Meta‐analysis of public perception toward xenotransplantation

International Xenotransplantation Association (IXA) Position Paper on Kidney Xenotransplantation

Porcine kidney xenotransplantation for end-stage renal disease (ESRD) has reached the stage of clinical testing following major advances in donor pig genetic modifications and effective immunosuppressive strategies through decades of rigorous translational research. Reports of pig kidney xenograft survival beyond 1 year post-transplant in nonhuman primate (NHP) models justify optimism for its potential as an alternative to allotransplantation. In the United States, experimental transplantations of genetically engineered (GE) porcine kidneys into brain-dead subjects and a small number of ESRD patients have shown no evidence of hyperacute rejection and adequate pig kidney function for up to several months. Here we discuss pre-clinical/clinical results, infectious disease, ethical, and regulatory considerations, and propose evidence-based recommendations. For initial clinical trials in kidney xenotransplantation, we make the following recommendations: (i) transplantation with organs from a triple knockout (TKO) donor pig, preferably with added human transgenes, (ii) an immunosuppressive regimen with induction therapy to deplete T (and possibly B) cells, and maintenance therapy based on a cluster of differentiation (CD)40/CD154 co-stimulation pathway blockade, (iii) the patient should be fully acceptable as a candidate for allotransplantation but should be unlikely ever to receive an allograft. Patients aged 60-69 years (extendable to 40-75 years, if one of the criteria mentioned below is present), of blood group B or O, and with diabetes are most at risk in this regard. Other patients who could be considered are (i) those who have lost two or more previous kidney allografts from recurrent disease in the graft, (ii) those with broad human leukocyte antigen (HLA)-reactivity but no evidence of anti-pig antibodies, including swine leukocyte antigen (SLA), and (iii) those with failing vascular access. Clinical pilot studies in carefully and highly selected patients with no alternative therapy will provide the foundation upon which to base subsequent formal expanded clinical trials.

International Xenotransplantation Association (IXA) Position Paper on Kidney Xenotransplantation

Porcine kidney xenotransplantation for end-stage renal disease (ESRD) has reached the stage of clinical testing following major advances in donor pig genetic modifications and effective immunosuppressive strategies through decades of rigorous translational research. Reports of pig kidney xenograft survival beyond 1 year posttranplant in nonhuman primate (NHP) models justify optimism for its potential as an alternative to allotransplantation. In the United States, experimental transplantations of genetically engineered (GE) porcine kidneys into brain-dead subjects and a small number of ESRD patients have shown no evidence of hyperacute rejection and adequate pig kidney function for up to several months. Here we discuss pre-clinical/clinical results, infectious disease, ethical, and regulatory considerations, and propose evidence-based recommendations. For initial clinical trials in kidney xenotransplantation, we make the following recommendations: (i) transplantation with organs from a triple knockout (TKO) donor pig, preferably with added human transgenes, (ii) an immunosuppressive regimen with induction therapy to deplete T (and possibly B) cells, and maintenance therapy based on a cluster of differentiation (CD)40/CD154 co-stimulation pathway blockade, (iii) the patient should be fully acceptable as a candidate for allotransplantation but should be unlikely ever to receive an allograft. Patients aged 60-69 years (extendable to 40-75 years, if one of the criteria mentioned below is present), of blood group B or O, and with diabetes are most at risk in this regard. Other patients who could be considered are (i) those who have lost two or more previous kidney allografts from recurrent disease in the graft, (ii) those with broad human leukocyte antigen (HLA)-reactivity but no evidence of anti-pig antibodies, including swine leukocyte antigen (SLA), and (iii) those with failing vascular access. Clinical pilot studies in carefully and highly selected patients with no alternative therapy will provide the foundation upon which to base subsequent formal expanded clinical trials.

