Islet Cell Xenotransplantation Research Articles

Ethical and legislative advances in xenotransplantation for clinical translation: focusing on cardiac, kidney and islet cell xenotransplantation.

In this state-of-the-art review we detail the journey of xenotransplantation from its infancy, detailing one of the first published cases and the subsequent journey the field took in its inception and development. With a focus on the science, technological advances, precautions required along with the potential limitations in application, the ethics, guidance's, and legislative advances that are required to reach the safe and efficacious clinical application of xenotransplantation. Along with a view over the past several decades with the overall significant advancements in pre-clinical study outcomes particularly in islet, kidney, and heart xenotransplantation, to ultimately reach the pinnacle of successful clinical heart and kidney xenotransplants. It outlines the importance for the appropriate guidance's required to have been developed by experts, scientists, clinicians, and other players who helped develop the field over the past decades. It also touches upon patient advocacy along with perspectives and expectations of patients, along with public opinion and media influence on the understanding and perception of xenotransplantation. It discusses the legislative environment in different jurisdictions which are reviewed in line with current clinical practices. All of which are ultimately based upon the guidance's developed from a strong long-term collaboration between the International Xenotransplantation Association, the World Health Organisation and The Transplantation Society; each having constantly undertaken consultation and outreach to help develop best practice for clinical xenotransplantation application. These clearly helped forge the legislative frameworks required along with harmonization and standardization of regulations which are detailed here. Also, in relation to the significant advances in the context of initial xeno-kidney trials and the even greater potential for clinical xeno-islet trials to commence we discuss the significant advantages of xenotransplantation and the ultimate benefit to our patients.

What does it take to consent to islet cell xenotransplantation?: Insights from an interview study with type 1 diabetes patients and review of the literature

BackgroundThe transplantation of porcine islet cells provides a new potential therapy to treat patients with type 1 diabetes mellitus (T1DM). Compared to other biomedical technologies, xenotransplantation stands out in terms of its involvement of animals as graft sources, as well as the possible transmission of infectious diseases. As these aspects are especially relevant for potential xenotransplantation recipients, it is important to assess their opinion regarding this technology, in particular in terms of the requirements that should be met in the informed consent process for xenotransplantation.MethodsWe conducted qualitative interviews with seven T1DM patients to assess their information needs prior to xenotransplantation. Before the interview, the participants received a model informed consent form for a clinical trial with porcine islet cells transplantation. The interviews were transcribed and analysed using qualitative content analysis.ResultsIn the interviews, we identified several requirements that are crucial for patients with T1DM in order to consider xenotransplantation as a potential treatment option: therapy-related requirements, professional care and supervision, successful behaviour and attitude management, improving quality of life, and managing control/self-determination challenges. Regarding the informed consent form, several of the participants’ questions remained open and should be addressed in more detail. The interviewees stressed the importance of personal consultations.ConclusionsTo become a sustainable therapeutic option, patients especially expected an improved diabetes control and a reduction of diabetes-related burdens. Health-related aspects prove to be pivotal for diabetic patients when considering porcine islet cell transplantation. The use of pigs as source for organ retrievals was not considered as problematic.

Xenotransplantation of islet cells: what can the non-human primate model bring for the evaluation of efficacy and safety?

Xenotransplantation of islet cells: what can the non-human primate model bring for the evaluation of efficacy and safety?

Islet cell xenotransplantation: a serious look toward the clinic.

Type I diabetes remains a significant clinical problem in need of a reliable, generally applicable solution. Both whole organ pancreas and islet allotransplantation have been shown to grant patients insulin independence, but organ availability has restricted these procedures to an exceptionally small subset of the diabetic population. Porcine islet xenotransplantation has been pursued as a potential means of overcoming the limits of allotransplantation, and several preclinical studies have achieved near-physiologic function and year-long survival in clinically relevant pig-to-primate model systems. These proof-of-concept studies have suggested that xenogeneic islets may be poised for use in clinical trials. In this review, we examine recent progress in islet xenotransplantation, with a critical eye toward the gaps between the current state of the art and the state required for appropriate clinical investigation.

