Posttransplantation diabetes mellitus (PTDM) is a common and significant complication related to immunosuppressive agents required to prevent organ or cell transplant rejection. To elucidate the effects of 2 commonly used agents, the calcineurin inhibitor tacrolimus (TAC) and the mTOR inhibitor sirolimus (SIR), on islet function and test whether these effects could be reversed or prevented, we investigated human islets transplanted into immunodeficient mice treated with TAC or SIR at clinically relevant levels. Both TAC and SIR impaired insulin secretion in fasted and/or stimulated conditions. Treatment with TAC or SIR increased amyloid deposition and islet macrophages, disrupted insulin granule formation, and induced broad transcriptional dysregulation related to peptide processing, ion/calcium flux, and the extracellular matrix; however, it did not affect regulation of beta cell mass. Interestingly, these beta cell abnormalities reversed after withdrawal of drug treatment. Furthermore, cotreatment with a GLP-1 receptor agonist completely prevented TAC-induced beta cell dysfunction and partially prevented SIR-induced beta cell dysfunction. These results highlight the importance of both calcineurin and mTOR signaling in normal human beta cell function in vivo and suggest that modulation of these pathways may prevent or ameliorate PTDM.

Inadequate pancreatic beta cell function underlies type 1 and type 2 diabetes mellitus. Strategies to expand functional cells have focused on discovering and controlling mechanisms that limit the proliferation of human beta cells. Here, we developed an engraftment strategy to examine age-associated human islet cell replication competence and reveal mechanisms underlying age-dependent decline of beta cell proliferation in human islets. We found that exendin-4 (Ex-4), an agonist of the glucagon-like peptide 1 receptor (GLP-1R), stimulates human beta cell proliferation in juvenile but not adult islets. This age-dependent responsiveness does not reflect loss of GLP-1R signaling in adult islets, since Ex-4 treatment stimulated insulin secretion by both juvenile and adult human beta cells. We show that the mitogenic effect of Ex-4 requires calcineurin/nuclear factor of activated T cells (NFAT) signaling. In juvenile islets, Ex-4 induced expression of calcineurin/NFAT signaling components as well as target genes for proliferation-promoting factors, including NFATC1, FOXM1, and CCNA1. By contrast, expression of these factors in adult islet beta cells was not affected by Ex-4 exposure. These studies reveal age-dependent signaling mechanisms regulating human beta cell proliferation, and identify elements that could be adapted for therapeutic expansion of human beta cells.

Type 1 diabetes (T1D) is an autoimmune disease characterized by the infiltration of lymphocytes into the insulin-producing β-cells in the pancreas. We have isolated live T cells sorted or grown directly from the isolated, handpicked islets of human donors with T1D. We received ~500 islet equivalent EQ of variable purity (10-90%) from 12 donors with T1D (disease duration 0.42-20 years) and from seven control donors and two donors with type 2 diabetes (T2D). A total of 321 T cell lines and clones were derived from the islets of donors with T1D (3 lines from the 9 control donors). These are 131 CD4+ lines and clones, 47 CD8+ lines and 143 lines that contain both CD4+ and CD8+ T cells. From 50 lines and clones examined to date, we have determined the autoreactivity of 19 and have seen a broad repertoire of T cell autoreactivity in the islets, including characterized targets and post-translationally modified targets. Autoreactivity of CD4+ T cell lines was to three different peptides from glutamic acid decarboxylase 65 (GAD; GAD115-127, GAD274-286, GAD555-567), proinsulin76-90, and to chromogranin A or proinsulin expressed by DR4+DQ8+ B cells transduced with lentivirus containing constructs with the open reading frames corresponding to whole autoantigens. Reactivity to modified peptides included the glucose-regulated protein 78 and islet amyloid polypeptide with arginine to citrulline modifications (GRP78292-305(Arg-Cit297) and IAPP65-84(Arg-Cit 73, 81)), deaminations (IA-2545-562(Gln-Glu 548, 551, 556), and to several insulin hybrid peptides. These autoreactive CD4+ T cell lines and clones secreted only pro-inflammatory cytokines (IFN-γ, TNFα) upon peptide stimulation. For CD8+ T cells from islets, from one donor with T1D, we saw binding of a pool of HLA-A2 pentamers loaded with insulin B10-18, IA-2797-805 and insulin specific glucose-6-phosphatase catalytic subunit related protein, IGRP265-273. These results have implications for the development of successful prevention and reversal therapeutic strategies in T1D.

