Immunotherapy with nondepleting anti-CD4 monoclonal antibodies but not CD28 antagonists protects islet graft in spontaneously diabetic nod mice from autoimmune destruction and allogeneic and xenogeneic graft rejection

Cluster of differentiation molecules in the metabolic syndrome

Metabolic syndrome (MetS) represents a significant public health concern due to its association with an increased risk of cardiovascular disease, type 2 diabetes, and other serious health conditions. Despite extensive research, the underlying molecular mechanisms contributing to MetS pathogenesis remain elusive. This review aims to provide a comprehensive overview of the molecular mechanisms linking MetS and cluster of differentiation (CD) markers, which play critical roles in immune regulation and cellular signaling. Through an extensive literature review with a systematic approach, we examine the involvement of various CD markers in MetS development and progression, including their roles in adipose tissue inflammation, insulin resistance, dyslipidemia, and hypertension. Additionally, we discuss potential therapeutic strategies targeting CD markers for the management of MetS. By synthesizing current evidence, this review contributes to a deeper understanding of the complex interplay between immune dysregulation and metabolic dysfunction in MetS, paving the way for the development of novel therapeutic interventions.

Invariant NKT Cells Promote the Development of Highly Cytotoxic Multipotent CXCR3+CCR4+CD8+ T Cells That Mediate Rapid Hepatocyte Allograft Rejection

Hepatocyte transplant represents a treatment for metabolic disorders but is limited by immunogenicity. Our prior work identified the critical role of CD8+ T cells, with or without CD4+ T cell help, in mediating hepatocyte rejection. In this study, we evaluated the influence of invariant NKT (iNKT) cells, uniquely abundant in the liver, upon CD8-mediated immune responses in the presence and absence of CD4+ T cells. To investigate this, C57BL/6 (wild-type) and iNKT-deficient Jα18 knockout mice (cohorts CD4 depleted) were transplanted with allogeneic hepatocytes. Recipients were evaluated for alloprimed CD8+ T cell subset composition, allocytotoxicity, and hepatocyte rejection. We found that CD8-mediated allocytotoxicity was significantly decreased in iNKT-deficient recipients and was restored by adoptive transfer of iNKT cells. In the absence of both iNKT cells and CD4+ T cells, CD8-mediated allocytotoxicity and hepatocyte rejection was abrogated. iNKT cells enhance the proportion of a novel subset of multipotent, alloprimed CXCR3+CCR4+CD8+ cytolytic T cells that develop after hepatocyte transplant and are abundant in the liver. Alloprimed CXCR3+CCR4+CD8+ T cells express cytotoxic effector molecules (perforin/granzyme and Fas ligand) and are distinguished from alloprimed CXCR3+CCR4-CD8+ T cells by a higher proportion of cells expressing TNF-α and IFN-γ. Furthermore, alloprimed CXCR3+CCR4+CD8+ T cells mediate higher allocytotoxicity and more rapid allograft rejection. Our data demonstrate the important role of iNKT cells in promoting the development of highly cytotoxic, multipotent CXCR3+CCR4+CD8+ T cells that mediate rapid rejection of allogeneic hepatocytes engrafted in the liver. Targeting iNKT cells may be an efficacious therapy to prevent rejection of intrahepatic cellular transplants.

Stimulating β-cell replication and improving islet graft function by AR231453, A GPR119 agonist

OBJECTIVE

G protein-coupled receptor 119 (GPR119) is predominantly expressed in β cells and intestinal L cells. AR231453 is a selective small-molecular GPR119 agonist that enhances glucose-dependent insulin secretion and glucagon-like peptide 1 (GLP-1) release. We investigated whether AR231453 can directly stimulate β-cell replication and improve islet graft function in diabetic mice.

METHODS

A total of 100 syngenic C57BL/6 mouse islets were transplanted under the left kidney of each chemically induced diabetic C57BL/6 mouse. Starting from the day of transplantation, these recipients were given bromodeoxyuridine (BrdU) daily with or without AR231453 at 10 mg/kg/d. Islet graft function was monitored by measuring blood glucose levels. At 4 weeks, left nephrectomy was performed to remove the kidney bearing the islet grafts to determine β-cell replication in the islet grafts. Insulin and BrdU immunofluorescence staining was performed to detect replicated β cells. Insulin(+) and BrdU(+) β cells in islet grafts were counted using a confocal microscope. To determine whether AR231453 increases plasma GLP-1 levels, we collected plasma from AR231453 treated mice at 30 minutes after treatment and measured plasma active GLP-1 by enzyme-linked immunosorbent assay.

RESULTS

Although all recipient mice achieved normoglycemia at 28 days with or without treatment, normoglycemia was achieved in significantly fewer days in AR231453-treated mice. The vehicle-treated mice achieved normoglycemia in 16 ± 6 days, while AR231453-treated mice only required only 8 ± 3 days (P < .01). The percentage of insulin(+) and BrdU(+) β cells in islet grafts was significantly higher in AR231453-treated mice than in vehicle-treated mice. The mean percentage of insulin(+) and BrdU(+) β cells in islet grafts was 21.5% ± 6.9% in AR231453-treated mice and 5.6% ± 3.7% in vehicle-treated mice (P < .01). The plasma active GLP-1 levels were also significantly higher in AR231453-treated mice than in vehicle-treated mice (P < .05).

CONCLUSION

Our data demonstrate that AR231453, a GPR119 agonist, can stimulate β-cell replication and improve islet graft function.

