Rapid failure of pig islet transplantation in non human primates

The future treatment for type 1 diabetes: Pig islet- or stem cell-derived β cells?

Replacement of β cells is only a curative approach for type 1 diabetes (T1D) patients to avoid the threat of iatrogenic hypoglycemia. In this pursuit, islet allotransplantation under Edmonton's protocol emerged as a medical miracle to attain hypoglycemia-free insulin independence in T1D. Shortage of allo-islet donors and post-transplantation (post-tx) islet loss are still unmet hurdles for the widespread application of this therapeutic regimen. The long-term survival and effective insulin independence in preclinical studies have strongly suggested pig islets to cure overt hyperglycemia. Importantly, CRISPR-Cas9 technology is pursuing to develop "humanized" pig islets that could overcome the lifelong immunosuppression drug regimen. Lately, induced pluripotent stem cell (iPSC)-derived β cell approaches are also gaining momentum and may hold promise to yield a significant supply of insulin-producing cells. Theoretically, personalized β cells derived from a patient's iPSCs is one exciting approach, but β cell-specific immunity in T1D recipients would still be a challenge. In this context, encapsulation studies on both pig islet as well as iPSC-β cells were found promising and rendered long-term survival in mice. Oxygen tension and blood vessel growth within the capsules are a few of the hurdles that need to be addressed. In conclusion, challenges associated with both procedures, xenotransplantation (of pig-derived islets) and stem cell transplantation, are required to be cautiously resolved before their clinical application.

Xenotransplantation of Genetically Modified Neonatal Pig Islets Cures Diabetes in Baboons

Xenotransplantation using porcine donors is rapidly approaching clinical applicability as an alternative therapy for treatment of many end-stage diseases including type 1 diabetes. Porcine neonatal islet cell clusters (NICC) have normalised blood sugar levels for relatively short periods in the preclinical diabetic rhesus model but have met with limited success in the stringent baboon model. Here we report that NICC from genetically modified (GM) pigs deleted for αGal and expressing the human complement regulators CD55 and CD59 can cure diabetes long-term in immunosuppressed baboons, with maximum graft survival exceeding 22 months. Five diabetic baboons were transplanted intraportally with 9,673 – 56,913 islet equivalents (IEQ) per kg recipient weight. Immunosuppression consisted of T cell depletion with an anti-CD2 mAb, tacrolimus for the first 4 months, and maintenance with belatacept and anti-CD154; no anti-inflammatory treatment or cytomegalovirus (CMV) prophylaxis/treatment was given. This protocol was well tolerated, with all recipients maintaining or gaining weight. Recipients became insulin-independent at a mean of 87 ± 43 days post-transplant and remained insulin-independent for 397 ± 174 days. Maximum graft survival was 675 days. Liver biopsies showed functional islets staining for all islet endocrine components, with no evidence of the inflammatory blood-mediated inflammatory reaction (IBMIR) and minimal leukocytic infiltration. The costimulation blockade-based immunosuppressive protocol prevented an anti-pig antibody response in all recipients. In conclusion, we demonstrate that genetic modification of the donor pig enables attenuation of early islet xenograft injury, and in conjunction with judicious immunosuppression provides excellent long-term function and graft survival in the diabetic baboon model.

Clinically available immunosuppression averts rejection but not systemic inflammation after porcine islet xenotransplant in cynomolgus macaques

A safe, efficacious, and clinically applicable immunosuppressive regimen is necessary for islet xenotransplantation to become a viable treatment option for diabetes. We performed intraportal transplants of wild-type adult porcine islets in 25 streptozotocin-diabetic cynomolgus monkeys. Islet engraftment was good in 21, partial in 3, and poor in 1 recipient. Median xenograft survival was 25 days with rapamycin and CTLA4Ig immunosuppression. Adding basiliximab induction and maintenance tacrolimus to the base regimen significantly extended median graft survival to 147 days (p < .0001), with three animals maintaining insulin-free xenograft survival for 265, 282, and 288 days. We demonstrate that this regimen suppresses non-Gal anti-pig antibody responses, circulating effector memory T cell expansion, effector function, and infiltration of the graft. However, a chronic systemic inflammatory state manifested in the majority of recipients with long-term graft survival indicated by increased neutrophil to lymphocyte ratio, IL-6, MCP-1, CD40, and CRP expression. This suggests that this immunosuppression regimen fails to regulate innate immunity and resulting inflammation is significantly associated with increased incidence and severity of adverse events making this regimen unacceptable for translation. Additional studies are needed to optimize a maintenance regimen for regulating the innate inflammatory response.

Carbohydrate antigen microarray analysis of serum IgG and IgM antibodies before and after adult porcine islet xenotransplantation in cynomolgus macaques

Understanding the anti-carbohydrate antibody response toward epitopes expressed on porcine cells, tissues, and organs is critical to advancing xenotransplantation toward clinical application. In this study, we determined IgM and IgG antibody specificities and relative concentrations in five cynomolgus monkeys at baseline and at intervals following intraportal xenotransplantation of adult porcine islets. This study utilized a carbohydrate antigen microarray that comprised more than 400 glycoconjugates, including historically reported α-Gal and non-α-Gal carbohydrate antigens with various modifications. The elicited anti-carbohydrate antibody responses were predominantly IgM compared to IgG in 4 out of 5 monkeys. Patterns of elicited antibody responses greater than 1.5 difference (log2 base units; 2.8-fold on a linear scale) from pre-serum to post-serum sampling specific for carbohydrate antigens were heterogeneous and recipient-specific. Increases in the elicited antibody response to α-Gal, Sda, GM2 antigens, or Lexis X antigen were found in individual monkeys. The novel carbohydrate structures Galβ1-4GlcNAcβ1-3Galβ1 and N-linked glycans with Manα1-6(GlcNAcβ1-2Manα1-3)Manβ1-4GlcNAcβ structure were common targets of elicited IgM antibodies. These results provide important insights into the carbohydrate epitopes that elicit antibodies following pig-to-monkey islet xenotransplantation and reveal possible targets for gene editing.

Mycophenolate mofetil and animal models

Mycophenolate mofetil (MMF), is the morpholinoethyl ester of mycophenolic acid (MPA). Though initially developed as an anti-rejection treatment, MMF is beginning to find application in more common immune-mediated diseases. MMF has been shown to be effective against transplant-associated vascular disease, lupus and other inflammatory diseases via multiple mechanisms in several animal models. MMF treatment blocks the proliferation of T cells and B cells, attenuates the production of autoreactive IgG and IgM, diminishes complement deposition, and reduces the production of multiple proinflammatory cytokines including TNF-α, IFN-γ, IL-2, IL-3, IL-4, IL-5, IL-6 and IL-12. It also increases production of the anti-inflammatory mediator IL-10. In addition, MMF reduces the infiltration of immune cells into sites of inflammation by interfering with the expression of cell-surface molecules critical for this process, including MHC class II, CD40, CD80, CD86, I-A, and ICAM-1. Additional mechanisms involving mannosylation and N-linked glycosylation of cell-surface molecules are only beginning to be investigated. This article will focus on the contribution of animal models of disease as investigational tools in the development of MMF as an immunomodulatory drug. The use of mice, rats, rabbits, monkeys, baboons and interspecific xenografts will be discussed.

