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Objective: Curing type 1 diabetes by transplanting pancreatic islets into the liver is associated with poor long-term outcome and graft failure at least partly due to inadequate graft revascularization. The aim of the current study was to evaluate striated muscle as a potential angiogenic site for islet transplantation.Research Design and Methods: The current study presents a new experimental model that is found to be applicable to clinical islet transplantation. Islets were implanted into striated muscle and intraislet vascular density and blood flow were visualized with intravital and confocal microscopy in mice and by magnetic resonance imaging in three autotransplanted pancreatectomized patients. Mice were rendered neutropenic by repeated injections of Gr-1 antibody, and diabetes was induced by alloxan treatment.Results: Contrary to liver-engrafted islets, islets transplanted to mouse muscle were revascularized with vessel densities and blood flow entirely comparable with those of islets within intact pancreas. Initiation of islet revascularization at the muscular site was dependent on neutrophils, and the function of islets transplanted to muscle was proven by curing diabetic mice. The experimental data were confirmed in autotransplanted patients where higher plasma volumes were measured in islets engrafted in forearm muscle compared with adjacent muscle tissue through high-resolution magnetic resonance imaging.Conclusions: This study presents a novel paradigm in islet transplantation whereby recruited neutrophils are crucial for the functionally restored intraislet blood perfusion following transplantation to striated muscle under experimental and clinical situations. [ABSTRACT FROM AUTHOR]

Objective: Mesenchymal stem cells (MSCs) contribute to endothelial cell (EC) migration by producing proteases, thereby paving the way into the tissues for ECs. MSCs were added to our previously described composite EC islets as a potential means to improve their capacity for islet angiogenesis.Research Design and Methods: Human islets were coated with primary human bone marrow-derived MSCs and dermal microvascular ECs. The capacity of ECs, with or without MSCs, to adhere to and grow into human islets was analyzed. The survival and functionality of these composite islets were evaluated in a dynamic perifusion assay, and their capacity for angiogenesis in vitro was assessed in a three-dimensional fibrin gel assay.Results: ECs proliferated after culture in MSC-conditioned medium, and MSCs improved the EC coverage threefold compared with EC islets alone. Islet survival in vitro and the functionality of the composite islets after culture were equal to those of control islets. The EC-MSC islets showed a twofold increase in total sprout formation compared with EC islets, and vascular sprouts emanating from the EC-MSC-islet surface showed migration of ECs into the islets and also into the surrounding matrix, either alone or in concert with MSCs.Conclusions: EC proliferation, sprout formation, and ingrowth of ECs into the islets were enhanced by MSCs. The use of composite EC-MSC islets may have beneficial effects on revascularization and immune regulation. The technique presented allows for pretreatment of donor islets with recipient-derived ECs and MSCs as a means of improving islet engraftment. [ABSTRACT FROM AUTHOR]

This study examines, at the ultrastructural level, whether the fetal porcine endocrine pancreas (insulin, glucagon, somatostatin, and pancreatic polypeptide [PP]- and islet amyloid polypeptide [IAPP]-containing cells) develops normally after transplantation under the kidney capsule in athymic mice. We have thus used an in vivo pig-to-mouse model for the differentiation of the endocrine pancreas removed from its normal milieu. Islet-like cell clusters (ICCs) were prepared from the fetal porcine pancreas as previously described and transplanted under the renal capsule of athymic mice. At various times after transplantation, the endocrine pancreas was removed and the level of differentiation was compared with the native pancreas of the same biological age. At the ultrastructural level, several sequential steps could be identified based on the morphology and hormone content of the secretory granules of the endocrine cell examined. Applying this approach, we could demonstrate that the ontogeny of the transplanted fetal pig pancreas follows the same sequential differentiation as the native pancreas. The process seems to be under stringent control, apparently directly related to the biological age of the tissue, and independent not only of the new environment under the kidney capsule but also of the adult and xenogeneic milieu provided after transplantation to the athymic nude mouse. Therefore, all four major hormone-producing cells seem to develop normally after transplantation when compared with the development in the native pancreas. IAPP was produced by the pluripotent fetal endocrine cells as well as the adult alpha-, beta-, and delta-cell granules in the native pancreas; however, in the transplanted pancreas, IAPP expression was demonstrated only in beta-cells, delta-cells, and PP cells. No IAPP was found in granules of the alpha-cell lineage. The results suggest a sequential differentiation of all four major types of islet cells from a common pluripotent progenitor cell, which seems to be located in the pancreatic ducts. Therefore, the results presented strongly suggest that the ontogeny of the four major endocrine islet cells is determined by genetic information carried by the progenitor cells and not by the systemic or local environment. [ABSTRACT FROM AUTHOR]