Transient B-cell depletion combined with apoptotic donor splenocytes induces xeno-specific T- and B-cell tolerance to islet xenografts

Peritransplant infusion of apoptotic donor splenocytes cross-linked with ethylene carbodiimide (ECDI-SPs) has been demonstrated to effectively induce allogeneic donor-specific tolerance. The objective of the current study is to determine the effectiveness and additional requirements for tolerance induction for xenogeneic islet transplantation using donor ECDI-SPs. In a rat-to-mouse xenogeneic islet transplant model, we show that rat ECDI-SPs alone significantly prolonged islet xenograft survival but failed to induce tolerance. In contrast to allogeneic donor ECDI-SPs, xenogeneic donor ECDI-SPs induced production of xenodonor-specific antibodies partially responsible for the eventual islet xenograft rejection. Consequently, depletion of B cells prior to infusions of rat ECDI-SPs effectively prevented such antibody production and led to the indefinite survival of rat islet xenografts. In addition to controlling antibody responses, transient B-cell depletion combined with ECDI-SPs synergistically suppressed xenodonor-specific T-cell priming as well as memory T-cell generation. Reciprocally, after initial depletion, the recovered B cells in long-term tolerized mice exhibited xenodonor-specific hyporesponsiveness. We conclude that transient B-cell depletion combined with donor ECDI-SPs is a robust strategy for induction of xenodonor-specific T- and B-cell tolerance. This combinatorial therapy may be a promising strategy for tolerance induction for clinical xenogeneic islet transplantation.

Stimulating beta cell replication and improving islet graft function by GPR119 agonists

G protein-coupled receptor 119 (GPR119) is predominantly expressed in β cells and intestinal L cells. In this study, we investigated whether oleoylethanolamide (OEA), a GPR119 endogenous ligand, and PSN632408, a GPR119 synthetic agonist, can stimulate β-cell replication in vitro and in vivo and improve islet graft function in diabetic mice. We found that OEA and PSN632408 significantly increased numbers of insulin(+)/5-bromo-2'-deoxyuridine (BrdU)(+) β cells in cultured mouse islets in a dose-dependent manner. All diabetic recipient mice, given marginal syngeneic islet transplants with OEA or PSN632408 or vehicle, achieved normoglycemia at 4 weeks after transplantation. However, normoglycemia was achieved significantly faster in OEA- or PSN632408-treated diabetic mice than in vehicle-treated diabetic mice (P < 0.05). The percentage of insulin(+)/BrdU(+) β cells in islet grafts in OEA- and PSN632408-treated mice was significantly higher than in vehicle-treated mice (P < 0.01). Our data demonstrated that OEA and PSN632408 can stimulate β-cell replication in vitro and in vivo and improve islet graft function. Targeting GPR119 is a novel therapeutic approach to increase β-cell mass and to improve islet graft function by stimulating β-cell replication.

Pig islets for clinical islet xenotransplantation

PURPOSE OF REVIEW

Allogeneic islet transplantation faces difficulties because organ shortage is recurrent; several pancreas donors are often needed to treat one diabetic recipient; and the intrahepatic site of islet implantation may not be the most appropriate one. Another source of insulin-producing cells, therefore, would be of major interest, and pigs represent a possible and serious source for obtaining such cells.

RECENT FINDINGS

Pig islet grafts may appear difficult because of the species barrier, but recent studies demonstrate that pig islets may function in diabetic primates for at least 6 months.

SUMMARY

Pig islet xenotransplantation, however, must still overcome the selection of a suitable pig donor to translate preclinical findings into clinical applications. This review summarizes the actual acquired knowledge of pig islet transplantation in primates to select the 'ideal' pig donor.

Pig-to-nonhuman primate islet xenotransplantation

Type 1 diabetes continues to present a therapeutic challenge. The restoration of normoglycemia and insulin independence in immunosuppressed type 1 diabetic recipients of human islet allografts has highlighted the potential of cell-based diabetes therapy. The unlimited and on-demand availability of pig islets from healthy, young, living, designated pathogen-free, and potentially genetically modified donors presents unique opportunities for improving the availability and outcomes of islet replacement therapies in diabetes. One of the fundamental prerequisites for initiating clinical research is a favorable benefit-over-harm determination in the stringent preclinical transplant model in nonhuman primates. To date, xenotransplants of pig islet cell therapy products have been reported by 15 institutions in 181 NHPs, including xenotransplants in 72 non-diabetic and 109 diabetic recipients. These studies have demonstrated the feasibility of successful preclinical islet xenotransplantation and have provided insights into the critical events operative in the immune recognition and destruction of islet xenografts in nonhuman primates. Particularly promising is the recent achievement of prolonged insulin independence in this model by means of several distinct islet xenotransplantation products, implantation sites, and immunotherapeutic strategies. Further progress appears likely and the development of suitable source pigs will position the scientific community to translate these findings safely to the clinic.

Idd loci synergize to prolong islet allograft survival induced by costimulation blockade in NOD mice

OBJECTIVE

NOD mice model human type 1 diabetes and are used to investigate tolerance induction protocols for islet transplantation in a setting of autoimmunity. However, costimulation blockade-based tolerance protocols have failed in prolonging islet allograft survival in NOD mice.

RESEARCH DESIGN AND METHODS

To investigate the underlying mechanisms, we studied the ability of costimulation blockade to prolong islet allograft survival in congenic NOD mice bearing insulin-dependent diabetes (Idd) loci that reduce the frequency of diabetes.

