First update of the International Xenotransplantation Association consensus statement on conditions for undertaking clinical trials of porcine islet products in type 1 diabetes—Executive summary

The International Xenotransplantation Association has updated its original “Consensus Statement on Conditions for Undertaking Clinical Trials of Porcine Islet Products in Type 1 Diabetes,” which was published in Xenotransplantation in 2009. This update is timely and important in light of scientific progress and changes in the regulatory framework pertinent to islet xenotransplantation. Except for the chapter on “informed consent,” which has remained relevant in its 2009 version, all other chapters included in the initial consensus statement have been revised for inclusion in this update. These chapters will not provide complete revisions of the original chapters; rather, they restate the key points made in 2009, emphasize new and under‐appreciated topics not fully addressed in 2009, suggest relevant revisions, and communicate opinions that complement the consensus opinion. Chapter 1 provides an update on national regulatory frameworks addressing xenotransplantation. Chapter 2 a, previously Chapter 2, suggests several important revisions regarding the generation of suitable source pigs from the perspective of the prevention of xenozoonoses. The newly added Chapter 2b discusses conditions for the use of genetically modified source pigs in clinical islet xenotransplantation. Chapter 3 reviews porcine islet product manufacturing and release testing. Chapter 4 revisits the critically important topic of preclinical efficacy and safety data required to justify a clinical trial. The main achievements in the field of transmission of all porcine microorganisms, the rationale for more proportionate recipient monitoring, and response plans are reviewed in Chapter 5. Patient selection criteria and circumstances where trials of islet xenotransplantation would be both medically and ethically justified are examined in Chapter 6 in the context of recent advances in available and emerging alternative therapies for serious and potentially life‐threatening complications of diabetes. It is hoped that this first update of the International Xenotransplantation Association porcine islet transplant consensus statement will assist the islet xenotransplant scientific community, sponsors, regulators, and other stakeholders actively involved in the clinical translation of islet xenotransplantation.     

First update of the International Xenotransplantation Association consensus statement on conditions for undertaking clinical trials of porcine islet products in type 1 diabetes—Chapter 2a: source pigs—preventing xenozoonoses

Chapter 2 of the original consensus statement published in 2009 by IXA represents an excellent basis for the production of safe donor pigs and pig‐derived materials for porcine islet xenotransplantation. It was intended that the consensus statement was to be reviewed at interval to remain relevant. Indeed, many of the original salient points remain relevant today, especially when porcine islet xenotransplantation is performed in conjunction with immunosuppressants. However, progress in the field including demonstrated safe clinical porcine xenograft studies, increased understanding of risks including those posed by PERV, and advancement of diagnostic capabilities now allow for further consideration. Agents of known and unknown pathogenic significance continue to be identified and should be considered on a geographic, risk‐based, dynamic, and product‐specific basis, where appropriate using validated, advanced diagnostic techniques. PERV risk can be sufficiently reduced via multicomponent profiling including subtype expression levels in combination with infectivity assays. Barrier facilities built and operated against the AAALAC Ag Guide or suitable alternative criteria should be considered for source animal production as long as cGMPs and SOPs are followed. Bovine material‐free feed for source animals should be considered appropriate instead of mammalian free materials to sufficiently reduce TSE risks. Finally, the sponsor retention period for archival samples of donor materials was deemed sufficient until the death of the recipient if conclusively determined to be of unrelated and non‐infectious cause or for a reasonable period, that is, five to 10 yrs. In summary, the safe and economical production of suitable pigs and porcine islet xenograft materials, under appropriate guidance and regulatory control, is believed to be a viable means of addressing the unmet need for clinical islet replacement materials.     

