Recent insights into CD4+ T-cell specificity and function in type 1 diabetes

The role of islet autoantigen-specific T cells in the onset and treatment of type 1 diabetes mellitus

Type 1 diabetes mellitus (T1DM), a complex chronic disease with an intricate etiology and pathogenesis, involves the recognition of self-antigens by pancreatic islet autoantigen-specific T cells and plays crucial roles in both early- and late-stage destruction of beta cells, thus impacting disease progression. Antigen-specific T cells regulate and execute immune responses by recognizing particular antigens, playing broad roles in the treatment of various diseases. Immunotherapy targeting antigen-specific T cells holds promising potential as a targeted treatment approach. This review outlines the pathogenesis of diabetes, emphasizing the pivotal role of pancreatic islet autoantigen-specific T cells in the progression and treatment of T1DM. Exploring this avenue in research holds promise for identifying novel therapeutic targets for effectively managing diabetes.

Treatment of insulin-dependent diabetes by hematopoietic stem cell transplantation

Type 1 diabetes (T1D) is an autoimmune disease resulting from the demolition of β-cells that are responsible for producing insulin in the pancreas. Treatment with insulin (lifelong applying) and islet transplantation (in rare cases and severe diseases), are standards of care for T1D. Pancreas or islet transplantation have some limitations, such as lack of sufficient donors and longtime immune suppression for preventing allograft rejection. Recent studies demonstrate that autologous hematopoietic stem cells (HSC) can regenerate immune tolerance against auto-antigens. Taking advantage of this feature, autologous HSC transplantation (auto-HSCT) is likely the only treatment for T1D that is associated with lasting and complete remission. None of the other evaluated immunotherapies worldwide had the clinical efficacy of auto-HSCT. Therapy with auto-HSCT is insulin-independent rather than reducing insulin needs or delaying loss of insulin production. This review provided the latest findings in auto-HSCT for treatment of T1D.

Immune response after autologous hematopoietic stem cell transplantation in type 1 diabetes mellitus

Background

This study explored the details of the immune response after autologous hematopoietic stem cell transplantation (AHSCT) treatment in type 1 diabetes mellitus.

Methods

Peripheral blood mononuclear cells (PBMCs) from 18 patients with type 1 diabetes mellitus were taken at baseline and 12 months after AHSCT or insulin-only therapy. The lymphocyte proliferation, mRNA expression and secretion of pro-inflammatory and anti-inflammatory cytokines belonging to T-helper type 1 (Th1), T-helper type 17 (Th17) and regulatory T (Treg) cells in PBMC culture supernatants were assessed.

Results

Compared with patients receiving insulin-only treatment, the patients receiving AHSCT treatment showed better residual C-peptide secretion, lower anti-GAD titers and less exogenous insulin dosages after 12 months of follow-up. AHSCT treatment was associated with significantly reduced Th1 and Th17 cell proportions as well as decreased IFN-γ, IL-2, IL-12p40 and IL-17A levels in the PBMC culture supernatants (all P < 0.05). Although there was no significant Treg cell expansion after AHSCT treatment, we observed increased IL-10, TGF-β and Foxp3 mRNA expression and increased TGF-β levels. However, we found no significant changes in the T-cell subpopulations after insulin treatment, except for higher IL-12p40 mRNA expression and a lower proportion of Treg cells.

Conclusions

AHSCT treatment was associated with decreased expansion and function of Th1 and Th17 cells, which may explain the better therapeutic effect of AHSCT compared with the traditional intensive insulin therapy.

Trial registration

Clinicaltrials.gov NCT00807651. Registered 18 December 2008.

Proinsulin multi-peptide immunotherapy induces antigen-specific regulatory T cells and limits autoimmunity in a humanized model

Peptide immunotherapy (PIT) is a targeted therapeutic approach, involving administration of disease-associated peptides, with the aim of restoring antigen-specific immunological tolerance without generalized immunosuppression. In type 1 diabetes, proinsulin is a primary antigen targeted by the autoimmune response, and is therefore a strong candidate for exploitation via PIT in this setting. To elucidate the optimal conditions for proinsulin-based PIT and explore mechanisms of action, we developed a preclinical model of proinsulin autoimmunity in a humanized HLA-DRB1*0401 transgenic HLA-DR4 Tg mouse. Once proinsulin-specific tolerance is broken, HLA-DR4 Tg mice develop autoinflammatory responses, including proinsulin-specific T cell proliferation, interferon (IFN)-γ and autoantibody production. These are preventable and quenchable by pre- and post-induction treatment, respectively, using intradermal proinsulin-PIT injections. Intradermal proinsulin-PIT enhances proliferation of regulatory [forkhead box protein 3 (FoxP3(+))CD25(high) ] CD4 T cells, including those capable of proinsulin-specific regulation, suggesting this as its main mode of action. In contrast, peptide delivered intradermally on the surface of vitamin D3-modulated (tolerogenic) dendritic cells, controls autoimmunity in association with proinsulin-specific IL-10 production, but no change in regulatory CD4 T cells. These studies define a humanized, translational model for in vivo optimization of PIT to control autoimmunity in type 1 diabetes and indicate that dominant mechanisms of action differ according to mode of peptide delivery.

