Prolonged islet allograft survival in diabetic NOD mice by targeting CD45RB and CD154

Human stem cell derived beta-like cells engineered to present PD-L1 improve transplant survival in NOD mice carrying human HLA class I

There is a critical need for therapeutic approaches that combine renewable sources of replacement beta cells with localized immunomodulation to counter recurrence of autoimmunity in type 1 diabetes (T1D). However, there are few examples of animal models to study such approaches that incorporate spontaneous autoimmunity directed against human beta cells rather than allogenic rejection. Here, we address this critical limitation by demonstrating rejection and survival of transplanted human stem cell-derived beta-like cells clusters (sBCs) in a fully immune competent mouse model with matching human HLA class I and spontaneous diabetes development. We engineered localized immune tolerance toward transplanted sBCs via inducible cell surface overexpression of PD-L1 (iP-sBCs) with and without deletion of all HLA class I surface molecules via beta-2 microglobulin knockout (iP-BKO sBCs). NOD.HLA-A2.1 mice, which lack classical murine MHC I and instead express human HLA-A*02:01, underwent transplantation of 1,000 human HLA-A*02:01 sBCs under the kidney capsule and were separated into HLA-A2 positive iP-sBC and HLA-class I negative iP-BKO sBC groups, each with +/- doxycycline (DOX) induced PD-L1 expression. IVIS imaging showed significantly improved graft survival in mice transplanted with PD-L1 expressing iP-sBC at day 3 post transplantation compared to controls. However, luciferase signal dropped below in vivo detection limits by day 14 for all groups in this aggressive immune competent diabetes model. Nonetheless, histological examination revealed significant numbers of surviving insulin⁺/PD-L1⁺ sBCs cells for DOX-treated mice at day 16 post-transplant despite extensive infiltration with high numbers of CD3⁺ and CD45⁺ immune cells. These results show that T cells rapidly infiltrate and attack sBC grafts in this model but that significant numbers of PD-L1 expressing sBCs manage to survive in this harsh immunological environment. This investigation represents one of the first in vivo studies recapitulating key aspects of human autoimmune diabetes to test immune tolerance approaches with renewable sources of beta cells.

Immunosuppressive PLGA TGF-β1 Microparticles Induce Polyclonal and Antigen-Specific Regulatory T Cells for Local Immunomodulation of Allogeneic Islet Transplants

Allogeneic islet transplantation is a promising cell-based therapy for Type 1 Diabetes (T1D). The long-term efficacy of this approach, however, is impaired by allorejection. Current clinical practice relies on long-term systemic immunosuppression, leading to severe adverse events. To avoid these detrimental effects, poly(lactic-co-glycolic acid) (PLGA) microparticles (MPs) were engineered for the localized and controlled release of immunomodulatory TGF-β1. The in vitro co-incubation of TGF-β1 releasing PLGA MPs with naïve CD4⁺ T cells resulted in the efficient generation of both polyclonal and antigen-specific induced regulatory T cells (iTregs) with robust immunosuppressive function. The co-transplantation of TGF-β1 releasing PLGA MPs and Balb/c mouse islets within the extrahepatic epididymal fat pad (EFP) of diabetic C57BL/6J mice resulted in the prompt engraftment of the allogenic implants, supporting the compatibility of PLGA MPs and local TGF-β1 release. The presence of the TGF-β1-PLGA MPs, however, did not confer significant graft protection when compared to untreated controls, despite measurement of preserved insulin expression, reduced intra-islet CD3⁺ cells invasion, and elevated CD3⁺Foxp3⁺ T cells at the peri-transplantation site in long-term functioning grafts. Examination of the broader impacts of TGF-β1/PLGA MPs on the host immune system implicated a localized nature of the immunomodulation with no observed systemic impacts. In summary, this approach establishes the feasibility of a local and modular microparticle delivery system for the immunomodulation of an extrahepatic implant site. This approach can be easily adapted to deliver larger doses or other agents, as well as multi-drug approaches, within the local graft microenvironment to prevent transplant rejection.

In vivo imaging of type 1 diabetes immunopathology using eye-transplanted islets in NOD mice

AIMS/HYPOTHESIS

Autoimmune attack against the insulin-producing beta cells in the pancreatic islets results in type 1 diabetes. However, despite considerable research, details of the type 1 diabetes immunopathology in situ are not fully understood mainly because of difficult access to the pancreatic islets in vivo.

METHODS

Here, we used direct non-invasive confocal imaging of islets transplanted in the anterior chamber of the eye (ACE) to investigate the anti-islet autoimmunity in NOD mice before, during and after diabetes onset. ACE-transplanted islets allowed longitudinal studies of the autoimmune attack against islets and revealed the infiltration kinetics and in situ motility dynamics of fluorescence-labelled autoreactive T cells during diabetes development. Ex vivo immunostaining was also used to compare immune cell infiltrations into islet grafts in the eye and kidney as well as in pancreatic islets of the same diabetic NOD mice.

RESULTS

We found similar immune infiltration in native pancreatic and ACE-transplanted islets, which established the ACE-transplanted islets as reliable reporters of the autoimmune response. Longitudinal studies in ACE-transplanted islets identified in vivo hallmarks of islet inflammation that concurred with early immune infiltration of the islets and preceded their collapse and hyperglycaemia onset. A model incorporating data on ACE-transplanted islet degranulation and swelling allowed early prediction of the autoimmune attack in the pancreas and prompted treatments to intercept type 1 diabetes.