First update of the International Xenotransplantation Association consensus statement on conditions for undertaking clinical trials of porcine islet products in type 1 diabetes—Chapter 4: pre‐clinical efficacy and complication data required to justify a clinical trial

In 2009, the International Xenotransplantation Association (IXA) published a consensus document that provided guidelines and “recommendations” (not regulations) for those contemplating clinical trials of porcine islet transplantation. These guidelines included the IXA's opinion on what constituted “rigorous pre‐clinical studies using the most relevant animal models” and were based on “non‐human primate testing.” We now report our discussion following a careful review of the 2009 guidelines as they relate to pre‐clinical testing. In summary, we do not believe there is a need to greatly modify the conclusions and recommendations of the original consensus document. Pre‐clinical studies should be sufficiently rigorous to provide optimism that a clinical trial is likely to be safe and has a realistic chance of success, but need not be so demanding that success might only be achieved by very prolonged experimentation, as this would not be in the interests of patients whose quality of life might benefit immensely from a successful islet xenotransplant. We believe these guidelines will be of benefit to both investigators planning a clinical trial and to institutions and regulatory authorities considering a proposal for a clinical trial. In addition, we suggest consideration should be given to establishing an IXA Clinical Trial Advisory Committee that would be available to advise (but not regulate) researchers considering initiating a clinical trial of xenotransplantation.     

First update of the International Xenotransplantation Association consensus statement on conditions for undertaking clinical trials of porcine islet products in type 1 diabetes – Chapter 3: Porcine islet product manufacturing and release testing criteria

In the 2009 IXA consensus, the requirements for the quality and control of manufacturing of porcine islet products were based on the U.S. regulatory framework where the porcine islet products fall within the definition of somatic cell therapy under the statutory authority of the U.S. Food and Drug Administration (FDA). In addition, porcine islet products require pre‐market approval as a biologic product under the Public Health Services Act and they meet the definition of a drug under the Federal Food, Drug, and Cosmetic Act (FD&C Act). Thus, they are subject to applicable provisions of the law and as such, control of manufacturing as well as reproducibility and consistency of porcine islet products, safety of porcine islet products, and characterization of porcine islet products must be met before proceeding to clinical trials. In terms of control of manufacturing as well as reproducibility and consistency of porcine islet products, the manufacturing facility must be in compliance with current Good Manufacturing Practices (cGMP) guidelines appropriate for the initiation of Phase 1/2 clinical trials. Sponsors intending to conduct a Phase 1/2 trial of islet xenotransplantation products must be able to demonstrate the safety of the product through the establishment of particular quality assurance and quality control procedures. All materials (including animal source and pancreas) used in the manufacturing process of the porcine islet products must be free of adventitious agents. The final porcine islet product must undergo tests for the presence of these adventitious agents including sterility, mycoplasma (if they are cultured), and endotoxin. Assessments of the final product must include the safety specifications mentioned above even if the results are not available until after release as these data would be useful for patient diagnosis and treatment if necessary. In addition, a plan of action must be in place for patient notification and treatment in case the sterility culture results are positive. In terms of the characterization of porcine islet products and product release criteria, the information on the porcine islet products should be acquired from a sample of the final product to be used for transplantation and must include the morphology of the islets, specific identity, purity, viability, and potency of the product. In addition, information on the quantity of the islet products should also be provided in a standardized fashion and this should be in terms of islet equivalents and/or cell numbers. The current consensus was created to provide guidelines that manufacturing facilities may find helpful in the manufacture of and the release criteria for porcine islet products including encapsulated islets and combined islet products. Our intent with the above recommendations is to provide a framework for individual porcine islet manufacturing facilities to ensure a high level of safety for the initiation of Phase 1/2 clinical trials on porcine islet xenotransplantation.     