A Novel Device for Islet Transplantation Providing Immune Protection and Oxygen Supply

Islet transplantation as a biological β-cell replacement therapy has emerged as a promising option for achieving restoration of metabolic control in type 1 diabetes patients. However, partial or complete loss of islet graft function occurs in relatively short time (months to few years) after implantation. The high rate of early transplant dysfunction has been attributed to poorly viable and/or functional islets and is mediated by innate inflammatory response at the intravascular (hepatic) transplant site and critical lack of initial nutrient/oxygen supply prior to islet engraftment. In addition, the diabetogenic effect of mandatory immunosuppressive agents, limited control of alloimmunity, and the recurrence of autoimmunity limit the long-term success of islet transplantation. In order to abrogate instant blood-mediated inflammatory reaction and to provide oxygen supply for the islet graft, we have developed an extravascular (subcutaneous) transplant macrochamber (the 'βAir' device). This device contains islets immobilized in alginate, protected from the immune system by a thin hydrophilized teflon membrane impregnated with alginate and supplied with oxygen by daily refueling with oxygen-CO (2) mixture. We have demonstrated successful utilization of the oxygen-refueling macrochamber for sustained islet viability and function as well as immunoprotection after allogeneic subcutaneous transplantation in healthy minipigs. Considering the current limitations of intraportal islet engraftment and the restricted indication for islet transplantation mainly due to necessary immunosuppressive therapy, this work could very likely lead to remarkable improvements in the procedure and moreover opens up further strategies for porcine islet cell xenotransplantation.

A health-economic analysis of porcine islet xenotransplantation

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. 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. 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. 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.

Cell therapeutic strategies to improve pig islet graft survival after xenotransplantation

Transplantation of the whole pancreas organ or isolated Langerhans‐islets is the only methods to cure Type 1 diabetes. Transplantation is largely limited by the lack of organ donors and considerable side effects of immunosuppressive therapies. Porcine pancreas represents a promising cell source to overcome the shortage of islets. Due to the strong rejection of xenoantigens novel strategies such as the generation of transgenic pig islets are needed. Another complementary alternative is the co‐transplantation with immunomodulatory cells that mediate only local immunosuppression at the transplantation site.Mesenchymal stem cells (MSCs) are unique cells residing in different tissues which possess pleiotropic immunoregulatory activities. We isolated murine and human MSCs from bone‐marrow (CD73+, CD105+) and used them for in vitro experiments (mixed lymphocyte reaction after mitogen, allogenic and xenogenic stimulation) and co‐transplantation studies in diabetic C57BL/6 mice.Both murine and human MSCs exert strong immunosuppressive effects on lymphocyte proliferation (up to 75% and 80% respectively). Interestingly, there were major differences in the underlying mechanisms. We were able to demonstrate for the first time that mouse MSCs suppressed MLR by a combination of prostaglandin E2 production and adenosine formation. Only human but not mouse MSCs do express the tryptophan degrading enzyme indoleamine 2,3‐dioxygenase (IDO) upon stimulation with proinflammatory cytokines. Our features such as TGFβ and hepatocyte growth factor (HGF) production also contribute to the immunoregulatory effect. When human lymphocytes were challenges with porcine antigens there was a strong proliferative immune response which can be suppressed in a dose‐dependent manner by the addition of hMSCs (inhibition up to 95%). Co‐transplantation of allogenic islets with MSCs favoured islet cell function and survival. This effect was dependent on the MSC source as demonstrated by the fact that the use of donor MSCs resulted in longer survival rate as compared to syngenic MSCs. In current experiments we test the effect of hMSCs in the NOD SCID‐IL2R–/–mouse model to study immune response of human PBMCs towards porcine islets.In conclusion, our results strongly support and extend the concept that MSCs are potent candidates to control cellular immune rejection. We observed surprising differences in the immunosuppressive properties between mouse and human MSCs. Since human MSCs also strongly suppress immune response against pig antigens, they are promising novel candidates to modulate the local microenviroment for islet cell xenotransplantation. The next step is to analyse survival of transgenic pig islets (CTLA‐4 Ig) with and without hMSC in diabetic NOD SCID‐IL2R–/–mice.Supported by the Deutsche Forschungsgemeinschaft (Transregio Forschergruppe ‘‘Xenotransplantation’’, FOR 535).

