Tolerogenic Delivery of a Hybrid Insulin Peptide Markedly Prolongs Islet Graft Survival in the Non-Obese Diabetic (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 non-obese diabetic (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 to the expansion of Foxp3+ regulatory T cells specific for the same antigen. 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 a hybrid insulin peptide can delay recurrent autoimmunity in NOD mice, which could inform the development of an Ag-specific therapy for T1D.

Tolerogenic Delivery of a Hybrid Insulin Peptide Markedly Prolongs Islet Graft Survival in the Non-Obese Diabetic (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 non-obese diabetic (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 to the expansion of Foxp3+ regulatory T cells specific for the same antigen. 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 a hybrid insulin peptide can delay recurrent autoimmunity in NOD mice, which could inform the development of an Ag-specific therapy for T1D.

Tolerogenic Delivery of a Hybrid Insulin Peptide Markedly Prolongs Islet Graft Survival in the Non-Obese Diabetic (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 non-obese diabetic (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 to the expansion of Foxp3+ regulatory T cells specific for the same antigen. 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 a hybrid insulin peptide can delay recurrent autoimmunity in NOD mice, which could inform the development of an Ag-specific therapy for T1D.

Three-dimensional islet graft histology: panoramic imaging of neural plasticity in sympathetic reinnervation of transplanted islets under the kidney capsule

Microscopic examination of transplanted islets in an ectopic environment provides information to evaluate islet engraftment, including revascularization and reinnervation. However, because of the dispersed nature of blood vessels and nerves, global visualization of the graft neurovascular network has been difficult. In this research we revealed the neurovascular network by preparing transparent mouse islet grafts under the kidney capsule with optical clearing to investigate the sympathetic reinnervation via three-dimensional confocal microscopy. Normoglycemic and streptozotocin-induced diabetic mice were used in syngeneic islet transplantation, with both groups maintaining euglycemia after transplantation. Triple staining of insulin/glucagon, blood vessels, and tyrosine hydroxylase (sympathetic marker) was used to reveal the graft microstructure, vasculature, and sympathetic innervation. Three weeks after transplantation, we observed perigraft sympathetic innervation similar to the peri-islet sympathetic innervation in the pancreas. Six weeks after transplantation, prominent intragraft, perivascular sympathetic innervation was achieved, resembling the pancreatic intraislet, perivascular sympathetic innervation in situ. Meanwhile, in diabetic recipients, a higher graft sympathetic nerve density was found compared with grafts in normoglycemic recipients, indicating the graft neural plasticity in response to the physiological difference of the recipients and the resolving power of this imaging approach. Overall, this new graft imaging method provides a useful tool to identify the islet neurovascular complex in an ectopic environment to study islet engraftment.

Interleukin-1β and inducible form of nitric oxide synthase expression in early syngeneic islet transplantation

Islets are particularly vulnerable in the initial days after transplantation when cell death results in the loss of more than half of the transplanted islet tissue. To determine whether a non-specific inflammation at the grafted site mediated by the local expression of inflammatory cytokines could play a role on the initial damage to transplanted islets, we studied the expressions of interleukin-1β (IL-1β) and inducible form of nitric oxide synthase (iNOS) after syngeneic islet transplantation. Insulin-treated streptozotocin-diabetic Lewis rats were syngeneically transplanted with 500 islets. Grafts were harvested 1, 3, or 7 days after transplantation, and the expressions of IL-1β and iNOS genes were determined by RT-PCR. IL-1β and iNOS mRNAs were detected in islets immediately after isolation, and were upregulated after transplantation. IL-1β mRNA was ninefold increased on day 1, was still sevenfold increased on day 3 after transplantation, and declined towards pretransplantation levels on day 7. iNOS mRNA showed a similar pattern of expression to that of IL-1β: on days 1 and 3 after transplantation it was 14-and 4-fold higher respectively than in freshly isolated islets. In addition, IL-1β and iNOS were identified in islet grafts and found to be produced mainly by CD68-positive macrophages. A low number of IL-1β- and iNOS-positive but CD68-negative cells were also identified suggesting that other cell types, in addition to macrophages, were involved in the expression of IL-1β and NO production in islet grafts. The finding of increased IL-1β and iNOS gene expressions in the initial days after islet transplantation and the presence of IL-β and iNOS proteins in the graft confirmed the presence of an early non-specific inflammatory response after islet transplantation. Overall, the data suggest that IL-1β plays a role in the extensive β-cell death found in the initial days after islet transplantation.