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.

Progress and challenges in macroencapsulation approaches for type 1 diabetes (T1D) treatment: Cells, biomaterials, and devices

Macroencapsulation technology has been an attractive topic in the field of treatment for Type 1 diabetes due to mechanical stability, versatility, and retrievability of the macro-capsule design. Macro-capsules can be categorized into extravascular and intravascular devices, in which solute transport relies either on diffusion or convection, respectively. Failure of macroencapsulation strategies can be due to limited regenerative capacity of the encased insulin-producing cells, sub-optimal performance of encapsulation biomaterials, insufficient immunoisolation, excessive blood thrombosis for vascular perfusion devices, and inadequate modes of mass transfer to support cell viability and function. However, significant technical advancements have been achieved in macroencapsulation technology, namely reducing diffusion distance for oxygen and nutrients, using pro-angiogenic factors to increase vascularization for islet engraftment, and optimizing membrane permeability and selectivity to prevent immune attacks from host's body. This review presents an overview of existing macroencapsulation devices and discusses the advances based on tissue-engineering approaches that will stimulate future research and development of macroencapsulation technology. Biotechnol. Bioeng. 2016;113: 1381-1402. © 2015 Wiley Periodicals, Inc.

Progress in pig-to-non-human primate transplantation models (1998-2013): a comprehensive review of the literature

BACKGROUND

The pig-to-non-human primate model is the standard choice for in vivo studies of organ and cell xenotransplantation. In 1998, Lambrigts and his colleagues surveyed the entire world literature and reported all experimental studies in this model. With the increasing number of genetically engineered pigs that have become available during the past few years, this model is being utilized ever more frequently.

METHODS

We have now reviewed the literature again and have compiled the data we have been able to find for the period January 1, 1998 to December 31, 2013, a period of 16 yr.

RESULTS

The data are presented for transplants of the heart (heterotopic and orthotopic), kidney, liver, lung, islets, neuronal cells, hepatocytes, corneas, artery patches, and skin. Heart, kidney, and, particularly, islet xenograft survival have increased significantly since 1998.

DISCUSSION

The reasons for this are briefly discussed. A comment on the limitations of the model has been made, particularly with regard to those that will affect progression of xenotransplantation toward the clinic.

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.

Islet xenotransplantation from genetically engineered pigs

PURPOSE OF REVIEW

Pigs have emerged as potential sources of islets for clinical transplantation. Wild-type porcine islets (adult and neonatal) transplanted into the portal vein have successfully reversed diabetes in nonhuman primates. However, there is a rapid loss of the transplanted islets on exposure to blood, known as the instant blood-mediated inflammatory reaction (IBMIR), as well as a T-cell response that leads to rejection of the graft.

RECENT FINDINGS

Genetically modified pig islets offer a number of potential advantages, particularly with regard to reducing the IBMIR-related graft loss and protecting the islets from the primate immune response. Emerging data indicate that transgenes specifically targeted to pig β cells using an insulin promoter (in order to maximize target tissue expression while limiting host effects) can be achieved without significant effects on the pig's glucose metabolism.

SUMMARY

Experience with the transplantation of islets from genetically engineered pigs into nonhuman primates is steadily increasing, and has involved the deletion of pig antigenic targets to reduce the primate humoral response, the expression of transgenes for human complement-regulatory and coagulation-regulatory proteins, and manipulations to reduce the effect of the T-cell response. There is increasing evidence of the advantages of using genetically engineered pigs as sources of islets for future clinical trials.

Encapsulated islets for diabetes therapy: history, current progress, and critical issues requiring solution

Insulin therapy became a reality in 1921 dramatically saving lives of people with diabetes, but not protecting them from long-term complications. Clinically successful free islet implants began in 1989 but require life long immunosuppression. Several encapsulated islet approaches have been ongoing for over 30 years without defining a clinically relevant product. Macro-devices encapsulating islet mass in a single device have shown long-term success in large animals but human trials have been limited by critical challenges. Micro-capsules using alginate or similar hydrogels encapsulate individual islets with many hundreds of promising rodent results published, but a low incidence of successful translation to large animal and human results. Reduction of encapsulated islet mass for clinical transplantation is in progress. This review covers the status of both early and current studies including the presentation of corporate efforts involved. It concludes by defining the critical items requiring solution to enable a successful clinical diabetes therapy.

Caprine pancreatic islet xenotransplantation into diabetic immunosuppressed BALB/c mice

BACKGROUND

Type 1 diabetes mellitus is a devastating disease for which there is currently no cure, but only lifetime management. Islet xenotransplantation is a promising technique for the restoration of blood glucose control in patients with diabetes mellitus. The purpose of this study was to explore the potential use of caprine (goat) islet cells as xenogeneic grafts in the treatment for diabetes in a mouse model.

METHODS

Caprine pancreases were harvested and transported to the laboratory under conditions optimized to prevent ischemia. Islets were isolated, purified, and tested for functionality. Caprine islets (2000 islet equivalent) were transplanted beneath the kidney capsules of diabetic BALB/c mice under thalidomide-induced immunosuppression. Blood glucose and insulin levels of grafted mice were evaluated by glucometer and enzyme-linked immunosorbent assay kit, respectively. The functionality and quality of caprine pancreatic islet grafts were assessed by intraperitoneal glucose tolerance tests.

RESULTS

The viability of purified islet cells exceeded 90%. Recipient mice exhibited normoglycemia (<11 mM glucose) for 30 days. In addition, weight gain negatively correlated with blood glucose level. The findings verified diabetes reversal in caprine islet recipient mice. A significant drop in non-fasting blood glucose level (from 23.3 ± 5.4 to 8.04 ± 0.44 mM) and simultaneous increase in serum insulin level (from 0.01 ± 0.001 to 0.56 ± 0.17 μg/l) and body weights (from 23.64 ± 0.31 to 25.85 ± 0.34 g) were observed (P < 0.05). Immunohistochemical analysis verified insulin production in the transplanted islets.

CONCLUSIONS

Purified caprine islets were demonstrated to successfully sustain viability and functionality for controlling blood glucose levels in an immunosuppressed mouse model of diabetes. These results suggest the use of caprine islets as an addition to the supply of xenogeneic islets for diabetes research.

