Auto- and alloimmune reactivity to human islet allografts transplanted into type 1 diabetic patients

Choice of antibody immunotherapy influences cytomegalovirus viremia in simultaneous pancreas-kidney transplant recipients

OBJECTIVE

Simultaneous pancreas-kidney (SPK) transplantation in type 1 diabetic patients requires immunotherapy against allo- and autoreactive T-cells. Cytomegalovirus (CMV) infection is a major cause for morbidity after transplantation and is possibly related to recurrent autoimmunity. In this study, we assessed the pattern of CMV viremia in SPK transplant recipients receiving either antithymocyte globulin (ATG) or anti-CD25 (daclizumab) immunosuppressive induction therapy.

RESEARCH DESIGN AND METHODS

We evaluated 36 SPK transplant recipients from a randomized cohort that received either ATG or daclizumab as induction therapy. Patients at risk for CMV infection received oral prophylactic ganciclovir therapy. The CMV DNA level in plasma was measured for at least 180 days using a quantitative real-time PCR. Recipient peripheral blood mononuclear cells were cross-sectionally HLA tetramer-stained for CMV-specific CD8(+) T-cells.

RESULTS

Positive CMV serostatus in donors was correlated with a higher incidence of CMV viremia than negative serostatus. In patients at risk, daclizumab induction therapy significantly prolonged CMV-free survival. CMV viremia occurred earlier and was more severe in patients with rejection episodes than in patients without rejection episodes. CMV-specific CD8(+) T-cell counts were significantly lower in patients developing CMV viremia than in those who did not.

CONCLUSIONS

Despite their comparable immunosuppressive potential, daclizumab is safer than ATG regarding CMV infection risk in SPK transplantation. ATG-treated rejection episodes are associated with earlier and more severe infection. Furthermore, high CMV-specific tetramer counts reflect antiviral immunity rather than concurrent viremia because they imply low viremic activity. These findings may prove valuable in the discussion on both safety of induction therapy and recurrent autoimmunity in SPK and islet transplantation.

Integrin signaling via RGD peptides and anti-beta1 antibodies confers resistance to apoptosis in islets of Langerhans

Islet transplantation is associated with a high rate of early graft failure caused by early immune attack and poor functionality of islets. Apoptosis of islet cells appears soon after islet isolation and primarily involves the beta-cell. The purpose of this study was to determine the effect of ligation to extracellular matrix (ECM) proteins on survival of the islets of Langerhans following islet isolation. Islets that had been cultured for 24 h on collagen type I showed an islet survival of 59.7 +/- 8.7%, while islets that had been cultured on collagen type IV and laminin showed an islet survival of 88.6 +/- 10.3 and 94.3 +/- 5.6%, respectively. Islets that had been pretreated with anti-beta1 antibodies and argenin-glycin-aspartic acid (RGD) peptides showed a decrease in the level of apoptosis by a factor of 2.5 and 3.1, respectively, and an increase of phospho-Akt Ser 473 activity by a factor of 3.1 and 2.9, respectively, compared with untreated islets. When detached from their natural ECM surrounding in the pancreas, islet cells undergo apoptosis, unless islets are cultured on collagen IV or laminin or treated with anti-beta1 integrin antibodies or RGD peptides to mimic ECM ligation. These results indicate that inhibition of anoikis may offer opportunities to improve function and viability of islet cells.

Human fetal islet transplantation in type 1 diabetics: comparison of immunological effects between multiple implantation regimens

Previous studies have suggested that the multiple transplants might be equally metabolically efficient to a single regimen for human adult islets. The aim of this study was to compare immunological and metabolic parameters after each of the two regimens of human fetal islets (HFI). Group A single transplants (n = 9) had 180 +/- 20 x 1000 HFI equivalents (IEQs) implanted via a single intramuscular injection. In group B multiple transplants (n = 8) islets were implanted by three consecutive injections of 60 +/- 10 x 1000 IEQs at 7-day intervals. We analyzed the immunological parameters of CD4/CD8 T lymphocyte ratios; islet cell antibodies (ICAs) and insulin antibodies (IAs). We estimated insulin secreting capacity (ISC) as the metabolic parameter. We observed that the CD4+/CD8+ T-cell ratio increased, peaking on day 90, in similar fashion in both groups: day -1: A = 1.18 +/- 0.03 versus B = 1.19 +/- 0.04; on day 90: A = 1.79 +/- 0.09, versus B = 1.75 +/- 0.08 (P = NS) immediately before the decrease in C-peptide levels. Thereafter the ratios rapidly decreased without statistical differences. The levels of ICAs did not change. The levels of IAs, which were increased before transplant, then decreased without statistical differences between the groups. The values of ISC increased after transplant and then decreased similar to the T-cell ratio. Our results demonstrated that regimens of multiple and single HFIs did not show differences in the kinetics of the immunological response presumably mediating graft destruction. The CD4/CD8 ratio increased as the C-peptide level decreased, peaking on day 90 at the time of a decrease in C-peptide. These results may be useful for clinical studies of HFIs for type 1 diabetic patients.

Autoreactive CD8 T cells associated with beta cell destruction in type 1 diabetes

Type 1 diabetes is a T cell-mediated autoimmune disease, and insulin is an important target of the autoimmune response associated with beta cell destruction. The mechanism of destruction is still unknown. Here, we provide evidence for CD8 T cell autoreactivity associated with recurrent autoimmunity and loss of beta cell function in type 1 diabetic islet transplant recipients. We first identified an insulin B chain peptide (insB10-18) with extraordinary binding affinity to HLA-A2(*0201) that is expressed by the majority of type 1 diabetes patients. We next demonstrated that this peptide is naturally processed by both constitutive and immuno proteasomes and translocated to the endoplasmic reticulum by the peptide transporter TAP1 to allow binding to HLA-A2 in the endoplasmic reticulum and cell surface presentation. Peripheral blood mononuclear cells from a healthy donor were primed in vitro with this peptide, and CD8 T cells were isolated that specifically recognize target cells expressing the insulin B chain peptide. HLA-A2(insB10-18) tetramer staining revealed a strong association between detection of autoreactive CD8 T cells and recurrent autoimmunity after islet transplantation and graft failure in type 1 diabetic patients. We demonstrate that CD8 T cell autoreactivity is associated with beta cell destruction in type 1 diabetes in humans.