Justifying clinical trials for porcine islet xenotransplantation

The development of the Edmonton Protocol encouraged a great deal of optimism that a cell‐based cure for type I diabetes could be achieved. However, donor organ shortages prevent islet transplantation from being a widespread solution as the supply cannot possibly equal the demand. Porcine islet xenotransplantation has the potential to address these shortages, and recent preclinical and clinical trials show promising scientific support. Consequently, it is important to consider whether the current science meets the ethical requirements for moving toward clinical trials. Despite the potential risks and the scientific unknowns that remain to be investigated, there is optimism regarding the xenotransplantation of some types of tissue, and enough evidence has been gathered to ethically justify clinical trials for the most safe and advanced area of research, porcine islet transplantation. Researchers must make a concerted effort to maintain a positive image for xenotransplantation, as a few well‐publicized failed trials could irrevocably damage public perception of xenotransplantation. Because all of society carries the burden of risk, it is important that the public be involved in the decision to proceed. As new information from preclinical and clinical trials develops, policy decisions should be frequently updated. If at any point evidence shows that islet xenotransplantation is unsafe, then clinical trials will no longer be justified and they should be halted. However, as of now, the expected benefit of an unlimited supply of islets, combined with adequate informed consent, justifies clinical trials for islet xenotransplantation.     

Chapter 1: Key ethical requirements and progress toward the definition of an international regulatory framework

Abstract:  The outstanding results recently obtained in islet xenotransplantation suggest that porcine islet clinical trials may soon be scientifically appropriate. Before the initiation of such clinical studies, however, it is essential that a series of key ethical and regulatory conditions are satisfied. As far as ethics is concerned, the fundamental requirements have been previously reported in a position paper of the Ethics Committee of the International Xenotransplantation Association. These include aspects related to the selection of adequately informed, appropriate recipients; animal breeding and welfare; safety issues and the need for a favorable risk/benefit assessment based on strong efficacy data in relevant xenotransplantation studies in the primate. As most diabetic patients are not at risk of short-term mortality without islet transplantation, only a small subset of patients could currently be considered for any type of islet transplant. However, there are potential advantages to xenotransplantation that could result in a favorable benefit-over-harm determination for islet xenotransplantation in this subpopulation and ultimately in a broader population of diabetic patients. With regard to regulatory aspects, the key concepts underlying the development of the regulatory models in existence in the United States, Europe and New Zealand are discussed. Each of these models provides an example of a well-defined regulatory approach to ensure the initiation of well-regulated and ethically acceptable clinical islet xenotransplantation trials. At this stage, it becomes apparent that only a well-coordinated international effort such as that initiated by the World Health Organization, aimed at harmonizing xenotransplantation procedures according to the highest ethical and regulatory standards on a global scale, will enable the initiation of clinical xenotransplantation trials under the best auspices for its success and minimize any risk of failure.     

The International Xenotransplantation Association consensus statement on conditions for undertaking clinical trials of xenocorneal transplantation

To develop an international consensus regarding the appropriate conditions for undertaking clinical trials in xenocorneal transplantation, here we review specific ethical, logistical, scientific, and regulatory issues regarding xenocorneal transplantation, and propose guidelines for conduct of clinical xenocorneal transplantation trials. These proposed guidelines are modeled on the published consensus statement of the International Xenotransplantation Association regarding recommended guidelines for conduct of clinical islet xenotransplantation. It is expected that this initial consensus statement will be revised over time in response to scientific advances in the field, and changes in the regulatory framework based on accumulating clinical experience.     

Executive summary

Abstract:  The International Xenotransplantation Association islet xenotransplantation consensus statement describes the conditions for undertaking clinical trials of porcine islet products in type 1 diabetes. Chapter 1 reviews the key ethical requirements and progress toward the definition of an international regulatory framework for clinical trials of xenotransplantation. Chapters 2 to 7 provide in depth and agreed-upon recommendations on source pigs, pig islet product manufacturing and release testing, preclinical efficacy and complication data required to justify a clinical trial, strategies to prevent transmission of porcine endogenous retrovirus, patient selection for clinical trials, and informed consent. It is planned to update this initial consensus statement in a year's time in light of progress in research, changes in the regulatory framework, and comments submitted after publication.     