RESULTS

The frequency of diabetes is reduced in NOD.B6 Idd3 mice and is virtually absent in NOD.B6/B10 Idd3 Idd5 mice. Islet allograft survival in NOD.B6 Idd3 mice treated with costimulation blockade is prolonged compared with NOD mice, and in NOD.B6/B10 Idd3 Idd5, mice islet allograft survival is similar to that achieved in C57BL/6 mice. Conversely, some Idd loci were not beneficial for the induction of transplantation tolerance. Alloreactive CD8 T-cell depletion in (NOD x CBA)F1 mice treated with costimulation blockade was impaired compared with similarly treated (C57BL/6.H2(g7) x CBA)F1 mice. Injection of exogenous interleukin (IL)-2 into NOD mice treated with costimulation prolonged islet allograft survival. NOD.B6 Idd3 mice treated with costimulation blockade deleted alloreactive CD8 T-cells and exhibited prolonged islet allograft survival.

CONCLUSIONS

Il2 is the Idd3 diabetes susceptibility gene and can influence the outcome of T-cell deletion and islet allograft survival in mice treated with costimulation blockade. These data suggest that Idd loci can facilitate induction of transplantation tolerance by costimulation blockade and that IL-2/Idd3 is a critical component in this process.

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.

Blockade of OX40 signals enhance survival of xenoislet grafts in spontaneously diabetic NOD mice

Role of OX40 blockade was investigated in islet xenograft model in chemically diabetic C57B1/6 and spontaneously diabetic NOD mice. The effect of OX40/OX40L blockade on effector function of diabetogenic T cells was studied in an adoptive transfer model. 2000 IEQ of porcine islets were transplanted under the kidney capsule of diabetic C57B1/6 or NOD mice and were treated i.p. with control Ig, anti-OX40L, or CTLA4Ig. Graft survival was assessed using blood glucose (BG) measurement. Cells from diabetic NOD spleens and pancreatic lymphnodes were injected i.v. into NOD.scid mice. Recipients were treated i.p. with anti-OX40L, CTLA4Ig alone, or in combination; control mice received Ig. Diabetes incidence was assessed using BG measurement. Anti-OX40L treatment delayed xenoislet rejection significantly in chemically diabetic animals, although CTLA4Ig delayed rejection even further. Neither treatment completely prevented rejection. In spontaneously diabetic NOD mice, rejection of xenoislet graft was delayed by anti-OX40L treatment but not by CTLA4Ig. Anti-OX40L alone and in combination with CTLA4Ig significantly delayed diabetes transfer by activated diabetogenic T cells, compared with control and CTLA4Ig treatment. Preliminary mechanistic studies suggest that anti-OX40L treatment preserves Treg numbers, unlike CTLA4Ig that diminishes Tregs. Our studies show that OX40 blockade offers better xenoislet graft survival than CTLA4Ig in spontaneous autoimmune NOD model, suggesting that preactivated T cells use alternate costimulatory pathways, independent of CD28. Results from adoptive transfer studies further support the role of OX40 signaling in effector function of diabetogenic T cells. These data suggest that OX40/OX40L may offer novel therapeutic target for xenoislet graft protection in type 1 diabetic patients.

Combination of anti-CD4 with anti-LFA-1 and anti-CD154 monoclonal antibodies promotes long-term survival and function of neonatal porcine islet xenografts in spontaneously diabetic NOD mice

Type 1 diabetes mellitus (T1DM) is caused by the autoimmune destruction of pancreatic islet beta-cells, which are required for the production of insulin. Islet transplantation has been shown to be an effective treatment option for TIDM; however, the current shortage of human islet donors limits the application of this treatment to patients with brittle T1DM. Xenotransplantation of pig islets is a potential solution to the shortage of human donor islets provided xenograft rejection is prevented. We demonstrated that a short-term administration of a combination of anti-LFA-1 and anti-CD154 monoclonal antibodies (mAbs) was highly effective in preventing rejection of neonatal porcine islet (NPI) xenografts in non-autoimmune-prone B6 mice. However, the efficacy of this therapy in preventing rejection of NPI xenografts in autoimmune-prone nonobese diabetic (NOD) mice is not known. Given that the current application of islet transplantation is for the treatment of T1DM, we set out to determine whether a combination of anti-LFA-1 and anti-CD154 mAbs could promote long-term survival of NPI xenografts in NOD mice. Short-term administration of a combination of anti-LFA-1 and anti-CD154 mAbs, which we found highly effective in preventing rejection of NPI xenografts in B6 mice, failed to promote long-term survival of NPI xenografts in NOD mice. However, addition of anti-CD4 mAb to short-term treatment of a combination of anti-LFA-1 and anti-CD154 mAbs resulted in xenograft function in 9/12 animals and long-term graft (>100 days) survival in 2/12 mice. Immunohistochemical analysis of islet grafts from these mice identified numerous insulin-producing beta-cells. Moreover, the anti-porcine antibody as well as autoreactive antibody responses in these mice was reduced similar to those observed in naive nontransplanted mice. These data demonstrate that simultaneous targeting of LFA-1, CD154, and CD4 molecules can be effective in inducing long-term islet xenograft survival and function in autoimmune-prone NOD mice.

Long-term survival of transplanted allogeneic cells engineered to express a T cell chemorepellent

BACKGROUND

Alloantigen specific T cells have been shown to be required for allograft rejection. The chemokine, stromal cell derived factor-1 (SDF-1) at high concentration, has been shown to act as a T-cell chemorepellent and abrogate T-cell infiltration into a site of antigen challenge in vivo via a mechanism termed fugetaxis or chemorepulsion. We postulated that this mechanism could be exploited therapeutically and that allogeneic cells engineered to express a chemorepellent protein would not be rejected.