The longitudinal alterations of the pancreatic β-cell and islet mass in the progression of type 1 diabetes (T1D) are still poorly understood. The objective of this study was to repeatedly assess the endocrine volume and the morphology of the pancreas for up to 24 months after T1D diagnosis ( n = 16), by 11 C-5-hydroxytryptophan ( 11 C-5-HTP) positron emission tomography (PET) and MRI. Study participants were examined four times by PET/MRI: at recruitment and then after 6, 12, and 24 months. Clinical examinations and assessment of β-cell function by a mixed-meal tolerance test and fasting blood samples were performed in connection with the imaging examination. Pancreas volume has a tendency to decrease from 50.2 ± 10.3 mL at T1D debut to 42.2 ± 14.6 mL after 24 months ( P < 0.098). Pancreas uptake of 11 C-5-HTP (e.g., the volume of the endocrine pancreas) did not decrease from T1D diagnosis (0.23 ± 0.10 % of injected dose) to 24-month follow-up, 0.21 ± 0.14% of injected dose, and exhibited low interindividual changes. Pancreas perfusion was unchanged from diagnosis to 24-month follow-up. The pancreas uptake of 11 C-5-HTP correlated with the long-term metabolic control as estimated by HbA 1c ( P < 0.05). Our findings argue against a major destruction of β-cell or islet mass in the 2-year period after diagnosis of T1D., (© 2021 by the American Diabetes Association.)

In December 2018, Diabetes and Diabetologia began requiring authors of papers reporting data obtained from studies on human islets to report critical characteristics of the human islets used for research. The islet community was asked to provide feedback on it. Here is the contribution by the European Consortium for Islet Transplantation., (© 2019 by the American Diabetes Association.)

GPR44 expression has recently been described as highly β-cell selective in the human pancreas and constitutes a tentative surrogate imaging biomarker in diabetes. A radiolabeled small-molecule GPR44 antagonist, [ 11 C]AZ12204657, was evaluated for visualization of β-cells in pigs and nonhuman primates by positron emission tomography as well as in immunodeficient mice transplanted with human islets under the kidney capsule. In vitro autoradiography of human and animal pancreatic sections from subjects without and with diabetes, in combination with insulin staining, was performed to assess β-cell selectivity of the radiotracer. Proof of principle of in vivo targeting of human islets by [ 11 C]AZ12204657 was shown in the immunodeficient mouse transplantation model. Furthermore, [ 11 C]AZ12204657 bound by a GPR44-mediated mechanism in pancreatic sections from humans and pigs without diabetes, but not those with diabetes. In vivo [ 11 C]AZ12204657 bound specifically to GPR44 in pancreas and spleen and could be competed away dose-dependently in nondiabetic pigs and nonhuman primates. [ 11 C]AZ12204657 is a first-in-class surrogate imaging biomarker for pancreatic β-cells by targeting the protein GPR44., (© 2017 by the American Diabetes Association.)

A logical cure for type 1 diabetes (T1D) involves replacing the lost insulin-producing cells with new ones, preferably cells from a well-characterized and unlimited source of human insulin-producing cells. This straightforward and simple solution to provide a cure for T1D is immensely attractive but entails at least two inherent and thus far unresolved hurdles: 1 ) provision of an unlimited source of functional human insulin-producing cells and 2 ) prevention of rejection without the side effects of systemic immunosuppression. Generation of transplantable insulin-producing cells from human embryonic stem cells or induced pluripotent stem cells is at present close to reality, and we are currently awaiting the first clinical studies. Focus is now directed to foster development of novel means to control the immune system to enable large-scale clinical application. Encapsulation introduces a physical barrier that prevents access of immune cells to the transplanted cells but also hinders blood vessel ingrowth. Therefore, oxygen, nutrient, and hormonal passage over the encapsulation membrane is solely dependent on diffusion over the immune barrier, contributing to delays in glucose sensing and insulin secretion kinetics. This Perspective focuses on the physiological possibilities and limitations of an encapsulation strategy to establish near-normoglycemia in subjects with T1D, assuming that glucose-responsive insulin-producing cells are available for transplantation., (© 2017 by the American Diabetes Association.)

