Mapping of a hybrid insulin peptide in the inflamed islet β-cells from NOD mice

There is accumulating evidence that pathogenic T cells in T1D recognize epitopes formed by post-translational modifications of β-cell antigens, including hybrid insulin peptides (HIPs). The ligands for several CD4 T-cell clones derived from the NOD mouse are HIPs composed of a fragment of proinsulin joined to peptides from endogenous β-cell granule proteins. The diabetogenic T-cell clone BDC-6.9 reacts to a fragment of C-peptide fused to a cleavage product of pro-islet amyloid polypeptide (6.9HIP). In this study, we used a monoclonal antibody (MAb) to the 6.9HIP to determine when and where HIP antigens are present in NOD islets during disease progression and with which immune cells they associate. Immunogold labeling of the 6.9HIP MAb and organelle-specific markers for electron microscopy were employed to map the subcellular compartment(s) in which the HIP is localized within β-cells. While the insulin B9-23 peptide was present in nearly all islets, the 6.9HIP MAb stained infiltrated islets only in NOD mice at advanced stages of T1D development. Islets co-stained with the 6.9HIP MAb and antibodies to mark insulin, macrophages, and dendritic cells indicate that 6.9HIP co-localizes within insulin-positive β-cells as well as intra-islet antigen-presenting cells (APCs). In electron micrographs, the 6.9HIP co-localized with granule structures containing insulin alone or both insulin and LAMP1 within β-cells. Exposing NOD islets to the endoplasmic reticulum (ER) stress inducer tunicamycin significantly increased levels of 6.9HIP in subcellular fractions containing crinosomes and dense-core granules (DCGs). This work demonstrates that the 6.9HIP can be visualized in the infiltrated islets and suggests that intra-islet APCs may acquire and present HIP antigens within islets.

The Impact of Vitamin A Deficiency on Tuberculosis Progression

BACKGROUND

Although previous studies have shown that vitamin A deficiency is associated with incident tuberculosis (TB) disease, the direction of the association has not been established. We investigated the impact of vitamin A deficiency on TB disease progression.

METHODS

We conducted a longitudinal cohort study nested within a randomized clinical trial among HIV-infected patients in Haiti. We compared serial vitamin A levels in individuals who developed TB disease to controls matched on age, gender, follow-up time, and time to antiretroviral therapy initiation. We also evaluated histopathology, bacterial load, and immune outcomes in TB infection in a guinea pig model of dietary vitamin A deficiency.

RESULTS

Among 773 participants, 96 developed incident TB during follow-up, 62.5% (60) of whom had stored serum samples obtained 90-365 days before TB diagnosis. In age- and sex- adjusted and multivariate analyses, respectively, incident TB cases were 3.99 times (95% confidence interval [CI], 2.41 to 6.60) and 3.59 times (95% CI, 2.05 to 6.29) more likely to have been vitamin A deficient than matched controls. Vitamin A-deficient guinea pigs manifested more extensive pulmonary pathology, atypical granuloma morphology, and increased bacterial growth after experimental TB infection. Reintroduction of dietary vitamin A to deficient guinea pigs after established TB disease successfully abrogated severe disease manifestations and altered cellular immune profiles.

CONCLUSIONS

Human and animal studies support the role of baseline vitamin A deficiency as a determinant of future TB disease progression.

Insulin B-chain hybrid peptides are agonists for T cells reactive to insulin B:9-23 in autoimmune diabetes

Insulin is considered to be a key antigenic target of T cells in Type 1 Diabetes (T1D) and autoimmune diabetes in the NOD mouse with particular focus on the B-chain amino acid sequence B:9-23 as the primary epitope. Our lab previously discovered that hybrid insulin peptides (HIPs), comprised of insulin C-peptide fragments fused to other β-cell granule peptides, are ligands for several pathogenic CD4 T cell clones derived from NOD mice and for autoreactive CD4 T cells from T1D patients. A subset of CD4 T cell clones from our panel react to insulin and B:9-23 but only at high concentrations of antigen. We hypothesized that HIPs might also be formed from insulin B-chain sequences covalently bound to other endogenously cleaved ß-cell proteins. We report here on the identification of a B-chain HIP, termed the 6.3HIP, containing a fragment of B:9-23 joined to an endogenously processed peptide of ProSAAS, as a strong neo-epitope for the insulin-reactive CD4 T cell clone BDC-6.3. Using an I-Ag7 tetramer loaded with the 6.3HIP, we demonstrate that T cells reactive to this B-chain HIP can be readily detected in NOD mouse islet infiltrates. This work suggests that some portion of autoreactive T cells stimulated by insulin B:9-23 may be responding to B-chain HIPs as peptide ligands.

