transformation of normal resident hepatic stem/progenitor cells has a critical role in hepatocarcinogenesis and the recurrence of hepatocellular carcinoma (HCC). We defined such hepatic progenitor cells as hepatoma-initiating cells. An efficient strategy is required to target and kill the hepatoma-initiating cells. We isolated extracellular microparticles (MPs) derived from apoptotic hepatic progenitor cells (HPCs) and tested their ability to inhibit hepatocarcinogenesis. Extracellular MPs were isolated from HPCs, hepatocytes and liver tumor cells. Their effects on tumor growth were investigated in rat primary HCC models, in which hepatocarcinogenesis is induced by diethylnitrosamine (DEN). The extracellular MPs derived from apoptotic HPCs, apoptotic hepatocytes and apoptotic liver tumor cells were similar in morphology, diameter and zeta potential. However, they had different antitumor effects. In DEN-exposed rats, only the MPs derived from apoptotic HPCs effectively inhibit hepatocarcinogenesis. In vitro and in vivo analyses confirmed that HPCs preferentially take up MPs derived from apoptotic HPCs compared to MPs from other liver cell types. Proteomic analysis of MPs from apoptotic HPCs showed enrichment of proteins involved in cell death pathways. Thus, HPC-derived MPs contain a death signal to induce the killing of hepatoma-initiating cells. Our findings provide evidence that a death signal encapsulated in HPC-derived extracellular microparticles can efficiently clear hepatoma-initiating cells and prevent hepatocarcinogenesis.

Graphical Abstract

Early-life fingolimod treatment improves intestinal homeostasis and pancreatic immune tolerance in non-obese diabetic mice

Fingolimod has beneficial effects on multiple diseases, including type 1 diabetes (T1D) and numerous preclinical models of colitis. Intestinal dysbiosis and intestinal immune dysfunction contribute to disease pathogenesis of T1D. Thus, the beneficial effect of fingolimod on T1D may occur via the maintenance of intestinal homeostasis to some extent. Herein, we investigated the role of fingolimod in intestinal dysfunction in non-obese diabetic (NOD) mice and possible mechanisms. NOD mice were treated with fingolimod (1 mg · kg-1 per day, i.g.) from weaning (3-week-old) to 31 weeks of age. We found that fingolimod administration significantly enhanced the gut barrier (evidenced by enhanced expression of tight junction proteins and reduced intestinal permeability), attenuated intestinal microbial dysbiosis (evidenced by the reduction of enteric pathogenic Proteobacteria clusters), as well as intestinal immune dysfunction (evidenced by inhibition of CD4+ cells activation, reduction of T helper type 1 cells and macrophages, and the expansion of regulatory T cells). We further revealed that fingolimod administration suppressed the activation of CD4+ cells and the differentiation of T helper type 1 cells, promoted the expansion of regulatory T cells in the pancreas, which might contribute to the maintenance of pancreatic immune tolerance and the reduction of T1D incidence. The protection might be due to fingolimod inhibiting the toll-like receptor 2/4/nuclear factor-κB/NOD-like receptor protein 3 inflammasome pathway in the colon. Collectively, early-life fingolimod treatment attenuates intestinal microbial dysbiosis and intestinal immune dysfunction in the T1D setting, which might contribute to its anti-diabetic effect.

IFNγ-Induced MHC Class II Expression on Islet Endothelial Cells Is an Early Marker of Insulitis but Is Not Required for Diabetogenic CD4+ T Cell Migration

Diabetogenic T cells infiltrate the pancreatic islets by transmigrating across the microcapillaries residing close to, or within, the pancreatic islets. Deficiency in IFNγ signaling prevents efficient migration of T cells into the pancreatic islets, but the IFNγ-regulated molecules that mediate this are uncertain. Homing of autoreactive T cells into target tissues may require antigen specificity through presentation of cognate antigen by MHC expressed on the vascular endothelium. We investigated the hypothesis that IFNγ promotes the migration of islet antigen-specific CD4⁺ T cells by upregulating MHC class II on islet endothelial cells (IEC), thereby providing an antigen-specific signal for islet infiltration. Upon IFNγ stimulation, MHC class II, which is not constitutively expressed on IEC, was induced. IFNγ-dependent upregulation of MHC class II was detected in IEC isolated from prediabetic NOD mice at the earliest stages of insulitis, before other markers of inflammation were present. Using a CD4⁺ T cell-mediated adoptive transfer model of autoimmune diabetes we observed that even though diabetes does not develop in recipient mice lacking IFNγ receptors, mice with MHC class II-deficient IEC were not protected from disease. Thus, IFNγ-regulated molecules, but not MHC class II or antigen presentation by IECs is required for the early migration of antigen-specific CD4⁺ T cells into the pancreatic islets.

Gene therapy and type 1 diabetes mellitus

BACKGROUND

Type 1 diabetes mellitus (T1DM) is an autoimmune disorder characterized by T cell-mediated self-destruction of insulin-secreting islet β cells. Management of T1DM is challenging and complicated especially with conventional medications. Gene therapy has emerged as one of the potential therapeutic alternatives to treat T1DM. This review primarily focuses on the current status and the future perspectives of gene therapy in the management of T1DM. A vast number of the studies which are reported on gene therapy for the management of T1DM are done in animal models and in preclinical studies. In addition, the safety of such therapies is yet to be established in humans. Currently, there are several gene level interventions that are being investigated, notably, overexpression of genes and proteins needed against T1DM, transplantation of cells that express the genes against T1DM, stem-cells mediated gene therapy, genetic vaccination, immunological precursor cell-mediated gene therapy and vectors.

