Inhibition of thrombin abrogates the instant blood-mediated inflammatory reaction triggered by isolated human islets: possible application of the thrombin inhibitor melagatran in clinical islet transplantation

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

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

STATEMENT OF SIGNIFICANCE

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

The Spleen Is an Ideal Site for Inducing Transplanted Islet Graft Expansion in Mice

Alternative islet transplantation sites have the potential to reduce the marginal number of islets required to ameliorate hyperglycemia in recipients with diabetes. Previously, we reported that T cell leukemia homeobox 1 (Tlx1)+ stem cells in the spleen effectively regenerated into insulin-producing cells in the pancreas of non-obese diabetic mice with end-stage disease. Thus, we investigated the spleen as a potential alternative islet transplantation site. Streptozotocin-induced diabetic C57BL/6 mice received syngeneic islets into the portal vein (PV), beneath the kidney capsule (KC), or into the spleen (SP). The marginal number of islets by PV, KC, or SP was 200, 100, and 50, respectively. Some plasma inflammatory cytokine levels in the SP group were significantly lower than those of the PV group after receiving a marginal number of islets, indicating reduced inflammation in the SP group. Insulin contents were increased 280 days after islet transplantation compared with those immediately following transplantation (p<0.05). Additionally, Tlx1-related genes, including Rrm2b and Pla2g2d, were up-regulated, which indicates that islet grafts expanded in the spleen. The spleen is an ideal candidate for an alternative islet transplantation site because of the resulting reduced inflammation and expansion of the islet graft.

Human Recombinant Antithrombin (ATryn®) Administration Improves Survival and Prevents Intravascular Coagulation After Intraportal Islet Transplantation in a Piglet Model

Human islet transplantation is a viable treatment option for type 1 diabetes mellitus (T1DM). However, pancreatic islet inflammation after transplantation induced by innate immune responses is likely to hinder graft function. This is mediated by incompatibility between islets and the blood interface, known as instant blood-mediated inflammatory reaction (IBMIR). Herein we hypothesized that portal venous administration of islet cells with human recombinant antithrombin (ATryn®), a serine protease inhibitor (serpin), which plays a central role in the physiological regulation of coagulation and exerts indirect anti-inflammatory activities, may offset coagulation abnormalities such as disseminated intravascular coagulation (DIC) and IBMIR. The current prospective, randomized experiment was conducted using an established preclinical pig model. Three groups were constituted for digested pancreatic tissue transplantation (0.15 ml/kg): control, NaCl 0.9% (n = 7); gold standard, heparin (25 UI/kg) (n = 7); and human recombinant ATryn® (500 UI/kg) (n = 7). Blood samples were collected over time (T0 to 24 h), and biochemical, coagulation, and inflammatory parameters were evaluated. In both the control and heparin groups, one animal died after a portal thrombosis, while no deaths occurred in the ATryn®-treated group. As expected, islet transplantation was associated with an increase in plasma IL-6 or TNF-α levels in all three groups. However, DIC was only observed in the control group, an effect that was suppressed after ATryn® administration. ATryn® administration increased antithrombin activity by 800%, which remained at 200% for the remaining period of the study, without any hemorrhagic complications. These studies suggest that coadministration of ATryn® and pancreatic islets via intraportal transplantation may be a valuable therapeutic approach for DIC without risk for islets and subjects.

Characterizing the Mechanistic Pathways of the Instant Blood-Mediated Inflammatory Reaction in Xenogeneic Neonatal Islet Cell Transplantation

Supplemental digital content is available in the text.

Introduction

The instant blood-mediated inflammatory reaction (IBMIR) causes major loss of islets after transplantation and consequently represents the initial barrier to survival of porcine neonatal islet cell clusters (NICC) after xenotransplantation.

Methods

This study used novel assays designed to characterize the various immunologic components responsible for xenogeneic IBMIR to identify initiators and investigate processes of IBMIR-associated coagulation, complement activation and neutrophil infiltration. The IBMIR was induced in vitro by exposing NICC to platelet-poor or platelet-rich human plasma or isolated neutrophils.

Results

We found that xenogeneic IBMIR was characterized by rapid, platelet-independent thrombin generation, with addition of platelets both accelerating and exacerbating this response. Platelet-independent complement activation was observed as early as 30 minutes after NICC exposure to plasma. However, membrane attack complex formation was not observed in NICC histopathology sections until after 60 minutes. We demonstrated for the first time that NICC-mediated complement activation was necessary for neutrophil activation in the xenogeneic IBMIR setting. Finally, using the Seahorse extracellular flux analyzer, we identified substantial loss of islet function (up to 40%) after IBMIR with surviving NICC showing evidence of mitochondrial damage.

Conclusions

This study used novel assays to describe multiple key pathways by which xenogeneic IBMIR causes islet destruction, allowing further refinement of future interventions aimed at resolving the issue of IBMIR in xenotransplantation.

Bioengineering the Endocrine Pancreas: Intraomental Islet Transplantation Within a Biologic Resorbable Scaffold

Transplantation of pancreatic islets is a therapeutic option to preserve or restore β-cell function. Our study was aimed at developing a clinically applicable protocol for extrahepatic transplantation of pancreatic islets. The potency of islets implanted onto the omentum, using an in situ-generated adherent, resorbable plasma-thrombin biologic scaffold, was evaluated in diabetic rat and nonhuman primate (NHP) models. Intraomental islet engraftment in the biologic scaffold was confirmed by achievement of improved metabolic function and preservation of islet cytoarchitecture, with reconstitution of rich intrainsular vascular networks in both species. Long-term nonfasting normoglycemia and adequate glucose clearance (tolerance tests) were achieved in both intrahepatic and intraomental sites in rats. Intraomental graft recipients displayed lower levels of serum biomarkers of islet distress (e.g., acute serum insulin) and inflammation (e.g., leptin and α2-macroglobulin). Importantly, low-purity (30:70% endocrine:exocrine) syngeneic rat islet preparations displayed function equivalent to that of pure (>95% endocrine) preparations after intraomental biologic scaffold implantation. Moreover, the biologic scaffold sustained allogeneic islet engraftment in immunosuppressed recipients. Collectively, our feasibility/efficacy data, along with the simplicity of the procedure and the safety of the biologic scaffold components, represented sufficient preclinical testing to proceed to a pilot phase I/II clinical trial.