CONCLUSIONS/INTERPRETATION

The current findings highlight the value of ACE-transplanted islets in studying early type 1 diabetes pathogenesis in vivo and underscore the need for timely intervention to halt disease progression.

The impact of cell surface PEGylation and short-course immunotherapy on islet graft survival in an allogeneic murine model

Islet transplantation is a promising therapy for Type 1 diabetes mellitus; however, host inflammatory and immune responses lead to islet dysfunction and destruction, despite potent systemic immunosuppression. Grafting of poly(ethylene glycol) (PEG) to the periphery of cells or tissues can mitigate inflammation and immune recognition via generation of a steric barrier. Herein, we sought to evaluate the complementary impact of islet PEGylation with a short-course immunotherapy on the survival of fully-MHC mismatched islet allografts (DBA/2 islets into diabetic C57BL/6J recipients). Anti-Lymphocyte Function-associated Antigen 1 (LFA-1) antibody was selected as a complementary, transient, systemic immune monotherapy. Islets were PEGylated via an optimized protocol, with resulting islets exhibiting robust cell viability and function. Following transplantation, a significant subset of diabetic animals receiving PEGylated islets (60%) or anti-LFA-1 antibody (50%) exhibited long-term (>100d) normoglycemia. The combinatorial approach proved synergistic, with 78% of the grafts exhibiting euglycemia long-term. Additional studies examining graft cellular infiltrates at early time points characterized the local impact of the transplant protocol on graft survival. Results illustrate the capacity of a simple polymer grafting approach to impart significant immunoprotective effects via modulation of the local transplant environment, while short-term immunotherapy serves to complement this effect.

STATEMENT OF SIGNIFICANCE

We believe this study is important and of interest to the biomaterials and transplant community for several reasons: 1) it provides an optimized protocol for the PEGylation of islets, with minimal impact on the coated islets, which can be easily translated for clinical applications; 2) this optimized protocol demonstrates the benefits of islet PEGylation in providing modest immunosuppression in a murine model; 3) this work demonstrates the combinatory impact of PEGylation with short-course immunotherapy (via LFA-1 blockage), illustrating the capacity of PEGylation to complement existing immunotherapy; and 4) it suggests macrophage phenotype shifting as the potential mechanism for this observed benefit.

Regulating the expression of CD80/CD86 on dendritic cells to induce immune tolerance after xeno-islet transplantation

BACKGROUND

Antigen present cells (APCs) have been demonstrated to play dual roles in immune tolerance. Recently, compelling evidence indicates that APCs that express CD80, but not CD86 can protect allograft. We investigated whether modulation of CD80 in dendritic cells (DCs) offer protection for xeno-islets.

METHODS

In vitro, isolated mature murine DCs received untransfection, transfection with CD86 siRNA or negative control siRNA. The DCs were used in mixed lymphocyte reaction in which rat islets and murine splenocytes were further added. On day 3 of co-culturing, the proliferation of lymphocytes was measured and interleukin (IL)-2, IL-4, IL-10, transforming growth factor β (TGF-β), interferon γ (INF-γ) and indoleamine 2,3-dioxygenase (IDO) from the supernatants were determined. Islets viability and function were also assessed. In vivo, streptozotocin-induced diabetic mice underwent rat islets transplantation were pre-treated with above DCs. At designated time, xeno-islets were subjected to histopathology, immunohistochemistry, survival time and functional tests. Peripheral blood T lymphocyte profiles were also examined.

RESULTS

CD86-silenced-DCs had unchanged expression of CD80 and significantly suppressed the proliferation of lymphocytes. CD86-silenced-DCs simultaneously reduced IL-2 and INF-γ and increased IL-10, TGF-β and IDO, while had minimal effect on IL-4. The CD86-silenced-DCs also improved cell viability and function of xeno-islets when compared to untransfection and transfection control groups. In xeno-islets transplanted diabetic mice, transfer of CD86-silenced-DCs resulted in improved histopathology and dramatically prolonged survival time of the islets. These effects were also mirrored by the functional tests. Further analysis revealed that CD86-silenced-DCs had up-regulated levels of CD4(+)CD25(+)T cells in the peripheral blood compared to the other groups.

CONCLUSIONS

CD86-silenced-DCs induced immune tolerance of rat xeno-islets in recipient diabetic mice with up-regulated peripheral blood CD4(+)CD25(+)T cells.

Lupus-Prone Mice Resist Immune Regulation and Transplant Tolerance Induction

The strongly immunogenic environment in autoimmune diseases such as lupus may pose a stringent barrier to transplantation. Despite available murine models of lupus, transplant tolerance in this setting has yet to be fully investigated in highly penetrant genetic models of disease. Such studies are of clear clinical importance because lupus is a transplant indication in which transplanted kidneys have a substantially increased risk of rejection including a role for recurrent nephritis. In the fully penetrant B6.SLE123 mouse, we determined that CD4 T follicular helper and germinal center B cells were significantly expanded compared with healthy controls. We traced this expansion to resistance of effector CD4 T and B cells in B6.SLE123 mice to regulation by either CD4 T regulatory cells (CD4Tregs) or CD8 T regulatory cells (CD8Tregs), despite demonstrating normal function by Tregs in this strain. Finally, we determined that B6.SLE123 mice resist anti-CD45RB-mediated tolerance induction to foreign islet allografts, even in the absence of islet autoimmunity. Overall, B6.SLE123 lupus-prone mice are highly resistant to transplant tolerance induction, which provides a new model of failed tolerance in autoimmunity that may elucidate barriers to clinical transplantation in lupus through further cellular and genetic dissection.