METHODS

Allogeneic murine insulinoma beta-TC3 cells and primary islets from BALB/C mice were engineered to constitutively secrete differential levels of SDF-1 and transplanted into allogeneic diabetic C57BL/6 mice. Rejection was defined as the permanent return of hyperglycemia and was correlated with the level of T-cell infiltration. The migratory response of T-cells to SDF-1 was also analyzed by transwell migration assay and time-lapse videomicroscopy. The cytotoxicity of cytotoxic T cell (CTLs) against beta-TC3 cells expressing high levels of SDF-1 was measured in standard and modified chromium-release assays in order to determine the effect of CTL migration on killing efficacy.

RESULTS

Control animals rejected allogeneic cells and remained diabetic. In contrast, high level SDF-1 production by transplanted cells resulted in increased survival of the allograft and a significant reduction in blood glucose levels and T-cell infiltration into the transplanted tissue.

CONCLUSIONS

This is the first demonstration of a novel approach that exploits T-cell chemorepulsion to induce site specific immune isolation and thereby overcomes allograft rejection without the use of systemic immunosuppression.

Xenotransplantation of purified pre-natal porcine beta cells in mice normalizes diabetes when a short anti-CD4-CD8 antibody treatment is combined with transient insulin injections

BACKGROUND

Pre-natal porcine endocrine islet cell grafts were recently shown to contain immature beta cells with a marked potential for growth and differentiation following transplantation, and hence for a progressive and long-term correction of diabetes in immune-incompetent mice. The present study investigates whether these grafts are also capable of correcting hyperglycemia in immune-competent mice receiving a short treatment with anti-CD4-CD8 antibodies.

METHODS

Pure endocrine islet cell grafts with 0.5 to 1.0 million beta cells were prepared from pre-natal pigs and transplanted under the kidney capsule of alloxan-diabetic CBA/Ca mice. Survival, growth and function of implanted beta cells were followed by measuring plasma porcine C-peptide and glucose, and graft insulin content at start and at post-transplant (PT) week 35. The effect was studied of a 5-day treatment with non-depleting anti-CD4 YTS177 and depleting anti-CD8 YTS169 antibody, either without or with transient insulin injections.

RESULTS

Without antibody treatment, all graft recipients remained porcine C-peptide negative and died. Antibody treatment decreased CD4-expression and percentage CD8 cells for 10 and 18 weeks respectively. It resulted in a 30 week-survival of nine out of 14 graft recipients; all nine had progressively become C-peptide positive but only one proceeded to normoglycemia. When antibody treatment was combined with transient insulin injections, 11 out of 14 graft recipients survived long-term, eight became C-peptide positive and six were normoglycemic at PT week 30. In both groups, surviving recipients exhibited a graft insulin content that was 6- to 9-fold higher than at implantation.

CONCLUSIONS

Pre-natal porcine beta cells grow and differentiate when transplanted in diabetic immune-competent mice that have been transiently immune suppressed with anti-CD4 and anti-CD8 monoclonal antibodies. They develop metabolic control when recipients are also transiently treated with insulin injections.

Induction of dominant tolerance using monoclonal antibodies

Monoclonal antibodies (MAb) have been shown to be effective in inducing immune tolerance in transplantation and autoimmunity. Several different MAb have tolerogenic properties and their effect has been studied in a range of experimental animal models and, in some cases, in clinical trials. The tolerant state seems to be maintained by CD4+ regulatory T cells (Treg), induced in the periphery, capable of suppressing other T cells specific for the same antigens or antigens presented by the same antigen presenting cells. Furthermore, following the initial induction of Treg cells under MAb treatment, Treg cells themselves can maintain the tolerant state in a dominant way in the absence of the therapeutic MAb or other immunosuppressive agents, and are able to recruit other T cells into the regulatory pool--a process named infectious tolerance.

Costimulation and autoimmune diabetes in BB rats

Costimulatory signals regulate T-cell activation. To investigate the role of costimulation in autoimmunity and transplantation, we studied the BB rat model of type 1 diabetes. Diabetes-prone BB (BBDP) rats spontaneously develop disease when 55-120 days of age. We observed that two anti-CD28 monoclonal antibodies (mAb) with different functional activities completely prevented diabetes in BBDP rats. Anti-CD154 mAb delayed diabetes, whereas treatment with CTLA4-Ig or anti-CD80 mAb accelerated disease. Anti-CD86 or anti-CD134L mAbs had no effect. Diabetes resistant BB (BBDR) rats are disease-free, but >95% of them develop diabetes after treatment with polyinosinic-polycytidylic acid and an mAb that depletes Treg cells. In the induced BBDR model, anti-CD154 mAb delayed onset of diabetes, whereas CTLA4-Ig, anti-CD134L or either of the anti-CD28 mAbs had little or no effect. In contrast, blockade of the CD134-CD134L pathway was highly effective for preventing autoimmune recurrence against syngeneic islet grafts in diabetic BBDR hosts. Blockade of the CD40-CD154 pathway was also effective, but less so. These data suggest that the effectiveness of costimulation blockade in the treatment of type 1 diabetes is dependent on both the costimulatory pathway targeted and the mechanism of induction, stage, intensity and duration of the pathogenic process.