T-Cell Assays to Determine Disease Activity and Clinical Efficacy of Immune Therapy in Type 1 Diabetes

Type 1 (insulin-dependent) diabetes mellitus results from a T cell-mediated autoimmune destruction of the pancreatic beta cells in genetically predisposed individuals. Therapies directed against T cells have been demonstrated to halt the disease process and prevent recurrent beta-cell destruction after islet transplantation. Less is known about the nature and function of these T cells, the cause of the loss of tolerance to islet autoantigens, why the immune system apparently fails to suppress autoreactivity, and whether (or which) autoantigen(s) are critically involved in the initiation or progression of disease. Autoreactive T cells have proven to be valuable targets to study pathogenic or diabetes-related processes. Measuring T-cell autoreactivity also provided critical information to determine the fate of islet allografts transplanted to type 1 diabetic patients. Furthermore, these studies have provided proof of operational immunologic tolerance to islet allografts as well as valuable information to improve and customize immunosuppressive therapy. Currently, technologies to detect T-cell auto- and alloreactivity in type 1 diabetic recipients of islet allografts are applied to monitor islet allograft survival in relation with various immunosuppressive therapies and to guide tapering of these therapies after successful restoration of insulin production. Although it is generally appreciated that studies on cellular auto- and alloimmunity are hampered by the complex nature of such immune responses and the required technical and physical skills, it has been a worthwhile quest to unravel the role of T cells in the pathogenesis of type 1 diabetes and islet allograft destruction.

Alloreactivity Against Repeated HLA Mismatches of Sequential Islet Grafts Transplanted in Non-Uremic Type 1 Diabetes Patients

BACKGROUND

Islet transplantation can restore insulin production in type 1 diabetes patients. However, survival of the islet allografts will face rejection or recurrence of autoimmunity or a combination of both. In a study on islet-after-kidney transplants, we previously reported that islet cell recipients presented low T-cell alloresponses for HLA mismatches that were shared by the islet cell graft and the prior kidney graft, that is, repeated mismatch, while vigorous responses were measured against novel HLA mismatches.

METHODS

We now investigated T-cell alloreactivity to repeated HLA-mismatches in three non-uremic type 1 diabetic patients each receiving three sequential islet cell implants.

RESULTS

These islet-after-islet recipients patients exhibited low or absent responses to repeated mismatches to the first graft which was accompanied by sustained graft function, and reduced responsiveness towards subsequent grafts. In one patient, T-cell responses towards these mismatches were noticed following new mismatches in subsequent grafts, with loss of graft function.

CONCLUSION

These case reports further support the view that subsequent islet implantations can reduce alloreactivity for repeated HLA mismatches. They demonstrate the usefulness of monitoring T-cell reactivity against islet allografts to correlate immune function with graft survival and to identify conditions for preservation of beta-cell function.

Islet isolation for allotransplantation: variables associated with successful islet yield and graft function

AIMS/HYPOTHESIS

Efficient islet isolation is an important prerequisite for successful clinical islet transplantation. Although progressively improved, islet yield and quality are, however, unpredictable and variable and require standardisation.

METHODS

Since 1989 we have processed 437 pancreases using the automated method. The donor characteristics, pancreas procurement, and digestion and purification procedures including a wide enzyme characterisation of these pancreases were analysed and correlated with islet yield and transplant outcome.

RESULTS

By univariate analysis, islet yield was significantly associated with donor age (r=0.16; p=0.0009), BMI (r=0.19; p=0.0004), good pancreas condition (p=0.0031) and weight (r=0.15; p=0.0056), total collagenase activity (r=0.22; p=0.0001), adjusted collagenase activity/mg (r=0.18; p=0.0002), collagenase activity/solution volume (r=0.18; p=0.0002) and neutral protease activity/solution volume (r=0.14; p=0.0029). A statistically significant contribution to the variability of islet yield in a multivariate analysis performed on donor variables was found for donor BMI (p=0.0008). In a multivariate analysis performed on pancreas variables a contribution was found for pancreas weight (p=0.0064), and for a multivariate analysis performed on digestion variables we found a contribution for digestion time (p=0.0048) and total collagenase activity (p=0.0001). Twenty-four patients with type 1 diabetes received single islet preparations from single donors. In these patients, multivariate analyses showed that the reduction in insulin requirement was significantly associated with morphological aspects of islets (p=0.0010) and that 1-month C-peptide values were associated with islet purity (p=0.0071).

CONCLUSIONS/INTERPRETATION

These data provide baseline donor, digestion and purification selection criteria for islet isolation using the automated method and indicate that the morphological aspect may be a clinically relevant measure of islets on which the decision for transplant can be based.