Anti-TCR mAb induces peripheral tolerance to alloantigens and delays islet allograft rejection in autoimmune diabetic NOD mice

BACKGROUND

Clinical application of islet transplantation to treat type 1 diabetes has been limited by islet allograft destruction by both allogeneic and autoimmune diabetogenic T-cell responses. The current study aims at determining whether an anti-T-cell receptor (TCR) monoclonal antibody (mAb) has potential as a novel and potent induction immunotherapy for islet transplantation.

METHODS

We have investigated the therapeutic efficacy and mechanisms of action of anti-TCR therapy in four different murine models, which comprise either allo- or autoimmune responses alone or both together.

RESULTS

T-cell response to islet allografts was potently abrogated by a brief treatment with an anti-TCRβ mAb (clone H57-597), resulting in long-term survival of BALB/c islet allografts in streptozotocin-induced diabetic B6 mice. Moreover, transient anti-TCR treatment permanently prevented BALB/c skin allograft rejection on Rag1 B6 recipients that were reconstituted with Foxp3 cell-depleted B6 splenocytes, but did not impair the reconstituted cells' ability to reject the later transplanted C3H skin allografts (transplanted at 120 days after BALB/c skin grafting). Transient anti-TCR treatment was also able to completely prevent diabetes onset in NOD.SCID.γc mice that were transferred with lymphocytes from diabetic NOD mice. Next, transient anti-TCR treatment significantly prolonged the survival of transplanted BALB/c islets in overtly diabetic NOD mice, which comprise both allogeneic and autoimmune diabetogenic T-cell responses to the transplanted islets.

CONCLUSIONS

Overall, anti-TCR mAb induced peripheral tolerance to specific alloantigens even in the absence of Foxp3-expressing natural regulatory T cells. These findings reveal the potential for using TCR-targeting mAbs as induction immunotherapy for islet transplantation.

Transdisciplinary approach to restore pancreatic islet function

The focus of our research is on islet immunobiology. We are exploring novel strategies that could be of assistance in the treatment and prevention of type 1 diabetes, as well as in the restoration of metabolic control via transplantation of insulin producing cells (i.e., islet cells). The multiple facets of diabetes and β-cell replacement encompass different complementary disciplines, such as immunology, cell biology, pharmacology, and bioengineering, among others. Through their interaction and integration, a transdisciplinary dimension is needed in order to address and overcome all aspects of the complex puzzle toward a successful clinical translation of a biological cure for diabetes.

Homeostatic T cell proliferation after islet transplantation

Pancreatic islet transplantation in patients with type 1 diabetes mellitus is performed under immunosuppression to avoid alloreactive T cell responses and to control the reactivation of autoreactive memory T cells. However, lymphopenia associated with immunosuppression and T cell depletion can induce a paradoxical expansion of lymphocyte subsets under the influence of homeostatic proliferation. Homeostatic T cell proliferation is mainly driven by the IL-7/IL-7 receptor axis, a molecular pathway which is not affected by standard immune-suppressive drugs and, consequently, represents a novel potential target for immuno-modulatory strategies. In this review, we will discuss how homeostatic T cell proliferation can support autoimmunity recurrence after islet transplantation and how it can be targeted by new therapeutic approaches.

Prevention of autoimmune diabetes and induction of β-cell proliferation in NOD mice by hyperbaric oxygen therapy

We evaluated the effects of hyperbaric oxygen therapy (HOT) on autoimmune diabetes development in nonobese diabetic (NOD) mice. Animals received no treatment or daily 60-min HOT 100% oxygen (HOT-100%) at 2.0 atmospheres absolute and were monitored for diabetes onset, insulitis, infiltrating cells, immune cell function, and β-cell apoptosis and proliferation. Cyclophosphamide-induced diabetes onset was reduced from 85.3% in controls to 48% after HOT-100% (P < 0.005) and paralleled by lower insulitis. Spontaneous diabetes incidence reduced from 85% in controls to 65% in HOT-100% (P = 0.01). Prediabetic mice receiving HOT-100% showed lower insulitis scores, reduced T-cell proliferation upon stimulation in vitro (P < 0.03), increased CD62L expression in T cells (P < 0.04), reduced costimulation markers (CD40, DC80, and CD86), and reduced major histocompatibility complex class II expression in dendritic cells (DCs) (P < 0.025), compared with controls. After autoimmunity was established, HOT was less effective. HOT-100% yielded reduced apoptosis (transferase-mediated dUTP nick-end labeling-positive insulin-positive cells; P < 0.01) and increased proliferation (bromodeoxyuridine incorporation; P < 0.001) of insulin-positive cells compared with controls. HOT reduces autoimmune diabetes incidence in NOD mice via increased resting T cells and reduced activation of DCs with preservation of β-cell mass resulting from decreased apoptosis and increased proliferation. The safety profile and noninvasiveness makes HOT an appealing adjuvant therapy for diabetes prevention and intervention trials.