Religion and Attitudes Toward Xenotransplantation: Results of a Nationwide Survey in the United States

Religious viewpoints have been shown to influence the ways in which many persons approach medical decision-making and have been noted as a potential barrier to xenotransplantation acceptance. This study sought to explore how attitudes toward xenotransplantation differ among various religious beliefs. A national Likert-scale survey was conducted in 2023 with a representative sample in the United States. Religious belief was self-reported. Regression analysis was used to identify associations with religious belief and hesitations about xenotransplantation. Five thousand and eight individuals across the United States responded to the survey. The two biggest concerns about xenotransplantation across religious groups were the current lack of evidence about success and the risk of xenozoonosis. Although they still expressed concerns about certain issues, Catholic and Muslim respondents were most comfortable with xenotransplantation for all. On average, the risk of xenozoonosis was a concern among 25% across all religious beliefs (p <0.0001). Orthodox Christians expressed the highest rate of negative feelings toward the recent xenotransplantation experiments on brain dead and living individuals. Those who reported no religion were most likely to have negative feelings about killing pigs for human organ transplant (OR 1.26; 95% CI: 1.08-1.46). As xenotransplantation progresses from pre-clinical studies to clinical trials, and potentially to clinical therapy, hesitations among religious groups exist. Specific studies should be designed to investigate how religious viewpoints can affect xenotransplantation acceptance.

Transplant Patients' Perceptions About Participating in First-in-Human Pig Kidney Xenotransplant Clinical Trials: A Mixed Methods Study

First-in-human pig xenotransplant clinical trials may soon begin, which raises ethical concerns about patients' decision-making to participate in such trials. We assessed kidney transplant candidates' attitudes and hypothetical decision-making about participating in xenotransplant trials through semi-structured telephone interviews and an online survey. We analyzed qualitative data by thematic analysis and quantitative data by descriptive statistics. Twenty-eight patients participated in interviews; 142 patients participated in the survey. Most interview and survey respondents were male (68%, 56%), White (54%, 61%), or Black (36%, 22%). Although interview participants appreciated xenotransplantation research's potential to advance science, they expressed concerns about infection transmission and graft function. Few survey respondents were willing to participate in a pig kidney trial to test the safety of pig kidneys (12.6%) or pig kidney function (16.9%). Interview participants would be more likely to participate in a first-in-human pig kidney trial if receiving a human kidney was unlikely and their health status declined. Willingness would also depend on how long the pig kidney would function. Most interview participants were receptive to long-term monitoring, but not to family monitoring. Transplant programs planning xenotransplant trials should anticipate these types of concerns for optimizing human subject protections and conducting a robust informed consent process.

Public attitudes to xenotransplantation: A national survey in the United States

Xenotransplantation (XTx) presents a potential clinical alternative to the shortage of human organs for transplantation. Before clinical trials occur in the United States, public assessments are crucial to understand potential barriers to acceptance. The purpose of this study was to explore barriers and identify characteristics associated with attitudes toward XTx. A survey assessing demographic characteristics and attitudes toward XTx was distributed to a nationally representative sample of adults aged ≥18 years in the United States. Regression analysis was employed to identify characteristics associated with attitudes toward XTx. Between May 25 and June 14, 2023, 5008 respondents completed the survey. Importantly, half of the respondents expressed low or no knowledge of either transplantation or XTx. Approximately 40% expressed discomfort with receiving a pig organ for themselves or a loved one. Despite a lack of xenotransplant outcome data, 36% were open to experimental XTx if they needed a transplant. However, 57% rated lack of current evidence of success or fear of complications as top concerns. Regression models consistently associated being younger, female, not needing an organ, or being a member of a racial minority group with lower acceptance. This survey is the largest to date exploring public attitudes toward XTx. Despite overall acceptance, concerns persist. Increasing public acceptance is key as the field advances.

Pediatric Cardiac Xenotransplantation: Recommendations for the Ethical Design of Clinical Trials

For children with complex congenital heart problems, cardiac allotransplantation is sometimes the best therapeutic option. However, availability of hearts for pediatric patients is limited, resulting in a long and growing waitlist, and a high mortality rate while waiting. Cardiac xenotransplantation has been proposed as one therapeutic alternative for neonates and infants, either in lieu of allotransplantation or as a bridge until an allograft becomes available. Scientific and clinical developments in xenotransplantation appear likely to permit cardiac xenotransplantation clinical trials in adults in the coming years. The ethical issues around xenotransplantation of the heart and other organs and tissues have recently been examined, but to date, only limited literature is available on the ethical issues that are attendant with pediatric heart xenotransplantation. Here, we summarize the ethical issues, focusing on (1) whether cardiac xenotransplantation should proceed in adults or children first, (2) pediatric recipient selection for initial xenotransplantation trials, (3) special problems regarding informed consent in this context, and (4) related psychosocial and public perception considerations. We conclude with specific recommendations regarding ethically informed design of pediatric heart xenotransplantation trials.