HLA incompatibility and immunogenicity of human pancreatic islet preparations cocultured with blood cells of healthy donors

Type 1 diabetes mellitus (T1D) is a T-cell-mediated autoimmune disease characterized by the destruction of beta cells in the pancreas. An attractive novel therapy for type 1 diabetes is pancreatic islet transplantation, provided that recurrent islet autoimmunity and allograft rejection can be prevented. We analyzed the response of peripheral blood mononuclear cells (PBMC) from healthy blood donors to human islet-cell preparations with a composition similar to that of islet grafts used in clinical transplantation trials. It was examined whether the degree of major histocompatibility complex incompatibility between PBMC and donor islet cells is related to the degree of proliferative T-cell responses during coculture of human leukocyte antigen (HLA)-matched and mismatched PBMC with human islet cell-preparations (i.e., mixed islet/lymphocyte reaction). Prominent T-cell responses were observed in the vast majority of cases of double HLA class II mismatches. Intermediate T-cell responsiveness was observed in single HLA class II mismatches, whereas HLA matches did not induce a T-cell response. Our results identify the potential immunogenicity of islet preparations transplanted between HLA-DR incompatible subjects regardless of an autoimmune background of the recipient.

Satisfaction (not) guaranteed: re-evaluating the use of animal models of type 1 diabetes

Without a doubt, rodent models have been instrumental in describing pathways that lead to pancreatic beta-cell destruction, evaluating potential causes of type 1 diabetes and providing proof-of-principle for the potential of immune-based interventions. However, despite more than two decades of productive research, we are still yet to define an initiating autoantigen for the human disease, to determine the precise mechanisms of beta-cell destruction in humans and to design interventions that prevent or cure type 1 diabetes. In this Perspective article, we propose that a major philosophical change would benefit this field, a proposition that is based on evaluation of situations in which rodent models have provided useful guidance and in which they have led to disappointments.

Kinetics of diabetes-associated autoantibodies after sequential intraportal islet allograft associated with kidney transplantation in type 1 diabetes

OBJECTIVE

Presence or occurrence of pancreas auto-antibodies (aAb) has been shown to be of poor prognosis for islet cell transplantation. The aim of the study was to monitor the kinetics of these aAb after sequential intra-portal islet plus kidney transplantation with pre-Edmonton immunosuppressive regimen in order to determine whether the sequential protocol of transplantation was involved in the occurrence of the immune response.

PATIENTS AND METHODS

Three patients with IDDM and a previous (IAK) or simultaneous (SIK) kidney transplantation received 3 or 4 ABO compatible islet preparations. Islets (> 8 000 IEQ/kg post culture) were sequentially transplanted within a 12 day period via a per-cutaneous catheter. Immunosuppressive treatment included cyclosporine, steroïds and mycophenolate. Plasma ICAs, GAD 65, IA2 and C peptide (C-p) levels were monitored. Type II HLA phenotype was determined in donors and recipients.

RESULTS

Patient #1 had high anti-GAD levels (26.5 UI/l) before the IAK, while anti-IA2 and ICA levels were low. After the transplantation, C-p levels increased to 4.9 ng/ml at one month before becoming undetectable at 2 months. GAD levels remained high, ICA and IA2 aAb were undetectable. Patients #2 and #3 did not have significant levels of aAb before the islet transplantation. A slight increase in GAD was observed with each islet transplantation, followed by an overt but transient increase in ICA. IA2 levels remained undetectable. Three months after the transplantation and 2 weeks after the increase of ICA, C-p levels, that were >3.4 ng/ml at one month, fell below 0.2 (N: 0.5-2).

CONCLUSION

The immunosuppressive regimen used in kidney transplantation is unable to control perfectly anti-pancreas aAb production. Moreover, these results seem to indicate that the benefits of sequential islet transplantation lie more in the increased islet mass they provide than in potential immune benefit.

Prolonged survival of rat islet xenografts in mice after CD45RB monotherapy

BACKGROUND

Pancreatic islet transplantation can correct the disordered glucose metabolism of type 1 diabetes, but the number of successful transplants has been low because of the need for long-term immunosuppression and the limited availability of human islets. New approaches, such as the use of tolerance-inducing treatment modalities and the use of islets of nonhuman sources, can possibly improve the success of islet transplantation. In the present study, the authors investigated the effect of anti-CD45RB treatment on the survival of islet xenografts.

METHODS

Chemically induced diabetic mice underwent xenografting with rat islets and were treated with CD45RB antibodies on days -1, 0, and 5. Immunohistology and real-time polymerase chain reaction were used to study the effect of the treatment in the xenografts. The effect of anti-CD45RB treatment in peripheral blood of normal mice was measured with flow cytometry.

RESULTS

In the treated mice, survival of the grafts was prolonged substantially. In the treated mice with functioning grafts, no lymphocytes were found infiltrating the transplanted islets on day 6; whereas in the untreated animals with functioning grafts, signs of rejection were evident. In the grafts of the treated animals, significantly less mRNA for interleukin (IL)-2, interferon-gamma, and IL-4 was found compared with the untreated mice. After CD45RB treatment, there was depletion or decrease of CD45RBbright cells from the peripheral blood.

CONCLUSIONS

Our results show that a short course of anti-CD45RB monotherapy prolongs the survival of rat islet xenografts in C57BL/6 mice.

Auto-islet transplantation after pancreatectomy

Chronic pancreatitis (CP) is an inflammatory disease that causes progressive and irreversible structural changes to the pancreas, resulting in permanent impairment of both endocrine and exocrine functions. In advanced cases of CP, pain can be relieved only with pancreatic resection. However, even partial resection of the pancreas in this setting may cause diabetes. Furthermore, postsurgical diabetes (PSD) always occurs after total or near-total pancreatectomy, which is commonly performed for CP. Auto transplantation of pancreatic islets into the portal vein after pancreatic resection can prevent PSD. The results of this strategy, which are already encouraging, are likely to improve in the near future because of significant progress in the isolation and preservation of pancreatic islets. This review discusses the current status and future prospects for auto-islet transplantation after pancreatic resection for CP.