First update of the International Xenotransplantation Association consensus statement on conditions for undertaking clinical trials of porcine islet products in type 1 diabetes—Chapter 6: patient selection for pilot clinical trials of islet xenotransplantation

Patients in whom type 1 diabetes is complicated by impaired awareness of hypoglycemia and recurrent episodes of severe hypoglycemia are candidates for islet or pancreas transplantation if severe hypoglycemia persists after completion of a structured stepped care approach or a formalized medical optimization run‐in period that provides access to hypoglycemia‐specific education including behavioral therapies, insulin analogs, and diabetes technologies under the close supervision of a specialist hypoglycemia service. Patients with type 1 diabetes and end‐stage renal failure who cannot meet clinically appropriate glycemic goals or continue to experience severe hypoglycemia after completion of a formalized medical optimization program under the guidance of an expert diabetes care team are candidates for islet or pancreas transplantation either simultaneously with or after a previous kidney transplant. Similarly, patients with type 2 diabetes and problematic hypoglycemia or renal failure who meet these criteria are considered candidates for islet replacement. Likewise, patients with pancreatectomy‐induced diabetes in whom an islet autograft was not available or deemed inappropriate are candidates for islet or pancreas transplantation if extreme glycemic lability persists despite best medical therapy. To justify participation of these transplant candidates in early‐phase trials of porcine islet cell products, lack of timely access to islet or pancreas allotransplantation due to allosensitization, high islet dose requirements, or other factors, or alternatively, a more favorable benefit–risk determination associated with the xenoislet than the alloislet or allopancreas transplant must be demonstrated. Additionally, in non‐uremic xenoislet recipients, the risks associated with diabetes must be perceived to be more serious than the risks associated with the xenoislet product and the rejection prophylaxis, and in xenoislet recipients with renal failure, the xenoislet product and immunosuppression must not impact negatively on renal transplant outcomes. The most appropriate patient group for islet xenotransplantation trials will be defined by the specific characteristics of each investigational xenoislet product and related technologies applied for preventing rejection. Selecting recipients who are more likely to experience prolonged benefits associated with the islet xenograft will help these patients comply with lifelong monitoring and other public health measures.     

Ascites formation accompanied by portal vein thrombosis after porcine islet xenotransplantation via the portal vein in Rhesus macaque (Macaca mulatta)

Pig‐to‐nonhuman primate (NHP) islet transplantation has been widely conducted as a preclinical xenotransplantation model prior to human clinical trial. Portal vein thrombosis is one of the complications associated with islet infusion through the portal vein into the liver. Here, we briefly report severe case of ascites formation accompanied by portal vein thrombi after pig‐to‐NHP islet xenotransplantation in a rhesus monkey. Meticulous prophylactic treatment such as continuous heparin infusion should be implemented to prevent portal vein thrombi in pig‐to‐NHP islet transplantation models.     