The Time Has Come: The Case for Initiating Pilot Clinical Trials of Pig Kidney Xenotransplantation

In vitro studies indicate that kidney transplantation from gene-edited pigs in which expression of all three of the known glycan xenoantigens has been deleted may be more challenging in nonhuman primates (NHPs) than it will be in human recipients. Furthermore, pig-to-human xenotransplantation offers several other advantages - (i) the patient can communicate with the surgical team; (ii) recipient microbiological monitoring and environment will be clinical-grade; and (iii) sophisticated graft monitoring and imaging techniques, (v) therapeutic interventions, e.g., dialysis, plasmapheresis, and (v) intensive care can be deployed that are not easily available in NHP laboratory models. We suggest, therefore, that progress to develop safe, informative human clinical trials will be accelerated if pilot clinical cases are initiated. The selection of patients for kidney xenotransplantation can include those who are at high risk of dying imminently, e.g., those experiencing increasing vascular access challenges with no realistic alternative therapy available, and those who have been accepted onto the waitlist for an allograft, but who are unlikely ever to receive one. Patients with an increased risk of dying include those with (i) age >60 years, (ii) blood groups O or B, and (iii) diabetic nephropathy. UNOS data indicate that an average of 25 patients on the kidney waitlist in the USA die or are removed from the list every day (i.e., >9,000 each year). Given the improved xenograft survival observed in preclinical studies, we suggest that it is time to plan a small pilot clinical trial for healthy dialysis patients who understand the risks and potential benefits of kidney xenotransplantation.

Update on the ethical, legal and technical challenges of translating xenotransplantation

This manuscript reports on a landmark symposium on the ethical, legal and technical challenges of xenotransplantation in the UK. King's College London, with endorsement from the British Transplantation Society (BTS), and the European Society of Organ Transplantation (ESOT), brought together a group of experts in xenotransplantation science, ethics and law to discuss the ethical, regulatory and technical challenges surrounding translating xenotransplantation into the clinical setting. The symposium was the first of its kind in the UK for 20 years. This paper summarises the content of the expert lectures showcasing the progress which has been made in xenotransplantation including-the history of xenotransplantation, advances in gene edited animals and progress towards clinical xenotransplantation. We then set out the ethical and legal issues still to be resolved. Finally, we report the themes of the roundtable discussion highlighting areas of consensus and controversy. While the detail of the legal discussion was directed towards the UK, the principles and summary reported here are intended to be applicable to any jurisdiction seeking to implement clinical xenotransplantation.

Research opportunities and ethical considerations for heart and lung xenotransplantation research: A report from the National Heart, Lung, and Blood Institute workshop

Xenotransplantation offers the potential to meet the critical need for heart and lung transplantation presently constrained by the current human donor organ supply. Much was learned over the past decades regarding gene editing to prevent the immune activation and inflammation that cause early organ injury, and strategies for maintenance of immunosuppression to promote longer-term xenograft survival. However, many scientific questions remain regarding further requirements for genetic modification of donor organs, appropriate contexts for xenotransplantation research (including nonhuman primates, recently deceased humans, and living human recipients), and risk of xenozoonotic disease transmission. Related ethical questions include the appropriate selection of clinical trial participants, challenges with obtaining informed consent, animal rights and welfare considerations, and cost. Research involving recently deceased humans has also emerged as a potentially novel way to understand how xeno-organs will impact the human body. Clinical xenotransplantation and research involving decedents also raise ethical questions and will require consensus regarding regulatory oversight and protocol review. These considerations and the related opportunities for xenotransplantation research were discussed in a workshop sponsored by the National Heart, Lung, and Blood Institute, and are summarized in this meeting report.

Exploring attitudes toward xenotransplantation: A scoping review of healthcare workers, healthcare students, and kidney patients

BACKGROUND

Recent advances mean that formal clinical trials of solid organ xenotransplantation are increasingly likely to begin and patients requiring a kidney transplant could be the first participants. Healthcare workers and healthcare students constitute the current and future workforce that will influence public opinion of xenotransplantation. The attitudes of these populations are important to consider before recruitment for formal clinical trials begins.