The role of T-cells in the pathogenesis of Type 1 diabetes: from cause to cure

Type 1 diabetes mellitus results from a T-cell mediated autoimmune destruction of the pancreatic beta cells in genetically predisposed individuals. The knowledge of the immunopathogenesis has increased enormously in the last two decades. The contribution of T-cells in the pathogenesis is beyond doubt. Therapies directed against T-cells have been shown to halt the disease process and prevent recurrent beta-cell destruction after islet transplantation. Less is known about the nature and function of these T-cells, the cause of the loss of tolerance to islet autoantigens, why the immune system apparently fails to suppress autoreactivity, and whether (or which) autoantigen(s) are critically involved in the initiation or progression of the disease. The contribution of dendritic cells in directing the immune response is clear, while the contribution of B-cells and autoantibodies is subject to reconsideration. Autoreactive T-cells have proven to be valuable tools to study pathogenic or diabetes-related processes. Measuring T-cell autoreactivity has also provided critical information to determine the fate of islet allografts transplanted to Type 1 diabetic patients. Cellular autoimmunity is a difficult study subject, but it has been a worthwhile quest to unravel the role of T-cells in the pathogenesis of Type 1 diabetes. The challenge for the future is to determine which factors contribute to the loss of tolerance to beta-cell antigens, and to define what measures T-cells can provide to suppress autoreactivity, since it is becoming increasingly evident that T-cells provide a two-edged sword: some T-cells could be pathogenic, but others can regulate the disease process and thus form new targets for immunointervention.

Cytokine detection by ELISPOT: relevance for immunological studies in type 1 diabetes

Diabetes mellitus type 1 is a chronic disease in which the insulin-secreting ss-cells are selectively destroyed by an immune-mediated process. Autoantibodies directed against several islet antigens are useful parameters to estimate the risk to develop diabetes, but cell-mediated immunity involving T lymphocytes plays a major part in causing the specific destruction of ss-cells. T cells are characterized by their antigen-specificity, phenotype and cytokine-secreting profile. T cells that secrete cytokines of the T helper 1 (Th1) type have been shown to transfer diabetes in animal studies, in contrast to T helper 2 (Th2) cytokine-secreting T cells that are thought to be rather nondestructive. In the absence of phenotypic markers for Th1 and Th2 cells, several different approaches have been taken to examine T cell responses in detail. Methods involve T-cell proliferation assays, Enzyme-Linked-Immuno-Sorbent-Assay (ELISA) analysis of secreted cytokines and phenotype analysis applying flow cytometry. A more recent development is ELISPOT analysis, which enables the investigator to determine the qualitative and quantitative antigen-specific immune response on a single-cell level with regard to cytokine secretion. This article aims to give an introduction to the advantages and limitations inherent in the different techniques and their potential relevance for immunological studies in diabetes mellitus type 1.

Redirection of human autoreactive T-cells Upon interaction with dendritic cells modulated by TX527, an analog of 1,25 dihydroxyvitamin D(3)

The active form of vitamin D(3), 1alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), is a potent immunomodulator known to affect T-cells through targeting antigen-presenting cells such as dendritic cells (DCs). We studied the effects of a novel nonhypercalcemic 1,25(OH)(2)D(3) analog, TX527, on DC differentiation, maturation, and function with respect to stimulation of a committed human GAD65-specific autoreactive T-cell clone. Continuous addition of TX527 impaired interleukin (IL)-4 and granulocyte/macrophage colony-stimulating factor (GM-CSF)-driven DC differentiation as well as lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma)-induced maturation into Th1-promoting DC (DC1), as characterized by marked changes in DC morphology and abrogation of IL-12p70 release upon CD40 ligation. Addition of TX527 during maturation did not affect DC morphology but significantly changed DC cytokine profiles. The potential of treated DCs to alter the response pattern of committed autoreactive T-cells was found to depend on the timing of TX527 exposure. Continuously TX527-treated DCs significantly inhibited T-cell proliferation and blocked IFN-gamma, IL-10, but not IL-13 production, whereas DCs treated during maturation failed to inhibit T-cell proliferation but affected IL-10 and IFN-gamma production. Collectively, we provide evidence that nonhypercalcemic TX527 is a potent in vitro DC modulator, yielding DCs with the potential to change cytokine responses of committed autoreactive T-cells.

Cytokine and immunosuppressive therapies of type 1 diabetes mellitus

In this article, the authors covered a number of issues that affect how researchers approach prevention of diabetes. The focus has been the use of cytokines and immunosuppressive therapies. The historical understanding of cytokine and immunosuppressive approaches, new developments in using these agents in humans, and the issues involved in designing diabetes prevention trials were reviewed. Although progress at times appears slow, the current research activities predict new developments in the next few years that may improve the understanding of the progression of diabetes and possible ways to intervene.

A view on beta cell transplantation in diabetes

Organ donors also offer a source of insulin-producing tissue that might be used for the treatment of diabetes. Clinical protocols for transplantation of this tissue aim for the prevention of chronic diabetes complications without introducing new serious side effects. Pancreas and islet cell transplantation are discussed in this perspective. The future of islet cell implants looks favorable but depends on finding ways to induce immune tolerance to the donor beta cells. Clinical trials can take advantage of relevant progress in animal models. In a limited study, recipient treatment with antilymphocyte antibodies and culture of donor cell preparations appeared useful to induce a state of operational immune tolerance in type 1 diabetic patients, as indirectly judged by graft survival and by analysis of auto- and alloreactivities in recipients. Use of cultured beta cell preparations also allows donor cell recruitment from suboptimal donor organs and increases the degree of standardization and quality control of islet cell grafts. The future of these grafts will depend on the development of techniques for the neogenesis of beta cells.