In pancreatic β-cells, mitochondrial bioenergetics control glucose-stimulated insulin secretion. Mitochondrial dynamics are generally associated with quality control, maintaining the functionality of bioenergetics. By acute pharmacological inhibition of mitochondrial fission protein Drp1 , we demonstrate in this study that mitochondrial fission is necessary for glucose-stimulated insulin secretion in mouse and human islets. We confirm that genetic silencing of Drp1 increases mitochondrial proton leak in MIN6 cells. However, our comprehensive analysis of pancreatic islet bioenergetics reveals that Drp1 does not control insulin secretion via its effect on proton leak but instead via modulation of glucose-fueled respiration. Notably, pyruvate fully rescues the impaired insulin secretion of fission-deficient β-cells, demonstrating that defective mitochondrial dynamics solely affect substrate supply upstream of oxidative phosphorylation. The present findings provide novel insights into how mitochondrial dysfunction may cause pancreatic β-cell failure. In addition, the results will stimulate new thinking in the intersecting fields of mitochondrial dynamics and bioenergetics, as treatment of defective dynamics in mitochondrial diseases appears to be possible by improving metabolism upstream of mitochondria., (© 2017 by the American Diabetes Association.)

[ 11 C]5-hydroxy-tryptophan ([ 11 C]5-HTP) positron emission tomography of the pancreas has been shown to be a surrogate imaging biomarker of pancreatic islet mass. The change in islet mass in different stages of type 2 diabetes (T2D) as measured by noninvasive imaging is currently unknown. Here, we describe a cross-sectional study where subjects at different stages of T2D development with expected stratification of pancreatic islet mass were examined in relation to individuals without diabetes. The primary outcome was the [ 11 C]5-HTP uptake and retention in pancreas, as a surrogate marker for the endogenous islet mass. We found that metabolic testing indicated a progressive loss of β-cell function, but this was not mirrored by a decrease in [ 11 C]5-HTP tracer accumulation in the pancreas. This provides evidence of retained islet mass despite decreased β-cell function. The results herein indicate that β-cell dedifferentiation, and not necessarily endocrine cell loss, constitutes a major cause of β-cell failure in T2D., (© 2017 by the American Diabetes Association.)

Eight manufacturing facilities participating in the National Institutes of Health-sponsored Clinical Islet Transplantation (CIT) Consortium jointly developed and implemented a harmonized process for the manufacture of allogeneic purified human pancreatic islet (PHPI) product evaluated in a phase 3 trial in subjects with type 1 diabetes. Manufacturing was controlled by a common master production batch record, standard operating procedures that included acceptance criteria for deceased donor organ pancreata and critical raw materials, PHPI product specifications, certificate of analysis, and test methods. The process was compliant with Current Good Manufacturing Practices and Current Good Tissue Practices. This report describes the manufacturing process for 75 PHPI clinical lots and summarizes the results, including lot release. The results demonstrate the feasibility of implementing a harmonized process at multiple facilities for the manufacture of a complex cellular product. The quality systems and regulatory and operational strategies developed by the CIT Consortium yielded product lots that met the prespecified characteristics of safety, purity, potency, and identity and were successfully transplanted into 48 subjects. No adverse events attributable to the product and no cases of primary nonfunction were observed., (© 2016 by the American Diabetes Association.)

No imaging methodology currently exists to monitor viable islet mass after clinical intraportal islet transplantation. We investigated the potential of the endocrine positron emission tomography (PET) marker [(11)C]5-hydroxytryptophan ([(11)C]5-HTP) for this purpose. In a preclinical proof-of-concept study, the ex vivo and in vivo [(11)C]5-HTP signal was compared with the number of islets transplanted in rats. In a clinical study, human subjects with an intraportal islet graft (n = 8) underwent two [(11)C]5-HTP PET and MRI examinations 8 months apart. The tracer concentration in the liver as a whole, or in defined hotspots, was correlated to measurements of islet graft function. In rat, hepatic uptake of [(11)C]5-HTP correlated with the number of transplanted islets. In human subjects, uptake in hepatic hotspots showed a correlation with metabolic assessments of islet function. Change in hotspot standardized uptake value (SUV) predicted loss of graft function in one subject, whereas hotspot SUV was unchanged in subjects with stable graft function. The endocrine marker [(11)C]5-HTP thus shows a correlation between hepatic uptake and transplanted islet function and promise as a tool for noninvasive detection of viable islets. The evaluation procedure described can be used as a benchmark for novel agents targeting intraportally transplanted islets., (© 2016 by the American Diabetes Association.)