Anodic aluminium oxide membranes for immunoisolation with sufficient oxygen supply for pancreatic islets

Immunoisolation membranes have been developed for various cell encapsulations for therapeutic purposes. However effective encapsulation systems have been hindered by low oxygen (O2) permeability or imperfect immunoisolation caused by either low porosity or non-uniform pore geometry. Here, we report an encapsulation method that uses an anodic aluminum oxide membrane formed by polyethylene oxide self-assembly to obtain nanochannels with both high selectivity in excluding immune molecules and high permeability of nutrients such as glucose, insulin, and O2. The extracorporeal encapsulation system composed of these membranes allows O2 flux to meet the O2 demand of pancreatic islets of Langerhans and provides excellent in vitro viability and functionality of islets.

Macro- or microencapsulation of pig islets to cure type 1 diabetes

Although allogeneic islet transplantation can successfully cure type 1 diabetes, it has limited applicability. For example, organs are in short supply; several human pancreas donors are often needed to treat one diabetic recipient; the intrahepatic site may not be the most appropriate site for islet implantation; and immunosuppressive regimens, which are associated with side effects, are often required to prolong survival of the islet graft. An alternative source of insulin-producing cells would therefore be of major interest. Pigs represent a possible alternative source of beta cells. Grafting of pig islets may appear difficult because of the immunologic species barrier, but pig islets have been shown to function in primates for at least 6 mo with clinically incompatible immunosuppression. Therefore, a bioartificial pancreas made of encapsulated pig islets may resolve issues associated with islet allotransplantation. Although several groups have shown that encapsulated pig islets are functional in small-animal models, less is known about the use of bioartificial pancreases in large-animal models. In this review, we summarize current knowledge of encapsulated pig islets, to determine obstacles to implantation in humans and possible solutions to overcome these obstacles.

Islet xenotransplantation using gal-deficient neonatal donors improves engraftment and function

Significant deficiencies in understanding of xenospecific immunity have impeded the success of preclinical trials in xenoislet transplantation. Although galactose-α1,3-galactose, the gal epitope, has emerged as the principal target of rejection in pig-to-primate models of solid organ transplant, the importance of gal-specific immunity in islet xenotransplant models has yet to be clearly demonstrated. Here, we directly compare the immunogenicity, survival and function of neonatal porcine islets (NPIs) from gal-expressing wild-type (WT) or gal-deficient galactosyl transferase knockout (GTKO) donors. Paired diabetic rhesus macaques were transplanted with either WT (n = 5) or GTKO (n = 5) NPIs. Recipient blood glucose, transaminase and serum xenoantibody levels were used to monitor response to transplant. Four of five GTKO versus one of five WT recipients achieved insulin-independent normoglycemia; transplantation of WT islets resulted in significantly greater transaminitis. The WT NPIs were more susceptible to antibody and complement binding and destruction in vitro. Our results confirm that gal is an important variable in xenoislet transplantation. The GTKO NPI recipients have improved rates of normoglycemia, likely due to decreased susceptibility of xenografts to innate immunity mediated by complement and preformed xenoantibody. Therefore, the use of GTKO donors is an important step toward improved consistency and interpretability of results in future xenoislet studies.

Pig-to-nonhuman primates pancreatic islet xenotransplantation: an overview

The therapy of type 1 diabetes is an open challenging problem. The restoration of normoglycemia and insulin independence in immunosuppressed type 1 diabetic recipients of islet allotransplantation has shown the potential of a cell-based diabetes therapy. Even if successful, this approach poses a problem of scarce tissue supply. Xenotransplantation can be the answer to this limited donor availability and, among possible candidate tissues for xenotransplantation, porcine islets are the closest to a future clinical application. Xenotransplantation, with pigs as donors, offers the possibility of using healthy, living, and genetically modified islets from pathogen-free animals available in unlimited number of islets. Several studies in the pig-to-nonhuman primate model demonstrated the feasibility of successful preclinical islet xenotransplantation and have provided insights into the critical events and possible mechanisms of immune recognition and rejection of xenogeneic islet grafts. Particularly promising results in the achievement of prolonged insulin independence were obtained with newly developed, genetically modified pigs islets able to produce immunoregulatory products, using different implantation sites, and new immunotherapeutic strategies. Nonetheless, further efforts are needed to generate additional safety and efficacy data in nonhuman primate models to safely translate these findings into the clinic.

Engraftment of insulin-producing cells from porcine islets in non-immune-suppressed rats or nonhuman primates transplanted previously with embryonic pig pancreas

Transplantation therapy for diabetes is limited by unavailability of donor organs and outcomes complicated by immunosuppressive drug toxicity. Xenotransplantation is a strategy to overcome supply problems. Implantation of tissue obtained early during embryogenesis is a way to reduce transplant immunogenicity. Insulin-producing cells originating from embryonic pig pancreas obtained very early following pancreatic primordium formation (embryonic day 28 (E28)) engraft long-term in non-immune, suppressed diabetic rats or rhesus macaques. Morphologically, similar cells originating from adult porcine islets of Langerhans (islets) engraft in non-immune-suppressed rats or rhesus macaques previously transplanted with E28 pig pancreatic primordia. Our data are consistent with induction of tolerance to an endocrine cell component of porcine islets induced by previous transplantation of embryonic pig pancreas, a novel finding we designate organogenetic tolerance. The potential exists for its use to enable the use of pigs as islet cell donors for humans with no immune suppression requirement.

Engraftment of cells from porcine islets of Langerhans following transplantation of pig pancreatic primordia in non-immunosuppressed diabetic rhesus macaques

Transplantation therapy for human diabetes is limited by the toxicity of immunosuppressive drugs. If toxicity can be minimized, there will still be a shortage of human donor organs. Xenotransplantation of porcine islets is a strategy to overcome supply problems. Xenotransplantation in mesentery of pig pancreatic primordia obtained very early during organogenesis [embryonic day 28 (E28)] is a way to obviate the need for immunosuppression in rats or rhesus macaques and to enable engraftment of a cell component originating from porcine islets implanted beneath the renal capsule of rats. Here, we show engraftment in the kidney of insulin and porcine proinsulin mRNA-expressing cells following implantation of porcine islets beneath the renal capsule of diabetic rhesus macaques transplanted previously with E28 pig pancreatic primordia in mesentery. Donor cell engraftment is confirmed using fluorescent in situ hybridization (FISH) for the porcine X chromosome and is supported by glucose-stimulated insulin release in vitro. Cells from islets do not engraft in the kidney without prior transplantation of E28 pig pancreatic primordia in mesentery. This is the first report of engraftment following transplantation of porcine islets in non-immunosuppressed, immune-competent non-human primates. The data are consistent with tolerance to a cell component of porcine islets induced by previous transplantation of E28 pig pancreatic primordia.

The importance of tissue factor expression by porcine NICC in triggering IBMIR in the xenograft setting

BACKGROUND

In islet transplantation, tissue factor (TF) has been reported to be involved in triggering the instant blood-mediated inflammatory reaction (IBMIR), which causes early massive loss of islets transplanted intraportally. TF is synthesized and secreted by several cell sources including islets and inflammatory cells such as neutrophils, monocytes, and platelets. In this study, we investigated whether xenografts-mediated IBMIR could be inhibited by selectively inhibiting TF production by islets using small interfering RNA (siRNA)-mediated TF gene knockdown.