Protection from type 1 diabetes in the face of high levels of activated autoaggressive lymphocytes in a viral transgenic mouse model crossed to the SV129 strain

In comparing the incidence of virally induced type 1 diabetes in F(1) crosses of RIP-LCMV mice to three different mouse strains identical at the major histocompatibility complex H-2D(b) locus, we surprisingly found that disease development was reduced by 80% in F(1) crosses to the SV129 genetic background and by 60% after eight backcrosses to the original C57BL/6 RIP-LCMV mice. In this model, diabetes is strongly dependent on a virally induced H-2D(b)-restricted cytotoxic T-cell (CTL) response. Importantly, numbers and effector functions of autoaggressive CD4 and CD8 lymphocytes were not decreased in the protected mice, and CTLs were still able to kill syngeneic islet cells in vitro with equal efficacy compared with CTLs from the original RIP-LCMV strain. Furthermore, CTLs were able to extravasate into islets in vivo, and no evidence for induction of regulatory cells was observed. However, regeneration of beta-cells in islets under "attack" occurred only in the protected SV129-crossed animals, whereas it was not evident at any time in any mice that developed diabetes. Thus, genetic factors can "override" the diabetogenic potential of high numbers of autoaggressive lymphocytes through, for example, increased islet regeneration. This finding has important implications for interpreting numbers and pathogenicity of autoreactive lymphocytes in prediabetic patients of genetically diverse backgrounds.

Autoantibody response to islet transplantation in type 1 diabetes

Islet allotransplantation into patients with autoimmune type 1 diabetes represents a reexposure to autoantigen. Here, measurement of antibodies to GAD and IA-2 autoantigens before and after islet transplantation in 36 patients (33 receiving islet plus kidney grafts with cyclosporin and steroid-based immunosuppression, and 3 receiving solitary islet transplants with mycophenolate but cyclosporin-free immunosuppression) demonstrated marked rises in GAD antibodies within 7 days posttransplantation in 5 patients (3 receiving islet after kidney transplants, and 2 receiving solitary islet transplants) and within 30 days in the third patient receiving solitary islet transplantation. GAD antibodies were of the IgG1 subclass, against major autoantigenic epitopes, and in cases of islet after kidney transplants, the responses were short-lived and not accompanied by HLA antibodies. Two of these patients had subsequent marked rises of IA-2 antibodies, and an additional patient had a marked rise in IgM-GAD antibodies 3 years after transplantation. Insulin independence was not achieved in patients with autoantibody elevations and was significantly less frequent in these patients. These data are consistent with a reactivation of autoimmunity that may be dependent on immunosuppression therapy and is associated with impaired graft function.

Factors influencing Islet of Langerhans graft function and monitoring

Transplantation of islet of Langerhans represents a viable therapeutic option for insulin-dependent diabetes mellitus. Dramatic progress has been recently reported with the introduction of a glucocorticoid-free immunosuppressive regimen that improved success rate, namely, insulin independence for 1 year or more, from 8% to 100%. The fate of islet grafts is determined by many concurrent phenomena, some of which are common to organ grafts (i.e. rejection), while others are unique to nonvascularized cell transplants, including transplant cell mass and viability, as well as nonspecific inflammation at the site of implant. Moreover, islet grafts lack clinical markers of early rejection, making it difficult to recognize imminent rejection and to implement intervention with graft-saving immunosuppressive regimens. In the present review, we will address the problems influencing islet graft success and the monitoring of islet cell graft function.

Novel approaches toward early diagnosis of islet allograft rejection

BACKGROUND

The inability to diagnose early rejection of an islet allograft has previously proved to be a major impediment to progress in clinical islet transplantation. The need to detect early rejection will become even more relevant as new tolerance-inducing protocols are evaluated in the clinic. We explored three novel approaches toward development of early diagnostic markers of islet rejection after islet allotransplantation.

METHODS

(a) Canine islet allograft transplant recipients were immunosuppressed for 1 month, then therapy was withdrawn. Serum glutamic acid decarboxylase antigen (GAD65), an endogenous islet protein, was monitored daily with a CO2 release assay. (b) Rodent islets were genetically engineered to express a unique foreign protein (beta-galactosidase) by using adenoviral vectors, and after allograft transplantation, the viral-specific protein was measured in serum using optical luminescence. (c) Rodents receiving islet allografts were immunosuppressed temporarily, and daily glucose tolerance tests were followed until graft failure occurred.

RESULTS

(a) Although serum monitoring of GAD65 antigen demonstrated elevated levels preceding loss of graft function in preliminary studies, the effect was not reproducible in all animals. (b) Genetically engineered rodent islets demonstrated normal insulin kinetics in vitro (insulin stimulation index 2.57+/-0.2 vs. 2.95+/-0.3 for control islets, P=ns), and purified viral protein products had a stable half-life of 8 hr in vivo. After islet allotransplantation, there were two peak elevations in serum viral proteins, confirming that an intra-islet "sentinel signal" could be detected serologically during acute rejection. There was no lead-time ahead of hyperglycemia, however. (c) Daily sequential intravenous glucose tolerance (IVGT) tests demonstrated evidence of allograft dysfunction (decline in KG) with a 2-day lead time to hyperglycemia (2.58+/-0.3 vs. 1.63+/-0.2%/min, respectively, P<0.001), with an accuracy of 89%, sensitivity of 78%, and specificity of 95%.

CONCLUSIONS

Of the three diagnostic tests, metabolic assessment with an abbreviated IVGT was the most effective method of demonstrating early islet dysfunction due to rejection.

