Ethical Issues in Xenotransplantation: The First Pig-to-Human Heart Transplant

Ethical considerations in xenotransplantation of thoracic organs - a call for a debate on value based decisions

Xenotransplant covers a broad ethical territory and there are several ethical questions that have arisen in parallel with the technological advances that have allowed the first porcine transplants to occur. This brief communication highlights ethical considerations regarding heart and lung xenotransplantation, with an emphasis on unresolved value-based concerns in the field. The aim of this text is therefore to encourage the readers to consider the vast potential of this emerging technique to do good, but also the risk of doing harm, and to participate in a discussion. The list of questions presented here is not exhaustive but hopefully represents some of the questions that appear to be most pressing as the field advances. The focus is on the value-based, or ethical questions, not the questions related to the practical medical procedures.

Pyruvate Kinase M2: A Potential Regulator of Cardiac Injury Through Glycolytic and Non-glycolytic Pathways

ABSTRACT

Adult animals are unable to regenerate heart cells due to postnatal cardiomyocyte cycle arrest, leading to higher mortality rates in cardiomyopathy. However, reprogramming of energy metabolism in cardiomyocytes provides a new perspective on the contribution of glycolysis to repair, regeneration, and fibrosis after cardiac injury. Pyruvate kinase (PK) is a key enzyme in the glycolysis process. This review focuses on the glycolysis function of PKM2, although PKM1 and PKM2 both play significant roles in the process after cardiac injury. PKM2 exists in both low-activity dimer and high-activity tetramer forms. PKM2 dimers promote aerobic glycolysis but have low catalytic activity, leading to the accumulation of glycolytic intermediates. These intermediates enter the pentose phosphate pathway to promote cardiomyocyte proliferation and heart regeneration. Additionally, they activate adenosine triphosphate (ATP)-sensitive K + (K ATP ) channels, protecting the heart against ischemic damage. PKM2 tetramers function similar to PKM1 in glycolysis, promoting pyruvate oxidation and subsequently ATP generation to protect the heart from ischemic damage. They also activate KDM5 through the accumulation of αKG, thereby promoting cardiomyocyte proliferation and cardiac regeneration. Apart from glycolysis, PKM2 interacts with transcription factors like Jmjd4, RAC1, β-catenin, and hypoxia-inducible factor (HIF)-1α, playing various roles in homeostasis maintenance, remodeling, survival regulation, and neovascularization promotion. However, PKM2 has also been implicated in promoting cardiac fibrosis through mechanisms like sirtuin (SIRT) 3 deletion, TG2 expression enhancement, and activation of transforming growth factor-β1 (TGF-β1)/Smad2/3 and Jak2/Stat3 signals. Overall, PKM2 shows promising potential as a therapeutic target for promoting cardiomyocyte proliferation and cardiac regeneration and addressing cardiac fibrosis after injury.

Ethics, virtues and xenotransplantation

Early in 2022 the first pig to human cardiac xenotransplant was performed. The graft initially performed well, and rejection was well controlled. However, the graft failed, and the patient died 60 days after the procedure. The ethical issues relating to xenotransplantation include the risk/benefit to the individual, the risk of porcine-derived infectious agents crossing into humans, animal welfare and rights, issues of human and animal identity and concerns relating to fair allocation of organs and appropriate use of resources.These ethical issues are often addressed using emotional arguments, or through consequentialist or deontological lens. An alternative is to use approaches based on virtue ethics to understand the moral purpose (telos) of the research and the virtues (character traits) needed to be a good research clinician. In this review we will consider the virtues of justice, courage, temperance and practical wisdom, as well as the role of clinical curiosity, and their application to xenotransplantation. This provides an alternative approach for the clinical academic and others involved in the research to reflect on their practice.

Revisiting the Use of Ulysses Contracts in Xenotransplantation

BACKGROUND

Xenotransplantation clinical trials may begin soon. A persistent risk of xenotransplantation, known for decades, is the possibility that a xenozoonotic infection could be transferred from a xenograft to its recipient and then to other human contacts. Because of this risk, guidelines and commentators have advocated for xenograft recipients to agree to either long-term or lifelong surveillance mechanisms.

METHODS

For the past few decades, one solution that has been proposed to ensure that xenograft recipients will comply with surveillance protocols is the use of a heavily modified Ulysses contract, which we review.

RESULTS

These contracts are most often used in psychiatry, and their application to xenotransplantation has been espoused several times with minimal criticism.