METHODS

Porcine neonatal islet cell clusters (NICC) were transfected with siRNA specific for TF or a nonspecific siRNA. TF gene and protein expression were analyzed by real-time polymerase chain reaction and fluorescence-activated cell sorting, respectively. The effect of TF knockdown on IBMIR was evaluated using an in vitro tubing loop model of human blood-NICC interactions.

RESULTS

TF siRNA transfection of NICC resulted in reduced TF gene and protein expression. TF siRNA transfected NICC showed a significant reduction in the formation of blood clots, platelet activation, thrombin generation, and complement activation after exposure to human ABO compatible blood in vitro. In addition, there was reduced neutrophil infiltration within blood clots containing TF siRNA transfected NICC.

CONCLUSIONS

TF expression on porcine NICC is an important initiator of IBMIR in islet xenotransplantation. This study identifies porcine TF as a potential target for inhibiting this response.

Transplantation of Long-term Cultured Porcine Islets in the Rat: Prolonged Graft Survival and Recipient Growth on Reduced Immunosuppression

To evaluate whether further improvement in porcine islet xenotransplantation is feasible, a number of questions were addressed. Earlier we showed significant improvement in the nude mouse of the porcine islets by selection through long-term culture. Now these islets were tested in the stringent pig-to-rat model. Islets were isolated from adult pigs, cultured for 1.5–3 weeks and transplanted to rats. Possible rejection mechanisms were assessed by interference of the cellular response with cyclosporine A (CsA), blocking macrophages with gadolinium chloride (GdCl), and suppressing the humoral response with cyclophosphamide. Modifications in graft size and condition were analyzed. Untreated control recipients showed primary nonfunction (PNF). CsA treatment could fully overcome PNF and resulted in graft survival from 10 to over 134 days. Rejection was the main cause of function loss. Although rejection could not be prevented by intensifying the induction therapy, increased maintenance immunosuppression effectively blocked rejection, albeit at the expense of toxicity. Blocking the humoral response was ineffective; all grafts showed PNF. In contrast, depletion of macrophages fully prevented PNF. Combination of GdCl and CsA gave no additional effect, and grafts were rejected between 57 and 162 days. Generally, graft survivals were similar to those reported in the literature; however, long-term cultured islets required much less maintenance immunosuppression. Cessation of graft function was not always due to rejection; in some cases “islet exhaustion” was found, possibly caused by discrepancy between the graft size and the rapidly growing recipient. Neither the presence of damaged islet tissue in the graft nor the size of the graft exerted any influence on graft survival. On rejection, no real infiltration of the graft was seen; destruction gradually processed from the outside. The good functional capability of the cultured islets was illustrated by disappearance of the clinical symptoms and increase in body weight, which almost doubled in the long-term survivors.

Pig islets for clinical islet xenotransplantation

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

A new bioartificial pancreas utilizing amphiphilic membranes for the immunoisolation of porcine islets: a pilot study in the canine

We have developed a replaceable bioartificial pancreas to treat diabetes utilizing a unique cocontinous amphiphilic conetwork membrane created for macroencapsulation and immunoisolation of porcine islet cells (PICs). The membrane is assembled from hydrophilic poly(N,N-dimethyl acrylamide) and hydrophobic/oxyphilic polydimethylsiloxane chains cross-linked with hydrophobic/oxyphilic polymethylhydrosiloxane chains. Our hypothesis is that this membrane allows the survival of xenotransplanted PICs in the absence of prevascularization or immunosuppression because of its extraordinarily high-oxygen permeability and small hydrophilic channel dimensions (3-4 nm). The key components are a 5-10 microm thick semipermeable amphiphilic conetwork membrane reinforced with an electrospun nanomat of polydimethylsiloxane-containing polyurethane, and a laser-perforated nitinol scaffold to provide geometric stability. Devices were loaded with PICs and tested for their ability to maintain islet viability without prevascularization, prevent rejection, and reverse hyperglycemia in three pancreatectomized dogs without immunosuppression. Tissue tolerance was good and there was no systemic toxicity. The bioartificial pancreas protected PICs from toxic environments in vitro and in vivo. Islets remained viable for up to 3 weeks without signs of rejection. Neovascularization was observed. Hyperglycemia was not reversed, most likely because of insufficient islet mass. Further studies to determine long-term islet viability and correction of hyperglycemia are warranted.

Cellular xenotransplantation

PURPOSE OF REVIEW

Expectations are high on cellular therapy. Being fundamental to elucidate organogenesis, it is unlikely that embryonic stem cells will be used for clinical purposes. Postembryonic stage, developing cells are, therefore, the front-runner for regenerative medicine. In addition to autologous cells, both allogeneic and xenogeneic cells are hypothetical candidates to treat specific diseases. This review summarizes the current knowledge on immunological and functional aspects of xeno(allo)-cellular transplantation for cardiomyopathy, diabetes, liver failure, neural diseases, and bone regeneration.

RECENT FINDINGS

Xenocellular transplantation is promising for tissue repair in immunologically privileged sites such as the central nervous system or nonvascularized tissues in which no or moderate immunosuppression is required. In vascularized organs, major immune responses are present when cells are transplanted without additional conditioning. Positive results from encapsulation methods that protect cells from the immune system should further stimulate preclinical research. Also, conditioning immunosuppression could be used to circumvent the initial immune response. Transgenic pigs cells are probably the best xenogeneic substitute for human application, although basic research on innate and noninnate immunity toward pig cells is still required.

SUMMARY

In several fields of medicine, cellular xenotransplantation is slowly emerging as a potential therapeutic tool.

Pig-to-nonhuman primate islet xenotransplantation

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

Dissecting the instant blood-mediated inflammatory reaction in islet xenotransplantation

BACKGROUND

A massive destruction of transplanted tissue occurs immediately following transplantation of pancreatic islets from pig to non-human primates. The detrimental instant blood-mediated inflammatory reaction (IBMIR), triggered by the porcine islets, is a likely explanation for this tissue loss. This reaction may also be responsible for mediating an adaptive immune response in the recipient that requires a heavy immunosuppressive regimen.

MATERIALS AND METHODS

Low molecular weight dextran sulfate (LMW-DS) and the complement inhibitor Compstatin were used in a combination of in vitro and in vivo studies designed to dissect the xenogeneic IBMIR in a non-human primate model of pancreatic islet transplantation. Adult porcine islets (10,000 IEQs/kg) were transplanted intraportally into three pairs of cynomolgus monkeys that had been treated with LMW-DS or heparin (control), and the effects on the IBMIR were characterized. Porcine islets were also incubated in human blood plasma in vitro to assess complement inhibition by LMW-DS and Compstatin.