Self-antigen-presenting cells expressing diabetes-associated autoantigens exist in both thymus and peripheral lymphoid organs

Recent reports indicate that genes with tissue-restricted expression, including those encoding the type 1 diabetes autoantigens insulin, glutamic acid decarboxylase (GAD), and the tyrosine-phosphatase-like protein IA-2 (or ICA512), are transcribed in the thymus. The reported modulation of diabetes susceptibility by genetically determined differences in thymic insulin levels and studies in transgenic mice provide correlative and functional evidence that thymic expression of peripheral proteins is crucial for immunological self-tolerance. However, there are no specific data about the existence, tissue distribution, phenotype, and function of those cells that express insulin and other self-antigens in the human thymus. We find that the human thymus harbors specialized cells synthesizing (pro)insulin, GAD, and IA-2, mainly localized in the medulla, and we demonstrate such cells also in peripheral lymphoid organs (spleen and lymph nodes). Phenotypic analysis qualifies these cells as antigen-presenting cells (APCs), including both dendritic cells and macrophages. These cells often appear surrounded by apoptotic lymphocytes, both in thymus and spleen, and may therefore be involved in the deletion of autoreactive lymphocytes. Our findings demonstrate the existence of, and define the tissue distribution and phenotype of, a novel subset of APCs expressing self-antigens in human lymphoid organs that appear to be involved in the regulation of self-tolerance throughout life.

Bone marrow cell graft engineering: from bench to bedside

Bone marrow transplantation (BMT) has the potential to treat hemoglobinopathies (sickle cell and thalassemia) autoimmunity (diabetes, lupus, multiple sclerosis, rheumatoid arthritis, Crohn's colitis) and enzyme deficiency states. Graft versus host disease (GVHD) is a major complication and limitation to the therapeutic application of BMT. There have been many clinical trials and experimental animal models that have attempted to control GVHD through the engineering of the donor bone marrow cells (BMC). Historically, several methods have demonstrated effectiveness in controlling GVHD; however they were also associated with a marked increase in the rate of graft failure. Highly purified hematopoietic stem cells (HSC) engraft quite readily in genetically-matched recipients while they do not engraft as easily in MHC-disparate recipients. The numbers of HSC must be increased 100-200 fold in order to overcome the allogeneic barrier. We were the first to phenotypically and to functionally characterize a novel cell in the bone marrow that enables engraftment of highly purified HSC in allogeneic recipients. The discovery of graft facilitating cell populations has resulted in the restoration of the engraftment-potential of purified HSC between genetically-disparate individuals. The addition of facilitating cells (FC) to T cell-depleted BMC grafts results in allogeneic engraftment without GVHD or graft failure. New strategies of BMC engineering that retain FC and HSC but avoid GVHD have allowed successful engraftment in mismatched and older recipients. These techniques have expanded the therapeutic potential of BMT to virtually every candidate as well as to non-malignant diseases in which the morbidity associated with conventional BMT could not be accepted. This article reviews the transition of the FC technology from bench to bedside and discuss the potentially broad-reaching applications of BMT and mixed chimerism.

Human islet cell transplantation--future prospects

BACKGROUND

Islet transplantation has the potential to cure diabetes mellitus. Nevertheless despite successful reversal of diabetes in many small animal models, the clinical situation has been far more challenging. The aim of this review is to discuss why insulin-independence after islet allotransplantation has been so difficult to achieve.

METHODS

A literature review was undertaken using Medline from 1975 to July 2000. Results reported to the International Islet Transplant Registry (ITR) up to December 1998 were also analysed.

RESULTS

Up to December 1998, 405 islet allotransplants have been reported the ITR. Of those accurately documented between 1990 and 1998 (n = 267) only 12% have achieved insulin-independence (greater than 7 days). However with refined peri-transplant protocols insulin independence at 1 year can reach 20%.

CONCLUSIONS

There are many factors which can explain the failure of achieving insulin-independence after islet allotransplantation. These include the use of diabetogenic immunosuppressive agents to abrogate both islet allo-immunity and auto-immunity, the critical islet mass to achieve insulin-independence and the detrimental effects of transplanting islets in an ectopic site. However recent evidence most notably from the Edmonton group demonstrates that islet allotransplantation still has great potential to become an established treatment option for diabetic patients.

Bovine islets are less susceptible than human islets to damage by human cytokines

BACKGROUND

The potential benefits of islet xenografting in type 1 diabetes include the intriguing, but still unanswered, possibility that the grafted xenoislets may be less subjected to human autoimmune attack. Cytokines may play a major role in the pathogenesis of autoimmune diabetes by causing impairment of insulin release and pancreatic islet cell toxicity.

METHODS

We compared insulin secretion, islet cell death and survival, inducible nitric oxide synthase (iNOS) mRNA expression, nitrite production, and Bcl-2 and Bax mRNA expression in isolated human and large mammal (bovine) islets exposed to 50 U/ml recombinant human interleukin-1, 1,000 U/ml recombinant human tumor necrosis factor-alpha and 1,000 U/ml recombinant human interferon-gamma.

RESULTS

After 24-hr exposure, a marked decrease of glucose-stimulated insulin secretion was observed with human, but not with bovine islets. After 48-hr exposure, human, but not bovine, pancreatic islets showed a significantly higher percentage of apoptotic cells compared to controls. Treatment of human islets with human cytokines induced up-regulation of iNOS mRNA, increased levels of nitrites, and down-regulation of Bcl-2 mRNA, with unchanged levels of Bax mRNA. These parameters were not affected by cytokines in bovine islets.

CONCLUSIONS

Bovine islets are less susceptible than human islets to the effects of human cytokines, which may be a potential advantage of xenotransplantation.

Appropriateness and timing of kidney and/or pancreas transplants in type 1 and type 2 diabetes

Cure of diabetes through cell or organ transplantation remains an unattained but highly desirable goal. For now, prevention of end organ complications of diabetes is the most appropriate application of transplantation for patients with enough evidence of progressive disease to justify the substantial surgical and immunosuppression-based risks of pancreas transplantation. Uremic diabetics should, if possible, be offered renal transplantation, alone or in combination with pancreas transplantation, to obviate the excessive mortality associated with prolonged maintenance dialysis. Islet transplantation has been widely clinically unsuccessful but holds new promise as the therapy of choice for the future. This report reviews the history, state of the art, and selection process for timing and application of currently available transplantation modalities for diabetic patients.