CONCLUSIONS

In this article, we argue against the applicability of Ulysses contracts in xenotransplantation based upon (1) the telos of the advance directive that may not be applicable to this clinical context, (2) the suspect nature of enforcing Ulysses contracts in xenotransplantation, and (3) the ethical and regulatory hurdles that such enforcement would require. Although our focus is on the US regulatory landscape in preparation for clinical trials, there are applications globally.

Current status and future of gene engineering in livestock

The application of gene engineering in livestock is necessary for various reasons, such as increasing productivity and producing disease resistance and biomedicine models. Overall, gene engineering provides benefits to the agricultural and research aspects, and humans. In particular, productivity can be increased by producing livestock with enhanced growth and improved feed conversion efficiency. In addition, the application of the disease resistance models prevents the spread of infectious diseases, which reduces the need for treatment, such as the use of antibiotics; consequently, it promotes the overall health of the herd and reduces unexpected economic losses. The application of biomedicine could be a valuable tool for understanding specific livestock diseases and improving human welfare through the development and testing of new vaccines, research on human physiology, such as human metabolism or immune response, and research and development of xenotransplantation models. Gene engineering technology has been evolving, from random, time-consuming, and laborious methods to specific, time-saving, convenient, and stable methods. This paper reviews the overall trend of genetic engineering technologies development and their application for efficient production of genetically engineered livestock, and provides examples of technologies approved by the United States (US) Food and Drug Administration (FDA) for application in humans. [BMB Reports 2024; 57(1): 50-59].

Pharmacological and mechanical properties of isolated pig coronary veins

Recent successful cardiac transplantation from pig to non-human primates and the first pig-to-human transplantation has put the focus on the properties of the pig heart. In contrast to the coronary arteries, the coronary veins are less well characterized and the aim was to examine the mechanical and pharmacological properties of coronary veins in comparison to the arteries. Vessel segments from the left anterior descending coronary artery (LAD) and the concomitant vein were isolated from pig hearts in cardioplegia and examined in vitro. The wall thickness, active tension and active stress at optimal circumference were lower in coronary veins, reflecting the lower intravascular pressure in vivo. Reverse transcription polymerase chain reaction (RT-PCR) analysis of myosin isoforms showed that the vein could be characterized as having a slower smooth muscle phenotype compared to the artery. Both vessel types contracted in response to the thromboxane agonist U46619 with EC50 values of about 20 nM. The artery contracted in response to acetylcholine. Precontracted arteries relaxed in noradrenaline and substance P. In contrast, the veins relaxed in acetylcholine, contracted in noradrenaline and were unresponsive to substance P. In conclusion, these results demonstrate significant differences between the coronary artery and vein in the smooth muscle properties and in the responses to sympathetic and parasympathetic stimuli.

Xenorecognition and costimulation of porcine endothelium-derived extracellular vesicles in initiating human porcine-specific T cell immune responses

Porcine vascular endothelial cells (PECs) form a mechanistic centerpiece of xenograft rejection. Here, we determined that resting PECs release swine leukocyte antigen class I (SLA-I) but not swine leukocyte antigen class-II DR (SLA-DR) expressing extracellular vesicles (EVs) and investigated whether these EVs proficiently initiate xenoreactive T cell responses via direct xenorecognition and costimulation. Human T cells acquired SLA-I+ EVs with or without direct contact to PECs, and these EVs colocalized with T cell receptors. Although interferon gamma-activated PECs released SLA-DR+ EVs, the binding of SLA-DR+ EVs to T cells was sparse. Human T cells demonstrated low levels of proliferation without direct contact to PECs, but marked T cell proliferation was induced following exposure to EVs. EV-induced proliferation proceeded independent of monocytes/macrophages, suggesting that EVs delivered both a T cell receptor signal and costimulation. Costimulation blockade targeting B7, CD40L, or CD11a significantly reduced T cell proliferation to PEC-derived EVs. These findings indicate that endothelial-derived EVs can directly initiate T cell-mediated immune responses, and suggest that inhibiting the release of SLA-I EVs from organ xenografts has the potential to modify the xenograft rejection. We propose a secondary-direct pathway for T cell activation via xenoantigen recognition/costimulation by endothelial-derived EVs.

Establishment of a donor pig for xenotransplantation clinical trials based on the principle of Changsha Communiqué

Background

Xenotransplantation is a potential way to reduce the shortage of the needed organ grafts for the end-stage disease. Immune rejection, physiological incompatibility and bio-safety are the most critical issues.