Targeted deletion of one or two copies of the G protein β subunit Gβ5 gene has distinct effects on body weight and behavior in mice

We investigated the physiological role of Gβ5, a unique G protein β subunit that dimerizes with regulators of G protein signaling (RGS) proteins of the R7 family instead of Gγ. Gβ5 is essential for stability of these complexes, so that its knockout (KO)causes degradation of the entire Gβ5-R7 family. We report that the Gβ5-KO mice remain leaner than the wild type (WT) throughout their lifetime and are resistant to a high-fat diet. They have a 5-fold increase in locomotor activity, increased thermogenesis, and lower serum insulin, all of which correlate with a higher level of secreted epinephrine. Heterozygous (HET) mice are 2-fold more active than WT mice. Surprisingly, with respect to body weight, the HET mice display a phenotype opposite to that of the KO mice: by the age of 6 mo, they are ≥ 15% heavier than the WT and have increased adiposity, insulin resistance, and liver steatosis. These changes occur in HET mice fed a normal diet and without apparent hyperphagia, mimicking basic characteristics of human metabolic syndrome. We conclude that even a partial reduction in Gβ5-R7 level can perturb normal animal metabolism and behavior. Our data on Gβ5 haploinsufficient mice may explain earlier observations of genetic linkage between R7 family mutations and obesity in humans.

A novel clinically relevant strategy to abrogate autoimmunity and regulate alloimmunity in NOD mice

OBJECTIVE

To investigate a new clinically relevant immunoregulatory strategy based on treatment with murine Thymoglobulin mATG Genzyme and CTLA4-Ig in NOD mice to prevent allo- and autoimmune activation using a stringent model of islet transplantation and diabetes reversal.

RESEARCH DESIGN AND METHODS

Using allogeneic islet transplantation models as well as NOD mice with recent onset type 1 diabetes, we addressed the therapeutic efficacy and immunomodulatory mechanisms associated with a new immunoregulatory protocol based on prolonged low-dose mATG plus CTLA4-Ig.

RESULTS

BALB/c islets transplanted into hyperglycemic NOD mice under prolonged mATG+CTLA4-Ig treatment showed a pronounced delay in allograft rejection compared with untreated mice (mean survival time: 54 vs. 8 days, P < 0.0001). Immunologic analysis of mice receiving transplants revealed a complete abrogation of autoimmune responses and severe downregulation of alloimmunity in response to treatment. The striking effect on autoimmunity was confirmed by 100% diabetes reversal in newly hyperglycemic NOD mice and 100% indefinite survival of syngeneic islet transplantation (NOD.SCID into NOD mice).

CONCLUSIONS

The capacity to regulate alloimmunity and to abrogate the autoimmune response in NOD mice in different settings confirmed that prolonged mATG+CTLA4-Ig treatment is a clinically relevant strategy to translate to humans with type 1 diabetes.

Key developmental transitions in human germinal center B cells are revealed by differential CD45RB expression

We previously reported that RO(+) expression correlated with increased mutation, activation, and selection among human germinal center (GC) B cells. Here, we subdivided human tonsillar B cells, including IgD(-)CD38(+) GC B cells, into different fractions based on RB expression. Although each subset contained RB(+) cells, when used as an intrasubset marker, differential RB expression effectively discriminated between phenotypically distinct cells. For example, RB(+) GC B cells were enriched for activated cells with lower AID expression. RB inversely correlated with mutation frequency, demonstrating a key difference between RB- and RO-expressing GC B cells. Reduced RB expression during the transition from pre-GC (IgM(+)IgD(+)CD38(+)CD27(-)) to GCB cells was followed by a dramatic increase during the GC-to-plasmablast (IgD(-)CD38(++)CD27(+)) and memory (IgD(-)CD38(-)CD27(+)) transition. Interestingly, RB(+) GC B cells showed increased signs of terminal differentiation toward CD27(+) post-GC early plasmablast (increased CD38 and RO) or early memory (decreased CD38 and RO) B cells. We propose that as in T cells, differential RB expression directly correlates with development- and function-based transitions in tonsillar B cells. Application of this RB:RO system should advance our understanding of normal B-cell development and facilitate the isolation of more discrete B-cell populations with potentially different propensities in disease pathogenesis.

CD28/CD154 blockade prevents autoimmune diabetes by inducing nondeletional tolerance after effector t-cell inhibition and regulatory T-cell expansion

OBJECTIVE

Blocking T-cell signaling is an effective means to prevent autoimmunity and allograft rejection in many animal models, yet the clinical translation of many of these approaches has not resulted in the success witnessed in experimental systems. Improved understanding of these approaches may assist in developing safe and effective means to treat disorders such as autoimmune diabetes.

RESEARCH DESIGN AND METHODS

We studied the effect of anti-CD154 and CTLA4-Ig on diabetes development, and the requirements to induce tolerance in nod.scid mice after transfer of transgenic beta-cell reactive BDC2.5.NOD T-cells.