METHODS

This scoping review was reported according to the PRISMA extensions for scoping reviews checklist and the Joanna Briggs Institute methodology for scoping reviews. The Scopus, PubMed, and ScienceDirect databases were searched to identify articles that studied the attitudes of healthcare workers, healthcare students, or kidney patients toward xenotransplantation.

RESULTS

The search generated 816 articles, of which 27 met the eligibility criteria. The studies were conducted in 14 different countries on five different continents. Participants from the 27 studies totaled 29,836-this was constituted of 6,223 (21%) healthcare workers, 21,067 (71%) healthcare students, and 2,546 (8%) kidney patients. All three groups had an overall positive attitude toward xenotransplantation. However, in studies where participants were asked to consider xenotransplantation when the risks and results were not equal to allotransplantation-the overall attitude switched from positive to negative. The results also found that Spanish-speaking populations expressed more favorable views toward xenotransplantation compared to English-speaking populations.

CONCLUSION

The results of this review suggest that while attitudes of the three groups toward xenotransplantation are-on the face of it-positive, this positivity deteriorates when the risks and outcomes are framed in more clinically realistic terms. Only formal clinical trials can determine how the risks and outcomes of xenotransplantation compare to allotransplantation.

The importance of public engagement in clinical xenotransplantation

Over the past several decades, significant scientific progress in xenotransplantation has brought the field to the threshold of clinical trials. In the past 3 years in the United States, experimental pig kidney and heart xenotransplantation have been performed on human subjects recently declared dead by neurological criteria (decedents). In addition, two pig heart transplants have been carried out in living patients under the United States Food and Drug Administration's expanded access guidelines. However, though there has been a flurry of activity there remain unanswered questions regarding how the public views xenotransplantation, what concerns may exist, and how to address these concerns in a meaningful way. This paper aims to underscore the importance of public engagement in xenotransplantation, emphasizing the ongoing need for studies to assess public opinions. The current evidence on public engagement studies is reviewed and gaps in our understanding are identified. We propose practical steps to advance this field. Additional studies to determine the extent of racial/ethnic differences in attitudes to xenotransplantation should be conducted. Empirical and descriptive analysis of certain religious viewpoints-especially minority faiths-would be valuable. As public engagement is an important aspect of public acceptance of novel research that is accompanied by risk, we suggest that xenotransplantation biotechnology companies might consider leading the way in funding this research.

Moral approval of xenotransplantation in Egypt: associations with religion, attitudes towards animals and demographic factors

Xenotransplantation has great potential as an alternative to alleviate the shortage of organs for donation. However, given that the animal most suited for xenotransplantation is the pig, there are concerns that people in Muslim countries may be more hesitant to morally approve of these procedures. In this study, the moral approval of xenotransplantation was assessed in a group of 895 participants in Egypt. The results showed that religiosity itself does not predict moral approval of xenotransplantation, but religious identity does, as Muslims are less likely to approve of xenotransplantation than Christians. However, the strongest predictor of moral approval of xenotransplantation was gender, with women displaying less approval. A partial mediating factor in this association was concern for animal welfare. Based on these results, some implications for public policy are discussed.

Pressing ethical issues relating to clinical pig organ transplantation studies

Clinical pig heart transplant experiments have been undertaken, and further clinical experiments and/or clinical trials of gene-edited pig organ xenotransplantation are anticipated. The ethical issues relating to xenotransplantation have been discussed for decades but with little resolution. Consideration of certain ethical issues is more urgent than others, and the need to attain consensus is important. These issues include: (i) patient selection criteria for expanded access and/or clinical trials; (ii) appropriate protection of the patient from xenozoonoses, that is, infections caused by pig microorganisms transferred with the organ graft, (iii) minimization of the risk of a xenozoonosis to bystanders, and (iv) the need for additional public perception studies. We discuss why it is important and urgent to achieve consensus on these ethical issues prior to carrying out further expanded access experiments or initiating formal clinical trials. The ways forward on each issue are proposed.

Kidney xenotransplantation: Future clinical reality or science fiction?

