Cellular expression requirements for inhibition of type 1 diabetes by a dominantly protective major histocompatibility complex haplotype

Loss of Peripheral Protection in Pancreatic Islets by Proteolysis-Driven Impairment of VTCN1 (B7-H4) Presentation Is Associated with the Development of Autoimmune Diabetes

Ag-specific activation of T cells is an essential process in the control of effector immune responses. Defects in T cell activation, particularly in the costimulation step, have been associated with many autoimmune conditions, including type 1 diabetes (T1D). Recently, we demonstrated that the phenotype of impaired negative costimulation, due to reduced levels of V-set domain-containing T cell activation inhibitor 1 (VTCN1) protein on APCs, is shared between diabetes-susceptible NOD mice and human T1D patients. In this study, we show that a similar process takes place in the target organ, as both α and β cells within pancreatic islets gradually lose their VTCN1 protein during autoimmune diabetes development despite upregulation of the VTCN1 gene. Diminishment of functional islet cells' VTCN1 is caused by the active proteolysis by metalloproteinase N-arginine dibasic convertase 1 (NRD1) and leads to the significant induction of proliferation and cytokine production by diabetogenic T cells. Inhibition of NRD1 activity, alternatively, stabilizes VTCN1 and dulls the anti-islet T cell responses. Therefore, we suggest a general endogenous mechanism of defective VTCN1 negative costimulation, which affects both lymphoid and peripheral target tissues during T1D progression and results in aggressive anti-islet T cell responses. This mechanism is tied to upregulation of NRD1 expression and likely acts in two synergistic proteolytic modes: cell-intrinsic intracellular and cell-extrinsic systemic. Our results highlight an importance of VTCN1 stabilization on cell surfaces for the restoration of altered balance of immune control during T1D.

Bridging Mice to Men: Using HLA Transgenic Mice to Enhance the Future Prediction and Prevention of Autoimmune Type 1 Diabetes in Humans

Similar to the vast majority of cases in humans, the development of type 1 diabetes (T1D) in the NOD mouse model is due to T-cell mediated autoimmune destruction of insulin producing pancreatic β cells. Particular major histocompatibility complex (MHC) haplotypes (designated HLA in humans; and H2 in mice) provide the primary genetic risk factor for T1D development. It has long been appreciated that within the MHC, particular unusual class II genes contribute to the development of T1D in both humans and NOD mice by allowing for the development and functional activation of β cell autoreactive CD4 T cells. However, studies in NOD mice have revealed that through interactions with other background susceptibility genes, the quite common class I variants (K(d), D(b)) characterizing this strain's H2 (g7) MHC haplotype aberrantly acquire an ability to support the development of β cell autoreactive CD8 T cell responses also essential to T1D development. Similarly, recent studies indicate that in the proper genetic context some quite common HLA class I variants also aberrantly contribute to T1D development in humans. This review focuses on how "humanized" HLA transgenic NOD mice can be created and used to identify class I dependent β cell autoreactive CD8 T cell populations of clinical relevance to T1D development. There is also discussion on how HLA transgenic NOD mice can be used to develop protocols that may ultimately be useful for the prevention of T1D in humans by attenuating autoreactive CD8 T cell responses against pancreatic β cells.

MHC-mismatched mixed chimerism mediates thymic deletion of cross-reactive autoreactive T cells and prevents insulitis in nonobese diabetic mice