A health‐economic analysis of porcine islet xenotransplantation

Beckwith J, Nyman JA, Flanagan B, Schrover R, Schuurman H‐J. A health‐economic analysis of porcine islet xenotransplantation. Xenotransplantation 2010; 17: 233–242. © 2010 John Wiley & Sons A/S. Abstract: Background: Islet cell transplantation is a promising treatment for type 1 diabetes. To overcome the shortage of deceased human pancreas donors, porcine islet cell xenotransplantation is being developed as an alternative to allotransplantation. The objective of this study was to perform a cost‐effectiveness analysis of porcine islet transplantation in comparison with standard insulin therapy. The patient population for this study was young adults, ages 20 to 40, for whom standard medical care is inadequate in controlling blood glucose levels (hypoglycemia unawareness). Since trial data were lacking, estimates used extrapolations from data found in the literature and ongoing trials in clinical allotransplantation. Cost estimates were based on the data available in the USA. Methods: Markov modeling and Monte Carlo simulations using software specifically developed for health‐economic evaluations were used. Outcomes data for ongoing clinical islet allotransplantation from the University of Minnesota were used, along with probabilities of complications from the Diabetes Control and Complications Trial. Quality‐adjusted life years (QALYs) were the effectiveness measure. The upper limit of being cost‐effective is $100 000 per QALY. Cost data from the literature were used and adjusted to 2007 US dollars using the medical care portion of the Consumer Price Index. Results: In both Markov modeling and Monte Carlo simulations, porcine islet xenotransplantation was both more effective and less costly over the course of the 20‐yr model. For standard insulin therapy, cumulative cost per patient was $661 000, while cumulative effectiveness was 9.4 QALYs, for a cost of $71 100 per QALY. Transplantation had a cumulative cost of $659 000 per patient, a cumulative effectiveness of 10.9 QALYs, and a cost per QALY of $60 700. Islet transplantation became cost‐effective at 4 yr after transplantation, and was more cost‐effective than standard insulin treatment at 14 yr. These findings are related to relative high costs in the transplantation arm of the evaluation during the first years while those in the insulin arm became higher later in follow‐up. Throughout the follow‐up period, effectiveness of transplantation was higher than that of insulin treatment. In sensitivity analysis, duplication or triplication of one‐time initial costs such as costs of donor animal, islet manufacturing and transplantation had no effect on long‐term outcome in terms of cost‐saving or cost‐effectiveness, but the outcome of transplantation in terms of diabetes complications in cases with partial graft function could affect cost‐saving and cost‐effectiveness conclusions. Conclusion: Despite limitations in the model and lack of trial data, and under the assumption that islet transplantation outcomes for young adult type 1 diabetes patients are not dependent on the source of islet cells, this health‐economic evaluation suggests that porcine islet cell xenotransplantation may prove to be a cost‐effective and possibly cost‐saving procedure for type 1 diabetes compared to standard management.     

2007 IXA Presidential Address. Progress toward an ideal source animal: opportunities and challenges in a changing world

Abstract:  Xenotransplantation holds great promise for the treatment of end-stage organ failure and tissue injury. Recent advances in our understanding of the immunological hurdles to xenotransplantation and the development of genetic modification approaches to overcome them increase the likelihood of success. Exciting advances in these areas were presented at the Joint Congress of the IXA, the Cell Transplant Society and the International Pancreas and Islet Transplant Association in Minneapolis in September, 2007. However, in order to minimize infectious risks and encourage positive public perception of xenotransplantation, clinical trials should be initiated with appropriate monitoring and oversight procedures in place and only when there is high expectation of clinical benefit.     

Requirements for success in clinical islet transplantation

A few groups have endured the challenges of time, anecdotal success stories, logistic and funding impediments, to bring the field of clinical islet transplantation where it stands today. The recent improvement in clinical results has paralleled a renewed interest in islet transplantation and an increasing number of centers have entered the field. Selected institutions have now clearly demonstrated that insulin independence can be a reproducible and achievable goal. Other centers struggle with mixed results, while occasional early failures of islet transplants are still observed. This center effect underlines not just a learning curve, but also the complexity of the approach, which requires multidisciplinary expertise and attention to critical variables that need to be closely monitored to assure adequate clinical outcomes. The future success and large scale applicability of islet transplantation will rely on the synergistic research progress in critical areas that contribute to the sequential and integrated approach required for success in clinical islet transplantation.     

腹腔镜微囊化猪胰岛小网膜腔内异种移植的临床研究

目的 探讨腹腔镜技术应用于海藻酸钠－聚赖氨酸－海藻酸钠（APA）微囊包裹猪胰岛小网膜腔内异种移植术的可行性。方法 采用腹腔镜技术对5例6人次I型糖尿病病人进行了APA微囊新生猪胰岛小网膜腔内异种移植治疗，观察病人移植前后空腹血糖，C肽和胰岛素用量变化。结果 全部病例均未出现手术并发症。术后受体C肽较术前升高3－23倍，胰岛素用量明显减少，其中1例完全停用胰岛素，成为胰岛素不依赖者达31个月。结论 腹腔镜技术用于临床微囊化新生猪胰岛小网膜腔移植术治疗I型糖尿病安全可行，有较高的临床应用价值。     