There is a global shortage of organs for transplantation and despite many governments making significant changes to their organ donation systems, there are not enough kidneys available to meet the demand. This has led scientists and clinicians to explore alternative means of meeting this organ shortfall. One of the alternatives to human organ transplantation is xenotransplantation, which is the transplantation of organs, tissues, or cells between different species. The resurgence of interest in xenotransplantation and recent scientific breakthroughs suggest that genetically engineered pigs may soon present a realistic alternative as sources of kidneys for clinical transplantation. It is therefore important for healthcare professionals to understand what is involved in xenotransplantation and its future implications for their clinical practices. First, we explore the insufficiency of different organ donation systems to meet the kidney shortage. Second, we provide a background and a summary of the progress made so far in xenotransplantation research. Third, we discuss some of the scientific, technological, ethical, and public health issues associated with xenotransplantation. Finally, we summarize the literature on the attitudes of healthcare professionals toward xenotransplantation.

Future of Lung Transplantation: Xenotransplantation and Bioengineering Lungs

Xenotransplantation promises to alleviate the issue of donor organ shortages and to decrease waiting times for transplantation. Recent advances in genetic engineering have allowed for the creation of pigs with up to 16 genetic modifications. Several combinations of genetic modifications have been associated with extended graft survival and life-supporting function in experimental heart and kidney xenotransplants. Lung xenotransplantation carries specific challenges related to the large surface area of the lung vascular bed, its innate immune system's intrinsic hyperreactivity to perceived 'danger', and its anatomic vulnerability to airway flooding after even localized loss of alveolocapillary barrier function. This article discusses the current status of lung xenotransplantation, and challenges related to immunology, physiology, anatomy, and infection. Tissue engineering as a feasible alternative to develop a viable lung replacement solution is discussed.

Xenotransplantation: A historical-ethical account of viewpoints

Formal clinical trials of pig-to-human organ transplant-known asxenotransplantation-may begin this decade, with the first trials likely to consist of either adult renal transplants or pediatric cardiac transplant patients. Xenotransplantation as a systematic scientific study only reaches back to the latter half of the 20th century, with episodic xenotransplantation events occurring prior to that. As the science of xenotransplantation has progressed in the 20th and 21st centuries, the public's knowledge of the potential therapy has also increased. With this, there have been shifting ethical stances toward xenotransplantation in key areas, such as religious and public viewpoints towards xenotransplantation, animal rights, and public health concerns. This review provides a historical-ethical account of xenotransplantation and details if or how viewpoints have shifted over time.

Attitudes of patients with renal disease on xenotransplantation: A systematic review

BACKGROUND

Recent years have seen major advancements in xenotransplantation: the first pig-to-human heart transplant, the development of a brain-dead recipient model for kidney xenotransplantation, and the registration of the first xenokidney clinical trial. The attitudes of patients with kidney disease or transplants on xenotransplantation and an assessment of their reservations and considerations regarding the technology are crucial to successful clinical translation and eventual widespread implementation.

METHODS

This systematic review was registered through PROSPERO (CRD42022344581) prior to initiation of the study and reported using the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines. We included studies that evaluated attitudes towards and willingness to undergo xenotransplantation in patients with end-stage renal disease (ESRD), including those who had already undergone transplantation. MEDLINE (via Ovid), Embase (via Elsevier), and Web of Science (via Clarivate) were searched from database inception to July 15, 2022 by an experienced medical librarian for studies on xenotransplantation and attitudes. Abstracts and full text were screened using Covidence software and data items regarding study methodology, patient demographics, and attitudes regarding xenotransplantation were extracted using Microsoft Excel. Risk of bias assessments were performed using the Critical Appraisal Skills Programmed and National Institute of Health study quality assessment tools.

RESULTS

Of 1992 studies identified, 14 studies met the inclusion criteria. These studies were conducted across eight countries, four in the United States, for a total of 3114 patients on the kidney waitlist or with a kidney transplant. All patients were over 17 years old and 58% were male. Acceptance of a xenotransplant was assessed using surveys in 12 studies. Sixty-three percent (n = 1354) of kidney patients reported that they would accept a xenotransplant with function comparable to that of an allotransplant. Acceptance of xenografts with inferior function to allografts (15%) or as bridge organs (35%) to allotransplantation was lower. Specific concerns expressed by patients included graft function, infection, social stigma, and animal rights. Subgroup analyses showed higher acceptance in already transplanted compared to waitlist patients and white compared to Black Americans.