Objective: Impaired awareness of hypoglycemia (IAH) and severe hypoglycemic events (SHEs) cause substantial morbidity and mortality in patients with type 1 diabetes (T1D). Current therapies are effective in preventing SHEs in 50-80% of patients with IAH and SHEs, leaving a substantial number of patients at risk. We evaluated the effectiveness and safety of a standardized human pancreatic islet product in subjects in whom IAH and SHEs persisted despite medical treatment., Research Design and Methods: This multicenter, single-arm, phase 3 study of the investigational product purified human pancreatic islets (PHPI) was conducted at eight centers in North America. Forty-eight adults with T1D for >5 years, absent stimulated C-peptide, and documented IAH and SHEs despite expert care were enrolled. Each received immunosuppression and one or more transplants of PHPI, manufactured on-site under good manufacturing practice conditions using a common batch record and standardized lot release criteria and test methods. The primary end point was the achievement of HbA1c <7.0% (53 mmol/mol) at day 365 and freedom from SHEs from day 28 to day 365 after the first transplant., Results: The primary end point was successfully met by 87.5% of subjects at 1 year and by 71% at 2 years. The median HbA1c level was 5.6% (38 mmol/mol) at both 1 and 2 years. Hypoglycemia awareness was restored, with highly significant improvements in Clarke and HYPO scores (P > 0.0001). No study-related deaths or disabilities occurred. Five of the enrollees (10.4%) experienced bleeds requiring transfusions (corresponding to 5 of 75 procedures), and two enrollees (4.1%) had infections attributed to immunosuppression. Glomerular filtration rate decreased significantly on immunosuppression, and donor-specific antibodies developed in two patients., Conclusions: Transplanted PHPI provided glycemic control, restoration of hypoglycemia awareness, and protection from SHEs in subjects with intractable IAH and SHEs. Safety events occurred related to the infusion procedure and immunosuppression, including bleeding and decreased renal function. Islet transplantation should be considered for patients with T1D and IAH in whom other, less invasive current treatments have been ineffective in preventing SHEs., (© 2016 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.)

The lymphatic system is crucial for efficient immune surveillance and for the maintenance of a physiological pressure in the interstitial space. Even so, almost no information is available concerning the lymph drainage of the islets of Langerhans in the human pancreas. Immunohistochemical staining allowed us to distinguish lymphatic capillaries from blood capillaries. Almost no lymphatic capillaries were found within the islets in pancreatic biopsy specimens from subjects without diabetes or from subjects with type 1 or type 2 diabetes. Lymphatic capillaries were, however, found at the islet-exocrine interface, frequently located along blood capillaries and other fibrotic structures within or close to the islet capsule. Lymphatic capillaries were regularly found in the exocrine pancreas, with small lymphatic vessels located close to and around acini. Larger collecting lymphatic vessels were located in fibrotic septa between the exocrine lobules and adjacent to the ductal system of the pancreas. In summary, we report a pronounced deficiency of lymphatic capillaries in human islets, a finding with implications for immune surveillance and the regulation of interstitial fluid transport in the endocrine pancreas as well as for the pathophysiology of both type 1 and type 2 diabetes., (© 2016 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.)

The understanding of the etiology of type 1 diabetes (T1D) remains limited. One objective of the Diabetes Virus Detection (DiViD) study was to collect pancreatic tissue from living subjects shortly after the diagnosis of T1D. Here we report the insulin secretion ability by in vitro glucose perifusion and explore the expression of insulin pathway genes in isolated islets of Langerhans from these patients. Whole-genome RNA sequencing was performed on islets from six DiViD study patients and two organ donors who died at the onset of T1D, and the findings were compared with those from three nondiabetic organ donors. All human transcripts involved in the insulin pathway were present in the islets at the onset of T1D. Glucose-induced insulin secretion was present in some patients at the onset of T1D, and a perfectly normalized biphasic insulin release was obtained after some days in a nondiabetogenic environment in vitro. This indicates that the potential for endogenous insulin production is good, which could be taken advantage of if the disease process was reversed at diagnosis., (© 2015 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.)