In vivo Neutralization of Naturally Existing Antibodies against Linear ?(1,3)-Galactosidic Carbohydrate Epitopes by Multivalent Antigen Presentation: A Solution for the First Hurdle of Pig-to-Human Xenotransplantation

Pig-to-human xenotransplantation of islet cells or of vascularized organs would offer a welcome treatment alternative for the ever-increasing number of patients with end-stage organ failure who are waiting for a suitable allograph. The main hurdle are preexisting antibodies, most of which are specific for 'Linear-B', carbohydrate epitopes terminated by the unbranched Gal-alpha(1,3)Gal disaccharide. These antibodies are responsible for the 'hyper-acute rejection' of the xenograft by complement mediated hemorrhage. For depletion of such antibodies we have developed an artificial injectable antigen, a glycopolymer (GAS914) with a charge neutral poly-lysine backbone (degree of polymerization n = 1000) and 25% of its side chains coupled to Linear-B-trisaccharide. With an average molecular weight of 400 to 500 kD, presenting 250 trisaccharide epitopes per molecule, this multivalent array binds anti-alphaGal antibodies with at least three orders of magnitude higher avidity on a per-saccharide basis than the monomeric epitope. In vivo experiments with non-human primates documented that rather low doses--1 to 5 mg/kg of GAS914 injected i.v.--efficiently reduce the load of anti-Linear-B antibodies quickly by at least 80%. This treatment can be repeated without any sensitization to GAS914. Interestingly, although the antibody levels start raising 12 h after injection, they do not reach pretreatment levels. The polymer is degraded and excreted within hours, with a minute fraction remaining in lymphoid tissue of anti-alphaGal producing animals only, probably binding to and inhibiting antibody-producing B-cells. The results of pig-to-non-human primate xenotransplantations established GAS914 as a relevant therapeutic option for pig-to-human transplantations as well. The synthesis of GAS914 was successfully scaled up to kg amounts needed for first clinical studies. Key was the use of galactosyl transferases and UDP-galactose for the synthesis of the trisaccharide.

PVA hydrogel sheet macroencapsulation for the bioartificial pancreas

We newly developed a sheet-type macroencapsulation device entrapping rat islets from 3% polyvinyl alcohol (PVA) dissolved in Euro-Collins solution containing 10% fetal bovine serum and 5% dimethyl sulfoxide (PVA+EC) using a freezing/thawing technique. The same encapsulation technique but with 3% PVA dissolved only in double-distilled water (PVA) and a culture of free islets were served as controls. After 14-day culture in the CMRL-1066 medium, the islet recovery rate, morphological changes, insulin content, and insulin secretion were evaluated in vitro to prove the feasibility of this method of encapsulation. We also xenotransplanted the device into the peritoneal cavity of diabetic C57BL/6 mice to check its function in vivo. After 1-day culture, the islet recovery rate and insulin content in the PVA group were significantly lower than that in the PVA+EC and free islet groups. After 14-day culture, only the islets in the PVA+EC group maintained a normal morphology and effective insulin secretory response to high glucose while the response was not observed in the PVA group after 1-day culture and no longer observed in the free islets after 7-day culture. After transplantation of rat islets encapsulated in the PVA+EC device to diabetic C57BL/6 mice, nonfasting blood glucose levels showed a rapid decrease from high glucose levels of pre-transplantation, maintaining significantly lower glucose levels during the whole course of study in comparison with the sham-operated group. Our results indicated that this freezing/thawing macroencapsulation technique using 3% PVA+EC was effective for xenotransplantation of islet cells.

Islet transplantation in the discordant tilapia-to-mouse model: a novel application of alginate microencapsulation in the study of xenograft rejection.