CONCLUSION

An understanding of patient attitudes and reservations is key to the successful execution of the first xenotransplantation clinical trials. This study compiles important factors to consider, such as patient concerns, attitudes regarding practical clinical scenarios for the use of xenotransplantation, and the impact of demographic factors on acceptance of this emerging technology.

A Technological and Regulatory Review on Human-Animal Chimera Research: The Current Landscape of Biology, Law, and Public Opinion

Organ transplantation is a highly utilized treatment for many medical conditions, yet the number of patients waiting for organs far exceeds the number available. The challenges and limitations currently associated with organ transplantation and technological advances in gene editing techniques have led scientists to pursue alternate solutions to the donor organ shortage. Growing human organs in animals and harvesting those organs for transplantation into humans is one such solution. These chimeric animals usually have certain genes necessary for a specific organ's development inhibited at an early developmental stage, followed by the addition of cultured pluripotent human cells to fill that developmental niche. The result is a chimeric animal that contains human organs which are available for transplant into a patient, circumventing some of the limitations currently involved in donor organ transplantation. In this review, we will discuss both the current scientific and legal landscape of human-animal chimera (HAC) research. We present an overview of the technological advances that allow for the creation of HACs, the patents that currently exist on these methods, as well as current public attitude and understanding that can influence HAC research policy. We complement our scientific and public attitude discussion with a regulatory overview of chimera research at both the national and state level, while also contrasting current U.S. legislation with regulations in other countries. Overall, we provide a comprehensive analysis of the legal and scientific barriers to conducting research on HACs for the generation of transplantable human organs, as well as provide recommendations for the future.

Expert consensus on clinical trials of human xenotransplantation in China

The history of xenotransplantation started in the 19th century. After a few decades of investigation, significant breakthroughs and preclinical milestones have been achieved worldwide. With the recent transplantation of genetically modified porcine kidneys and heart into humans, these ground-breaking achievements have attracted great attention worldwide, in the hope that xenotransplantation might alleviate or even solve the problem of organ shortage. On January 20, 2022, the China Organ Transplantation Development Foundation convened a symposium on "The History, Current Situation and Future of Human Xenotransplantation Clinical Trials," where ways to promote the ethical and sustainable development of xenotransplantation in China were discussed among the participating experts. A formal consensus was reached as the product of the symposium, outlining the expert opinions on scientific, regulatory, and ethical issues of clinical trials of xenotransplantation in China.

Ethics and Theoretical Issues in Kidney Xenotransplantation

Xenotransplantation has seen recent global interest peak as a result of several clinical xenotransplants being performed in decedents and a live cardiac recipient. However, underpinning these latest transplants have been decades of invested scientific research programs that have been developing the ideal donor source animals to avoid the overwhelming hyperacute xenograft rejection seen using nongenetically modified animal organs, tissues, and cells. However, this also needs to be undertaken along with the development of safe and efficacious xenotransplantation technologies, immunosuppression, monitoring, disease screening, patient selection, societal education, and acceptance. Paralleling the advent of such extraordinary transplants have been several decades of establishment of world xenotransplantation authorities such as the International Xenotransplantation Association, and the development of guidance documents and regulations for the assessment of these cutting-edge technologies. Similar to all new technologies there remain outdated concerns and fears of the theoretical potential for transmission of xenozoonosis, ethical concerns, and outdated or appropriately educated societal concerns and religious views of the benefits or risks and issues for xenotransplantation use of organs, tissues, or cells from animals to human beings. Here, we discuss the development of xenotransplantation and the intricate balance in managing the various challenges with which we are faced: in the absolute benefits of xenotransplantation and the dichotomy in balancing the pros and cons of xenotransplantation with social, religious, ethical, scientific, and medical opinions. Ultimately, the benefits are to those patients suffering from the many and various diseases that drive the need for xenotransplantation. The hope is that it will be implemented as soon as possible to help the many millions of patients who can truly benefit.