Induction of tolerance to a CD4 T cell hybrid insulin peptide epitope prolongs islet graft survival and suppresses autoreactive CD8 T cells

Autoreactive T cells are thought to drive autoimmune diabetes by recognizing beta cell-derived peptide antigens. We previously discovered that hybrid insulin peptides (HIPs) are potent neoantigen peptide ligands for a subset of autoreactive CD4 T cells in both the NOD mouse model and human type 1 diabetes patients. Inducing tolerance to prominent T cell autoantigens through antigen-specific immunotherapy could prevent disease onset or recurrence after islet transplantation without the need for broad immunosuppression. Here we show that tolerogenic nanoparticle (NP) delivery of the 2.5HIP, a dominant CD4 T cell HIP epitope in the NOD mouse, can prolong islet graft survival in transplanted diabetic NOD mice. Tolerance induction to the 2.5HIP not only suppressed 2.5HIP tetramer+ CD4 T cells but also autoreactive CD4 and CD8 T cells specific for different islet antigens. 2.5HIP NP treatment induced a dysfunctional state in graft-infiltrating T cells characterized by increased expression of anergic markers on CD4 T cells and reduced inflammatory cytokine production in 2.5HIP tetramer+ CD4 T cells as well as IGRP (islet specific glucose-6-phosphatase catalytic subunit-related protein) tetramer+ CD8 T cells. In conclusion, we demonstrate that antigen-specific immunotherapy aimed at inducing tolerance to a single CD4 T cell HIP epitope can prolong islet graft survival and suppress autoreactive CD8 T cells in the NOD mouse model of autoimmune diabetes.

Supported by grants from NIH (R01 DK122566, R01 DK081166, T32 DK120520)  and JDRF (2-SRA-2018-566-S-B)

Tolerogenic Delivery of a Hybrid Insulin Peptide Markedly Prolongs Islet Graft Survival in the NOD Mouse

The induction of antigen (Ag)-specific tolerance and replacement of islet β-cells are major ongoing goals for the treatment of type 1 diabetes (T1D). Our group previously showed that a hybrid insulin peptide (2.5HIP) is a critical autoantigen for diabetogenic CD4+ T cells in the NOD mouse model. In this study, we investigated whether induction of Ag-specific tolerance using 2.5HIP-coupled tolerogenic nanoparticles (NPs) could protect diabetic NOD mice from disease recurrence upon syngeneic islet transplantation. Islet graft survival was significantly prolonged in mice treated with 2.5HIP NPs, but not NPs containing the insulin B chain peptide 9-23. Protection in 2.5HIP NP-treated mice was attributed both to the simultaneous induction of anergy in 2.5HIP-specific effector T cells and the expansion of Foxp3+ regulatory T cells specific for the same Ag. Notably, our results indicate that effector function of graft-infiltrating CD4+ and CD8+ T cells specific for other β-cell epitopes was significantly impaired, suggesting a novel mechanism of therapeutically induced linked suppression. This work establishes that tolerance induction with an HIP can delay recurrent autoimmunity in NOD mice, which could inform the development of an Ag-specific therapy for T1D.

Induction of Antigen-Specific Tolerance in Autoimmune Diabetes with Nanoparticles Containing Hybrid Insulin Peptides

Autoreactive T cells are thought to orchestrate the onset and progression of autoimmune diabetes. Key cognate antigens of these diabetogenic T cells include hybrid insulin peptides, formed by the fusion of insulin fragments to cleavage products of other β-cell granule proteins. Here we review initial work exploring tolerance induction to a hybrid insulin peptide using a biodegradable, nanoparticle delivery system in non-obese diabetic (NOD) mice. The immune phenotype(s) and possible mechanism(s) behind antigen-specific tolerance induction were dissected with a disease transfer model using transgenic autoreactive mouse T cells. Treatment of NOD mice with peptide-coupled nanoparticles appeared to have a dual function in preventing diabetes onset, inducing anergy in effector T cells and enhancing the activity of regulatory T cells. Importantly, the ratio of these two cell types in the pancreas was pushed toward tolerance. Antigen-specific tolerance induction to hybrid insulin peptides has the translational potential to preserve islet β-cells in new-onset or at-risk patients and prevent recurrent autoimmunity in transplant patients.

A model of type 2 diabetes in the guinea pig using sequential diet-induced glucose intolerance and streptozotocin treatment

Type 2 diabetes is a leading cause of morbidity and mortality among noncommunicable diseases, and additional animal models that more closely replicate the pathogenesis of human type 2 diabetes are needed. The goal of this study was to develop a model of type 2 diabetes in guinea pigs, in which diet-induced glucose intolerance precedes β-cell cytotoxicity, two processes that are crucial to the development of human type 2 diabetes. Guinea pigs developed impaired glucose tolerance after 8 weeks of feeding on a high-fat, high-carbohydrate diet, as determined by oral glucose challenge. Diet-induced glucose intolerance was accompanied by β-cell hyperplasia, compensatory hyperinsulinemia, and dyslipidemia with hepatocellular steatosis. Streptozotocin (STZ) treatment alone was ineffective at inducing diabetic hyperglycemia in guinea pigs, which failed to develop sustained glucose intolerance or fasting hyperglycemia and returned to euglycemia within 21 days after treatment. However, when high-fat, high-carbohydrate diet-fed guinea pigs were treated with STZ, glucose intolerance and fasting hyperglycemia persisted beyond 21 days post-STZ treatment. Guinea pigs with diet-induced glucose intolerance subsequently treated with STZ demonstrated an insulin-secretory capacity consistent with insulin-independent diabetes. This insulin-independent state was confirmed by response to oral antihyperglycemic drugs, metformin and glipizide, which resolved glucose intolerance and extended survival compared with guinea pigs with uncontrolled diabetes. In this study, we have developed a model of sequential glucose intolerance and β-cell loss, through high-fat, high-carbohydrate diet and extensive optimization of STZ treatment in the guinea pig, which closely resembles human type 2 diabetes. This model will prove useful in the study of insulin-independent diabetes pathogenesis with or without comorbidities, where the guinea pig serves as a relevant model species.