RESULTS

Nod.scid recipients of diabetogenic BDC2.5.NOD cells were protected indefinitely from diabetes by a short course of combined costimulation blockade, despite the continued diabetogenic potential of their T-cells. The presence of pathogenic T-cells in the absence of disease indicates peripheral immune tolerance. T-cell maturation occurred in protected recipients, yet costimulation blockade temporarily blunted early T-cell proliferation in draining pancreatic nodes. Tolerance required preexisting regulatory T-cells (Tregs), and protected recipients had greater numbers of Tregs than diabetic recipients. Diabetes protection was successful in the presence of homeostatic expansion and high T-cell precursor frequency, both obstacles to tolerance induction in other models of antigen-specific immunity.

CONCLUSIONS

Immunotherapies that selectively suppress effector T-cells while permitting the development of natural regulatory mechanisms may have a unique role in establishing targeted long-standing immune protection and peripheral tolerance. Understanding the mechanism of these approaches may assist in the design and use of therapies for human conditions, such as type 1 diabetes.

Human alpha 1-antitrypsin therapy induces fatal anaphylaxis in non-obese diabetic mice

Previous studies have shown that human alpha-1 antitrypsin (hAAT) gene delivery prevents type 1 diabetes (T1D) in non-obese diabetic (NOD) mice. Furthermore, hAAT protein administration prolongs acceptance of islet allografts. Therefore, we evaluated the use of purified hAAT protein therapy to prevent T1D in NOD mice. Female NOD, non-obese resistant (NOR), Balb/c and C57BL/6 mice were injected intraperitoneally with vehicle alone or vehicle containing hAAT, human albumin or mouse albumin (or mg/injection/mouse; 2x/week). Preparations of clinical-grade hAAT included API(R), Aralast, Prolastin and Zemaira. Surprisingly, hAAT administration was associated with a high rate of fatal anaphylaxis. In studies seeking T1D prevention at 4 weeks of age, 100% mice died after six injections of hAAT. When administrated at 8-10 weeks of age, most (80-100%) NOD mice died following the fourth injection of hAAT, while 0% of Balb/c and C57BL/6 mice and 10% of NOR mice died. Interestingly, repeated injections of human albumin, but not mouse albumin, also induced sudden death in NOD mice. Antibodies to hAAT were induced 2-3 weeks after hAAT administration and death was prevented by treatment with anti-platelet-activating factor along with anti-histamine. In studies of disease reversal in NOD mice, using the four pharmaceutical grade formulations of hAAT, anaphylactic deaths were observed with all hAAT preparations. The propensity for fatal anaphylaxis following antigenic administration appears to be NOD- but not hAAT-specific. The susceptibility of NOD mice to hypersensitivity provides a significant limitation for testing of hAAT. Development of strategies to avoid this unwanted response is required to use this promising therapeutic agent for T1D.

Immunoglobulin-like transcript 3-Fc suppresses T-cell responses to allogeneic human islet transplants in hu-NOD/SCID mice

OBJECTIVE

The aim of our study was to explore the immunomodulatory activity of soluble immunoglobulin (Ig)-like transcript (ILT) 3-Fc in pancreatic islet transplantation and to determine its mechanism of action.

RESEARCH DESIGN AND METHODS

NOD/SCID mice in which diabetes was induced by streptozotocin injection were transplanted with human pancreatic islet cells. Mice in which the transplant restored euglycemia were humanized with allogeneic peripheral blood mononuclear cells and treated with ILT3-Fc or control human IgG or left untreated. The blood glucose level was monitored twice a week, and rejection was diagnosed after two consecutive readings >350 mg/dl. Tolerated and rejected grafts were studied histologically and by immunostaining for human T-cells and insulin production. CD4 and CD8 T-cells from the spleen were studied for suppressor activity, expression of cytokines, and CD40L.

RESULTS

Although human T-cell engraftment was similar in all groups, ILT3-Fc-treated mice tolerated the islets for the entire period of observation (91 days), whereas control mice rejected the graft within 7 weeks (P < 0.0001). ILT3-Fc treatment suppressed the expression of cytokines and CD40L and induced the differentiation of human CD8(+) T suppressor cells that inhibited Th alloreactivity against graft HLA antigens. T-cells allostimulated in vitro in the presence of ILT3-Fc inhibited CD40L-induced upregulation of CD40 in human pancreatic islet cells. Histochemical studies showed dramatic differences between human pancreatic islets from tolerant, ILT3-Fc-treated mice and control recipients rejecting the grafts.

CONCLUSIONS

The data indicated that ILT3-Fc is a potent immunoregulatory agent that suppressed islet allograft rejection in humanized NOD/SCID mice.

Prolonged islet allograft survival in diabetic mice upon macrophage depletion by clodronate-loaded erythrocytes

Early impairment of islet function and graft loss strongly limit the success of allogenic islet transplantation in insulin-dependent diabetes. Macrophages play a key role in this process thus the depletion of these cells may strongly affect islet survival. In this study, we have evaluated the effect of the depletion of macrophages in mouse allograft rejection using a new approach based on a single infusion of red blood cells loaded with the synthetic analogue of pyrophosphate clodronate. Graft survival was 19.4+/-0.89 and 20+/-2 days in the two control groups treated with physiological solution and unloaded erythrocytes, respectively; 25+/-1.9 days in the group treated with free-clodronate and 35+/-6 days in the erythrocytes-loaded group. Our results indicate clodronate selectively targeted to the macrophagic cells by a single administration of engineered erythrocytes can significantly prolong islet graft survival and open new therapeutic strategies in islet transplantation.