Reactivation of type 1 diabetes in patients receiving human fetal pancreatic tissue transplants without immunosuppression

BACKGROUND

Type 1 diabetes is a cell-mediated autoimmune disease. Successful transplantation of human fetal pancreatic tissue into type 1 diabetic patients must address both autoimmunity and allograft rejection. We investigated whether humoral and cellular responses to islet antigens could be demonstrated in the peripheral blood of type 1 diabetic subjects receiving human fetal pancreatic tissue transplants.

METHODS

We investigated peripheral blood mononuclear cell (PBMC) responses, using cellular immunoblotting, and autoantibody responses to islet proteins, before transplant and at 3-month intervals after transplant, of nine long-term type 1 diabetes patients (mean disease duration of 21 years) receiving human fetal pancreatic tissue subcutaneously into the abdominal wall without immunosuppression.

RESULTS

Before transplant, all nine subjects were islet cell autoantibody (ICA)-negative and seven out of nine subjects were glutamic acid decarboxylase autoantibody (GADAb)-positive. After transplant, all subjects became ICA(+) and the two patients who were GADAb(-) before transplant became GADAb(+) after transplant. Maximum PBMC reactivity to separated human fetal pancreatic proteins was observed in four patients 3 months after transplant, in one patient at 6 months, in two patients at 9 months, and in one patient at 12 months after transplant. One subject, who had PBMC reactivity to multiple islet proteins before transplant, continued to respond to multiple islet proteins throughout the study.

CONCLUSIONS

We conclude that the development in the peripheral blood of ICA, GADAb, and PBMC reactivity to human fetal pancreatic proteins in the trans plant recipients is most consistent with reactivation of the type 1 diabetes disease process.

Human islet transplantation: lessons from 13 autologous and 13 allogeneic transplantations

BACKGROUND

A series of 13 islet autotransplantations and 13 islet allotransplantations performed between 1992 and 1999 at the University Hospital of Geneva are presented. Factors affecting the outcome are analyzed.

METHODS

Islet autotransplantation has been performed in seven patients with chronic pancreatitis and in six patients with benign tumors undergoing extensive pancreatectomy. Islet allografts were performed in C-peptide-negative patients simultaneously or after a kidney or lung transplantation. Each recipient received islets from one to four donors. Panel-reactive antibodies were monitored by microlymphocytotoxicity test.

RESULTS

Eleven of 13 patients who underwent autotransplantation maintained insulin independence for 6 months to 5 years. Two years after autologous islet transplantation, five of nine patients were insulin independent with an glycosylated hemoglobin of 5.9%. Three late islet failures occurred in patients with chronic pancreatitis. Islet yield was significantly lower in patients with chronic pancreatitis than in patients with benign tumors (2044 equivalent islet number/gram resected pancreas versus 5184 equivalent islet number/gram; P=0.037). In islet allotransplantation, no early graft loss was found. All 13 patients who underwent allotransplantation had basal C-peptide levels above 0.3 nmol/L for 3 months to 5 years. Mean glycosylated hemoglobin decreased from 9.1% before transplantation to 5.5% at month 3. Insulin independence was achieved in two type I diabetic patients. In four of six patients with graft failure, the graft had induced panel-reactive antibodies.

CONCLUSIONS

In islet autotransplantation, the reduced number of islets that can be isolated from fibrotic pancreata may be the major limiting factor. In islet allotransplantation, early graft function can now be consistently achieved. Islet allografts seem to be highly immunogenic, and chronic islet failure cannot be prevented consistently by conventional immunosuppression.

Chronically decreased oxygen tension in rat pancreatic islets transplanted under the kidney capsule

BACKGROUND

A factor of potential importance in the failure of islet grafts is poor or inadequate engraftment of the islets in the implantation organ. This study measured the oxygen tension and blood perfusion in 1-, 2-, and 9-month-old islet grafts.

METHODS

The partial pressure of oxygen was measured in pancreatic islets transplanted beneath the renal capsule of diabetic and nondiabetic recipient rats with a modified Clark electrode (outer tip diameter 2-6 microm). The size of the graft (250 islets) was by purpose not large enough to cure the diabetic recipients. The oxygen tension in islets within the pancreas was also recorded. Blood perfusion was measured with the laser-Doppler technique.

RESULTS

Within native pancreatic islets, the partial pressure of oxygen was approximately 40 mm Hg (n=8). In islets transplanted to nondiabetic animals, the oxygen tension was approximately 6-7 mm Hg 1, 2, and 9 months posttransplantation. No differences could be seen between the different time points after transplantation. In the diabetic recipients, an even more pronounced decrease in graft tissue oxygen tension was recorded. The mean oxygen tension in the superficial renal cortex surrounding the implanted islets was similar in all groups (approximately 15 mm Hg). Intravenous administration of glucose (0.1 gxkg(-1)x min(-1)) did not affect the oxygen tension in any of the investigated tissues. The islet graft blood flow was similar in all groups, measuring approximately 50% of the blood flow in the kidney cortex.

CONCLUSION

The oxygen tension in islets implanted beneath the kidney capsule is markedly lower than in native islets up to 9 months after transplantation. Moreover, persistent hyperglycemia in the recipient causes an even further decrease in graft oxygen tension, despite similar blood perfusion. To what extent this may contribute to islet graft failure remains to be determined.

Reactivation of type 1 diabetes in patients receiving human fetal pancreatic tissue transplants without immunosuppression

BACKGROUND

Insulin-dependent (type 1) diabetes is a cell-mediated autoimmune disease. Successful transplantation of human fetal pancreatic tissue into type 1 diabetic patients must address both autoimmunity and allograft rejection. We investigated whether humoral and cellular responses to islet antigens could be demonstrated in the peripheral blood of type 1 diabetic subjects receiving human fetal pancreatic tissue transplants.