METHODS

We searched the current literature through searchable online databases, journals and other library sources using relevant keywords and search parameters. Only relevant publications in English, between the years 2000 and 2018, with evidences and proper citations, were considered. The publications were then analyzed and segregated into several subtopics based on common words and content. A total of 126 studies were found suitable for this review.

FINDINGS

Generally, the pros and cons of each of the gene-based therapies have been discussed based on the results collected from the literature. However, there are certain interventions that require further detailed studies to ensure their effectiveness. We have also highlighted the future direction and perspectives in gene therapy, which, researchers could benefit from.

The Type 1 Diabetes-Resistance Locus Idd22 Controls Trafficking of Autoreactive CTLs into the Pancreatic Islets of NOD Mice

Type 1 diabetes (T1D) has a strong genetic component. The insulin dependent diabetes (Idd)22 locus was identified in crosses of T1D-susceptible NOD mice with the strongly T1D-resistant ALR strain. The NODcALR-(D8Mit293-D8Mit137)/Mx (NOD-Idd22) recombinant congenic mouse strain was generated in which NOD mice carry the full Idd22 confidence interval. NOD-Idd22 mice exhibit almost complete protection from spontaneous T1D and a significant reduction in insulitis. Our goal was to unravel the mode of Idd22-based protection using in vivo and in vitro models. We determined that Idd22 did not impact immune cell diabetogenicity or β cell resistance to cytotoxicity in vitro. However, NOD-Idd22 mice were highly protected against adoptive transfer of T1D. Transferred CTLs trafficked to the pancreatic lymph node and proliferated to the same extent in NOD and NOD-Idd22 mice, yet the accumulation of pathogenic CTLs in the islets was significantly reduced in NOD-Idd22 mice, correlating with disease resistance. Pancreatic endothelial cells from NOD-Idd22 animals expressed lower levels of adhesion molecules, even in response to inflammatory stimuli. Lower adhesion molecule expression resulted in weaker adherence of T cells to NOD-Idd22 endothelium compared with NOD-derived endothelium. Taken together, these results provide evidence that Idd22 regulates the ability of β cell-autoreactive T cells to traffic into the pancreatic islets and may represent a new target for pharmaceutical intervention to potentially prevent T1D.

Autoimmune diabetes is suppressed by treatment with recombinant human tissue Kallikrein-1

The kallikrein-kinin system (KKS) comprises a cascade of proteolytic enzymes and biogenic peptides that regulate several physiological processes. Over-expression of tissue kallikrein-1 and modulation of the KKS shows beneficial effects on insulin sensitivity and other parameters relevant to type 2 diabetes mellitus. However, much less is known about the role of kallikreins, in particular tissue kallikrein-1, in type 1 diabetes mellitus (T1D). We report that chronic administration of recombinant human tissue kallikrein-1 protein (DM199) to non-obese diabetic mice delayed the onset of T1D, attenuated the degree of insulitis, and improved pancreatic beta cell mass in a dose- and treatment frequency-dependent manner. Suppression of the autoimmune reaction against pancreatic beta cells was evidenced by a reduction in the relative numbers of infiltrating cytotoxic lymphocytes and an increase in the relative numbers of regulatory T cells in the pancreas and pancreatic lymph nodes. These effects may be due in part to a DM199 treatment-dependent increase in active TGF-beta1. Treatment with DM199 also resulted in elevated C-peptide levels, elevated glucagon like peptide-1 levels and a reduction in dipeptidyl peptidase-4 activity. Overall, the data suggest that DM199 may have a beneficial effect on T1D by attenuating the autoimmune reaction and improving beta cell health.

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

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

Intravital imaging of CTLs killing islet cells in diabetic mice

Type 1 diabetes (T1D) is caused by autoimmune destruction of the insulin-producing β cells in the pancreatic islets, which are essentially mini-organs embedded in exocrine tissue. CTLs are considered to have a predominant role in the autoimmune destruction underlying T1D. Visualization of CTL-mediated killing of β cells would provide new insight into the pathogenesis of T1D, but has been technically challenging to achieve. Here, we report our use of intravital 2-photon imaging in mice to visualize the dynamic behavior of a virally expanded, diabetogenic CTL population in the pancreas at cellular resolution. Following vascular arrest and extravasation, CTLs adopted a random motility pattern throughout the compact exocrine tissue and displayed unimpeded yet nonlinear migration between anatomically nearby islets. Upon antigen encounter within islets, a confined motility pattern was acquired that allowed the CTLs to scan the target cell surface. A minority of infiltrating CTLs subsequently arrested at the β cell junction, while duration of stable CTL-target cell contact was on the order of hours. Slow-rate killing occurred in the sustained local presence of substantial numbers of effector cells. Collectively, these data portray the kinetics of CTL homing to and between antigenic target sites as a stochastic process at the sub-organ level and argue against a dominant influence of chemotactic gradients.