RESULTS

Morphological scoring and immunohistochemical staining revealed that the severe islet destruction and macrophage, neutrophilic granulocyte, and T-cell infiltration observed in the control (heparin-treated) animals were abrogated in the LMW-DS-treated monkeys. Both coagulation and complement activation were significantly reduced in monkeys treated with LMW-DS, but IgM and complement fragments were still found on the islet surface. This residual complement activation could be inhibited by Compstatin in vitro.

CONCLUSIONS

The xenogeneic IBMIR in this non-human primate model is characterized by an immediate binding of antibodies that triggers deleterious complement activation and a subsequent clotting reaction that leads to further complement activation. The effectiveness of LMW-DS (in vivo and in vitro) and Compstatin (in vitro) in inhibiting this IBMIR provides the basis for a protocol that can be used to abrogate the IBMIR in pig-human clinical islet transplantation.

The Baboon in Xenotransplant Research

If cross-species transplantation is ever to become a reasonable therapeutic modality for human beings, it will be because the potential for success has been demonstrated in a nonhuman primate model. The imperative has always been to select a primate research subject from a species that is plentiful, is not endangered, readily procreates in a managed environment, and mimics the human response (immunologic homology) to both organ transplantation and potential transfer of infectious disease. Several Papio subspecies of baboons, including Papio hamadryas anubis (olive baboon), meet these important criteria. These animals remain ubiquitous throughout sub-Saharan Africa and have adapted well to the managed environments of major primate centers worldwide. A list of United States-based primate centers housing breeding colonies of baboons can be found in Table 19.1. The Surgical Research Laboratory at Loma Linda University, for instance, has maintained a salutary relationship with the Southwest National Primate Research Center in San Antonio, Texas, for the procurement of juvenile baboon research subjects.

Pig islet xenograft rejection in a mouse model with an established human immune system

BACKGROUND

Xenotransplantation from pigs provides a potential solution to the severe shortage of human pancreata, but strong immunological rejection prevents its clinical application. A better understanding of the human immune response to pig islets would help develop effective strategies for preventing graft rejection.

METHODS

We assessed pig islet rejection by human immune cells in humanized mice with a functional human immune system. Humanized mice were prepared by transplantation of human fetal thymus/liver tissues and CD34(+) fetal liver cells into immunodeficient mice. Islet xenograft survival/rejection was determined by histological analysis of the grafts and measurement of porcine C-peptide in the sera of the recipients.

RESULTS

In untreated humanized mice, adult pig islets were completely rejected by 4 weeks. These mice showed no detectable porcine C-peptide in the sera, and severe intra-graft infiltration by human T cells, macrophages, and B cells, as well as deposition of human antibodies. Pig islet rejection was prevented by human T-cell depletion prior to islet xenotransplantation. Islet xenografts harvested from T-cell-depleted humanized mice were functional, and showed no human cell infiltration or antibody deposition.

CONCLUSIONS

Pig islet rejection in humanized mice is largely T-cell-dependent, which is consistent with previous observations in non-human primates. These humanized mice provide a useful model for the study of human xenoimmune responses in vivo.

Pig islet xenotransplantation into non-human primate model

Allogeneic islet transplantation faces difficulties because (1) organ shortage is recurrent; (2) several pancreas donors are often needed to treat one diabetic recipient; and (3) the intrahepatic site of islet implantation may not be the most appropriate site. Another source of insulin-producing cells, therefore, would be of major interest, and pigs represent a possible and serious source for obtaining such cells. Pig islet grafts may seem difficult because of the species barrier, but recent reports demonstrate that pig islets may function in primates for at least 6 months. Pig islet xenotransplantation, however, must still overcome several hurdles before becoming clinically applicable. The actual consensus is to produce more preclinical data in the pig-to-primate model as a necessary requirement to envisage any pig-to-human transplantation of islets; therefore, a summary of the actual acquired knowledge of pig islet transplantation in primates seemed useful and is summarized in this overview.

Parameters favouring successful adult pig islet isolations for xenotransplantation in pig-to-primate models

BACKGROUND

In the near future, adult porcine islets of Langerhans appear as an unlimited source of insulin-producing cells which could play a major role for treating diabetes mellitus. There is, however, an obvious lack of pre-clinical results and data in the pig-to-primate model. One of the main hurdles of this model is certainly related to the difficulty of reproducing regularly successful porcine islet isolation. This experimental work was designed to provide guidelines applicable in pig pancreas procurement and islet isolation for successful islet xenotransplantation into primates.

METHODS

Pancreases were harvested from adult Belgium Landrace pigs (n = 79) in a single centre. The impact on islet yield of (1) pancreas procurement (blood exsanguination and warm ischaemia time (WIT)), (2) cold storage solutions (classic UW and modified UW (without hydroxyethyl starch and inverse K+/Na+ concentration)), (3) a dynamic or static method of pancreas digestion, and (4) the endotoxin content and enzymatic activity from five different batches of Liberase PI was studied. In addition, pancreatic biopsies (n = 18), performed before isolation, were retrospectively analyzed to study the impact of histomorphometry on porcine islet yield. Finally, two diabetic cynomolgus monkeys were transplanted without immunosuppression with 15,000 pig islet equivalents/kg body weight of recipient to assess in vivo the function of freshly isolated islets. Univariate and multivariate analyses were performed.

RESULTS

By multiple linear regression, the most significant variables that significantly improved islet yield were, firstly, the presence of <30 EU (endotoxin units) of endotoxin in Liberase batches, followed by a WIT under 10 min and the use of blood exsanguination before pancreas harvesting (P < 0.005). In contrast, isolation method (dynamic vs. static) and the solution used for storage (short-term) (UW vs. modified UW) did not significantly influence islet yield. The correlation of retrospective histomorphometry analysis of native pancreas and extemporaneous biopsy before isolation clearly determined a positive relationship between isolated islet number and the number of islets/cm2 (r = 0.708, P < 0.01) or with the percentage of large islets (r = 0.680, P < 0.01) found in pancreas biopsies. Pig pancreases containing more than 82 islets/cm2 and more than 42% of large islets (>100 microm) thus enabled more than 120,000 islet equivalents to be obtained in 90% of the cases, which is an ideal amount of islets to transplant into a primate of 4 to 5 kg. In vivo, a reduction of blood glucose (<200 mg/dl), associated with porcine C-peptide production, was observed in two primates after transplantation with adult pig islets. At day 7 post-transplantation, however, loss of islet function was associated with graft destruction and immune reaction.

CONCLUSIONS

Morphological screening of the pig pancreas before isolation, optimal blood exsanguination, WIT <10 min, and an endotoxin content <30 EU/mg in Liberase PI batches determine successful pig islet isolation for xenotransplantation in primates.