Enhanced effect of human mesenchymal stem cells expressing human TNF‐αR‐Fc and HO‐1 gene on porcine islet xenotransplantation in humanized mice

Background

Porcine islet xenotransplantation is considered an attractive alternative treatment for type 1 diabetes mellitus. However, it is largely limited because of initial rejection due to Instant Blood‐Mediated Inflammatory Reaction (IBMIR), oxidative stress, and inflammatory responses. Recently, soluble tumor necrosis factor‐ɑ receptor type I (sTNF‐αR) and heme oxygenase (HO)‐1 genes (HO‐1/sTNF‐αR) have been shown to improve the viability and functionality of porcine islets after transplantation.

Methods

In this study, genetically modified mesenchymal stem cells (MSCs) expressing the HO‐1/sTNF‐αR genes (HO‐1/sTNF‐αR‐MSC) were developed using an adenoviral system, and porcine islet viability and function were confirmed by in vitro tests such as GSIS, AO/PI, and the ADP/ATP ratio after coculturing with HO‐1/sTNF‐αR‐MSCs. Subsequently, isolated porcine islets were transplanted underneath the kidney capsule of diabetic humanized mice without MSCs, with MSCs or with HO‐1/sTNF‐αR‐MSCs.

Results

According to the results, the HO‐1/sTNF‐αR‐MSC‐treated group exhibited improved survival of porcine islets and could reverse hyperglycemia more than porcine islets not treated with MSCs or islets cotransplanted with MSCs. Moreover, the HO‐1/sTNF‐αR‐MSC group maintained its morphological characteristics and the insulin secretion pattern of transplanted porcine islets similar to endogenous islets in immunocompetent humanized mice.

Conclusions

Our results suggest that HO‐1/sTNF‐αR‐MSCs are efficient tools for porcine islet xenotransplantation, and this study may provide basic information for pre‐clinical animal models and future clinical trials of porcine islet xenotransplantation.     

Update regarding xenotransplantation in Japan

To overcome the donor shortage, a promising solution could be xenotransplantation. The pig is generally considered the most suitable donor species for xenotransplantation. A clinical xenotransplantation has not been conducted in Japan. However, many progresses have recently been made in this field. Japan has regulations for conducting cell xenotransplantation and guidelines to prevent zoonosis. Most Japanese patients and their family members have a positive opinion about islet xenotransplantation. A grant for clinical islet xenotransplantation research and development has been approved, and germ‐free pigs have been developed. Further research may bring the successful application of xenotransplantation closer to reality.     

The immunobiology of pig‐to‐nonhuman primate islet xenotransplantation: insights,innovation, and impact