Heparinization of cell surfaces with short peptide-conjugated PEG-lipid regulates thromboinflammation in transplantation of human MSCs and hepatocytes

Infusion of therapeutic cells into humans is associated with immune responses, including thromboinflammation, which result in a large loss of transplanted cells. To address these problems, heparinization of the cell surfaces was achieved by a cell-surface modification technique using polyethylene glycol-conjugated phospholipid (PEG-lipid) derivatives. A short heparin-binding peptide was conjugated to the PEG-lipid for immobilization of heparin conjugates on the surface of human mesenchymal stem cells (hMSCs) and human hepatocytes. Here three kinds of heparin-binding peptides were used for immobilizing heparin conjugates and examined for the antithrombogenic effects on the cell surface. The heparinized cells were incubated in human whole blood to evaluate their hemocompatibility by measuring blood parameters such as platelet count, coagulation markers, complement markers, and Factor Xa activity. We found that one of the heparin-binding peptides did not show cytotoxicity after the immobilization with heparin conjugates. The degree of binding of the heparin conjugates on the cell surface (analyzed by flow cytometer) depended on the ratio of the active peptide to control peptide. For both human MSCs and hepatocytes in whole-blood experiments, no platelet aggregation was seen in the heparin conjugate-immobilized cell group vs. the controls (non-coated cells or control peptide). Also, the levels of thrombin-antithrombin complex (TAT), C3a, and sC5b-9 were significantly lower than those of the controls, indicating a lower activation of coagulation and complement. Factor Xa analysis indicated that the heparin conjugate was still active on the cell surface at 24h post-coating. It is possible to immobilize heparin conjugates onto hMSC and human hepatocyte surfaces and thereby protect the cell surfaces from damaging thromboinflammation.

STATEMENT OF SIGNIGFICANCE

We present a promising approach to enhance the biocompatibility of therapeutic cells. Here we used short peptide-conjugated PEG-lipid for cell surface modification and heparin conjugates for the coating of human hepatocytes and MSCs. We screened the short peptides to find higher affinity for heparinization of cell surface and performed hemocompatibility assay of heparinized human hepatocytes and human MSCs in human whole blood. Using heparin-binding peptide with higher affinity, not only coagulation activation but also complement activation was significantly suppressed. Thus, it was possible to protect human hepatocytes and human MSCs from the attack of thromboinflammatory activation, which can contribute to the improvement graft survival.

A hybrid of cells and pancreatic islets toward a new bioartificial pancreas

Cell surface engineering using single-stranded DNA-poly(ethylene glycol)-conjugated phospholipid (ssDNA-PEG-lipid) is useful for inducing cell-cell attachment two and three dimensionally. In this review, we summarize our recent techniques for cell surface engineering and their applications to islet transplantation. Because any DNA sequence can be immobilized onto the cell surface by hydrophobic interactions between ssDNA-PEG-lipid and the cellular membrane without impairing cell function, a cell-cell hybrid can be formed through the DNA hybridization. With this technique, it would be possible to create three-dimensional hybrid structures of pancreatic islets coated with various accessory cells, such as patients' own cells, mesenchymal and adipose-derived stem cells, endothelial progenitor cells, neural crest stem cells or regulatory T cells, which might significantly improve the outcome of islet transplantation in diabetic patients.

Instant Blood-Mediated Inflammatory Reaction in Hepatocyte Transplantation: Current Status and Future Perspectives

Hepatocyte transplantation (HT) is emerging as a promising alternative to orthotopic liver transplantation (OLT) in patients with certain liver-based metabolic disease and acute liver failure. Hepatocytes are generally infused into the portal venous system, from which they migrate into the liver cell plates of the native organ. One of the major hurdles to the sustained success of this therapy is early cell loss, with up to 70% of hepatocytes lost immediately following infusion. This is largely thought to be due to the instant blood-mediated inflammatory reaction (IBMIR), resulting in the activation of complement and coagulation pathways. Transplanted hepatocytes produce and release tissue factor (TF), which activates the coagulation pathway, leading to the formation of thrombin and fibrin clots. Thrombin can further activate a number of complement proteins, leading to the activation of the membrane attack complex (MAC) and subsequent hepatocyte cell death. Inflammatory cells including granulocytes, monocytes, Kupffer cells, and natural killer (NK) cells have been shown to cluster around transplanted hepatocytes, leading to their rapid clearance shortly after transplantation. Current research aims to improve cell engraftment and prevent early cell loss. This has been proven successful in vitro using pharmacological interventions such as melagatran, low-molecular-weight dextran sulphate, and N-acetylcysteine (NAC). Effective inhibition of IBMIR would significantly improve hepatocyte engraftment, proliferation, and function, providing successful treatment for patients with liver-based metabolic diseases.

