Trials Of Xenotransplantation Research Articles

Preclinical rationale and current pathways to support the first human clinical trials in cardiac xenotransplantation

Recent initiation of the first FDA-approved cardiac xenotransplantation suggests xenotransplantation could soon become a therapeutic option for patients unable to undergo allotransplantation. Until xenotransplantation is widely applied in clinical practice, consideration of benefit versus risk and approaches to management of clinical xenografts will based at least in part on observations made in experimental xenotransplantation in non-human primates. Indeed, the decision to proceed with clinical trials reflects significant progress in last few years in experimental solid organ and cellular xenotransplantation. Our laboratory at the NIH and now at University of Maryland contributed to this progress, with heterotopic cardiac xenografts surviving more than two years and life-supporting cardiac xenografts survival up to 9 months. Here we describe our contributions to the understanding of the mechanism of cardiac xenograft rejection and development of methods to overcome past hurdles, and finally we share our opinion on the remaining barriers to clinical translation. We also discuss how the first in human xenotransplants might be performed, recipients managed, and graft function monitored.

The respective relevance of sensitization to alloantigens and xenoantigens in pig organ xenotransplantation

BackgroundAntibody-mediated rejection is a major cause of graft injury and contributes to failure of pig xenografts in nonhuman primates (NHPs). Most ‘natural’ or elicited antibodies found in humans and NHPs are directed against pig glycan antigens, but antibodies binding to swine leukocyte antigens (SLA) have also been detected. Of clinical importance is (i) whether the presence of high levels of antibodies directed towards human leukocyte antigens (HLA) (i.e., high panel-reactive antibodies) would be detrimental to the outcome of a pig organ xenograft; and (ii) whether, in the event of sensitization to pig antigens, a subsequent allotransplant would be at increased risk of graft failure due to elicited anti-pig antibodies that cross-react with human HLA or other antigens. SummaryA literature review of pig-to-primate studies indicates that relatively few highly-HLA-sensitized humans have antibodies that cross-react with pigs, predicting that most would not be at increased risk of rejecting an organ xenograft. Furthermore, the existing evidence indicates that sensitization to pig antigens will probably not elicit increased alloantibody titers; if so, ‘bridging’ with a pig organ could be carried out without increased risk of subsequent antibody-mediated allograft failure. Key MessageThese issues have important implications for the design and conduct of clinical xenotransplantation trials.

Are we ready for pig-to-human clinical xenotransplantation trials?

The invention and widely use of organ allotransplantation provides effective treatment of some originally fetal diseases such as liver/kidney failure and has saved million of lives around the globe. However, the scarcity of human organs has caused many patients, who could have been treated, to die while waiting for suitable organs around the world. Pig-to human xenotransplantation provides a potential solution to solve this tough problem. Pig organs have been considered as major sources of xenotransplantation because of the sufficient number of donors, the sizes of organs, and physiologically structural similarities. However, xenotransplantation also has some problems, such as the possibility of spreading animal diseases to human, the interspecies immunological barrier, organs of animal origin challenging human nature, and potential informed consent issues. This article will discuss these potential issues and to see whether it is the suitable time to conduct clinical xenotransplantation trials in humans.

Informed Consent for Potential Recipients of Pig Kidney Xenotransplantation in the United States.

Clinical trials of kidney xenotransplantation are being considered in the United States. Before this novel procedure can take place, investigators will have to obtain approval from the institutional review board. The consent form that will be used for such a trial and that will receive approval from the institutional review board will be complex. Informed consent-the process by which a research participant provides his/her permission to participate in a clinical trial-is a staple of the research process and most commonly is in the form of a physical document. In the case of a novel procedure with uncertain benefits and risks and a participant population in acute need of a transplant, the consent process is crucial. These complexities may raise several ethical considerations for the initial pig kidney xenotransplantation recipients in the United States that will require adaptations of the required elements of the informed consent process by the US Department of Human and Health Services. The ethical issues include (1) a subject's ability to withdraw from the trial, (2) restrictions on their reproductive rights, and (3) the possibility of the need for quarantine if there is a perceived risk of xenozoonosis. This article aims to discuss ethical considerations that may challenge the general required elements of the informed consent form stipulated by the 45 Code of Federal Regulations 46 of the US Department of Health and Human Services and to suggest recommendations for deliberation.