Heme oxygenase-1, carbon monoxide, and bilirubin induce tolerance in recipients toward islet allografts by modulating T regulatory cells

Heme oxygenase-1 (HO-1) induction in, or carbon monoxide (CO), or bilirubin administration to, donors and/or recipients frequently lead to long-term survival (>100 days) of DBA/2 islets into B6AF1 recipients. We tested here whether similar treatments show value in a stronger immunogenetic combination, i.e., BALB/c to C57BL/6, and attempted to elucidate the mechanism accounting for tolerance. Induction of HO-1, administering CO or bilirubin to the donor, the islets or the recipient, prolonged islet allograft survival to different extents. Combining all the above treatments (the "combined" protocol) led to survival for >100 days and antigen-specific tolerance to 60% of the transplanted grafts. A high level of forkhead box P3 (Foxp3) and transforming growth factor beta (TGF-beta) expression was detected in the long-term surviving grafts. With the combined protocol, significantly more T regulatory cells (Tregs) were observed surrounding islets 7 days following transplantation. No prolongation of graft survival was observed using the combined protocol when CD4+ CD25+ T cells were predepleted from the recipients before transplantation. In conclusion, our combined protocol led to long-term survival and tolerance to islets in the BALB/c to C57BL/6 combination by promoting Foxp3+ Tregs; these cells played a critical role in the induction and maintenance of tolerance in the recipient.

Toll‐like receptor 4 suppression leads to islet allograft survival

Carbon monoxide (CO) exposure of an islet donor frequently leads to islet allograft long-term survival and tolerance in recipients. We show here that CO confers its protective effects at least in part by suppressing Toll-like receptor 4 (TLR4) up-regulation in pancreatic beta cells. TLR4 is normally up-regulated in islets during the isolation procedure; donor treatment with CO suppresses TLR4 expression in isolated islets as well as in transplanted grafts. TLR4 up-regulation allows initiation of inflammation, which leads to islet allograft rejection; islet grafts from TLR4-deficient mice survive indefinitely in BALB/c recipients and show significantly less inflammation at various days after transplantation compared with grafts from a control donor. Isolated islets preinfected with a TLR4 dominant negative virus before transplantation demonstrated prolonged survival in recipients. Despite the salutary effects of TLR4 suppression, HO-1 expression is still needed in the recipient for islet survival: TLR4-deficient islets were rejected promptly after being transplanted into recipients in which HO-1 activity was blocked. In addition, incubation of an insulinoma cell line, betaTC3, with an anti-TLR4 antibody protects those cells from cytokine-induced apoptosis. Our data suggest that TLR4 induction in beta cells is involved in beta cell death and graft rejection after transplantation. CO exposure protects islets from rejection by blocking TLR4 up-regulation.

Beneficial effects of simultaneous treatment with 15-deoxyspergualin and monoclonal antibodies to CD45RB and CD154 on murine islet transplantation recipients

BACKGROUND

Treatment of transplant recipients with either 15-deoxyspergualin (DSG) or monoclonal antibodies (mAbs) to T-cell proteins CD45RB and CD154 (a two-signal blockade) has been shown to prolong islet graft survival. Therefore, we investigated the combined effect of DSG, anti-CD45RB, and anti-CD154 in murine islet model.

METHODS

Chemically induced diabetic C57BL/6 mice underwent allografting with islets from BALB/c mice or xenografting with rat islets. After transplantation, they were treated with either DSG, the two-signal blockade, or both (the triple treatment). The tolerogenic effects of the posttransplant treatments were measured with an intraperitoneal glucose tolerance test (IPGTT), immunohistology, enzyme-linked immunosorbent assays, and flow cytometry.

RESULTS

Blood glucose profiles measured after glucose challenges were improved in all islet recipients. Enhancement of xenograft survival in triple-treated groups was not statistically significant (P = 0.08), compared to graft survival in group received only the two-signal blockade. However, 15 days after transplantation, xenografts in the triple-treated group showed a significant decrease in the proportion of CD4, CD8, and CD4CD45RB T-cells, and in the expression of interleukin-10 and interferon-gamma, relative to grafts in the other treatment groups. In addition, reduced infiltration of the xenografts by CD3 T-cells was observed in groups that had received either the two-signal blockade or the triple treatment. With long-term (>248 days) xenografts, only those in the triple-treated group were free of inflammatory infiltrates. These grafts also exhibited larger islet clusters and contained more insulin- and glucagon-positive cells, relative to grafts in the other treatment groups.

CONCLUSION

Triple treatment has a beneficial effect in murine islet xenotransplantation.