Pig-to-nonhuman primate islet xenotransplantation: a review of current problems

Islet allotransplantation has been shown to have potential as a treatment for type 1 diabetic patients. Xenotransplantation, using the pig as a donor, offers the possibility of an unlimited number of islets. This comprehensive review focuses on experience obtained in pig-to-nonhuman primate models, particularly with regard to the different types of islets (fetal, neonatal, adult) and isolation procedures used, and the methods to determine islet viability. The advantages and disadvantages of the methods to induce diabetes (pancreatectomy, streptozotocin) are discussed. Experience in pig-to-nonhuman primate islet transplantation studies is reviewed, including discussion of the possible mechanisms of rejection and the immunosuppressive regimens used. The research carried out to date has led to workable animal models to study islet xenotransplantation, but several questions regarding methodology remain unanswered, and details of these practicalities require to be adequately addressed. The encouraging porcine islet survival reported recently provides an indicator for future immunosuppressive regimens.

Post-transplant upregulation of chemokine messenger RNA in non-human primate recipients of intraportal pig islet xenografts

BACKGROUND

We have previously shown that pig-to-primate intraportal islet xenografts reverse diabetes, escape hyperacute rejection, and undergo acute cellular rejection in non-immunosuppressed recipients. To gain a better understanding of mechanisms contributing to xenoislet rejection in non-human primates we examined gene expression in livers bearing islet xenografts in the first 72 h after transplantation.

METHODS

Liver specimens were collected at sacrifice from seven non-immunosuppressed rhesus macaques at 12, 24, 48 and 72 h after intraportal porcine islet transplantation. Following total RNA extraction, mRNA was quantified using SYBR green real-time reverse transcription polymerase chain reaction (RT-PCR) for species-specific immune response genes. Data were analyzed using comparative cycle threshold (Ct) analysis, adjusted for specific primer-efficiencies and normalized to cyclophilin expression.

RESULTS

Porcine insulin mRNA was detected in all liver samples. Cluster analysis revealed differential gene expression patterns at 12 and 24 h (early) compared with at 48 and 72 h (late) post-transplant. Gene expression patterns were associated with histological findings of predominantly neutrophils and only a few lymphocytes at 12 and 24 h and an increasing number of lymphocytes and macrophages at 48 and 72 h. Transcript levels of CXCR3 and its ligands, interferon-inducible protein 10 (IP-10) and monokine induced by IFN-gamma (Mig), significantly increased between early and late time points together with expression of MIP-1alpha, regulated on activation normal T expressed and secreted protein (RANTES) and MCP-1. CCR5 showed only a marginal, non-significant increase. Fas ligand, perforin and granzyme B transcripts were all elevated at 48 and 72 h post-transplant.

CONCLUSIONS

Our data suggest that CXCR3, with ligands IP-10 and Mig, is involved in T cell recruitment in acute islet xenograft rejection in non-human primates. Upregulation of RANTES and MIP-1alpha transcripts in the absence of a significant CCR5 increase suggests a possible involvement of other chemokine receptors. MCP-1 expression is associated with T cell and macrophage infiltration. Elevated cytotoxic effector molecule expression (Fas ligand, perforin, granzyme B) indicates T-cell mediated graft destruction by cytotoxic and cytolytic mechanisms within 48 to 72 h after transplantation. These results identify the CXCR3-mediated chemoattractant pathway as an immunosuppressive target in pig-to-primate islet xenotransplantation.

Effect of glucose toxicity on intraportal tilapia islet xenotransplantation in nude mice

BACKGROUND

Discordant xenogeneic islets transplanted intraportally into athymic nude rats experience primary non-function and are rapidly destroyed. Recently, it has been reported that adult porcine islets transplanted intraportally into nude mice are also rapidly destroyed and that this constitutes a new model for instant blood-mediated inflammatory reaction (IBMIR).

METHODS

Tilapia (fish) islets were harvested, mechanically broken into mammalian islet-sized fragments, cultured for 48 h, and transplanted via the portal vein into athymic or euthymic mice.

RESULTS

There were several groups of recipient mice. Streptozotocin-diabetic nude mice received 400 islets via the portal vein (n = 12). Recipients were killed when hyperglycemic (>200 mg/dl); livers and native pancreases were examined histologically. Mean graft survival time, based on function, was 5.4 +/- 1.2 days; at autopsy, histology showed occasional viable islets. We also performed a group of transplants in non-diabetic nude mice (n = 6) and then killed the recipients 2 or 4 weeks later; all had abundant viable, well-granulated islet grafts based on histology. Therefore, the intraportal environs in nude mice are not incompatible with discordant fish islets; rather, it appears as if hyperglycemia adversely affects the intraportal islet grafts (i.e. ''glucose toxicity''). To test this hypothesis, transplants were performed into non-diabetic nude mice and allowed to engraft for either 3 days (n = 6) or 10 days (n = 8) prior to injection of streptozotocin (200 to 220 mg/kg i.v.) to destroy the beta-cells in the recipients' native islets (n.b. tilapia islets are exceedingly resistant to streptozotocin); these recipients were followed for 28 days post-transplantation (or until hyperglycemic) and then killed for histology. Mean graft function exceeded 25 days for both groups and viable well-granulated, tilapia islets grafts were readily identified in all recipients; in all but one, the native pancreases were markedly beta-cell depleted -- confirming that normoglycemia was due to functional fish islet xenografts.

CONCLUSIONS

Our results suggest that ''glucose toxicity'' plays a role in the immediate demise of intraportal tilapia islet xenografts.

Survival of adult islet grafts from transgenic pigs with N-acetylglucosaminyltransferase-III (GnT-III) in cynomolgus monkeys

BACKGROUND

Because of a severe shortage of human donor pancreases, pig islets are considered to be an attractive donor source. Our previous in vitro study revealed that adult pig islets have strong non-Galalpha1-3Galbeta1-4GlcNAc-R (alpha-Gal) antigenicity, including the Hanganutziu-Deicher (H-D) antigen, especially in N-linked sugars. In this study, the issue of whether islets from N-acetylglucosaminyltransferase-III (GnT-III) transgenic pigs can prolong their survival in cynomolgus monkeys was examined.

METHODS

Adult pig islets were isolated from transgenic pigs with GnT-III and wild-type genes. GnT-III enzyme activity in pig islets was measured by high performance liquid chromatography (HPLC). The antigenicity of the islets to human natural antibodies was examined by flow cytometry. Pig islets were transplanted under the kidney capsule of streptozotocin-induced diabetic monkeys. After transplantation, blood samples were obtained and plasma insulin levels were monitored on a daily basis.

RESULTS

While GnT-III was barely expressed in wild-type islets, it was expressed at high levels in islets from transgenic pigs, and xenoantigenicity was significantly reduced. There was a trend for islets isolated from GnT-III-transgenic pigs to survive longer than those from wild-type pigs in cynomolgus monkeys (wild type: 1, 1, and 3 days; GnT-III: 1, >3, 4 and 5 days). Humoral and histological studies indicated up-regulated anti-pig islet antibodies and a relatively high deposition in islet grafts from wild-type pigs, respectively.