Increasing donor chimerism and inducing tolerance to islet allografts by post-transplant donor lymphocyte infusion

Inducing donor chimerism is the most consistently successful approach to achieve transplant tolerance. We found that a low level of donor chimerism, which was induced by a relatively non-toxic approach, induced donor-specific tolerance to islet allografts in chemically induced diabetic mice. However, a similar level of donor chimerism could not protect donor islet allografts in non-obese diabetic (NOD) mice that spontaneously developed autoimmune diabetes. Rejection of donor islet allografts in diabetic NOD mice with a low level of donor chimerism was mediated by recurrent autoimmunity. We used post-transplant donor lymphocyte infusion (DLI) to increase donor chimerism and to induce tolerance to islet allografts. DLI significantly increased donor chimerism and promoted donor-specific tolerance to islet allografts in diabetic NOD mice. Self-tolerance to islet autoantigens was restored and restoring self-tolerance is mediated by immunoregulation. Thus, our data showed that adoptive immunotherapy with post-transplant DLI after establishing a low level of donor chimerism as a platform enhances donor chimerism, induces donor-specific tolerance to islet allografts and restores self-tolerance in the setting of autoimmune diabetes. Our data also showed that central tolerance is not sufficient to induce tolerance and peripheral tolerance through immunoregulation for restoring self-tolerance is required in the setting of autoimmune diabetes.

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.

Characterization of the Role of Major Histocompatibility Complex in Type 1 Diabetes Recurrence after Islet Transplantation

BACKGROUND

Major histocompatibility complex (MHC) molecules are essential determinants of beta-cell destruction in type 1 diabetes (T1D). MHC class I- or class II-null nonobese diabetic (NOD) mice do not spontaneously develop autoimmune diabetes and are resistant to adoptive transfer of disease. Both CD4+ and CD8+ T cells are associated with graft destruction after syngeneic islet transplantation. MHC molecules within the graft (i.e., on beta-cells or donor lymphocytes) may influence the interactions between antigen presenting cells and effector T cells and, therefore, the survival outcome of the graft.

METHODS

Donor islets from NOD mice deficient in one or both of beta2-microglobulin and class II transactivator genes were transplanted into diabetic NOD mice. Immunohistochemistry was performed to identify the phenotype of infiltrating cells and to assess graft insulin production. The presence of cytokines in the grafts was assayed by reverse transcription polymerase chain reaction.

RESULTS

MHC class II-null islets demonstrated rates of rejection comparable with control wild-type (wt) islets. In contrast, MHC class I- and II-null islets demonstrated indefinite survival (over 100 days). Infiltrates of both failed and surviving grafts were comprised of cytotoxic lymphocytes (CTL), helper T cells, and macrophages. Grafts also showed the presence of both Th1- and Th2-type cytokines (interleukin [IL]-2, IL-4, IL-10, and interferon-gamma), independent of graft status.

CONCLUSIONS

These results demonstrate the primary importance of MHC class I molecules in the pathogenesis of diabetes recurrence postislet transplantation. Conversely, MHC class II expression is not a necessary mechanistic component of transplant destruction. In addition, these results implicate MHC class I-restricted CTLs but not MHC class II-restricted T cells in disease recurrence.

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.

DEPLETING ANTI-CD4 MONOCLONAL ANTIBODY CURES NEW-ONSET DIABETES, PREVENTS RECURRENT AUTOIMMUNE DIABETES, AND DELAYS ALLOGRAFT REJECTION IN NONOBESE DIABETIC MICE1

BACKGROUND

The prevention of recurrent autoimmunity is a prerequisite for successful islet transplantation in patients with type I diabetes. Therapies effective in preserving pancreatic beta-cell mass in patients with newly diagnosed diabetes are good candidates for achieving this goal. Anti-CD3 monoclonal antibody (mAb) and antilymphocyte antisera are the only therapies to date that have cured early diabetic disease in the nonobese diabetic (NOD) mouse. We investigated whether other immunosuppressive therapies, including short-term depleting anti-CD4 mAb or costimulation blockade, would affect the disease progression in recently diabetic NOD mice. We also evaluated the effect of the anti-CD4 mAb on syngeneic and allogeneic graft survival in diabetic NOD recipients.

METHODS AND RESULTS

We demonstrate that a short course of anti-CD4 mAb early after hyperglycemia onset cured diabetes. Normal islets and islets with CD4+ and CD8+ T-cell peri-insulitic infiltrate were found in the pancreata of cured NOD mice. A similar regimen prevented the recurrence of autoimmune diabetes in NOD/severe combined immunodeficient disease (SCID) islet isografts and delayed the rejection of allogeneic C57BL/6 islet allografts in diabetic female NOD mice. The co-transfer of diabetogenic splenocytes with splenocytes from anti-CD4 mAb-treated and cured NOD mice into 7-week-old, irradiated, NOD male mice was not able to protect from diabetes occurrence. This indicates that an anti-CD4-mediated cure of diabetes is independent of the induction of immunoregulatory T cells. Anti-CD154 mAb and cytotoxic T-lymphocyte antigen 4 immunoglobulin were ineffective in early-onset diabetes.

CONCLUSION

Our results provide the first evidence that newly established autoimmune islet destruction in NOD mice responds to a short course of anti-CD4 mAb. In contrast, costimulation blockade is ineffective in this clinically relevant model.

Induction of operational tolerance and generation of regulatory cells after intratracheal delivery of alloantigen combined with nondepleting anti-CD4 monoclonal antibody

BACKGROUND

We previously showed that intratracheal delivery of alloantigen induced prolonged survival of fully allogeneic cardiac grafts in mice. Here, this treatment protocol was combined with nondepleting anti-CD4 monoclonal antibody (mAb) to induce operational tolerance.