The Diabetes Virus Detection study (DiViD) is the first to examine fresh pancreatic tissue at the diagnosis of type 1 diabetes for the presence of viruses. Minimal pancreatic tail resection was performed 3-9 weeks after onset of type 1 diabetes in six adult patients (age 24-35 years). The presence of enteroviral capsid protein 1 (VP1) and the expression of class I HLA were investigated by immunohistochemistry. Enterovirus RNA was analyzed from isolated pancreatic islets and from fresh-frozen whole pancreatic tissue using PCR and sequencing. Nondiabetic organ donors served as controls. VP1 was detected in the islets of all type 1 diabetic patients (two of nine controls). Hyperexpression of class I HLA molecules was found in the islets of all patients (one of nine controls). Enterovirus-specific RNA sequences were detected in four of six patients (zero of six controls). The results were confirmed in various laboratories. Only 1.7% of the islets contained VP1(+) cells, and the amount of enterovirus RNA was low. The results provide evidence for the presence of enterovirus in pancreatic islets of type 1 diabetic patients, which is consistent with the possibility that a low-grade enteroviral infection in the pancreatic islets contributes to disease progression in humans., (© 2015 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.)

The retention of endogenous insulin secretion in type 1 diabetes is an attractive clinical goal, which opens possibilities for long-term restoration of glucose metabolism. Mesenchymal stromal cells (MSCs) constitute, based on animal studies, a promising interventional strategy for the disease. This prospective clinical study describes the translation of this cellular intervention strategy to patients with recent-onset type 1 diabetes. Twenty adult patients with newly diagnosed type 1 diabetes were enrolled and randomized to MSC treatment or to the control group. Residual β-cell function was analyzed as C-peptide concentrations in blood in response to a mixed-meal tolerance test (MMTT) at 1-year follow-up. In contrast to the patients in the control arm, who showed loss in both C-peptide peak values and C-peptide when calculated as area under the curve during the 1st year, these responses were preserved or even increased in the MSC-treated patients. Importantly, no side effects of MSC treatment were observed. We conclude that autologous MSC treatment in new-onset type 1 diabetes constitutes a safe and promising strategy to intervene in disease progression and preserve β-cell function., (© 2015 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.)

In humans, a well-developed serotonin system is localized to the pancreatic islets while being absent in exocrine pancreas. Assessment of pancreatic serotonin biosynthesis could therefore be used to estimate the human endocrine pancreas. Proof of concept was tested in a prospective clinical trial by comparisons of type 1 diabetic (T1D) patients, with extensive reduction of β-cells, with healthy volunteers (HVs). C-peptide-negative (i.e., insulin-deficient) T1D subjects (n = 10) and HVs (n = 9) underwent dynamic positron emission tomography with the radiolabeled serotonin precursor [(11)C]5-hydroxy-tryptophan ([(11)C]5-HTP). A significant accumulation of [(11)C]5-HTP was obtained in the pancreas of the HVs, with large interindividual variation. A substantial and highly significant reduction (66%) in the pancreatic uptake of [(11)C]5-HTP in T1D subjects was observed, and this was most evident in the corpus and caudal regions of the pancreas where β-cells normally are the major constituent of the islets. [(11)C]5-HTP retention in the pancreas was reduced in T1D compared with nondiabetic subjects. Accumulation of [(11)C]5-HTP in the pancreas of both HVs and subjects with T1D was in agreement with previously reported morphological observations on the β-cell volume, implying that [(11)C]5-HTP retention is a useful noninvasive surrogate marker for the human endocrine pancreas., (© 2014 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.)