Type 1 diabetic NOD mice have defects in both thymic negative selection and peripheral regulation of autoreactive T cells, and induction of mixed chimerism can effectively reverse these defects. Our recent studies suggest that MHC-mismatched mixed chimerism mediates negative selection of autoreactive thymocytes in wild-type NOD and TCR-transgenic NOD.Rag1(+/+).BDC2.5 mice. However, it remains unknown how mismatched I-A(b) MHC class II can mediate deletion of autoreactive T cells positively selected by I-A(g7). In the present study, we directly tested the hypothesis that mismatched MHC class II in mixed chimeras mediates deletion of cross-reactive autoreactive thymocytes. We first identify that transgenic BDC2.5 T cells from NOD.Rag1(+/+).BDC2.5 but not NOD.Rag1(-/-).BDC2.5 mice possess cross-reactive TCRs with endogenous TCRα-chains; MHC-mismatched H-2(b) but not matched H-2(g7) mixed chimerism mediates thymic deletion of the cross-reactive transgenic T cells in NOD.Rag1(+/+).BDC2.5 mice. Second, by transplanting T cell-depleted (TCD) bone marrow (BM) cells from NOD.Rag1(+/+).BDC2.5 or NOD.Rag1(-/-).BDC2.5 mice into lethally irradiated MHC-mismatched H-2(b) C57BL/6 or MHC-matched congenic B6.H-2(g7) recipients, we demonstrate that NOD.Rag1(+/+).BDC2.5 BM-derived cross-reactive transgenic T cells, but not NOD.Rag1(-/-).BDC2.5 BM-derived non-cross-reactive transgenic T cells, can be positively selected in MHC-mismatched H-2(b) thymus. Third, by cotransplanting NOD.Rag1(+/+).BDC2.5 TCD BM cells with BM cells from MHC-mismatched T cell-deficient C57BL/6 mice into lethally irradiated MHC-matched B6.H-2(g7) recipients, we demonstrate that thymic deletion of the cross-reactive transgenic T cells is dependent on MHC-mismatched donor BM-derived APCs but not on donor BM-derived T cells. Taken together, our studies indicate that MHC-mismatched mixed chimerism can mediate thymic deletion of cross-reactive autoreactive T cells that express more than one TCR.

Transcriptome analysis of epigenetically modulated genome indicates signature genes in manifestation of type 1 diabetes and its prevention in NOD mice

Classic genetic studies implicated several genes including immune response genes in the risk of developing type 1 diabetes in humans. However, recent evidence including discordant diabetes incidence among monozygotic twins suggested a role for epigenetics in disease manifestation. NOD mice spontaneously develop type 1 diabetes like humans and serve as an excellent model system to study the mechanisms of type 1 diabetes as well as the efficacy of maneuvers to manipulate the disease. Using this preclinical model, we have recently demonstrated that pharmacological inhibition of histone deacetylases can lead to histone hyperacetylation, selective up-regulation of interferon-γ and its transactivator Tbx21/Tbet, and amelioration of autoimmune diabetes. In the current study, we show that chromatin remodeling can render splenocytes incapable of transferring diabetes into immunodeficient NOD.scid mice. To elucidate the underlying mechanisms of drug-mediated protection against type 1 diabetes, we performed global gene expression profiling of splenocytes using high throughput microarray technology. This unbiased transcriptome analysis unraveled the exaggerated expression of a novel set of closely related inflammatory genes in splenocytes of acutely diabetic mice and their repression in mice cured of diabetes by chromatin remodeling. Analysis of gene expression by qRT-PCR using RNA derived from spleens and pancreata of cured mice validated the suppression of most of these genes, indicating an inverse correlation between the high levels of these inflammatory genes and protection against diabetes in NOD mice. In addition, higher-level expression of genes involved in insulin sensitivity, erythropoiesis, hemangioblast generation, and cellular redox control was evident in spleens of cured mice, indicating their possible contribution to protection against type 1 diabetes. Taken together, these results are consistent with the involvement of epistatic mechanisms in the manifestation of autoimmune diabetes and further indicate the utility of chromatin remodeling in curing this complex autoimmune disorder.