First clinical-grade porcine kidney xenotransplant using a human decedent model

A radical solution is needed for the organ supply crisis, and the domestic pig is a promising organ source. In preparation for a clinical trial of xenotransplantation, we developed an in vivo pre-clinical human model to test safety and feasibility tenets established in animal models. After performance of a novel, prospective compatible crossmatch, we performed bilateral native nephrectomies in a human brain-dead decedent and subsequently transplanted two kidneys from a pig genetically engineered for human xenotransplantation. The decedent was hemodynamically stable through reperfusion, and vascular integrity was maintained despite the exposure of the xenografts to human blood pressure. No hyperacute rejection was observed, and the kidneys remained viable until termination 74h later. No chimerism or transmission of porcine retroviruses was detected. Longitudinal biopsies revealed thrombotic microangiopathy that did not progress in severity, without evidence of cellular rejection or deposition of antibody or complement proteins. Although the xenografts produced variable amounts of urine, creatinine clearance did not recover. Whether renal recovery was impacted by the milieu of brain death and/or microvascular injury remains unknown. In summary, our study suggests that major barriers to human xenotransplantation have been surmounted and identifies where new knowledge is needed to optimize xenotransplantation outcomes in humans.

The potential of genetically engineered pig heart transplantation in infants with complex congenital heart disease.

Despite advances in surgical and medical techniques, complex congenital heart disease in neonates and infants continues to be associated with significant mortality and morbidity. More than 500 infants in the USA are placed on the cardiac transplantation wait-list annually. However, there remains a critical shortage of deceased human donor organs for transplantation with a median wait-time of 4months. Hence, infant mortality on the heart transplant wait-list in the USA is higher than for any other solid organ transplant group. Orthotopic transplantation of a pig heart as a bridge to allotransplantation might offer the best prospect of long-term survival of these patients. In recent years, there have been several advances in genetic engineering of pigs to mitigate the vigorous antibody-mediated rejection of a pig heart transplanted into a nonhuman primate. In this review, we briefly highlight (i) the history of clinical heart xenotransplantation, (ii) current advances and techniques of genetically engineering pigs, (iii) the current status of pig orthotopic cardiac graft survival in nonhuman primates, and (iv) progress toward pursuing clinical trials of cardiac xenotransplantation. Ultimately, we argue that pig heart xenotransplantation should initially be used as a bridge to cardiac allotransplantation in neonates and infants.

Scientific and psychosocial ethical considerations for initial clinical trials of kidney xenotransplantation.

The initial clinical trials of pig solid organ xenotransplantation (XTx) are drawing closer and could begin in the coming years. The first clinical trials may aim to transplant genetically-modified pig kidneys into adult humans. The impetus for beginning these first-in-human trials is the severe lack of deceased donor kidneys for transplantation and the number of patients with end-stage renal disease currently on transplant waitlists, which in the USA approaches 100000. The majority of patients on the kidney transplant waitlist receive continuous renal replacement therapy. In the United States, for patients on the kidney waitlist, the median wait-time to receive a deceased human donor organ is approximately 4.5 years for patients aged 45-74, with a 5-year mortality (or removal from the waitlist because of deteriorating health) of approximately 40%. XTx has the potential to reduce the kidney waitlist morbidity and mortality while improving quality of life. By focusing on scientific and psychosocial criteria, we present ethical considerations of certain inclusion and exclusion criteria for these first-in-human clinical trials that we suggest have not yet been fully explored.

Organ transplants of the future: planning for innovations including xenotransplantation.

The future clinical application of animal-to-human transplantation (xenotransplantation) is of importance to society as a whole. Favourable preclinical data relevant to cell, tissue and solid organ xenotransplants have been obtained from many animal models utilizing genetic engineering and protocols of pathogen-free husbandry. Findings have reached a tipping point, and xenotransplantation of solid organs is approaching clinical evaluation, the process of which now requires close deliberation. Such discussions include considering when there is sufficient evidence from preclinical animal studies to start first-in-human xenotransplantation trials. The present article is based on evidence and opinions formulated by members of the European Society for Organ Transplantation who are involved in the Transplantation Learning Journey project. The article includes a brief overview of preclinical concepts and biology of solid organ xenotransplantation, discusses the selection of candidates for first-in-human studies and considers requirements for study design and conduct. In addition, the paper emphasizes the need for a regulatory framework for xenotransplantation of solid organs and the essential requirement for input from public and patient stakeholders.