METHODS

CBA (H-2k) mice were pretreated with intratracheal delivery of whole splenocytes from C57BL/10 (H-2b) mice or a 15-mer Kb peptide, with or without intraperitoneal administration of nondepleting anti-CD4 mAb (YTS177). Seven days later, C57BL/10 hearts were transplanted into the pretreated CBA mice. In addition, some naive CBA mice underwent adoptive transfer of splenocytes from pretreated CBA mice and transplantation of a C57BL/10 heart on the same day.

RESULTS

Untreated CBA mice rejected C57BL/10 cardiac grafts acutely (median survival time, 12 days). Mice given intratracheal delivery of whole splenocytes or Kb peptide demonstrated prolonged graft survival (median survival time, 84 and 76 days, respectively). Concurrent administration of YTS177 and intratracheal delivery of splenocytes or Kb peptide resulted in indefinite graft survival. Mice with long-surviving C57BL/10 cardiac grafts showed acceptance of skin grafts from C57BL/10 mice but not BALB/c mice, demonstrating that operational tolerance had been induced. Adoptive transfer of splenocytes from mice pretreated with intratracheal delivery of splenocytes or Kb peptide plus YTS177 induced indefinite survival of cardiac grafts in secondary recipients, indicating that regulatory cells had been generated.

CONCLUSION

In a murine model, intratracheal delivery of donor splenocytes or Kb peptide combined with YTS177 induced operational tolerance and generated regulatory cells.

Effects of streptozotocin on autoimmune diabetes in NOD mice

Non-obese diabetic (NOD) mice develop autoimmunity that destroys their native beta cells causing diabetes. Their autoimmunity will also destroy syngeneic transplanted islets and transfer both autoimmunity and diabetes via spleen cells to non-diabetic mice. In this report, we studied the effects of streptozotocin (STZ) on the autoimmune diabetes in NOD mice. We transplanted NOD.SCID islets into three groups of NOD mice: (1) spontaneously diabetic NOD mice (NOD-sp.); (2) prediabetic NOD mice made diabetic by streptozotocin (NOD-stz); and (3) diabetic NOD mice also treated with streptozotocin (NOD-sp./stz). In the first group, the transplants were rejected within 3 weeks. In the second and third groups, the transplants survived indefinitely. Alloxan, a drug similar to streptozotocin, did not have the same effect as streptozotocin. The ability of streptozotocin to prevent diabetes in young NOD mice was reversed by anti-CD8 antibody treatment but not by anti-CD4 treatment. Streptozotocin also made spleen cells from diabetic NOD mice less effective transferring diabetes. These results indicate that streptozotocin treatment both prevents and reverses the islet destructive autoimmunity in NOD mice. We postulate that the effects of streptozotocin treatment may be mediated in part by regulatory T cells.

Allorecognition and effector pathways of islet allograft rejection in normal versus nonobese diabetic mice

Islet transplantation is becoming an accepted therapy to cure type I diabetes mellitus. The exact mechanisms of islet allograft rejection remain unclear, however. In vivo CD4(+) and CD8(+) T cell-depleting strategies and genetically altered mice that did not express MHC class I or class II antigens were used to study the allorecognition and effector pathways of islet allograft rejection in different strains of mice, including autoimmunity-prone nonobese diabetic (NOD) mice. In BALB/c mice, islet rejection depended on both CD4(+) and CD8(+) T cells. In C57BL/6 mice, CD8(+) T cells could eventually mediate islet rejection by themselves, but they produced rejection more efficiently with help from CD4(+) T cells stimulated through either the direct or indirect pathway. In C57BL/6 mice, CD4(+) T cells alone caused islet rejection when only the direct pathway was available but not when only the indirect pathway was available. In contrast, in NOD mice, CD4(+) T cells alone, with only the indirect pathway, could mediate islet and cardiac allograft rejection. These findings indicate that different mouse strains can make use of different pathways for T cell-mediated rejection of islet allografts. In addition, they demonstrate that NOD mice, which develop autoimmunity and are known to be resistant to tolerance induction, have an unusually powerful CD4(+) cell indirect mechanism that can cause rejection of both islet and cardiac allografts. These data shed light on the mechanisms of islet allograft rejection in different responder strains, including those with autoimmunity.

Clinical trials of transplant tolerance: slow but steady progress

The search for tolerance therapies that would thwart the alloimmune response following organ transplantation while preserving a patient's protective immune response has been a formidable goal for clinical immunologists. Over the past few decades, a more detailed understanding of the molecular events associated with T-cell recognition and activation has demonstrated the feasibility of various tolerance approaches, such as costimulation blockade, in numerous animal models of both autoimmunity and transplantation. Yet, only a few promising new therapies have reached the early stages of human clinical development. In contrast, the use of T-cell depleting induction therapy has become widespread, and new trials have been designed with immunosuppressive drug withdrawal in mind. Furthermore, nonmyeloablative mixed chimeric approaches have allowed complete immunosuppressive withdrawal in some limited cases. In the course of these investigations, however, what has become increasingly clear is that the distinctions between immunosuppression and tolerance have been blurred as the success and durability of the therapies rely as much on the state of the organ and organism as they do the mechanism of action of the drug. In this review, we provide a summary of the progress and lessons in promoting clinical transplant tolerance and an overview of promising agents.

A substantial level of donor hematopoietic chimerism is required to protect donor-specific islet grafts in diabetic NOD mice

BACKGROUND

Mixed chimerism can induce tolerance to alloantigens and restore self-tolerance to autoantigens, thereby permitting islet transplantation. However, the minimal level of donor chimerism that is required to prevent islet allograft rejection and recurrence of autoimmune diabetes has not been established.