Extraction of tissue antigens for functional assays

Many of the antigen targets of adaptive immune response, recognized by B and T cells, have not been defined (1). This is particularly true in autoimmune diseases and cancer(2). Our aim is to investigate the antigens recognized by human T cells in the autoimmune disease type 1 diabetes (1,3,4,5). To analyze human T-cell responses against tissue where the antigens recognized by T cells are not identified we developed a method to extract protein antigens from human tissue in a format that is compatible with functional assays (6). Previously, T-cell responses to unpurified tissue extracts could not be measured because the extraction methods yield a lysate that contained detergents that were toxic to human peripheral blood mononuclear cells. Here we describe a protocol for extracting proteins from human tissues in a format that is not toxic to human T cells. The tissue is homogenized in a mixture of butan-1-ol, acetonitrile and water (BAW). The protein concentration in the tissue extract is measured and a known mass of protein is aliquoted into tubes. After extraction, the organic solvents are removed by lyophilization. Lyophilized tissue extracts can be stored until required. For use in assays of immune function, a suspension of immune cells, in appropriate culture media, can be added directly to the lyophilized extract. Cytokine production and proliferation by PBMC, in response to extracts prepared using this method, were readily measured. Hence, our method allows the rapid preparation of human tissue lysates that can be used as a source of antigens in the analysis of T-cell responses. We suggest that this method will facilitate the analysis of adaptive immune responses to tissues in transplantation, cancer and autoimmunity.

Residual methylprednisolone suppresses human T-cell responses to spleen, but not islet, extracts from deceased organ donors

Pancreatic islets, transplanted into recipients with type 1 diabetes, are exposed to allogenic and auto-immune T-cell responses. We set out to develop an assay to measure these responses using PBMC. Our approach was to prepare spleen extract from the islet donors (allo-antigen) and islet extracts (auto-antigen). To our surprise, we found that spleen extracts potently inhibited the proliferation of human T cells driven by antigen (tetanus toxoid) and mitogen (anti-CD3 mAb, OKT3), whereas extracts prepared from pancreatic islets from the same donor did not suppress T-cell proliferation. Suppression mediated by spleen extracts was unaffected by blocking mAbs against the IL-10R, transforming growth factor-β or CD152 (CTLA-4). It was also unaffected by denaturing the spleen extracts by heating, exposing to reducing agents or protease digestion. Because deceased organ donors are commonly given the immunosuppressive glucocorticoid methylprednisolone prior to death, we hypothesized that suppression was due to residual methylprednisolone in the spleen extracts. Methylprednisolone could be detected by mass spectrometry in spleen extracts at concentrations that suppress T-cell proliferation. Finally, the glucocorticoid receptor antagonist mifepristone completely reversed the suppression caused by the spleen extracts. We conclude that extracts of human spleen, but not islets, from deceased organ donors contain sufficient residual methylprednisolone to suppress the proliferation of T-cells in vitro.

Current approaches to measuring human islet-antigen specific T cell function in type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease caused by the T cell-mediated destruction of the pancreatic insulin-producing beta cells. Currently there are no widely accepted and standardized assays available to analyse the function of autoreactive T cells involved in T1D. The development of such an assay would greatly aid efforts to understand the pathogenesis of T1D and is also urgently required to guide the development of antigen-based therapies intended to prevent, or cure, T1D. Here we describe some of the assays used currently to detect autoreactive T cells in human blood and review critically their strengths and weaknesses. The challenges and future prospects for the T cell assays are discussed.

The A-chain of insulin is a hot-spot for CD4+ T cell epitopes in human type 1 diabetes

Type 1 diabetes (T1D) is caused by T cell-mediated destruction of the pancreatic insulin-producing beta cells. While the role of CD4(+) T cells in the pathogenesis of T1D is accepted widely, the epitopes recognized by pathogenic human CD4(+) T cells remain poorly defined. None the less, responses to the N-terminal region of the insulin A-chain have been described. Human CD4(+) T cells from the pancreatic lymph nodes of subjects with T1D respond to the first 15 amino acids of the insulin A-chain. We identified a human leucocyte antigen-DR4-restricted epitope comprising the first 13 amino acids of the insulin A-chain (A1-13), dependent upon generation of a vicinal disulphide bond between adjacent cysteines (A6-A7). Here we describe the analysis of a CD4(+) T cell clone, isolated from a subject with T1D, which recognizes a new HLR-DR4-restricted epitope (KRGIVEQCCTSICS) that overlaps the insulin A1-13 epitope. This is a novel epitope, because the clone responds to proinsulin but not to insulin, T cell recognition requires the last two residues of the C-peptide (Lys, Arg) and recognition does not depend upon a vicinal disulphide bond between the A6 and A7 cysteines. The finding of a further CD4(+) T cell epitope in the N-terminal A-chain region of human insulin underscores the importance of this region as a target of CD4(+) T cell responses in human T1D.