Methods

To ensure the safety and efficacy of gene editing, second- and third-generation sequencing technologies have allowed us to obtain a clearer genetic background of donor pigs for xenotransplantation. Based on the Changsha Communiqué, the local DPF- excluded lists and DPF donor facility were established in Changsha, China. A pig-to-human islet clinical trial was conducted and overseen by the respective Chinese governmental agency.

Results

The DPF standards for pig husbandry eliminated specific pathogens in donor pigs. We have established a PERV-C free, genetic information clean, DPF donor for xenotransplantation. A clinical trial of ten adult patients (9M:1F) with type 1 diabetes who received DPF porcine islet xenotransplantation via the portal vein were performed. Clinical accepted immunosuppressant drugs and autologous Treg were used for controlling immune rejection. No cross-species infection events occurred in this trial, and importantly, no cross-species transmission of PERV was found.

Conclusions

Xenotransplantation is a pioneer study and safety is the most important issue. The fundamental principles for establishing xenotransplantation donor pigs should follow the Changsha Communiqué (2008), the second WHO consultation,and the 2018 Changsha Communiqué which would finally help reducing the risks of xenotransplantation.

Evolution of Xenotransplantation as an Alternative to Shortage of Donors in Heart Transplantation

This review aims to show and illustrate the history, current, ethical considerations, and limitations concerning xenotransplantation. Due to the current shortage of available donor organs for transplantation, many alternative sources are being examined to solve the donor shortage. One of them is xenotransplantation which refers to the transplantation of organs from one species to another. Compared to other nonhuman primates (NHP), pigs are ideal species for organ harvesting as they rapidly grow to human size in a handful of months. There is much advancement in the genetic engineering of pigs, which have hearts structurally and functionally similar to the human heart. The role of genetic engineering is to overcome the immune barriers in xenotransplantation and can be used in hyperacute rejection and T cell-mediated rejection. It is technically difficult to use large animal models for orthotopic, life-sustaining heart transplantation. Despite the fact that some religious traditions, such as Jewish and Muslim, prohibit the ingestion of pork products, few religious leaders consider that donating porcine organs is ethical because it saves human life. Although recent technologies have lowered the risk of a xenograft producing a novel virus that causes an epidemic, the risk still exists. It has major implications for the informed consent procedure connected with clinical research on heart xenotransplantation.

Ethical considerations during a pioneering surgical procedure: porcine cardiac xenotransplantation

Preclinical advances in life-sustaining porcine cardiac xenotransplantation from donor pigs to baboons have paved the way for the performance of porcine cardiac xenotransplantation in a human. This procedure was performed with emergency use authorisation granted by the United States Food and Drug Administration under the umbrella of investigational new drug use on compassionate grounds. The patient was denied candidacy for durable mechanical circulatory support and heart transplantation as a result of non-adherence to medical advice.

Successful porcine cardiac xenotransplantation in humans will significantly increase the availability of potential donor organs for long-term management of end-stage heart failure. Human porcine cardiac xenotransplantation is associated with ethical conflicts encompassing multiple ethical principles which are not mutually exclusive and are sometimes conflicting. This article focuses on some of the ethical conflicts encountered in relation to the use of mechanical circulatory support, pretransplant evaluation, shared decision making during informed consent, infectious disease risk, preclinical and clinical testing, and the role of regulatory bodies during performance of the first human porcine cardiac xenotransplantation.

An increase in human trials of xenotransplantation procedures is imminent. Potential ethical conflicts associated with xenotransplantation should be addressed appropriately.

Year in Review 2021: Noteworthy Literature in Cardiothoracic Anesthesia

In 2021, progress in clinical science related to Cardiac Anesthesiology continued, but at a slower rate due to the ongoing pandemic and disruptions to clinical research. Most progress was incremental and addressed persistent questions related to our field. To identify articles for this review, we completed a structured review using our previously reported methods (1). Specifically, we used the search terms: "cardiac anesthesiology and outcomes" (n = 177), "cardiothoracic anesthesiology" (n = 34), "cardiac anesthesia," and "clinical outcomes" (n = 42) filtered on clinical trials and the year 2021 in PubMed. We also reviewed clinical trials from the most prominent clinical journals to identify additional studies for a narrative review. We then selected the most noteworthy publications for inclusion in this review and identified key themes.