Previous studies of pig‐to‐non‐human primate (NHP) islet xenotransplantation have provided important insights into the immune recognition and effector pathways operative in this relevant preclinical model. The specifics of the xenograft product, microenvironment at the implantation site, and the immunosuppressive regimen significantly influence the mechanisms underlying the rejection of xenogeneic islets. Our current understanding of the immunological barriers to survival of pig islets in NHPs is largely based on studies on intraportal islet xenografts and on comparisons with islet allografts. The demonstration of cell‐mediated rejection of intraportal porcine islet xenografts at about 1 month posttransplant in monkeys immunosuppressed with the same protocols that prevent monkey islet allograft rejection indicates that islet xenograft rejection involves cellular mechanisms that are not present in acute islet allograft rejection. While these mechanisms remain poorly defined the demonstration of long‐term diabetes reversal after intraportal islet xenotransplantation in non‐human primates immunosuppressed with anti‐CD40L but not with anti‐CD40 antibody‐based protocols suggests that the therapeutic efficacy of anti‐CD40L in this transplantation setting likely involves the depletion of donor‐reactive, activated T cells besides CD40:CD40L costimulation blockade. Rejection of intraportal islet xenografts in NHPs immunosuppressed with CTLA4‐Ig and rapamycin was mediated largely by IL‐15‐primed, CXCR3+CD8+ memory T cells recruited by IP‐10 (CXCL10) positive pig islets and macrophages that showed staining for IL‐12 and iNOS. Adding basiliximab induction and tacrolimus maintenance therapy to this protocol prevented rejection in 24 of 26 recipients followed for up to 275 days. Comparison of both groups suggests, though by no means conclusive, that prolongation of graft survival in this large cohort was associated with reduced direct T cell responses to xenoantigens, reduced proportion of intrahepatic (intragraft) B cells and IFN‐γ+ and IL‐17+ CD4 and CD8 T cells, and increased local production of immunoregulatory molecules linked with Tregs, including TGF‐β, Foxp3, HO‐1, and IL‐10. Anti‐pig non‐Gal IgG antibody elicitation was suppressed in both groups. We are currently exploring the concept of negative vaccination to markedly minimize the need for immunosuppression in islet xenotransplantation. Peritransplant administration of donor apoptotic cells extended pig‐to‐mouse islet xenograft survival to >250 days when combined with peritransplant B cell‐depletion and rapamycin. This costimulation blockade‐sparing, antigen‐specific immunotherapy is expected to cause rapid pretransplant clonal deletion of indirect and anergy of direct xenospecific T cells while inducing regulatory T cells. As anti‐CD40L antibodies, B cell depleting antibodies are expected to interfere with indirect antigen presentation, costimulation, and cytokine production required for optimal T cell proliferation, memory formation, and intragraft CD8+ effector function. It is conceivable that additional strategies must be employed in NHPs and eventually in diabetic patients to achieve – as previously with anti‐CD40L antibodies – more complete, yet selective depletion of donor‐reactive, activated T‐cells for the purpose of stable xenograft acceptance.     

ABO-incompatible allotransplantation as a basis for clinical xenotransplantation

The 8th Congress of the International Xenotransplantation Association (IXA), held in Goteborg in September, 2005, immediately followed the 2nd International Symposium on ABO-Incompatibility in Transplantation, both congresses organized by Michael Breimer and Lennart Rydberg. The Proceedings of the Symposium on ABO-Incompatibility in Transplantation have been published (Xenotransplantation 2006; 13 (2)). The present paper provides an overview of a workshop held at the 8th Congress of the IXA, and highlights the immunological concepts emerging from ABO-incompatible allotransplants and discusses them in relation to xenotransplantation. Using specified immunomodulatory protocols, ABO-incompatible solid organ allotransplantation has become a clinical reality for a small number of patients over the last two decades. ABO-incompatible adult kidney and infant heart transplants have similar patient and graft survivals as their ABO-compatible counterparts. In contrast, ABO-incompatibility is present in up to 30% of all patients receiving hematopoietic stem cell transplants in the absence of specific immunomodulation, without affecting overall survival. Consequently, ABO-incompatible solid organ transplants and hematopoietic stem cell transplants may serve as in vivo models to elucidate the immunological mechanisms of accommodation and/or tolerance in the clinical setting. Because of similarities in the immunological hurdles that need to be overcome, knowledge obtained from ABO-incompatible allotransplantation might further promote advances in the field of xenotransplantation. The similarities and differences between ABO-incompatible allotransplantation and xenotransplantation are discussed.     