Objective: In clinical islet transplantation, the instant blood-mediated inflammatory reaction (IBMIR) is a major factor contributing to the poor initial engraftment of the islets. This reaction is triggered by tissue factor and monocyte chemoattractant protein (MCP)-1, expressed by the transplanted pancreatic islets when the islets come in contact with blood in the portal vein. All currently identified systemic inhibitors of the IBMIR are associated with a significantly increased risk of bleeding or other side effects. To avoid systemic treatment, the aim of the present study was to render the islet graft blood biocompatible by applying a continuous heparin coating to the islet surface., Research Design and Methods: A biotin/avidin technique was used to conjugate preformed heparin complexes to the surface of pancreatic islets. This endothelial-like coating was achieved by conjugating barely 40 IU heparin per full-size clinical islet transplant., Results: Both in an in vitro loop model and in an allogeneic porcine model of clinical islet transplantation, this heparin coating provided protection against the IBMIR. Culturing heparinized islets for 24 h did not affect insulin release after glucose challenge, and heparin-coated islets cured diabetic mice in a manner similar to untreated islets., Conclusions: This novel pretreatment procedure prevents intraportal thrombosis and efficiently inhibits the IBMIR without increasing the bleeding risk and, unlike other pretreatment procedures (e.g., gene therapy), without inducing acute or chronic toxicity in the islets.

There are strong indications that only a small fraction of grafts successfully engraft in clinical islet transplantation. One explanation may be the instant blood-mediated inflammatory reaction (IBMIR) elicited by tissue factor, which is produced by the endocrine cells. In the present study, we show that islets intended for islet transplantation produce tissue factor in both the transmembrane and the alternatively spliced form and that the membrane-bound form is released as microparticles often associated with both insulin and glucagon granules. A low-molecular mass factor VIIa (FVIIa) inhibitor that indirectly blocks both forms of tissue factor was shown in vitro to be a promising drug to eliminate the IBMIR. Thrombin-antithrombin complex (TAT) and FVIIa-antithrombin complex (FVIIa-AT) were measured in nine patients who together received 20 infusions of isolated human islets. Both the TAT and FVIIa-AT complexes increased rapidly within 15-60 min after infusion. When the initial TAT and FVIIa-AT levels were plotted against the increase in C-peptide concentration after 7 days, patients with an initially strong IBMIR showed no significant increase in insulin synthesis after 7 days. In conclusion, tissue factor present in both the islets and the culture medium and elicits IBMIR, which affects the function of the transplanted islets.

We have reproduced a previously described method for the in vitro generation of endocrine cells in adult human pancreatic tissue culture. The aim of this study was to characterize the nature of pancreatic progenitor cells and to identify the factors necessary for their differentiation in this model. During monolayer expansion, two types of cells proliferated sequentially; first cytokeratin 19 (CK19)-positive ductal epithelial cells and then nestin-positive fibroblastoid cells. After the bromodeoxyuridine-labeled cells were traced in differentiated islet buds, some of the proliferating ductal cells had differentiated into endocrine cells, whereas nestin-positive cells could not give rise to endocrine tissue. Serum-free culture was found to be an absolute requirement for the endocrine differentiation to occur. Also, overlay of the cells with Matrigel was essential, whereas nicotinamide had a potentiating effect. The in vitro-generated islet buds released insulin in response to glucose nearly as efficiently as native islets. When transplanted under the kidney capsule of nude mice, only one of five grafts demonstrated further growth with foci of both endocrine and exocrine differentiation. Our results support the previous notion that pancreatic progenitor cells represent a subpopulation of ductal epithelial cells. No evidence was found for the development of endocrine cells from nestin-positive stem cells.

A new murine model of porcine islet-like cell cluster (ICC) xenograft rejection, avoiding interference of unspecific inflammation, was introduced and used to investigate rejection mechanisms. Athymic (nu/nu) mice were transplanted with syngeneic, allogeneic, or xenogeneic islets under the kidney capsule. After the original transplantation, immune cells in porcine ICC xenografts undergoing rejection in native immunocompetent mice were transferred to the peritoneal cavity of the athymic mice. At defined time points after transfer, the primary grafts were evaluated by immunohistochemistry and real-time quantitative RT-PCR to estimate cytokine and chemokine mRNA expression. Transfer of immunocompetent cells enabled athymic (nu/nu) mice to reject a previously tolerated ICC xenograft only when donor and recipient were matched for major histocompatibility complex (MHC). In contrast, allogeneic and syngeneic islets were not rejected. The ICC xenograft rejection was mediated by transferred T-cells. The main effector cells, macrophages, were shown to be part of a specific immune response. By day 4 after transplantation, there was an upreglation of both Th1- and Th2-associated cytokine transcripts. The transferred T-cells were xenospecific and required MHC compatibility to induce rejection. Interaction between the TCR of transferred T-cells and MHC on host endothelial cells and/or macrophages seems necessary for inducing ICC xenograft rejection.