Suggested Patient Selection Criteria for Initial Clinical Trials of Pig Kidney Xenotransplantation in the United States.

Suggested Patient Selection Criteria for Initial Clinical Trials of Pig Kidney Xenotransplantation in the United States.

Genetic engineering of porcine endothelial cell lines for evaluation of human-to-pig xenoreactive immune responses

Xenotransplantation (cross-species transplantation) using genetically-engineered pig organs offers a potential solution to address persistent organ shortage. Current evaluation of porcine genetic modifications is to monitor the nonhuman primate immune response and survival after pig organ xenotransplantation. This measure is an essential step before clinical xenotransplantation trials, but it is time-consuming, costly, and inefficient with many variables. We developed an efficient approach to quickly examine human-to-pig xeno-immune responses in vitro. A porcine endothelial cell was characterized and immortalized for genetic modification. Five genes including GGTA1, CMAH, β4galNT2, SLA-I α chain, and β2-microglobulin that are responsible for the production of major xenoantigens (αGal, Neu5Gc, Sda, and SLA-I) were sequentially disrupted in immortalized porcine endothelial cells using CRISPR/Cas9 technology. The elimination of αGal, Neu5Gc, Sda, and SLA-I dramatically reduced the antigenicity of the porcine cells, though the cells still retained their ability to provoke human natural killer cell activation. In summary, evaluation of human immune responses to genetically modified porcine cells in vitro provides an efficient method to identify ideal combinations of genetic modifications for improving pig-to-human compatibility, which should accelerate the application of xenotransplantation to humans.

Clinical trials in cardiac xenotransplantation: Are we ready to overcome barriers?

Heart allotransplantation has become one of the methods of choice in the treatment of severe heart failure. In the face of its difficulties, such as the unmet balance between organ supply and demand, the use of xenotransplantation (XTx) might be an attractive option shortly, even more with the ongoing progress achieved regarding the avoidance of hyperacute rejection and primary organ disfunction, maintenance of xenograft function and control of xenograft growth. To make possible this translational challenge, some points must be taken into account indeed, and they are the equipoise of human benefit and animal suffering, the risk of unknown infections, a well prepared informed consent, ethical and religious beliefs, and the role of cardiac XTx in a ventricular assistance device era.

The Use of Zebrafish Xenotransplant Assays to Analyze the Role of lncRNAs in Breast Cancer.

Breast cancer represents a great challenge since it is the first cause of death by cancer in women worldwide. LncRNAs are a newly described class of non-coding RNAs that participate in cancer progression. Their use as cancer markers and possible therapeutic targets has recently gained strength. Animal xenotransplants allows for in vivo monitoring of disease development, molecular elucidation of pathogenesis and the design of new therapeutic strategies. Nevertheless, the cost and complexities of mice husbandry makes medium to high throughput assays difficult. Zebrafishes (Danio rerio) represent a novel model for these assays, given the ease with which xenotransplantation trials can be performed and the economic and experimental advantages it offers. In this review we propose the use of xenotransplants in zebrafish to study the role of breast cancer lncRNAs using low to medium high throughput assays.

Factors influencing attitudes toward xenotransplantation clinical trials: A report of focus group studies

Clinical trials of xenotransplantation (XTx, ie, cross-species transplantation, specifically the transplantation of genetically engineered pig organs into human recipients) are due to start within a few years. Five focus groups were conducted in April-May 2019, among local religious leaders (N=10), organ procurement staff/administrators (N=5), patients and parents of patients who may need an organ transplant or are transplant recipients (N=9), and local businesspersons in the community (N=3). Groups were audio-recorded, transcribed, and analyzed with NVivo software to identify themes of participants' thoughts to XTx. An overall Cohen's kappa statistic of 0.71 was established. In general, there was wide agreement among participants that XTx is an exciting and acceptable option to explore as an organ alternative. Concerns were expressed primarily regarding issues of animal ethics, stigma regarding how pigs are viewed in society, organ allocation logistics, quality of life after receiving a xenograft, and how XTx would be accepted by certain theological traditions. Overall, various stakeholders accepted XTx as a clinical option. However, there were ethical, social, and physical concerns raised. Future studies exploring the development of education strategies that may help alleviate concerns related to XTx before it becomes a clinical alternative are needed among the general public, potential XTx candidates, and their family members.