The pathobiology of pig-to-primate xenotransplantation: a historical review

The immunologic barriers to successful xenotransplantation are related to the presence of natural anti-pig antibodies in humans and non-human primates that bind to antigens expressed on the transplanted pig organ (the most important of which is galactose-α1,3-galactose [Gal]), and activate the complement cascade, which results in rapid destruction of the graft, a process known as hyperacute rejection. High levels of elicited anti-pig IgG may develop if the adaptive immune response is not prevented by adequate immunosuppressive therapy, resulting in activation and injury of the vascular endothelium. The transplantation of organs and cells from pigs that do not express the important Gal antigen (α1,3-galactosyltransferase gene-knockout [GTKO] pigs) and express one or more human complement-regulatory proteins (hCRP, e.g., CD46, CD55), when combined with an effective costimulation blockade-based immunosuppressive regimen, prevents early antibody-mediated and cellular rejection. However, low levels of anti-non-Gal antibody and innate immune cells and/or platelets may initiate the development of a thrombotic microangiopathy in the graft that may be associated with a consumptive coagulopathy in the recipient. This pathogenic process is accentuated by the dysregulation of the coagulation-anticoagulation systems between pigs and primates. The expression in GTKO/hCRP pigs of a human coagulation-regulatory protein, for example, thrombomodulin, is increasingly being associated with prolonged pig graft survival in non-human primates. Initial clinical trials of islet and corneal xenotransplantation are already underway, and trials of pig kidney or heart transplantation are anticipated within the next few years.

THERAPY OF ENDOCRINE DISEASE: Islet transplantation for type 1 diabetes: so close and yet so far away

Over the past decades, tremendous efforts have been made to establish pancreatic islet transplantation as a standard therapy for type 1 diabetes. Recent advances in islet transplantation have resulted in steady improvements in the 5-year insulin independence rates for diabetic patients. Here we review the key challenges encountered in the islet transplantation field which include islet source limitation, sub-optimal engraftment of islets, lack of oxygen and blood supply for transplanted islets, and immune rejection of islets. Additionally, we discuss possible solutions for these challenges.

Dual islet transplantation modeling of the instant blood-mediated inflammatory reaction

Islet xenotransplantation is a potential treatment for diabetes without the limitations of tissue availability. Although successful experimentally, early islet loss remains substantial and attributed to an instant blood-mediated inflammatory reaction (IBMIR). This syndrome of islet destruction has been incompletely defined and characterization in pig-to-primate models has been hampered by logistical and statistical limitations of large animal studies. To further investigate IBMIR, we developed a novel in vivo dual islet transplant model to precisely characterize IBMIR as proof-of-concept that this model can serve to properly control experiments comparing modified xenoislet preparations. WT and α1,3-galactosyltransferase knockout (GTKO) neonatal porcine islets were studied in nonimmunosuppressed rhesus macaques. Inert polyethylene microspheres served as a control for the effects of portal embolization. Digital analysis of immunohistochemistry targeting IBMIR mediators was performed at 1 and 24 h after intraportal islet infusion. Early findings observed in transplanted islets include complement and antibody deposition, and infiltration by neutrophils, macrophages and platelets. Insulin, complement, antibody, neutrophils, macrophages and platelets were similar between GTKO and WT islets, with increasing macrophage infiltration at 24 h in both phenotypes. This model provides an objective and internally controlled study of distinct islet preparations and documents the temporal histology of IBMIR.

Mesenchymal stem cells in the treatment of type 1 diabetes mellitus

Diabetes mellitus type 1 is a form of diabetes mellitus that results from the autoimmune destruction of insulin-producing beta cells in the pancreas. The current gold standard therapy for pancreas transplantation has limitations because of the long list of waiting patients and the limited supply of donor pancreas. Mesenchymal stem cells (MSCs), a relatively new potential therapy in various fields, have already made their mark in the young field of regenerative medicine. Recent studies have shown that the implantation of MSCs decreases glucose levels through paracrine influences rather than through direct transdifferentiation into insulin-producing cells. Therefore, these cells may use pro-angiogenic and immunomodulatory effects to control diabetes following the cotransplantation with pancreatic islets. In this review, we present and discuss new approaches of using MSCs in the treatment of diabetes mellitus type 1.

Cell Surface Engineering for Regulation of Immune Reactions in Cell Therapy

Transplantation of the pancreatic islets of Langerhans (islets) is a promising cell therapy for treating insulin-dependent type 1 diabetes mellitus. Islet transplantation is a minimally-invasive technique involving relatively simple surgery. However, after intraportal transplantation, the transplanted islets are attacked by the recipient's immune system, because they activate a number of systems, including coagulation, complement response, inflammation, immune rejection, and recurrence of autoimmune disease. We have developed a surface modification and microencapsulation technique that protects cells and islets with biomaterials and bioactive substances, which may be useful in clinical settings. This approach employs amphiphilic polymers, which can interact with lipid bilayer membranes, without increasing cell volume. Molecules attached to these polymers can protect transplanted cells and islets from attack by the host immune system. We expect that this surface modification technique will improve graft survival in clinical islet transplantation.

Alleviation of instant blood-mediated inflammatory reaction in autologous conditions through treatment of human islets with NF-κB inhibitors

BACKGROUND

The instant blood-mediated inflammatory response (IBMIR) has been shown as a major factor that causes damage to transplanted islets. Withaferin A (WA), an inhibitor of nuclear factor (NF) κB, was shown to suppress the inflammatory response in islets and improve syngeneic islet graft survival in mice. We investigated how treating islets with NF-κB inhibitors affected IBMIR using an in vitro human autologous blood islet model.

METHODS

Human islets were pretreated with or without NF-κB inhibitors WA or CAY10512 before mixing autologous blood in a miniaturized in vitro tube model. Plasma samples were collected at multiple time points and used for the measurement of C-peptide, proinsulin, thrombin-antithrombin (TAT) complex, and a panel of proinflammatory cytokines. Infiltration of neutrophils into islets was analyzed using immunohistochemistry.