The 2021 IXA Keith Reemtsma Lecture: Moving xenotransplantation to the clinic

Keith Reemtsma was a pioneer in xenotransplantation, the Honorary Founding President of the International Xenotransplantation Association (in 1998), and a wonderful personality. It is a privilege to be invited to give this lecture in his memory. If he were alive today, he would be delighted to see the progress that has been made in pig organ transplantation into nonhuman primate recipients. This progress has largely resulted from two major advances: (i) the increasing availability of pigs with multiple genetic manipulations aimed at protecting the cells of the organ from the primate immune response and (ii) the introduction of novel immunosuppressive agents that block the CD40/CD154 costimulation pathway. There is strong evidence from numerous in vitro studies that the transplantation of a triple-knockout pig organ, particularly if expressing several human protective proteins, into a patient is likely to be significantly more successful than if that same organ is transplanted into a nonhuman primate recipient. With this fact in mind, and in view of the advances currently being made, the time has surely come when we need to consider moving from the laboratory to the clinic. However, there are still questions we need to definitively resolve: (i) What exact genetic modifications do we need in the organ-source pig? (ii) What exact immunosuppressive regimen will we choose? (iii) How will we monitor the immune response and diagnose and treat rejection? and (iv) How do we plan to prevent or treat potential infectious complications? Furthermore, when these matters have been resolved, which patients will be offered a pig organ in the first trial? We have suggested that patients who are very unlikely to survive until a suitable deceased human donor kidney becomes available are those who should be considered for the initial trials. Assessing public attitudes to xenotransplantation is also important before embarking on a clinical trial. I suggest that progress is much more likely to be made from a small clinical trial than if we persist in carrying out experiments in an animal model that no longer mimics the clinical situation.

Should you need an organ… Flemish secondary school students' attitudes toward xenotransplantation and transgenetic organ donation

BACKGROUND

The supply of human organs available for transplantation remains grossly inadequate globally. Animal-to-human transplantation, and even more so humanized organ grown in animals, holds promising results for the start of clinical trials in humans. Very little is known about the public's willingness to accept different xenotransplantation techniques. This study aims to determine attitudes toward human-to-human transplantation, animal-to-human transplantation, and chimera-to-human transplantation in the Belgium context.

METHODS

Secondary school students from Flanders, Belgium, were surveyed between January and June 2019. Socio-demographic details likely to influence participants' attitudes were gathered. Participants were presented with three hypothetical cases (human-to-human transplantation, animal-to-human transplantation, and chimera-to-human transplantation) and asked about their willingness to accept the particular organ. Their risk appetite to accept organs with potentially worse outcomes than the status quo was also evaluated.

RESULTS

Seven hundred forty-one complete questionnaires were analyzed. It can be concluded that Flemish secondary school students favored the techniques of xenotransplantation to a lesser extent than allotransplantation; however, most of them did consider it a good solution for organ shortage. Compared to animal-to-human transplantation, chimera-to-human transplantation showed a more positive attitude among the respondents when considered a good organ transplantation solution.

CONCLUSION

Flemish secondary school students favored the techniques of xenotransplantation to a lesser extent than allotransplantation; however, most of them did consider it a good solution for organ shortage. In comparison to animal-to-human transplantation, chimera-to-human transplantation showed a more positive attitude among the respondents when considered a good solution for organ transplantation.

Genetically engineered pig kidney transplantation in a brain-dead human subject

In September 2021, a kidney (with donor-specific thymic tissue) from an α1, 3-galactosyltransferase gene-knockout (GTKO) pig was transplanted into the groin (with anastomoses to the femoral vessels) of a brain-dead subject by a surgical team at New York University Langone Health (NYU). It was reported to function immediately, passing urine and excreting creatinine. The experiment was terminated after 54 h and, during this period, the kidney did not show macroscopic features of rejection. Does this experiment provide information not available to us previously and does it move the field forward to clinical trials? The information provided was very limited, but the following points are worthy of note. (i) Numerous in vivo studies in nonhuman primates have predicted that the pig kidney would function immediately. (ii) Numerous in vitro studies have predicted that a GTKO pig kidney would not be rejected within the first few days after transplantation into a human subject. (iii) GTKO kidneys are not optimal for clinical transplantation, and the transplantation of a triple-knockout (TKO) pig kidney would have been more relevant. (iv) There was no purpose in transplanting a "thymokidney" without pre-transplant conditioning therapy and follow-up for several months. (v) Because the native kidneys were retained, it is difficult to determine whether the function of the graft was sufficient to support life. (vi) The experiment was announced to the media rather than published in a peer-reviewed medical journal (although hopefully this will follow), suggesting that it was primarily carried out to gain attention to the great potential of xenotransplantation (and/or possibly to NYU). In this respect the experiment was successful. Because of the very limited period of time for which a brain-dead subject can be maintained in a metabolically and hemodynamically stable state, the value of experiments in such subjects will remain very limited. It is hoped that any future similar experiments will be planned to be more relevant to the clinical situation. Nevertheless, the report has stimulated public attention towards xenotransplantation which, unless there is an adverse response to what some might consider to be a bizarre experiment, should be of significant benefit to future progress.