CONCLUSION

A reduction in xenoantigenicity by GnT-III may have prolonged the survival of porcine islets, suggesting the importance of non-alpha-Gal and non-H-D antigens, as they relate to N-linked sugars in the early rejection of porcine islets in the monkey. This approach may be useful in the clinical xenotransplantation of islets in the future.

Reversal of diabetes in non-immunosuppressed rhesus macaques by intraportal porcine islet xenografts precedes acute cellular rejection

BACKGROUND

The functional response and immunobiology of primarily non-vascularized islet cell xenografts remain poorly defined in non-human primates.

METHODS

We transplanted 20,000 adult porcine islet equivalents/kg (purified and cultured for 48-h) intraportally into six streptozotocin-diabetic and two non-diabetic rhesus macaques. Two recipients were killed at various intervals post-transplant for histologic examination of livers bearing xenografts.

RESULTS

Plasma glucose levels in diabetic recipients averaged 94 mg/dl at 12 h, 92 mg/dl at 24 h, 147 mg/dl at 48 h, and 157 mg/dl at 72 h post-transplant. Serum porcine C-peptide was present in eight of eight recipients at 12 h, in five of six at 24 h, in four of four at 48 h, and in one of two at 72 h post-transplant. C3a and SC5b-9 plasma levels increased at 12 h post-transplant and returned to pre-transplant levels by 24 h. IgG, IgM anti-pig and anti-Gal IgG serum antibody levels did not increase post-transplant. Rejection was initiated by IgM and complement deposition on islets. Neutrophils dominated the cellular infiltrate at 12 h; CD4+ and CD8+ T cells were the main infiltrating cells at 24, 48, and 72 h; and macrophages increasingly infiltrated xenografts starting at 24 h post-transplant. Numerous xenoislets were present at all time points; their proportion without intraislet infiltrates decreased from 65% at 24 h to 17% at 72 h post-transplant.

CONCLUSIONS

Pig-to-primate intraportal islet xenografts reverse diabetes and the majority of intraportally transplanted xenogeneic islets are not subject to hyperacute rejection. They undergo acute cellular rejection mediated by CD4+- and CD8+ T cells and macrophages.

Adult porcine islets produce MCP-1 and recruit human monocytes in vitro

Type 1 diabetes can be cured by transplantation of isolated pancreatic islets. Because of the shortage of human donor tissue, adult porcine islets (APIs) constitute a possible alternative tissue source. Upon intraportal injection, islets are subjected to an instant blood-mediated inflammatory reaction (IBMIR) leading to blood clotting, leukocyte islet-infiltration, islet damage and insulin release. Xenogeneic islets surviving IBMIR are rejected in a cellular process involving CD4(+) T lymphocytes and macrophages. We have investigated whether APIs themselves produce and secrete chemokines and/or inflammatory cytokines that may contribute to IBMIR and/or cell-mediated rejection. APIs, cultured for 1, 4, 8 and 11 days post-isolation, expressed mRNA for monocyte chemoattractant protein-1 (MCP-1), IL-1beta and TNF-alpha. API culture supernatants induced migration of human monocytes, which was significantly blocked by an anti-human MCP-1 antibody (Ab). Immunohistochemistry revealed MCP-1 in the cytoplasm of alpha- and beta-cells in isolated islets and in islets in situ. However, APIs or their supernatants were not able to activate human aortic endothelial cells (HAECs) in vitro, and neither IL-1beta nor TNF-alpha were detected by enzyme-linked immunosorbent assay (ELISA) in API culture supernatants. Both recombinant porcine IL-1beta and TNF-alpha were able to activate human endothelial cells (ECs) inducing CD62E and CD106 expression as analyzed by flow cytometry. In conclusion, MCP-1 secreted by APIs may contribute to both IBMIR and rejection by attracting monocytes into the islet; monocytes which upon transformation into macrophages will potentiate antigen presentation and execute islet rejection.

Evidence that tilapia islets do not express alpha-(1,3)gal: implications for islet xenotransplantation

BACKGROUND

Cell therapy for diabetes using teleost fish islet tissue has emerged as an intriguing alternative to the use of islet tissue from mammalian pancreases. The islet tissue, called Brockman bodies (BBs), is anatomically distinct from the pancreatic exocrine tissue and can be easily identified and isolated. Islets harvested from Nile tilapia (Oreochromis niloticus), when transplanted into streptozotocin-diabetic nude mice, produce long-term normoglycemia and achieve mammalian-like glucose tolerance profiles. We asked whether tilapia express the alpha-(1,3)gal epitope, the immunodominant target of human xenogeneic responses.

METHODS AND RESULTS

Immunostaining with the alpha-(1,3)gal-specific IB4 lectin on tilapia BB, liver, heart, spleen, and head kidney was negative, as was staining with murine anti-alpha-gal-specific monoclonal antibodies. Absence of alpha-gal-specific binding of IB4 or murine anti-gal mAbs to dispersed BBs was confirmed by fluorescent-activated cell sorter analysis. Tilapia BB cell membranes failed to reduce binding of anti-alpha-(1,3)gal-specific mAb in an enzyme-linked immunosorbent assay (ELISA) inhibition assay, while porcine and murine tissue lysates did. Tilapia BB cell lysates were shown to be devoid of alpha-1,3 galactosyltransferase activity by ELISA. Transplantation of tilapia BBs into diabetic alpha-gal knockout (gal KO) mice was not associated with accelerated xenograft rejection when compared with wild type control recipients (mean survival time 6.5 days vs. 7.2 days). Tilapia BBs failed to induce a rise in anti-gal IgG and IgM titers in gal KO mice, while the transplant of wild type mouse islets into gal KO mice caused a significant rise in anti-gal IgG and IgM antibodies.

CONCLUSIONS

We conclude that tilapia BBs are devoid of alpha-gal expression, and may offer an alternative to swine as a donor species for islet xenotransplantation.

Low molecular weight dextran sulfate prevents the instant blood-mediated inflammatory reaction induced by adult porcine islets

BACKGROUND

One of the main obstacles to clinical islet xenotransplantation is the injurious instant blood-mediated inflammatory reaction (IBMIR) that causes rapid binding of platelets to the islet surface, activation of the coagulation and complement systems, and leukocyte infiltration of the islets when the islets are exposed to blood.

METHODS

This study assesses the effect of low molecular weight dextran sulfate (LMW-DS) on IBMIR induced by porcine islets in an in vitro tubing loop assay using human blood and in an in vivo model using diabetic athymic mice.

RESULTS

In vitro experiments demonstrated that platelet consumption, coagulation, and complement activation were already reduced in the presence of LMW-DS at 0.01 mg/mL, and that at 0.1 mg/mL, LMW-DS prevented IBMIR. Immunohistochemical investigation showed that the leukocyte infiltration was abrogated at the highest dose. In vivo experiments showed that the transplanted pig islets survived for a significantly longer period in recipients treated with LMW-DS, and morphologic examination of transplanted islets showed a reduction in IBMIR analogous to that demonstrated by in vitro studies.