RESULTS

Rapid release of C-peptide and proinsulin was observed 3 hr after mixing islets and blood in the control group, but not in the NF-κB inhibitor-treated groups, whereas TAT levels were elevated in all three groups with a peak at 6 hr. Significant elevation of proinflammatory cytokines was observed in the control group after 3 hr, but not in the treatment groups. Significant inhibition of neutrophil infiltration was also observed in the WA group compared with the control (P<0.001) and CAY10512 (P<0.001) groups.

CONCLUSIONS

A miniaturized in vitro tube model can be useful in investigating IBMIR. The presence of NF-κB inhibitor could alleviate IBMIR, thus improving the survival of transplanted islets. Protection of islets in the peritransplant phase may improve long-term graft outcomes.

Minimizing immunosuppression in islet xenotransplantation

Pancreatic islet transplantation is a promising treatment option for Type 1 diabetes, but organ supply shortage limits its wide adoption. Pig islets are the most promising alternative source and many important measures such as donor animal selection, pig islet production release criteria, preclinical data and zoonosis surveillance prior to human clinical trials have been put forward as a consensus through the efforts of the International Xenotransplantation Association. To bring pig islet transplantation to clinical reality, the development of clinically applicable immunosuppression regimens and methods to minimize immunosuppression to reduce side effects should be established. This review encompasses immune rejection mechanisms in islet xenotransplantation, immunosuppression regimens that have enabled long-term graft survival in pig-to-nonhuman primate experiments and strategies for minimizing immunosuppression in islet xenotransplantation. By thoroughly examining the drugs that are currently available and in development and their individual targets within the immune response, the best strategy for enabling clinical trials of pig islets for Type 1 diabetes will be proposed.

In Vitro Assessment of Human Islet Vulnerability to Instant Blood-Mediated Inflammatory Reaction (IBMIR) and Its Use to Demonstrate a Beneficial Effect of Tissue Culture

Culture of human pancreatic islets is now routinely carried out prior to clinical islet allotransplantation, using conditions that have been developed empirically. One of the major causes of early islet destruction after transplantation is the process termed instant blood-mediated inflammatory reaction (IBMIR). The aim of this study was to develop in vitro methods to investigate IBMIR and apply them to the culture conditions used routinely in our human islet isolation laboratory. Freshly isolated or precultured (24 h, 48 h) human islets were incubated in either ABO-compatible allogeneic human blood or Hank's buffered salt solution (HBSS) for 1 h at 37°C. Tissue factor (TF) expression and leukocyte migration were assessed by light microscopy. TF was also quantified by ELISA. To assess β-cell function, glucose-stimulated insulin secretion (GSIS) assay was carried out. The extent of islet β-cell damage was quantified using a proinsulin assay. Islets cultured for 24 h had higher GSIS when compared to freshly isolated or 48-h precultured islets. Freshly isolated islets had significantly higher TF content than 24-h and 48-h precultured islets. Incubation of freshly isolated human islets in allogeneic human blood released 6.5-fold higher level of proinsulin in comparison to freshly isolated human islets in HBSS. The high level of proinsulin released was significantly attenuated when precultured islets (24 h or 48 h) were exposed to fresh blood. Histological examination of fresh islets in blood clot showed that some islets were fragmented, showing signs of extraislet insulin leakage and extensive neutrophil infiltration and necrosis. These features were markedly reduced when the islets were cultured for 24 h. These results suggest that our standard 24-h islet culture is markedly beneficial in attenuating IBMIR, as evidenced by increased GSIS, lower content of TF, decrease islet fragmentation, and proinsulin release.

The use of hydrogen gas clearance for blood flow measurements in single endogenous and transplanted pancreatic islets

The blood perfusion of pancreatic islets is regulated independently from that of the exocrine pancreas, and is of importance for multiple aspects of normal islet function, and probably also during impaired glucose tolerance. Single islet blood flow has been difficult to evaluate due to technical limitations. We therefore adapted a hydrogen gas washout technique using microelectrodes to allow such measurements. Platinum micro-electrodes monitored hydrogen gas clearance from individual endogenous and transplanted islets in the pancreas of male Lewis rats and in human and mouse islets implanted under the renal capsule of male athymic mice. Both in the rat endogenous pancreatic islets as well as in the intra-pancreatically transplanted islets, the vascular conductance and blood flow values displayed a highly heterogeneous distribution, varying by factors 6-10 within the same pancreas. The blood flow of human and mouse islet grafts transplanted in athymic mice was approximately 30% lower than that in the surrounding renal parenchyma. The present technique provides unique opportunities to study the islet vascular dysfunction seen after transplantation, but also allows for investigating the effects of genetic and environmental perturbations on islet blood flow at the single islet level in vivo.

Pig-to-monkey islet xenotransplantation using multi-transgenic pigs

The generation of pigs with genetic modifications has significantly advanced the field of xenotransplantation. New genetically engineered pigs were produced on an α1,3-galactosyltransferase gene-knockout background with ubiquitous expression of human CD46, with islet beta cell-specific expression of human tissue factor pathway inhibitor and/or human CD39 and/or porcine CTLA4-lg. Isolated islets from pigs with 3, 4 or 5 genetic modifications were transplanted intraportally into streptozotocin-diabetic, immunosuppressed cynomolgus monkeys (n = 5). Immunosuppression was based on anti-CD154 mAb costimulation blockade. Monitoring included features of early islet destruction, glycemia, exogenous insulin requirement and histopathology of the islets at necropsy. Using these modified pig islets, there was evidence of reduced islet destruction in the first hours after transplantation, compared with two series of historical controls that received identical therapy but were transplanted with islets from pigs with either no or only one genetic modification. Despite encouraging effects on early islet loss, these multi-transgenic islet grafts did not demonstrate consistency in regard to long-term success, with only two of five demonstrating function beyond 5 months.