METHODS

We investigated whether allogeneic Balb/c donor chimerism can be induced in C57BL/6 mice, in prediabetic NOD mice, and in diabetic NOD mice after transplantation of a modest dose of bone marrow by using purine nucleoside analogue, fludarabine phosphate and cyclophosphamide conditioning therapy, followed by short-term anti-CD40 ligand monoclonal antibody and rapamycin posttransplant treatment. We also investigated whether the induced donor chimerism is sufficient to prevent the onset of diabetes in prediabetic NOD mice and protect donor islet grafts in diabetic NOD mice.

RESULTS

Allogeneic donor chimerism could be induced under the authors' approach that is nonmyeloablative and radiation-free. Diabetes onset was prevented in chimeric prediabetic NOD mice. The induction of mixed chimerism protected donor-specific islet grafts in diabetic NOD mice. At 60 days after islet transplantation, all donor Balb/c islet grafts survived in diabetic NOD mice whose level of donor-derived lymphocytes was higher than 30% at the time of islet transplantation (n=8). In contrast, Balb/c islet grafts were rejected in five of seven diabetic NOD mice whose level was lower than 30%.

CONCLUSIONS

Our data demonstrate that a donor lymphocyte chimerism (>30%) at the time of islet transplantation is required to protect donor-specific islet grafts, and indicate that a strictly non-irradiation-based protocol can be used to achieve this goal.

Indefinite islet protection from autoimmune destruction in nonobese diabetic mice by agarose microencapsulation without immunosuppression

BACKGROUND

The recurrence of autoimmunity and allograft rejection act as major barriers to the widespread use of islet transplantation as a cure for type 1 diabetes. The aim of this study was to evaluate the feasibility of immunoisolation by use of an agarose microcapsule to prevent autoimmune recurrence after islet transplantation.

METHODS

Highly purified islets were isolated from 6- to 8-week-old prediabetic male nonobese diabetic (NOD) mice and microencapsulated in 5% agarose hydrogel as a semipermeable membrane. Islet function was evaluated by a syngeneic islet transplantation model, in which islets were transplanted into spontaneously diabetic NOD mice.

RESULTS

The nonencapsulated islet grafts were destroyed and diabetes recurred within 2 weeks after transplantation in all 12 mice. In contrast, 13 of the 16 mice that underwent transplantation with microencapsulated islets maintained normoglycemia for more than 100 days after islet transplantation. Histologic examination of the nonencapsulated islet grafts showed massive mononuclear cellular infiltration with beta-cell destruction. In contrast, the microencapsulated islets showed well-granulated beta cells with no mononuclear cellular infiltration around the microcapsules or in the accompanying blood capillaries between the microcapsules.

CONCLUSIONS

Agarose microcapsules were able to completely protect NOD islet isografts from autoimmune destruction in the syngeneic islet transplantation model.

Pig islet xenografts are resistant to autoimmune destruction by non-obese diabetic recipients after anti-CD4 treatment

In addition to providing a large source of donor tissue, xenogeneic islet transplantation might avoid recurrent autoimmunity in patients with type 1 diabetes. To examine this possibility further, xenogeneic pig islets were transplanted into recipient mice in the presence or absence of autoimmunity. Spontaneously, non-obese diabetic (NOD) recipients rejected isografts rapidly whether or not the recipients were depleted of CD4+ T-cells. Young NOD mice made diabetic with streptozotocin accepted islet isografts without immunosuppression, indicating that destructive autoimmunity did not develop in these recipients. Pig xenografts were rejected equally quickly in the two types of NOD recipients in the absence of immunosuppression and survived for up to 9 weeks in both types of NOD recipients after CD4 depletion. BALB/c mice often accepted pig xenografts indefinitely after anti-CD4 antibody treatment. These results suggest that pig islets are resistant to recurrent autoimmunity when CD4+ T-cells are depleted. The difficulty in obtaining indefinite islet xenograft survival in NOD recipients occurs independently from the development of destructive autoimmunity.

The role of autoimmunity in islet allograft destruction: major histocompatibility complex class II matching is necessary for autoimmune destruction of allogeneic islet transplants after T-cell costimulatory blockade

Although it has often been assumed that transplanted allogeneic islets can be destroyed by recurrent autoimmunity in recipients with type 1 diabetes, definitive evidence is lacking and the settings in which this may occur have not been defined. To address these issues, we compared the survival of islet transplants (subject to tissue-specific autoimmunity) with cardiac transplants (not subject to tissue-specific autoimmunity) from various major histocompatibility complex (MHC)-matched and -mismatched donors transplanted into autoimmune NOD recipients. We found that when recipients were treated with combined B7 and CD154 T-cell costimulatory blockade, hearts survived best with better MHC matching, whereas islets survived worst when the donor and recipient shared MHC class II antigens. In the absence of full or MHC class II matching, there was no difference in the survival of islet and cardiac allografts. We also found that the tendency of NOD mice to resist tolerance induction by costimulation blockade is mediated by both CD4+ and CD8+ T-cells, not directly linked to the presence of autoimmunity, and conferred by non-MHC background genes. These findings have clinical importance because they suggest that under some circumstances, avoiding MHC class II sharing may provide better islet allograft survival in recipients with autoimmune diabetes, since mismatched allogeneic islets may be resistant to recurrent autoimmunity. Our results may have implications for the design of future clinical trials in islet transplantation.

Nondepleting anti-CD4 and soluble interleukin-1 receptor prevent autoimmune destruction of syngeneic islet grafts in diabetic NOD mice

BACKGROUND

Successful islet transplantation in type 1 diabetes requires tolerance induction of both allo- and autoreactive T-cell responses. Monoclonal antibodies targeting the CD4 coreceptor on T-helper cells have been shown to be effective in this regard. In type 1 diabetes, there is some evidence to suggest that cytokines such as interleukin (IL)-1 may be involved in beta-cell destruction. The high glucose levels associated with type 1 diabetes are also known to be toxic to beta cells.