Lessons on autoimmune diabetes from animal models

T1DM (Type I diabetes mellitus) results from selective destruction of the insulin-producing beta-cells of the pancreas by the immune system, and is characterized by hyperglycaemia and vascular complications arising from suboptimal control of blood glucose levels. The discovery of animal models of T1DM in the late 1970s and early 1980s, particularly the NOD (non-obese diabetic) mouse and the BB (BioBreeding) diabetes-prone rat, had a fundamental impact on our ability to understand the genetics, aetiology and pathogenesis of this disease. NOD and BB diabetes-prone rats spontaneously develop a form of diabetes that closely resembles the human counterpart. Early studies of these animals quickly led to the realization that T1DM is caused by autoreactive T-lymphocytes and revealed that the development of T1DM is controlled by numerous polymorphic genetic elements that are scattered throughout the genome. The development of transgenic and gene-targeting technologies during the 1980s allowed the generation of models of T1DM of reduced genetic and pathogenic complexity, and a more detailed understanding of the immunogenetics of T1DM. In this review, we summarize the contribution of studies in animal models of T1DM to our current understanding of four fundamental aspects of T1DM: (i) the nature of genetic elements affording T1DM susceptibility or resistance; (ii) the mechanisms underlying the development and recruitment of pathogenic autoreactive T-cells; (iii) the identity of islet antigens that contribute to the initiation and/or progression of islet inflammation and beta-cell destruction; and (iv) the design of avenues for therapeutic intervention that are rooted in the knowledge gained from studies of animal models. Development of new animal models will ensure continued progress in these four areas.

Prospective and challenges of islet transplantation for the therapy of autoimmune diabetes

Pancreatic islet cell transplantation is an attractive treatment of type 1 diabetes (T1D). The success enhanced by the Edmonton protocol has fostered phenomenal progress in the field of clinical islet transplantation in the past 5 years, with 1-year rates of insulin independence after transplantation near 80%. Long-term function of the transplanted islets, however, even under the Edmonton protocol, seems difficult to accomplish, with only 10% of patients maintaining insulin independence 5 years after transplantation. These results differ from the higher metabolic performance achieved by whole pancreas allotransplantation, and autologous islet cell transplantation, and form the basis for a limited applicability of islet allografts to selected adult patients. Candidate problems in islet allotransplantation deal with alloimmunity, autoimmunity, and the need for larger islet cell masses. Employment of animal islets and stem cells, as alternative sources of insulin production, will be considered to face the problem of human tissue shortage. Emerging evidence of the ability to reestablish endogenous insulin production in the pancreas even after the diabetic damage occurs envisions the exogenous supplementation of islets to patients also as a temporary therapeutic aid, useful to buy time toward a possible self-healing process of the pancreatic islets. All together, islet cell transplantation is moving forward.

Bilirubin can induce tolerance to islet allografts

Induction of heme oxygenase-1 (HO-1) expression in recipients of allogeneic islets can lead to long-term survival (>100 d) of those islets. We tested whether administration of bilirubin would substitute for the beneficial effects of HO-1 expression in islet transplantation. Administering bilirubin to the recipient (B6AF1) or incubating islets in a bilirubin-containing solution ex vivo led to long-term survival of allogeneic islets in a significant percentage of cases. In addition, administering bilirubin to only the donor frequently led to long-term survival of DBA/2 islets in B6AF1 recipients and significantly prolonged graft survival of BALB/c islets in C57BL/6 recipients. Donor treatment with bilirubin up-regulated mRNA expression of protective genes such as HO-1 and bcl-2 and suppressed proinflammatory and proapoptotic genes including monocyte chemoattractant protein-1 and caspase-3 and -8 in the islet grafts before transplantation. Furthermore, treatment of only the donor suppressed the expression of proinflammatory cytokines including TNF-alpha, inducible nitric oxide synthase, monocyte chemoattractant protein-1, and other proapoptotic and proinflammatory genes normally seen in the islets after transplantation. Donor treatment also reduced the number of macrophages that infiltrated the islet grafts in the recipients. Preincubation of betaTC3 cells with bilirubin also protected the cells from lipid peroxidation. Our data suggests that the potent antioxidant and antiinflammatory actions of bilirubin may contribute to islet survival.

Islet allograft survival induced by costimulation blockade in NOD mice is controlled by allelic variants of Idd3

NOD mice develop type 1 autoimmune diabetes and exhibit genetically dominant resistance to transplantation tolerance induction. These two phenotypes are genetically separable. Costimulation blockade fails to prolong skin allograft survival in (NOD x C57BL/6)F1 mice and in NOD-related strains made diabetes-resistant by congenic introduction of protective major histocompatibility complex (MHC) or non-MHC Idd region genes. Here, we tested the hypothesis that the genetic basis for the resistance of NOD mice to skin allograft tolerance also applies to islet allografts. Surprisingly, costimulation blockade induced permanent islet allograft survival in (NOD x C57BL/6)F1 mice but not in NOD mice. After costimulation blockade, islet allograft survival was prolonged in diabetes-resistant NOD.B6 Idd3 mice and shortened in diabetes-free C57BL/6 mice congenic for the NOD Idd3 variant. Islet allograft tolerance could not be induced in diabetes-resistant NOD.B10 Idd5 and NOD.B10 Idd9 mice. The data demonstrate that 1) NOD mice resist islet allograft tolerance induction; 2) unlike skin allografts, resistance to islet allograft tolerance is a genetically recessive trait; 3) an Idd3 region gene(s) is an important determinant of islet allograft tolerance induction; and 4) there may be overlap in the mechanism by which the Idd3 resistance locus improves self-tolerance and the induction of allotolerance.