The role and regulation of complement activation as part of the thromboinflammation elicited in cell therapies

Cell therapies in which the cells come into direct contact with blood and other body fluids are emerging treatment procedures for patients with various diseases, such as diabetes mellitus, liver insufficiency, and graft-versus-host disease. However, despite recent progress, these procedures are associated with tissue loss caused by thromboinflammatory reactions. These deleterious reactions involve the activation of the complement and coagulation cascades and platelet and leukocyte activation, ultimately resulting in clot formation and damage to the implanted cells. In this concept review, we discuss the basic mechanisms underlying the thrombininflammatory process, with special reference to the engagement of complement and emerging strategies for the therapeutic regulation of these reactions that include the use of selective systemic inhibitors and various procedures to coat the surfaces of the cells. The coating procedures may also be applied to other treatment modalities in which similar mechanisms are involved, including whole organ transplantation, treatment with biomaterials in contact with blood, and extracorporeal procedures.

Islet cell transplantation for the treatment of type 1 diabetes: recent advances and future challenges

Islet transplantation is a well-established therapeutic treatment for a subset of patients with complicated type I diabetes mellitus. Prior to the Edmonton Protocol, only 9% of the 267 islet transplant recipients since 1999 were insulin independent for >1 year. In 2000, the Edmonton group reported the achievement of insulin independence in seven consecutive patients, which in a collaborative team effort propagated expansion of clinical islet transplantation centers worldwide in an effort to ameliorate the consequences of this disease. To date, clinical islet transplantation has established improved success with insulin independence rates up to 5 years post-transplant with minimal complications. In spite of marked clinical success, donor availability and selection, engraftment, and side effects of immunosuppression remain as existing obstacles to be addressed to further improve this therapy. Clinical trials to improve engraftment, the availability of insulin-producing cell sources, as well as alternative transplant sites are currently under investigation to expand treatment. With ongoing experimental and clinical studies, islet transplantation continues to be an exciting and attractive therapy to treat type I diabetes mellitus with the prospect of shifting from a treatment for some to a cure for all.

Control of IBMIR in neonatal porcine islet xenotransplantation in baboons

The instant blood-mediated inflammatory reaction (IBMIR) is a major obstacle to the engraftment of intraportal pig islet xenografts in primates. Higher expression of the galactose-α1,3-galactose (αGal) xenoantigen on neonatal islet cell clusters (NICC) than on adult pig islets may provoke a stronger reaction, but this has not been tested in the baboon model. Here, we report that WT pig NICC xenografts triggered profound IBMIR in baboons, with intravascular clotting and graft destruction occurring within hours, which was not prevented by anti-thrombin treatment. In contrast, IBMIR was minimal when recipients were immunosuppressed with a clinically relevant protocol and transplanted with NICC from αGal-deficient pigs transgenic for the human complement regulators CD55 and CD59. These genetically modified (GM) NICC were less susceptible to humoral injury in vitro than WT NICC, inducing significantly less complement activation and thrombin generation when incubated with baboon platelet-poor plasma. Recipients of GM NICC developed a variable anti-pig antibody response, and examination of the grafts 1 month after transplant revealed significant cell-mediated rejection, although scattered insulin-positive cells were still present. Our results indicate that IBMIR can be attenuated in this model, but long-term graft survival may require more effective immunosuppression or further donor genetic modification.

Inflammatory response in islet transplantation

Islet cell transplantation is a promising beta cell replacement therapy for patients with brittle type 1 diabetes as well as refractory chronic pancreatitis. Despite the vast advancements made in this field, challenges still remain in achieving high frequency and long-term successful transplant outcomes. Here we review recent advances in understanding the role of inflammation in islet transplantation and development of strategies to prevent damage to islets from inflammation. The inflammatory response associated with islets has been recognized as the primary cause of early damage to islets and graft loss after transplantation. Details on cell signaling pathways in islets triggered by cytokines and harmful inflammatory events during pancreas procurement, pancreas preservation, islet isolation, and islet infusion are presented. Robust control of pre- and peritransplant islet inflammation could improve posttransplant islet survival and in turn enhance the benefits of islet cell transplantation for patients who are insulin dependent. We discuss several potent anti-inflammatory strategies that show promise for improving islet engraftment. Further understanding of molecular mechanisms involved in the inflammatory response will provide the basis for developing potent therapeutic strategies for enhancing the quality and success of islet transplantation.

The role of platelets in coagulation dysfunction in xenotransplantation, and therapeutic options

Xenotransplantation could resolve the increasing discrepancy between the availability of deceased human donor organs and the demand for transplantation. Most advances in this field have resulted from the introduction of genetically engineered pigs, e.g., α1,3-galactosyltransferase gene-knockout (GTKO) pigs transgenic for one or more human complement-regulatory proteins (e.g., CD55, CD46, CD59). Failure of these grafts has not been associated with the classical features of acute humoral xenograft rejection, but with the development of thrombotic microangiopathy in the graft and/or consumptive coagulopathy in the recipient. Although the precise mechanisms of coagulation dysregulation remain unclear, molecular incompatibilities between primate coagulation factors and pig natural anticoagulants exacerbate the thrombotic state within the xenograft vasculature. Platelets play a crucial role in thrombosis and contribute to the coagulation disorder in xenotransplantation. They are therefore important targets if this barrier is to be overcome. Further genetic manipulation of the organ-source pigs, such as pigs that express one or more coagulation-regulatory genes (e.g., thrombomodulin, endothelial protein C receptor, tissue factor pathway inhibitor, CD39), is anticipated to inhibit platelet activation and the generation of thrombus. In addition, adjunctive pharmacologic anti-platelet therapy may be required. The genetic manipulations that are currently being tested are reviewed, as are the potential pharmacologic agents that may prove beneficial.