Tilapia islet xenograft rejection is characterized by infiltration with macrophages (Mphis), eosinophils (Ephis), and T lymphocytes. The presence of these cells indicates they contribute to rejection; therefore, an attempt was made to assess their role through host immunomodulation. Tilapia islet cells were transplanted under the kidney capsule of streptozotocin diabetic Balb/c mice, which were then treated with one of several immunomodulatory regimes targeting Mphis, Ephis, or T cells. Mphis were depleted using either silica or liposome-entrapped Cl2MDP. Ephi migration was blocked using monoclonal antibodies (mAbs) targeting interleukin (IL)-4 or IL-5. T-cell function was altered with mAbs targeting CD3, CD4, or CD8. Finally, T helper (Th)1 and Th2 activity was altered by depleting essential Th1 or Th2 cytokines with mAbs or by promoting a Th1 response with the injection of exogenous IL-12. The effects of antibody-mediated immunomodulation on graft survival were initially screened by cotransplanting alginate-encapsulated, mAb-secreting hybridoma cells into the peritoneal cavity at the time of islet transplantation. Significant prolongation was then confirmed using purified antibodies injected at the time of islet transplantation. Rejected grafts were examined histologically, and immunohistochemistry was used to assess the cellular infiltrates for each of the treatment groups. Modulation of Mphis and Ephis alone did not significantly delay functional rejection of tilapia islet grafts (maximal mean graft survival time [mGST]=7.1+/-1.7 and 9.4+/-3.4, respectively) compared with untreated controls (mGST=8.2+/-1.0). Treatment of transplanted animals with antibodies against CD3 or CD4 significantly promoted graft survival (maximal mGST=16.3+/-5.8 and 34.0+/-11.6, respectively), whereas targeting CD8 and Th1 and Th2 cytokines showed no prolonging effect (maximal mGST=7.8+/-2.9 and 9.5+/-4.3, respectively). Our results indicate that rejection in the tilapia-to-mouse model follows a pattern similar to other models of discordant islet cell xenotransplantation.

Prevention of Morphological Changes in Alginate Microcapsules for Islet Xenotransplantation

BackgroundAlginate microcapsule swelling, which occurs as a result of increased hydrophilicity owing to the Ca++ that remains after rapid chelation of the inner alginate core, is a problem in encapsulation....

Starting clinical trials of xenotransplantation—reflections on the ethics of the early phase

What kind of patients may be recruited to early clinical trials of xenotransplantation? This is discussed under the assumption that the risk of viral infection to the public is non-negligible....

Humoral Xenoreactivity in Pig-to-Human Islet Cell Xenotransplantation

Humoral Xenoreactivity in Pig-to-Human Islet Cell Xenotransplantation

RETRIEVABLE, REPLACEABLE, MACROENCAPSULATED PANCREATIC ISLET XENOGRAFTS LONG-TERM ENGRAFTMENT WITHOUT IMMUNOSUPPRESSION

Prevention of rejection and prolongation of graft survival are critical to achieving successful islet cell transplantation. Various techniques have been utilized to prolong graft survival. Recently, protection of pancreatic islets from host immune mechanisms by isolating the islets in artificial membranes has emerged as an attractive alternative to the use of immunosuppression. In this Rapid Communication, we describe a novel method for macroencapsulation of rat islets in hydrophilic macrobeads made with various combinations of agarose, collagen, and Gelfoam. Encapsulated xenotypic islets were placed intraperitoneally in mice in which diabetes was induced by streptozotocin. The encapsulated xenografts maintained normoglycemia > 170 days. Recipients mice had normal glucose tolerance tests, which indicates that the islets in the macrobeads were functioning as they would in an intact pancreas. Macrobeads retrieved up to 103 days after transplantation showed no evidence of tissue reaction or local inflammation. These retrieved macrobeads could also be retransplanted and replaced. Our studies indicate that the agarose-collagen/Gelfoam macrobeads we have developed serve both to protect islet xenografts from rejection and to provide a microenvironment in which the islets maintain and support their normal function in vivo. Because they may be retrieved after implantation and replaced, these macrobeads may be suitable for human clinical islet cell xenotransplantation.

Immunological Characteristics of Islet Cell Xenotransplantation in Humans and Rodents

Immunological Characteristics of Islet Cell Xenotransplantation in Humans and Rodents