Induction of mixed chimerism with MHC-mismatched but not matched bone marrow transplants results in thymic deletion of host-type autoreactive T-cells in NOD mice

OBJECTIVE

Induction of mixed or complete chimerism via hematopoietic cell transplantation (HCT) from nonautoimmune donors could prevent or reverse type 1 diabetes (T1D). In clinical settings, HLA-matched HCT is preferred to facilitate engraftment and reduce the risk for graft versus host disease (GVHD). Yet autoimmune T1D susceptibility is associated with certain HLA types. Therefore, we tested whether induction of mixed chimerism with major histocompatibility complex (MHC)-matched donors could reverse autoimmunity in the NOD mouse model of T1D.

RESEARCH DESIGN AND METHODS

Prediabetic wild-type or transgenic BDC2.5 NOD mice were conditioned with a radiation-free GVHD preventative anti-CD3/CD8 conditioning regimen and transplanted with bone marrow (BM) from MHC-matched or mismatched donors to induce mixed or complete chimerism. T1D development and thymic deletion of host-type autoreactive T-cells in the chimeric recipients were evaluated.

RESULTS

Induction of mixed chimerism with MHC-matched nonautoimmune donor BM transplants did not prevent T1D in wild-type NOD mice, although induction of complete chimerism did prevent the disease. However, induction of either mixed or complete chimerism with MHC-mismatched BM transplants prevented T1D in such mice. Furthermore, induction of mixed chimerism in transgenic BDC2.5-NOD mice with MHC-matched or -mismatched MHC II(-/-) BM transplants failed to induce thymic deletion of de novo developed host-type autoreactive T-cells, whereas induction of mixed chimerism with mismatched BM transplants did.

CONCLUSIONS

Induction of mixed chimerism with MHC-mismatched, but not matched, donor BM transplants re-establishes thymic deletion of host-type autoreactive T-cells and prevents T1D, with donor antigen-presenting cell expression of mismatched MHC II molecules being required.

Emerging roles for B lymphocytes in Type 1 diabetes

Self-reactive B lymphocytes play two main pathological roles in autoimmune diseases: as secretors of autoantibodies and as specialized antigen-presenting cells that present self-components to autoreactive T lymphocytes. In recognition of these roles, recent clinical trials have utilized B-lymphocyte-depleting monoclonal antibodies to treat various autoimmune diseases, with encouraging results in those where humoral autoimmunity is clearly important. Surprisingly, recent results in animal models suggest that B-lymphocyte depletion may also be effective in the treatment of T-lymphocyte-mediated autoimmune diseases, such as Type 1 diabetes (T1D). This article reviews the experimental evidence that has uncovered pathogenic as well as regulatory roles for B lymphocytes in the prodrome of T1D and how this information is being used to develop novel therapeutic strategies to treat the disease.

Bridging mice to men: using HLA transgenic mice to enhance the future prediction and prevention of autoimmune type 1 diabetes in humans

Similar to the vast majority of cases in humans, the development of type 1 diabetes (T1D) in the NOD mouse model is due to T-cell mediated autoimmune destruction of insulin-producing pancreatic beta cells. Particular major histocompatibility complex (MHC) haplotypes (designated HLA in humans and H2 in mice) provide the primary genetic risk factor for T1D development. It has long been appreciated that within the MHC, particular unusual class II genes contribute to the development of T1D in both humans and NOD mice by allowing for the development and functional activation of beta-cell autoreactive CD4 T cells. However, studies in NOD mice have revealed that through interactions with other background susceptibility genes, the quite common class I variants (K(d), D(b)) characterizing this strain's H2 ( g7 ) MHC haplotype aberrantly acquire an ability to support the development of beta cell autoreactive CD8 T-cell responses also essential to T1D development. Similarly, recent studies indicate that in the proper genetic context some quite common HLA class I variants also aberrantly contribute to T1D development in humans. This chapter will focus on how "humanized" HLA transgenic NOD mice can be created and used to identify class I-dependent beta cell autoreactive CD8 T-cell populations of clinical relevance to T1D development. There is also discussion on how HLA transgenic NOD mice can be used to develop protocols that may ultimately be useful for the prevention of T1D in humans by attenuating autoreactive CD8 T-cell responses against pancreatic beta cells.