Evidence for instant blood-mediated inflammatory reaction in clinical autologous islet transplantation

A nonspecific inflammatory and thrombotic reaction termed instant blood-mediated inflammatory reaction (IBMIR) has been reported when allogenic or xenogenic islets come into contact with blood. This reaction is known to cause significant loss of transplanted islets. We hypothesized that IBMIR occurs in patients undergoing total pancreatectomy followed by autologous islet transplantation (TP-AIT) and tested this hypothesis in 24 patients and in an in vitro model. Blood samples drawn during the peritransplant period showed a significant and rapid increase of thrombin-anti-thrombin III complex (TAT) and C-peptide during islet infusion, which persisted for up to 3 h, along with a decreased platelet count. A concomitant increase in levels of inflammatory proteins IL-6, IL-8 and interferon-inducible protein-10 was observed. An in vitro model composed of pure islets plus autologous blood also demonstrated significantly increased levels of TAT (p<0.05), C-peptide (p<0.05), tumor necrosis factor-alpha (p<0.05) and MCP-1 (p<0.05), as well as strong tissue factor expression in islets. Islet viability decreased significantly but was rescued by the presence of low-molecular-weight dextran sulfate. In conclusion, AIT-induced elevation of TAT and destruction of islets suggests that IBMIR might occur during AIT. Modulating this process may help improve islet engraftment and the insulin independence rate in TP-AIT patients.

Transplantation of Encapsulated Pancreatic Islets as a Treatment for Patients with Type 1 Diabetes Mellitus

Encapsulation of pancreatic islets has been proposed and investigated for over three decades to improve islet transplantation outcomes and to eliminate the side effects of immunosuppressive medications. Of the numerous encapsulation systems developed in the past, microencapsulation have been studied most extensively so far. A wide variety of materials has been tested for microencapsulation in various animal models (including nonhuman primates or NHPs) and some materials were shown to induce immunoprotection to islet grafts without the need for chronic immunosuppression. Despite the initial success of microcapsules in NHP models, the combined use of islet transplantation (allograft) and microencapsulation has not yet been successful in clinical trials. This review consists of three sections: introduction to islet transplantation, transplantation of encapsulated pancreatic islets as a treatment for patients with type 1 diabetes mellitus (T1DM), and present challenges and future perspectives.

Making surrogate β-cells from mesenchymal stromal cells: perspectives and future endeavors

Generation of surrogate β-cells is the need of the day to compensate the short supply of islets for transplantation to diabetic patients requiring daily shots of insulin. Over the years several sources of stem cells have been claimed to cater to the need of insulin producing cells. These include human embryonic stem cells, induced pluripotent stem cells, human perinatal tissues such as amnion, placenta, umbilical cord and postnatal tissues involving adipose tissue, bone marrow, blood monocytes, cord blood, dental pulp, endometrium, liver, labia minora dermis-derived fibroblasts and pancreas. Despite the availability of such heterogonous sources, there is no substantial breakthrough in selecting and implementing an ideal source for generating large number of stable insulin producing cells. Although the progress in derivation of β-cell like cells from embryonic stem cells has taken a greater leap, their application is limited due to controversy surrounding the destruction of human embryo and immune rejection. Since multipotent mesenchymal stromal cells are free of ethical and immunological complications, they could provide unprecedented opportunity as starting material to derive insulin secreting cells. The main focus of this review is to discuss the merits and demerits of MSCs obtained from human peri- and post-natal tissue sources to yield abundant glucose responsive insulin producing cells as ideal candidates for prospective stem cell therapy to treat diabetes.

Thrombin-activatable fibrinolysis inhibitor is activated in an instant blood-mediated inflammatory reaction after intraportal islet transplant

OBJECTIVES

Activated thrombin-activatable fibrinolysis inhibitor is a coagulation factor in some thrombotic diseases. However, available data on whether thrombin-activatable fibrinolysis inhibitor is activated in islet transplant are limited. In this study, changes of plasma-activated thrombin-activatable fibrinolysis inhibitor levels in instant blood-mediated inflammatory reaction after islet transplant were assessed.

MATERIALS AND METHODS

Plasma concentrations of thrombin-antithrombin complex, D-dimer, C-peptide, and activated thrombin-activatable fibrinolysis inhibitor were assessed at 0 minutes, 30 minutes, 1 hour, 6 hours, 12 hours, and 24 hours after an intraportal islet transplant using rats via an enzyme-linked immunosorbent assay, or solid-phase, 2-site chemiluminescent immunometric assay. We recovered the liver at 1 hour after the transplant for histologic examination.

RESULTS

Thrombin-antithrombin complex, C-peptide, and activated thrombin-activatable fibrinolysis inhibitor levels increased immediately after we stopped islet infusion, and their peak levels occurred at 1 hour after islet infusion. D-dimer levels increased continually after islet infusion was stopped, and peaked 24 hours after infusion. Histologic examination of the liver 1 hour after islet infusion revealed frequent portal venous thrombi, with entrapped islets. The entrapped islets showed a disrupted morphology.

CONCLUSIONS

Activated thrombin-activatable fibrinolysis inhibitor was generated and peaked 1 hour after islet transplant according with activating coagulation, indicating that thrombin-activatable fibrinolysis inhibitor is activated and accumulated at levels in instant blood-mediated inflammatory reaction was sufficient to affect fibrinolysis.