METHODS

We investigated peripheral blood mononuclear cell (PBMC) responses, using cellular immunoblotting, and autoantibody responses to islet proteins, before transplantation and at 3-month intervals after transplantation. Our study population included nine long-term type 1 diabetes patients (mean disease duration of 21 years) receiving human fetal pancreatic tissue subcutaneously into the abdominal wall without immunosuppression.

RESULTS

Before transplantation, all nine subjects tested negative for islet cell autoantibody (ICA), and seven of nine subjects tested positive for glutamic acid decarboxylase autoantibody (GADAb). After transplantation, all subjects became ICA(+), and the two patients who were GADAb(-) before transplantation, became GADAb(+) after transplantation. Maximum PBMC reactivity to separated human fetal pancreatic proteins was observed in four patients at 3 months, in one patient at 6 months, in two patients at 9 months, and in one patient at 12 months after transplantation. One subject, who had PBMC reactivity to multiple islet proteins before transplantation, continued to respond to multiple islet proteins throughout the study.

CONCLUSIONS

We conclude that the development in the peripheral blood of ICA, GADAb, and PBMC reactivity to human fetal pancreatic proteins in the transplant recipients is most consistent with reactivation of the type 1 diabetes disease process.

Autoreactive T cell responses in insulin-dependent (Type 1) diabetes mellitus. Report of the first international workshop for standardization of T cell assays

Type 1 diabetes is thought to result from a T cell-mediated destruction of the pancreatic beta-cells. Multiple and sometimes conflicting studies have identified a variety of aberrations in the cellular immune response to autoantigens in persons with the disease. Potential explanations for these discrepancies include incomparable techniques or culture conditions, diversity in the populations of patients or controls tested, and differences in autoantigen preparations. A T cell workshop was organized by the Immunology of Diabetes Society with the aim of appreciating and identifying problems associated with autoreactive T cell assays in type 1 diabetes. As a first phase, a series of candidate autoantigens were analysed by reference laboratories for quality. Subsequently, these preparations, as well as control stimuli, were distributed in a blind fashion to 26 laboratories worldwide, including all experienced centres, for analysis of T cell proliferation assays in 10 recent onset type 1 diabetes and 10 non-diabetic controls. For this analysis, participants used their own assays and references. The islet autoantigen quality control analyses performed prior to the distribution indicate that the quality of recombinant autoantigen preparations requires improvement. For example, several T cell clones specific for glutamic acid decarboxylase (GAD65) were unable to cross-react with GAD65 expressed in baculovirus, yeast or bacteria. Moreover, autoantigens expressed in E. coli interfered with autoantigen-specific proliferation of both T cell clones and peripheral blood mononuclear cells. Nonetheless, responses could be measured to all autoantigen preparations evaluated in the workshop. During the blind phase of the study, all centres were able to reproducibly measure T cell responses to two identical samples of tetanus toxoid, but there was significant interlaboratory variation in sensitivity and extent of the proliferative response measured. Third, the results using candidate autoantigens indicated that although a few laboratories could distinguish type 1 diabetes patients from non-diabetic controls in proliferative responses to individual islet autoantigens, in general, no differences in T cell proliferation between the two groups could be identified. This first T cell workshop on T cell autoreactivity in type 1 diabetes confirms that this was a difficult area for interlaboratory investigations, but provided insight towards future efforts focused on standardizing autoreactive T cell measurements. Some previously reported conflicting results can in part be explained by the observed interlaboratory variability. The inability to discriminate normal controls from new onset type 1 diabetes patients suggests that measuring proliferative responses in PBMC represents an incomplete picture of the immune response, perhaps complicated by difficulties in identifying suitable antigens and assays for standardized use.

Type 1 Diabetes

Type 1 (insulin-dependent) diabetes occurs worldwide and can appear at any age. The genetic susceptibility is strongly associated with HLA-DQ and DR on chromosome 6, but genetic factors on other chromosomes such as the insulin gene on chromosome 11 and the cytotoxic T-lymphocyte antigen gene on chromosome 2 may modulate disease risk. Numerous studies further support the view that environmental factors are important. Gestational infections may contribute to initiation, whereas later infections may accelerate islet β-cell autoimmunity. The pathogenesis is strongly related to autoimmunity against the islet β cells. Markers of autoimmunity include autoantibodies against glutamic acid decarboxylase, insulin, and islet cell antigen-2, a tyrosine phosphatase-like protein. Molecular techniques are used to establish reproducible and precise autoantibody assays, which have been subject to worldwide standardization. The diagnostic sensitivity (40–80%) and specificity (99%) of all three autoantibodies for type 1 diabetes are high, and double or triple positivity among first-degree relatives predicts disease. Combined genetic and antibody testing improved prediction in the general population despite the transient nature of these autoantibodies. Classification of diabetes has also been improved by autoantibody testing and may be used in type 2 diabetes to predict secondary failure and insulin requirement. Islet autoantibodies do not seem to be related to late complications but rather to metabolic control, perhaps because the presence of islet cell autoantibodies marks different residual β-cell function. Combined genetic and autoantibody screening permit rational approaches to identify subjects for secondary and tertiary intervention trials.

Immune markers for monitoring the progression of autoimmune disease

The incidence of immune-mediated diseases is increasing worldwide. Reliable immune markers for monitoring disease progression and also the effect of therapeutic interventions are urgently needed in order to investigate preventive or therapeutic measures effectively. At a recent workshop held on 5 December 1998 in Copenhagen, the state of research on surrogate markers in Type 1 diabetes was discussed and compared with the experience in multiple sclerosis, inflammatory bowel disease and transplantation.