The Role of SLAs in Xenotransplantation.

Advances in genetic engineering, particularly CRISPR/Cas9, have resulted in the development of a triple glycan-knockout (TKO) pig. There is minimal human antipig antibody binding to TKO pig cells. The TKO background has decreased antibody binding to a sufficiently low level that any additional xenoantigens expressed on the cells can now be more easily detected. One of these xenoantigens is the swine major histocompatibility complex, termed swine leukocyte antigens (SLA). SLA are the homolog to HLAs, a protein complex expressed on human tissue capable of stimulating the development of new antibodies in allotransplantation. These antibodies can result in graft failure through hyperacute, acute, or chronic rejection. Our knowledge of SLA, particularly in the last 5 years, has grown considerably. The presence, cause, and methods to detect anti-SLA antibodies will need to be carefully considered for the first clinical trial of xenotransplantation. The focus of this review is to summarize the role of SLA in xenotransplantation and consider whether it will prove to be a major barrier. Techniques are now available to mutate target SLA amino acids to ensure that cross-reactive anti-HLA antibodies no longer bind to SLA on the cells of the organ-source pigs. While deletion of SLA expression is possible, it would render the pig at risk for infectious complications. The ideal organ-source pig for HLA highly sensitized recipients may therefore be 1 with site-specific mutations to eliminate cross-reactive binding.

Differences in platelet aggregometers to study platelet function and coagulation dysregulation in xenotransplantation.

Xenotransplantation (ie, cross-species transplantation) using genetically engineered pig organs could be a limitless source to solve the shortage of organs and tissues worldwide. However, despite prolonged survival in preclinical pig-to-nonhuman primate xenotransplantation trials, interspecies coagulation dysregulation remains to be overcome in order to achieve continuous long-term success. Different platelet aggregometry methods have been previously used to study the coagulation dysregulation with wild-type and genetically engineered pig cells, including the impact of possible treatment options. Among these methods, while thromboelastography and rotational thromboelastometry measure the change in viscoelasticity, optical aggregometry measures the change in opacity. Recently, impedance aggregometry has been used to measure changes in platelet aggregation in electrical conductance, providing more information to our understanding of coagulation dysregulation in xenotransplantation compared to previous methods. The present study reviews the merits and differences of the above-mentioned platelet aggregometers in xenotransplantation research.

Evidence for GTKO/β4GalNT2KO Pigs as the Preferred Organ-source for Old World Nonhuman Primates as a Preclinical Model of Xenotransplantation.

Background.Triple-knockout (TKO) pigs (in which expression of the 3 known pig carbohydrate xenoantigens has been deleted) are likely to be an optimal source of organs for transplantation into human recipients, many of whom do not have natural antibodies against TKO pig cells. However, old world monkeys, for example, baboons, have natural antibodies directed to TKO cells (to a “fourth” xenoantigen that is exposed after TKO).Methods.We measured (1) anti-pig IgM/IgG binding, and (2) complement-dependent cytotoxicity (CDC), by flow cytometry to α1,3-galactosyltransfearse gene-knockout (GTKO), GTKO/β4GalNT2KO (that do not express the “fourth” xenoantigen), and TKO pig peripheral blood mononuclear cells (PBMCs) using 72 baboon sera (30 specific pathogen-free [SPF], and 42 non-SPF baboons).Results.Mean IgM antibody binding to GTKO/β4GalNT2KO pig PBMCs was significantly lower than to GTKO or TKO pig PBMCs (P < 0.01). Mean IgG antibody binding to GTKO/β4GalNT2KO pig PBMCs was significantly lower than to TKO PBMCs (P < 0.01). Mean CDC of GTKO/β4GalNT2KO pig PBMCs was significantly lower than of GTKO or TKO pig PBMCs (P < 0.01). SPF baboon serum IgM and IgG binding to, and CDC of, GTKO/β4GalNT2KO or TKO PBMCs were significantly lower than non-SPF baboon sera (P < 0.01).Conclusions.Although TKO pigs form the basis for proposed clinical trials of xenotransplantation, it is difficult to identify baboons with a low or negative CDC to TKO pigs. For pig-to-baboon organ transplantation, the use of GTKO/β4GalNT2KO pigs would be preferable. The use of SPF baboons as recipients might be a minor advantage.