Correction of diabetes mellitus by transplanting minimal mass of syngeneic islets into vascularized small intestinal segment

Transplantation of mature islets into portal vein has been most effective thus far, although attrition of transplanted islets constitutes a major limitation, and alternative approaches are required. We analyzed the mechanisms by which islets engrafted, vascularized and functioned over the long term in the small intestinal submucosa. To determine engraftment, survival and function, 350 syngenic islets were transplanted into either intestinal segments or portal vein of diabetic rats. Islet reorganization, vascularization and function were analyzed by histological analysis, RT-PCR analysis as well as glycemic control over up to 1 year. Transplantation of syngeneic islets in marginal numbers successfully restored normoglycemia in diabetic rats. Transplantation of semi-pure islet preparation did not impair their engraftment, vascularization and function. Islets were morphologically intact and expressed insulin as well as glucagon over the year. Expression of angiogenic genes permitted revascularization of transplanted islets. We identified the expression of transcription factors required for maintenance of beta cells. These studies demonstrated that marginal mass of transplanted islets was sufficient to restore euglycemia in streptozotocin-treated rats. These superior results were obtained despite use of an impure preparation of islets in animals with small intestinal segment. Our findings will help advance new horizons for cell therapy in patients with diabetes.

Transplantation of xenogeneic islets: are we there yet?

Beta cell replacement therapy has been proposed as a novel therapy for the treatment of type 1 diabetes. The proof of concept has been demonstrated with successful islet allotransplantation. Islet xenotransplantation has been proposed as an alternative, more reliable, and infinite source of beta cells. The advantages of islet xenotransplantation are the ability to transplant a well differentiated cell that is responsive to glucose and the potential for genetic modification which focuses the treatment on the donor rather than the recipient. The major hurdle remains overcoming the severe cellular rejection that affects xenografts. This review will focus on the major advances that have occurred with genetic modification and the successful therapeutic strategies that have been demonstrated in nonhuman primates. Novel approaches to overcome cell-mediated rejection including biological agents that target selectively costimulation molecules, the development of local immunosuppression through genetic manipulation, and encapsulation will be discussed. Overall, there has been considerable progress in all these areas, which eventually should lead to clinical trials.

Anti-inflammatory strategies to enhance islet engraftment and survival

Early innate inflammatory reaction strongly affects islet engraftment and survival after intrahepatic transplantation. This early immune response is triggered by ischemia-reperfusion injury and instant blood mediated inflammatory reaction (IBMIR) occurring hours and days after islet infusion. Evidence in both mouse model and in human counterpart suggest the involvement of coagulation, complement system, and proinflammatory chemokines/cytokines. Identification and targeting of pathway(s), playing a role as "master regulator(s)" in post-transplant detrimental inflammatory events, is now mandatory to improve islet transplantation success. This review will focus on inflammatory pathway(s) differentially modulated by islet isolation and mainly associated with the early post-transplant events. Moreover, we will take into account anti-inflammatory strategies that have been tested at 2 levels: on the graft, ex vivo, during islet culture (i.e., donor) and/or on the graft site, in vivo, early after islet infusion (i.e., recipient).

Revascularization of transplanted pancreatic islets and role of the transplantation site

Since the initial reporting of the successful reversal of hyperglycemia through the transplantation of pancreatic islets, significant research efforts have been conducted in elucidating the process of revascularization and the influence of engraftment site on graft function and survival. During the isolation process the intrinsic islet vascular networks are destroyed, leading to impaired revascularization after transplant. As a result, in some cases a significant quantity of the beta cell mass transplanted dies acutely following the infusion into the portal vein, the most clinically used site of engraftment. Subsequently, despite the majority of patients achieving insulin independence after transplant, a proportion of them recommence small, supplemental exogenous insulin over time. Herein, this review considers the process of islet revascularization after transplant, its limiting factors, and potential strategies to improve this critical step. Furthermore, we provide a characterization of alternative transplant sites, analyzing the historical evolution and their role towards advancing transplant outcomes in both the experimental and clinical settings.

Preconditioning with associated blocking of Ca2+ inflow alleviates hypoxia-induced damage to pancreatic β-cells

Objective

Beta cells of pancreatic islets are susceptible to functional deficits and damage by hypoxia. Here we aimed to characterize such effects and to test for and pharmacological means to alleviate a negative impact of hypoxia.

Methods and Design

Rat and human pancreatic islets were subjected to 5.5 h of hypoxia after which functional and viability parameters were measured subsequent to the hypoxic period and/or following a 22 h re-oxygenation period. Preconditioning with diazoxide or other agents was usually done during a 22 h period prior to hypoxia.

Results

Insulin contents decreased by 23% after 5.5 h of hypoxia and by 61% after a re-oxygenation period. Preconditioning with diazoxide time-dependently alleviated these hypoxia effects in rat and human islets. Hypoxia reduced proinsulin biosynthesis (³H-leucine incorporation into proinsulin) by 35%. Preconditioning counteracted this decrease by 91%. Preconditioning reduced hypoxia-induced necrosis by 40%, attenuated lowering of proteins of mitochondrial complexes I–IV and enhanced stimulation of HIF-1-alpha and phosphorylated AMPK proteins. Preconditioning by diazoxide was abolished by co-exposure to tolbutamide or elevated potassium (i.e. conditions which increase Ca²⁺ inflow). Preconditioning with nifedipine, a calcium channel blocker, partly reproduced effects of diazoxide. Both diazoxide and nifedipine moderately reduced basal glucose oxidation whereas glucose-induced oxygen consumption (tested with diazoxide) was unaffected. Preconditioning with diaxoxide enhanced insulin contents in transplants of rat islets to non-diabetic rats and lowered hyperglycemia vs. non-preconditioned islets in streptozotocin-diabetic rats. Preconditioning of human islet transplants lowered hyperglycemia in streptozotocin-diabetic nude mice.