The CD40/CD40L costimulatory pathway in inflammatory bowel disease

The CD154-CD40 ligand pair interaction plays a central role in both induction of the immune response and in immune effector functions. Indeed, many animal disease models and human autoimmune diseases have demonstrated a central role for CD154 expression. The expression of CD154 is very tightly regulated by the immune system through a number of non-redundant overlapping mechanisms that ensure its limited initial induction, along with its temporal maintenance and rapid elimination from the cell surface, and its functional neutralization by the release of soluble CD40. In this review, we discuss the current state of understanding of CD154 regulation during the activation of the immune system and describe numerous strategic mechanisms by which modulation of CD154-CD40 interactions may be applied to treat autoimmune disease.

Islet transplantation: immunological perspectives

Clinical trials of islet transplantation are showing remarkable success, but they require administration of chronic immunosuppression, and are underscoring the large gap that exists between the number of human donors available and the number of patients that could benefit from the procedure. Recent progress has been made in the definition of key immunological mechanisms that are involved in determining islet transplant outcome. Clinical and preclinical studies, and studies in small animal model systems, will all eventually contribute to the definition of efficient and safe protocols for islet transplantation. If the use of xenografts is successful, it might represent a solution to the shortage of human organs.

Islet transplantation in patients with diabetes mellitus: choice of immunosuppression

Islet transplantation offers patients with type 1 diabetes mellitus freedom from long-term insulin therapy and a degree of metabolic control that is far superior to injected insulin. The hope is that near-perfect glucose control sustained over time will prevent progression of secondary diabetic complications. The selection of optimal immunosuppressive agents for islet transplantation has been a formidable challenge, given the need to overcome both autoimmune and alloimmune barriers, as well as the potential toxicity of immunosuppressive agents on transplanted islets. Early strategies relied on protocols that had proven success in solid organ transplantation and consisted of azathioprine, cyclosporine and corticosteroids. Under these protocols, fewer than 10% of patients were able to achieve insulin independence. The development of the 'Edmonton Protocol' dramatically transformed clinical outcomes in islet transplantation in recent years through the introduction of a more potent, less diabetogenic, and corticosteroid-free immunosuppressive regimen consisting of sirolimus, low-dose tacrolimus, and induction anti-interleukin-2 receptor antibody. While insulin independence rates under this protocol have been highly successful, patients must be maintained on lifelong immunosuppression. While the risk of malignancy, post-transplant lymphoma and sepsis have been low and diminishing in transplanted patients to date, fears of these complications and a host of drug-related adverse effects have precluded broader application. Patients undergoing islet transplantation today must exchange insulin for chronic immunosuppressive therapy, and therefore the procedure can only be justified in patients with very unstable forms of diabetes, or in those with another solid organ allograft who already endure the risks of immunosuppression. Advances in more specific and less toxic immunosuppressive agents together with progress in better understanding the biology of diabetes will lead to more suitable strategies to control both alloimmune and recurrent autoimmune reactions. These protocols, ultimately aimed at establishing tolerance, are an essential pre-requisite to move towards providing islet transplantation earlier in the course of the disease, including transplantation in children. This review addresses the evolution of immunosuppressive strategies in islet transplantation, and highlights some novel agents in pre-clinical development or in early clinical trials that may offer considerable promise in facilitating the induction of tolerance.

The effect of simultaneous CD154 and LFA-1 blockade on the survival of allogeneic islet grafts in nonobese diabetic mice1

BACKGROUND

The rate of success in clinical transplantation of islets of Langerhans has dramatically improved with perspectives of wide-scale applicability for patients with type 1 diabetes. One drawback is the need for lifelong immunosuppression, which is associated with significant side effects. Immunomodulatory strategies devoid of side effects and with tolerogenic potential, such as co-stimulatory blockade, would be a great improvement if successful. In this study, the authors have explored the effect of simultaneous blockade of CD40/CD154 and intercellular adhesion molecule (ICAM)/lymphocyte function-associated antigen (LFA)-1 interactions.

METHODS

Spontaneously diabetic nonobese diabetic (NOD) mice underwent transplantation with allogeneic (C57BL/6) islets and were treated with anti-CD154 monoclonal antibody (mAb) (500 microg, three doses), anti-LFA-1 mAb (100 microg, three doses), or a combination of both in the early peritransplant period. In another set of experiments, LFA-1 engagement was impaired by transplanting islets isolated from ICAM-1-knockout (KO) mice.

RESULTS

Untreated animals rejected their grafts within 10 days. LFA-1 blockade alone did not result in improved islet graft survival, whereas CD154 blockade alone increased graft survival to 18 days. Simultaneous blockade of both pathways led to significantly improved islet graft survival to 30 days (ICAM-1-KO islets plus anti-CD154), 35 days (anti-LFA-1 plus anti-CD154), and 44 days (ICAM-1-KO islets plus anti-LFA-1 plus anti-CD154).

CONCLUSIONS

These data suggest that a synergistic effect for prolonged graft survival can be obtained by simultaneously targeting CD154 and LFA-1 in the challenging model of islet allotransplantation in NOD mice. The observation of similar results with anti-LFA-1 mAb and with ICAM-1-KO grafts suggests a key role of direct antigen presentation for the activation of LFA-1-driven signaling.