Attitudes to Clinical Pig Kidney Xenotransplantation among Medical Providers and Patients.

In addition to governmental regulation and scientific advancements, the World Health Organization requires extensive review of local opinions before initiating clinical trials of xenotransplantation (XTx). The purpose of this study was to assess the attitudes of health care providers and patients regarding XTx. An anonymous Likert-scale survey regarding attitudes toward XTx was distributed to pre- and post-kidney transplant patients, nephrologists, transplant surgeons, and nurses ("providers"). Patient and provider responses were described and compared. Regression analysis using patients' responses was performed to identify factors associated with XTx acceptance. Eighty percent (32/40) of providers and 69% (113/163) of patients were agreeable to clinical XTx if the risks and results were likely to be similar to kidney allotransplantation (P<0.05). Kidney providers rated the influence of religious beliefs in medical decisions (45% versus 15%) and genetic engineering (43% versus 25%) as being more important than did patients (P<0.05). A small proportion in both groups (<15%) reported concerns about (1) potential personality changes, (2) how others would interact, (3) a perception of being "less human," or (4) morals or ethics. Logistic regression found that the odds of patients accepting XTx were greater if they had no religious concerns (OR, 25.10; 95% CI, 2.59 to 243.00), but acceptance was less likely if they were not willing to use XTx as a bridge to allotransplantation (OR, 0.18; 95% CI, 0.51 to 0.70). (1) If outcomes were similar to allotransplantation, XTx support was strong among both providers and patients; (2) providers overestimated the influence of religious beliefs and genetic engineering on patient medical decisions, although religious beliefs are associated with XTx acceptance; (3) XTx use as a bridge to allotransplant was associated with XTx acceptance; and (4) psychosocial concerns were low for either group. Future studies among other communities are warranted to assess if similar attitudes exist.

Pig-to-human heart transplantation: Who goes first?

Cardiac xenotransplantation has recently taken an important step towards clinical reality. In anticipation of the "first-in-human" heart xenotransplantation trial, we propose a set of patient characteristics that define potential candidates. Our premise is that, to be ethically justified, the risks posed by current state-of-the-art options must outweigh the anticipated risks of a pioneering xenotransplant procedure. Suitable candidates include patients who are at high immunologic risk because of sensitization to alloantigens, including those who have exhibited early onset or accelerated cardiac allograft vasculopathy. In addition, patients should be considered (1) for whom mechanical circulatory support would be prohibitively risky due to a hypercoagulable state, a contraindication to anticoagulation, or restrictive physiology; (2) with severe biventricular dysfunction predicting unsuccessful univentricular left heart support; and (3) adults with complex congenital heart disease. In conclusion, because the published preclinical benchmark for clinical translation of heart xenotransplantation appears within reach, carefully and deliberately defining appropriate trial participants is timely as the basis for ethical clinical trial design.

Clinical trials of xenotransplantation: The need for a worldwide registry.

Clinical trials of xenotransplantation: The need for a worldwide registry.

Challenges and practical realities of long-term patient follow-up in three xeno-islet clinical trials: The experience in pig islet xenotransplantation trials in New Zealand and Argentina.

XenotransplantationVolume 27, Issue 3 e12605 COMMENTARY Challenges and practical realities of long-term patient follow-up in three xeno-islet clinical trials: The experience in pig islet xenotransplantation trials in New Zealand and Argentina Shaun Wynyard, Corresponding Author Shaun Wynyard swynyard@dolglobal.com Diatranz Otsuka Limited, Auckland, New Zealand Correspondence Diatranz Otsuka Limited, Auckland, New Zealand. Email: swynyard@dolglobal.comSearch for more papers by this author Shaun Wynyard, Corresponding Author Shaun Wynyard swynyard@dolglobal.com Diatranz Otsuka Limited, Auckland, New Zealand Correspondence Diatranz Otsuka Limited, Auckland, New Zealand. Email: swynyard@dolglobal.comSearch for more papers by this author First published: 07 June 2020 https://doi.org/10.1111/xen.12605Citations: 5Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume27, Issue3May/June 2020e12605 RelatedInformation