AIMS/HYPOTHESIS: To develop and validate a new immunodeficient mouse strain that spontaneously develops a non-autoimmune hyperglycaemia to serve as a diabetic host for human islets and human beta stem and progenitor cells without the need for induction of hyperglycaemia by toxic chemicals with their associated side effects. METHODS: We generated and characterised a new strain of immunodeficient spontaneously hyperglycaemic mice, the NOD-Rag1null Prf1null Ins2Akita strain and compared this strain with the NOD-scid Il2rgammanull (also known as Il2rg) immunodeficient strain rendered hyperglycaemic by administration of a single dose of streptozotocin. Hyperglycaemic mice were transplanted with human islets ranging from 1,000 to 4,000 islet equivalents (IEQ) and were monitored for normalisation of blood glucose levels. RESULTS: NOD-Rag1null Prf1null Ins2Akita mice developed spontaneous hyperglycaemia, similar to Ins2Akita-harbouring strains of immunocompetent mice. Histological examination of islets in the host pancreas validated the spontaneous loss of beta cell mass in the absence of mononuclear cell infiltration. Human islets transplanted into spontaneously diabetic NOD-Rag1null Prf1null Ins2Akita and chemically diabetic NOD-scid Il2rgammanull mice resulted in a return to euglycaemia that occurred with transplantation of similar beta cell masses. CONCLUSIONS/INTERPRETATION: The NOD-Rag1null Prf1null Ins2Akita mouse is the first immunodeficient, spontaneously hyperglycaemic mouse strain described that is based on the Ins2Akita mutation. This strain is suitable as hosts for human islet and human beta stem and progenitor cell transplantation in the absence of the need for pharmacological induction of diabetes. This strain of mice also has low levels of innate immunity and can be engrafted with a human immune system for the study of human islet allograft rejection.

Immunodeficient NOD-scid mice bearing a targeted mutation in the IL2 receptor common gamma chain (Il2rgamma(null)) readily engraft with human stem cells. Here we analyzed human peripheral blood mononuclear cells (PBMC) for their ability to engraft NOD-scid Il2rgamma(null) mice and established engraftment kinetics, optimal cell dose, and the influence of injection route. Even at low PBMC input, NOD-scid Il2rgamma(null) mice reproducibly support high human PBMC engraftment that plateaus within 3-4 weeks. In contrast to previous stocks of immunodeficient mice, we observed low intra- and inter-donor variability of engraftment. NOD-scid Il2rgamma(null) mice rendered hyperglycemic by streptozotocin treatment return to normoglycemia following transplantation with human islets. Interestingly, these human islet grafts are rejected following injection of HLA-mismatched human PBMC as evidenced by return to hyperglycemia and loss of human C-peptide. These data suggest that humanized NOD-scid Il2rgamma(null) mice may represent an important surrogate for investigating in vivo mechanisms of human islet allograft rejection.

The use of "humanized" mice represents an appealing translational model for studies of the pathogenesis of immune-mediated diseases and for the evaluation of potential therapeutics. The utility of humanized mice depends on their ability to model the human immune system with high fidelity, and, in this respect, previous models have fallen short. The recently developed NOD-scid Il2rgamma(null) mouse, however, exhibits greatly enhanced ability to support the engraftment of human peripheral blood mononuclear cells. Herein, we describe the challenges of recapitulating human immunity in humanized mice and features of NOD-scid Il2rgamma(null) mice that help overcome them.