CONCLUSIONS

Given that LMW-DS has been used in clinical studies without serious adverse reactions, it has potential as a drug candidate that can control the strong innate immune response induced by pig islets when transplanted through the portal vein.

Intraportal pig islet xenotransplantation into athymic mice as an in vivo model for the study of the instant blood-mediated inflammatory reaction

One of the main obstacles to successful intraportal islet transplantation is the instant blood-mediated inflammatory reaction (IBMIR) elicited by the isolated islets when exposed to fresh human blood. In the present study, we investigated whether intraportal transplantation of pig islets into diabetic athymic mice could be used as a small animal model to study xenogeneic IBMIR in vivo. Adult porcine islets (APIs) or rat islets were implanted into the portal vein or under the renal subcapsular space of diabetic athymic mice. Graft survival and morphology were evaluated by measuring blood glucose levels and by performing immunohistochemical staining, respectively. Transplantation of rat islets, irrespective of implantation site, cured all diabetic athymic mice. APIs transplanted subcapsularly also cured all diabetic athymic mice, while none of the animals transplanted with an equivalent amount of APIs via the portal vein remained normoglycemic for more than 10 days after transplantation. Immunohistochemical staining on day 7 showed that most of intraportally transplanted APIs were entrapped in clots and infiltrated with CD11b+ leukocytes. Intraportal transplantation of APIs into athymic mice induced IBMIR, thus providing a small animal model for studying xenogeneic IBMIR.

T-cell-specific immunosuppression results in more than 53 days survival of porcine islets of langerhans in the monkey

BACKGROUND

Transplantation of islets of Langerhans can restore insulin production in diabetic patients. Because of the shortage of human donor organs, transplantation of porcine islets may be an alternative solution. The present study was aimed at the characterization of rejection mechanisms of porcine islets transplanted into eight nondiabetic monkeys under the kidney capsule.

METHODS

Cultured adult pig islets were used, which showed no expression of the galactose(alpha1,3)galactose epitope, major histocompatibility complex class II, or CD45, and no binding of antibodies or complement after exposure to monkey serum. Immunosuppression consisted of cyclophosphamide, cyclosporine A (CsA), and steroids (group 1); or antithymocyte globulin, anti-interleukin-2 receptor antibody, CsA, and steroids (group 2). In three animals of group 2, islets were also transplanted in the portal vein.

RESULTS

Although all monkeys had preformed anti-pig antibodies, no correlation was found between antibody titers and rejection and no deposition of antibodies or complement was observed in the grafts. Group 1 showed islets up to day 11, followed by T-cell infiltration and rejection at approximately day 14. In group 2, two monkeys showed infiltrates consisting predominantly of T cells starting at approximately day 29, whereas two monkeys showed well-preserved islets without infiltration up to day 53. In the livers of the three monkeys that also received islets intraportally and were resectioned on days 21, 33, and 49, no islets could be detected.

CONCLUSIONS

This study demonstrates that cultured adult pig islets can survive in the monkey for more than 53 days without signs of rejection under standard immunosuppression.

Use of the Gottingen Minipig as a Model of Diabetes, with Special Focus on Type 1 Diabetes Research

Animal models of type 1 diabetes remain essential tools for investigation of the etiology and pathogenesis of the disease and, importantly, for the development of effective new treatments. Although a range of well-characterized and widely used models of type 1 diabetes in rodents are currently available, large animal models are a valuable complement to rodent models for both physiological and practical reasons. The pig is very useful in many aspects as a model for human physiology and pathophysiology because many organ systems of this species, as well as physiological and pathophysiological responses, resemble those of the human. The Göttingen minipig is particularly suitable for long-term studies because of its inherent small size and ease of handling, even at full maturity. Of particular relevance to the field of type 1 diabetes are the many similarities evident between humans and pigs with regard to pharmacokinetics of compounds after subcutaneous administration, structure and function of the gastrointestinal tract, morphology of the pancreas, and the overall metabolic status of the two species. Because spontaneous type 1-like diabetes is very rare in pigs, a model of the condition must be induced experimentally, either surgically or chemically. This process is discussed, and the use of the pig as a model in islet transplantation and diabetic complications is briefly summarized.

Xenogeneic transplantation of porcine islets: an overview

The extreme demand for human organs or tissues for transplantation has driven the search for viable alternatives. Pigs are considered a possible source of tissue for a number of reasons including shared physiology, plentiful supply, short gestation, and, more recently, the generation of transgenic animals. Porcine islets show promise as a source of islets for the treatment of type 1 diabetes mellitus. Porcine islets regulate glucose levels in the same physiologic range as humans, and porcine insulin has been used for years as an exogenous source of insulin for glucose control. In this review, we discuss the advantages and disadvantages of the use of adult or neonatal porcine islets, the immunologic challenges facing transplantation of xenogeneic islets, and the concerns regarding transmission of infectious agents between species. Porcine islets isolated from both adult and neonatal pigs are capable of restoring euglycemia in experimental animal models of diabetes. Adult islets are more difficult to isolate, whereas neonatal islets have great proliferation potential but require several weeks to function posttransplantation. Xenogeneic islets are susceptible to complement-mediated lysis after the binding of preformed natural antibodies and cellular immunity involving both macrophages and CD4+ T cells. In addition, the potential for transmission of porcine endogenous retroviruses, porcine cytomegalovirus, and porcine lymphotropic herpesvirus type 1 are all concerns that must be addressed. Despite the challenges facing xenotransplantation, the extreme need for donor organs and tissues continues to drive progress toward overcoming the unique issues associated with transplantation between species.

CD46 protects pig islets from antibody but not cell-mediated destruction in the mouse

We have previously reported that islets present in cultured fetal pig pancreas (FPP) are resistant to destruction by Galalpha(1,3)Gal antibodies and compliment, but are susceptible to the 'secondary' antibody response which occurs on transplanting pig islet tissue to Galo/o murine recipients. In a model of antibody-mediated graft rejection, we tested the resistance of porcine islets to antibody. Using FPP from human CD46 transgenic pigs, we now report that the complement regulator, CD46, affords protection from antibody-mediated rejection when mouse anti-pig serum (MAPS) was administered to scid mice bearing PFF grafts from either CD46 transgenic or normal pigs. Indeed, whereas normal pig islets were destroyed by an intraperitoneal (i.p.) injection of 0.1 to 0.2 ml of MAPS antibody, destruction of CD46-expressing transgenic islets required 0.5 ml, i.e. up to five times the amount. In contrast, there was no prolongation of the survival of CD46 transgenic mouse skin or heart major histocompatibility complex-compatible or -incompatible allografts--rejected by predominantly cellular immune mechanisms, as opposed to xenograft rejection. Although complement regulators have been examined for their protective role in hyperacute rejection of vascularized xenografts, it is clear that they also have protective effects in the later, antibody-mediated responses, but are unlikely to effect the inflammatory response in cell-mediated rejection.