METHOD

The tempo of T-cell and macrophage infiltration into syngeneic islets transplanted into diabetic nonobese diabetic (NOD) mice was examined by immunohistochemistry. We investigated the ability of a nondepleting anti-CD4 monoclonal antibody (YTS177) to induce tolerance to syngeneic islet grafts in female spontaneous diabetic NOD mice and in an adoptive transfer model of diabetes in NOD mice. The spontaneous model was used to test the effect on graft function of perioperative insulin therapy in mice treated with YTS177. The ability of soluble interleukin (sIL)-1 receptor (R) type II (sIL-1RII) to inhibit IL-1 effects in syngeneic islet transplants was also assessed.

RESULTS

Cellular infiltration of CD3 cells and macrophages into the islet graft coincided with loss of graft function in untreated mice. Self-tolerance to beta cells was restored with YTS177, allowing long-term graft survival in a proportion of animals. The use of perioperative insulin therapy increased the number of successful grafts in spontaneously diabetic NOD mice treated with YTS177. The combination of YTS177 with sIL-1RII significantly improved the rates of graft survival compared with graft survival in YTS177-treated spontaneously diabetic NOD mice.

CONCLUSIONS

Nondepleting anti-CD4 antibodies restore self tolerance to syngeneic islet transplants in diabetic NOD mice. Insulin therapy improves graft survival in mice treated with YTS177. Preventing the action of IL-1 greatly improves graft survival induced with YTS177.

Inducing tolerance to MHC-matched allogeneic islet grafts in diabetic NOD mice by simultaneous islet and bone marrow transplantation under nonirradiative and nonmyeloablative conditioning therapy

BACKGROUND

Human type 1 diabetes is associated with defects in the hematopoietic stem cells. Simultaneous donor islet and bone marrow transplantation may be an ideal therapeutic approach for inducing tolerance to islet allogeneic antigens and restoring self-tolerance to islet autoimmune antigens.

METHODS

Using a nonobese diabetic (NOD) mouse model of human type 1 diabetes, we investigated whether tolerance to MHC-matched allogeneic islet grafts from male nonobese diabetes-resistant (NOR) donors can be induced in female NOD recipients by simultaneous islet and bone marrow transplantation under fludarabine phosphate-based nonmyeloablative and irradiation-free conditioning therapy. Donor-specific chimerism in the peripheral blood of tolerant mice (n=7) was measured by semiquantitative polymerase chain reaction for a male-specific marker (SRY).

RESULTS

Donor-specific tolerance to NOR islet grafts was induced in all diabetic NOD mice after simultaneous islet and bone marrow transplantation and treated with fludarabine phosphate, cyclophosphamide, anti-mouse lymphocyte serum, and rapamycin. At 100 days and 200 days after transplantation, the average percentage of male NOR marker in DNA derived from the peripheral blood of NOD recipients that had long-term islet graft survival was over 10%.

CONCLUSION

Our data suggest that this approach may induce donor-specific tolerance in clinical islet transplantation and living-related donor solid organ transplantation.

Rapamycin and T cell costimulatory blockade as post-transplant treatment promote fully MHC-mismatched allogeneic bone marrow engraftment under irradiation-free conditioning therapy

Hematopoietic macrochimerism, established by bone marrow transplantation, can be used as an approach for treating autoimmune disease and inducing transplant tolerance. In this study, we investigated whether a stable, high level of fully MHC-mismatched hematopoietic macrochimerism can be induced by using irradiation-free protocols, and whether rapamycin and T cell costimulatory blockades (anti-CD40L monoclonal antibody (mAb) and CTLA4Ig) as post-transplant treatment promote bone marrow engraftment. Donor-specific blood transfusion (DST), anti-lymphocyte serum (ALS), busulfan, and cyclophosphamide were given pretransplantation. Balb/c (H-2(d)) bone marrow cells, at a dose of 4 x 10(7), were infused into each C57BL/6 mouse (H-2(b)). Rapamycin, anti-CD40L mAb, and CTLA4Ig were then administered, either alone or in combination. Without ALS or busulfan and cyclophosphamide, macrochimerism can only rarely be induced. Donor-specific transfusion (DST) enhances induction of hematopoietic macrochimerism. Rapamycin, anti-CD40L mAb and CTLA4Ig, alone or in combination, induce a stable and high level of hematopoietic macrochimerism. In the chimeric mice, donor-derived cells were detected in all lymphohematopoietic tissues and donor-specific tolerance was induced in vitro. We conclude that a stable and high level of fully MHC-mismatched hematopoietic macrochimerism can be induced in mice after transplanting a single modest dose of bone marrow cells without irradiation. Rapamycin and T cell costimulatory blockade as post-transplant treatment promote bone marrow engraftment.

Tolerogenic strategies to halt or prevent type 1 diabetes

A variety of therapeutic strategies have been developed to tolerize autoreactive T cells and prevent autoimmune pathology. In terms of type 1 diabetes, prevention strategies can inhibit the priming and expansion of autoreactive T cells; however, a cure for diabetes would require tolerance to be established in the presence of primed effector cells together with replacement of the destroyed beta cell mass. Replacement of beta cells could be accomplished by transplantation of islets or stem cells or through islet regeneration. We will focus here on tolerogenic strategies that have been used to prevent onset of type 1 diabetes and discuss the potential for a cure.