A thrombotic/inflammatory reaction is elicited when isolated islets of Langerhans come in contact with ABO-compatible blood. The detrimental effects of this instant blood-mediated inflammatory reaction (IBMIR) provide a reasonable explanation for the observation that an unexpectedly high number of islets, from several donors, are needed to produce normoglycemia in transplant patients with type 1 diabetes. In this study, the hypothesis that a specific thrombin inhibitor, Melagatran, could reduce IBMIR in an in vitro model in which human islets are exposed to ABO-compatible blood was tested. The administration of Melagatran abrogated IBMIR dose-dependently. Islets exposed to blood, in the absence or presence of 0.4 micromol/l Melagatran, exhibited a loss of integrity and were found to be trapped in macroscopic clots containing platelets and CD11b(+) leukocytes. At concentrations from 1 to 10 micromol/l, Melagatran inhibited both coagulation and complement activation. Also, platelet and leukocyte activation and consumption were decreased. Islet morphology was maintained with almost no platelets adhering to the surface, and infiltration by CD11b(+) leukocytes was considerably reduced. In conclusion, Melagatran significantly reduced IBMIR in this model system. This protective effect indicates that thrombin plays a pivotal role in IBMIR and suggests that thrombin inhibition can improve the outcome of clinical islet transplantation.

Previous studies using semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) have demonstrated that islet xenograft rejection in mice is dominated by Th2-associated cytokines, i.e., interleukin (IL)-4 and IL-10. However, immunohistochemical stainings show that the morphological pattern in this model is more reminiscent of a delayed-type hypersensitivity (DTH) reaction, which is associated with a Th1 response. This study was designed to resolve the mechanisms of acute cellular xenograft rejection in rats transplanted with fetal porcine islet-like cell clusters (ICCs). Real-time quantitative RT-PCR was used to quantify the mRNA expression of cytokines in the grafts and lymph nodes, and the findings were related to the immunopathology of the rejecting grafts. By day 1, mRNA expression levels of IL-1 beta, IL-2, IL-12p40, interferon-gamma, and tumor necrosis factor-alpha were already induced in the lymph nodes. From days 3 to 12, an increasing amount of activated macrophages was seen in the grafts, whereas T- and NK-cells were fewer and mainly accumulated in the periphery of the grafts. Most of the ICCs were rejected by day 5. Transcripts of Th1-associated cytokines were dominant in both regional lymph nodes and in the grafts, with peak levels on days 3 and 5, respectively. The mRNA expression of IL-4 was increased on day 12, and it correlated with the infiltration of eosinophils and an increased level of xenoreactive IgG. The data presented indicate that an islet xenograft triggers a sequential activation of 1) a Th1-associated response characterized by graft destruction in a DTH-like reaction and then 2) a subsequent Th2-associated response characterized by increased levels of xenoreactive antibodies.

Although transplantations of vascularized pancreas in diabetic patients show steadily improving results, the immediate operative risks and life-long immunosuppressive medication involved represent considerable disadvantages. Efforts are being made to develop simpler and safer methods of transplantation with isolated pancreatic islet grafts, e.g., isolated islets, fetal pancreas, or dispersed adult pancreas. Iso-, allo-, and xenografts of such preparations have been shown to reverse diabetes in animals. However, attempts to apply these techniques in clinical practice have remained largely unsuccessful, and major technical advances are needed before success is achieved. Attempts to use whole, segmented, or isolated islets from pancreatic grafts as a cure for diabetes in animals and in diabetic patients are reviewed. The importance to the graft's permanent function, of adequate preparation and storage of the graft, and of beta-cell growth and vascularization are reviewed. Various forms of immunomodulation by pretreatment of grafts in vitro have been employed in animal models of diabetes, but none of these have yet been employed with long-term success in humans. Recurrence of a specific autoimmune response toward the beta-cell in a spontaneously diabetic recipient is a potential mechanism for destruction of transplanted islet tissue.