Conclusions

1) Prior blocking of Ca²⁺ inflow associates with lesser hypoxia-induced damage, 2) preconditioning affects basal mitochondrial metabolism and accelerates activation of hypoxia-reactive and potentially protective factors, 3) results indicate that preconditioning by K⁺-ATP-channel openers has therapeutic potential for islet transplantations.

Silicon micro- and nanofabrication for medicine

This manuscript constitutes a review of several innovative biomedical technologies fabricated using the precision and accuracy of silicon micro- and nanofabrication. The technologies to be reviewed are subcutaneous nanochannel drug delivery implants for the continuous tunable zero-order release of therapeutics, multi-stage logic embedded vectors for the targeted systemic distribution of both therapeutic and imaging contrast agents, silicon and porous silicon nanowires for investigating cellular interactions and processes as well as for molecular and drug delivery applications, porous silicon (pSi) as inclusions into biocomposites for tissue engineering, especially as it applies to bone repair and regrowth, and porous silica chips for proteomic profiling. In the case of the biocomposites, the specifically designed pSi inclusions not only add to the structural robustness, but can also promote tissue and bone regrowth, fight infection, and reduce pain by releasing stimulating factors and other therapeutic agents stored within their porous network. The common material thread throughout all of these constructs, silicon and its associated dielectrics (silicon dioxide, silicon nitride, etc.), can be precisely and accurately machined using the same scalable micro- and nanofabrication protocols that are ubiquitous within the semiconductor industry. These techniques lend themselves to the high throughput production of exquisitely defined and monodispersed nanoscale features that should eliminate architectural randomness as a source of experimental variation thereby potentially leading to more rapid clinical translation.

Influence of liver histopathology on transaminitis following total pancreatectomy and autologous islet transplantation

BACKGROUND

In type 1 diabetics undergoing allogenic islet transplants, transaminitis and portal vein thrombosis (PVT) after transhepatic portal infusion of islets may be related to infusion pressure and the purity of islets. Complications of intraoperative portal infusion of islets in patients with chronic pancreatitis undergoing a total pancreatectomy (TP) and autologous islet transplant (AIT) and the relationship to liver histopathology have not been examined.

AIM

The purpose of this study was to examine complications of intraportal infusion of autologous islets after TP.

METHODS

Data on 26 TP-AIT patients were analyzed.

RESULTS

Infusion of islets [mean 304,473 ± 314,557 islet equivalents, median volume 300 mL (50-600)] resulted in mean postinfusion PV pressure of 9.15 ± 10.09 cmH2O which correlated with infused islets equivalents (r (2) = 33.6, P = 0.002) and volume (r (2) = 30.4, P = 0.005). Of 23 patients undergoing liver biopsy, 8 (35 %) were normal, 10 (43 %) had steatosis, and 5 (22 %) periportal fibrosis. Peak alanine aminotransferase (ALT; median 1 day after infusion) differed among the three histologic groups (P = 0.025). The difference in ALT was statistically significant between steatosis (showed the greatest increase) and the other two groups, but not between the normal and fibrosis groups. No correlation was found between the portal pressure increase at infusion and other variables. Two patients that developed PVT on day 1 had the highest infusion pressures; a third occurred on day 5.

CONCLUSION

Preexisting liver pathology is a contributing factor in the rise in liver enzymes but does not correlate with development of PV thrombosis.

The potential of endothelial colony-forming cells to improve early graft loss after intraportal islet transplantation

Early graft loss in islet transplantation means that a large amount of donor islets is required. Endothelial cells and endothelial colony-forming cells (ECFCs) have been reported to improve instant blood-mediated inflammatory reaction (IBMIR) in vitro. In this study, we examined if ECFC-coated porcine islets would prevent early graft loss in vivo. Human ECFCs were prepared from cord blood and cocultured with islets to make composite grafts. Diabetic nude mice underwent intraportal transplantation. Blood glucose levels were monitored, and morphological examination of the grafts along with analysis of the components of IBMIR and inflammatory reaction were performed with the liver tissues. The ECFC-coated islets significantly decreased blood glucose levels immediately after transplantation compared to the uncoated islets. Composite ECFC islet grafts were observed in the liver sections, associated with a more insulin(+) area compared to that of the uncoated group within 48 h after transplantation. Deposition of CD41a, C5b-9, and CD11b(+) cells was also decreased in the ECFC-coated group. Expression of porcine HMGB1 and mouse TNF-α was increased in the transplantated groups compared to the sham operation group, with a trend of a decreasing trend across the uncoated group, the ECFC-coated group, and the sham group. We demonstrated that the composite ECFC porcine islets transplanted into the portal vein of nude mice improved early graft loss and IBMIR in vivo.

Evaluation of the blood compatibility of materials, cells, and tissues: basic concepts, test models, and practical guidelines

Medicine today uses a wide range of biomaterials, most of which make contact with blood permanently or transiently upon implantation. Contact between blood and nonbiological materials or cells or tissue of nonhematologic origin initiates activation of the cascade systems (complement, contact activation/coagulation) of the blood, which induces platelet and leukocyte activation. Although substantial progress regarding biocompatibility has been made, many materials and medical treatment procedures are still associated with severe side effects. Therefore, there is a great need for adequate models and guidelines for evaluating the blood compatibility of biomaterials. Due to the substantial amount of cross talk between the different cascade systems and cell populations in the blood, it is advisable to use an intact system for evaluation. Here, we describe three such in vitro models for the evaluation of the biocompatibility of materials and therapeutic cells and tissues. The use of different anticoagulants and specific inhibitors in order to be able to dissect interactions between the different cascade systems and cells of the blood is discussed. In addition, we describe two clinically relevant medical treatment modalities, the integration of titanium implants and transplantation of islets of Langerhans to patients with type 1 diabetes, whose mechanisms of action we have addressed using these in vitro models.