"You cannot stay in the laboratory forever"*: Taking pig kidney xenotransplantation from the laboratory to the clinic

Progress in life-supporting kidney transplantation in the genetically-engineered pig-to-nonhuman primate model has been encouraging, with pig kidneys sometimes supporting life for > 1 year. What steps need to be taken by (i) the laboratory team, and (ii) the clinical team to prepare for the first clinical trial? The major topics include (i) what currently-available genetic modifications are optimal to reduce the possibility of graft rejection, (ii) what immunosuppressive therapeutic regimen is optimal, and (iii) what steps need to be taken to minimize the risk of transfer of an infectious microorganism with the graft. We suggest that patients who are unlikely to live long enough to receive a kidney from a deceased human donor would benefit from the opportunity of a period of dialysis-free support by a pig kidney, and the experience gained would enable xenotransplantation to progress much more rapidly than if we remain in the laboratory.

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.

Pig kidney xenotransplantation: Progress toward clinical trials

Pig organ xenotransplantation offers a solution to the shortage of deceased human organs for transplantation. The pathobiological response to a pig xenograft is complex, involving antibody, complement, coagulation, inflammatory, and cellular responses. To overcome these barriers, genetic manipulation of the organ-source pigs has largely been directed to two major aims-(a) deletion of expression of the known carbohydrate xenoantigens against which humans have natural (preformed) antibodies, and (b) transgenic expression of human protective proteins, for example, complement- and coagulation-regulatory proteins. Conventional (FDA-approved) immunosuppressive therapy is unsuccessful in preventing an adaptive immune response to pig cells, but blockade of the CD40:CD154 costimulation pathway is successful. Survival of genetically engineered pig kidneys in immunosuppressed nonhuman primates can now be measured in months. Non-immunological aspects, for example, pig renal function, a hypovolemia syndrome, and rapid growth of the pig kidney after transplantation, are briefly discussed. We suggest that patients on the wait-list for a deceased human kidney graft who are unlikely to receive one due to long waiting times are those for whom kidney xenotransplantation might first be considered. The potential risk of infection, public attitudes to xenotransplantation, and ethical, regulatory, and financial aspects are briefly addressed.

How the COVID-19 pandemic may impact public support for clinical xenotransplantation in the United States?

Many patients who would undergo organ transplantation cannot proceed due to the inability of human organ donation to satisfy medical needs. Xenotransplantation has the potential to offer unlimited availability of pig organs for transplantation, and pig-to-non-human primate models have demonstrated outcomes that may soon justify clinical trials. However, one of the unique ethical challenges faced by xenotransplantation is that the risk of introducing potential zoonotic disease into the community must be weighed along with the benefit to the patient. While most experts believe that zoonosis is manageable, apprehension over disease transmission from animal donors to human recipients remains a frequent concern of many who are undecided or opposed to clinical xenotransplantation. The COVID-19 pandemic represents a scenario (rapid worldwide spread of a highly contagious novel zoonotic disease with no natural defense in humans) that would seem to justify apprehension, especially in the United States, which has largely avoided previous pandemic outbreaks. However, there are many differences between zoonosis found in the wild or after xenotransplantation that favor the safety of the latter. Still, these differences, as well as the benefits of xenotransplantation, are not widely understood outside of the field. We must therefore ask what impact the COVID-19 pandemic will have on attitudes toward xenotransplantation.

Attitudes to Clinical Pig Kidney Xenotransplantation among Medical Providers and Patients

Background

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.

Methods

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.

Results

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).

Conclusions

(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.