The potential of local immunomodulation and tolerance induction in porcine islet xenotransplantation

Transplantation of pancreas or isolated islet cells is currently the only option to cure type 1 diabetes. The success of islet transplantation is still limited by the requirement of large numbers of high quality islets and the shortage of organ donors. Porcine islets are a promising cell source, but the intensive immunosuppressive regimen required to suppress rejection prevents the translation into clinical practice. We aimed to develop a novel method to inhibit the human‐anti‐pig immune reaction by the expression of immunomodulatory molecules in porcine beta cells. Thus, a transgenic pig was generated expressing LEA29Y – a second generation human CTLA4‐Ig fusion protein, which inhibits activation of T cells by CD80/CD86‐CD28 costimulation – under the control of the porcine insulin promotor. Islet‐like clusters (ICC) from neonatal pigs were isolated and transplanted under the kidney capsule of diabetic NOD‐scid‐IL2γnull (NSG) mice. After an in vivo maturation period mice transplanted with wildtype (wt) as well as with LEA29Y transgenic (tg) ICCs developed normal glucose homeostasis. Within 30 days after the transfer of human PBMCs 80% of NSG mice transplanted with wt‐ICCs developed diabetes indicating xenograft rejection. By contrast, LEA‐tg ICCs were completely protected from rejection in all animals (1). Immunohistochemistry revealed a massive intra‐islet T cell infiltration, which was absent in the LEA‐tg ICCs. This proof of principle study suggests that specific expression of immunomodulatory molecules in beta cells does not disturb beta cell function and may have the potential to modulate immune response locally at the transplantation site without systemic immunosuppression. To overcome the strong xenogeneic barrier of the human and cellular immune system a combination of LEA29Y with additional immunomodulatory factors may be required. Recently, Yi and coworkers demonstrated that the treatment with in vitro expanded regulatory T cells (Treg) prevents porcine islet rejection in humanized NSG mice by the suppression of the T cell‐mediated graft destruction (2). Other potential candidates to induce a state of tolerance against porcine islets currently under investigation are molecules targeting innate immunity and factors that prevent the reoccurrence of autoimmunity. Recent advances in xenotransplantation suggest that it may be possible to start with clinical trials using porcine neonatal or adult islets within the near future. References: 1. KLYMIUK N, VAN BÜRCK L, BÄHR Aet al. Xenografted islet‐cell‐clusters from INSLEA29Y transgenic pigs rescue diabetes and prevent immune rejection in humanized mice. Diabetes 2012; 61:1527–1532. 2. YI S, JI M, WU J et al. Adoptive transfer with in vitro expanded human regulatory T cells protects against porcine islet xenograft rejection via interleukin‐10 in humanized mice. Diabetes 2012; 61:1180–1191.     

Influence of strain and age differences on the yields of porcine islet isolation: extremely high islet yields from SPF CMS miniature pigs

BACKGROUND: Porcine pancreas is a potential source of material for islet xenotransplantation. However, the difficulty in isolating islets, because of their fragility and the variability of isolation outcome in donor age and breed, represents a major obstacle to porcine islet xenotransplantation. In this study, we compared the islet isolation yield of specific pathogen-free (SPF) Chicago Medical School (CMS) miniature pigs with that of another miniature pig breed and market pigs from a local slaughterhouse. METHODS: Nine adult CMS miniature (ACM) pigs (>12 months), six young CMS miniature (YCM) pigs (6-7 months), four adult Prestige World Genetics (PWG) miniature (APM) pigs (>12 months), and 13 adult market (AM) pigs from a local slaughterhouse were used for islet isolation. RESULTS: The islet yield per gram of pancreas from ACM pigs (9589 +/- 2823 IEQ/g) was significantly higher than that from APM pigs (1752 +/- 874 IEQ/g, P < 0.05), AM pigs (1931 +/- 947 IEQ/g, P < 0.05), or YCM pigs (3460 +/- 1985 IEQ/g, P < 0.05). Isolated islets from ACM pigs were significantly larger than those from AM pigs or YCM pigs. The in vitro and in vivo function of isolated islets showed no difference among experimental groups. The pancreases of ACM pigs contained higher mean islet volume density percentages and larger size of islets than those of AM or APM pigs. CONCLUSIONS: We isolated extremely high yields of well-functioning islets from ACM pigs bred under SPF conditions. SPF CMS miniature pigs should be one of the best porcine islet donors for clinical porcine islet xenotransplantation.