Scientific progress and ethical benchmarks : Xenografts was recently the subject of a publication by the Pontifical Academy for Life.
I. A worldwide fact: A shortage of organs to save human lives
Clinical tests of animal organ grafts on humans – xenografts – have been conducted in recent years. Alliance VITA reported the grafting of a pig heart on a 57-year-old man in 2022, which was a world first. Such medical feats are impressive but also raise many questions. Facing the prospect of the increasing number of clinical tests, the Pontifical Academy for Life recently published a document on the subject "Xenotransplants: Scientific aspects and ethical considerations".
The document updates a publication dating back to 2001 without overturning its conclusions: subject to careful application, and ethical discernment, xenografts are morally justified for the well-being of patients who could benefit from them.
The shortage of organs for patients in need is well known. The "greffes de vie" (“grafts for life”) web site, a foundation under the aegis of the medical academy, provides a few figures for 2025 in France:
- 6,148 grafts were conducted including 614 from living donors;
- Over 70,000 people in France are currently living thanks to an organ graft;
- 33,000 patients are waiting for an organ donation;
- 966 needing a graft have died.
The number of people in the queue has increased over the years. In 2018, the discrepancy between those queuing and those receiving a graft was 19,150, and the figure increased to 26,852 in 2025. Such needs are not specific to France. According to the WHO, "Ethical concerns have become a major problem. The shortage of organs can lead to illegal activities, such as the trafficking of body parts for transplants". The risk is far from theoretical. NGOs have confirmed suspicions of organ trafficking in China from political prisoners executed during 2000-2020.
In view of the vital needs of patients, and such serious abuses, could xenografts represent a more ethical alternative?
II. Xenografts: What exactly are we talking about?
The idea of using animal sources to treat humans is not new. The first insulin was extracted from the pancreas of cattle or pigs. Currently, heart valves manufactured from animal tissues such as a pig valve or a cattle pericardium ("bioprosthesis") enable the replacement of failing human heart valves. One of the research themes concerns their durability, which is currently limited.
Following a few tests using organs taken from primates, the research on xenografts has turned to pig organs, essentially for practical reasons: the ease of reproducing and raising of pigs. Research on the compatibility of pig organs for humans has been conducted on "non-human primates". It has been found for example that liver grafts continued to function for over a year.
Clinical tests have also been conducted on humans in a state of encephalic death.
In 2022, 5 organ transplants on living human patients were announced. David Benett an American patient having received a pig heart survived for 60 days. We are therefore a long way off the results achieved in the case of organ transplants between humans (so-called "allografts"). In fact, half of patients survive at least 10 years following a heart transplant.
Research into improving the compatibility of xenotransplants is concentrating on two aspects:
- Genetic engineering of animals to provide organs which are more compatible with humans;
- Immuno-suppression strategies and treatments to reduce the risk of rejection.
1 – The advances in genetic engineering and the inherent risks of xenografts
Various advances in cellular and molecular biology have been used in order to produce pig lineages specifically raised for the purpose of organ donations:
- In vitro modifications to the pig genome,
- Cloning in order to reproduce a genetically modified lineage,
- Editing of some particular genes.
Such genetic modifications are intended to deactivate the production of pig enzymes which cause immunity rejection responses once the organ is grafted on a human being. Research is also being conducted on the addition of human genes in order to improve the compatibility of the organ to be grafted. The Crispr-Cas 9 technique has facilitated this "genetic editing" process.
Research is continuing at an industrial level. The Revivicor company, in the US State of Virginia, is specialised in the rearing of genetically modified pigs in order to provide more compatible organs for grafting. In France, the Xenothera company, in the Loire Atlantique region, is also working on pig cloning projects for the same purpose.
The grafts involve numerous risks which demand strict medical supervision. The INSERM web site provides an overview of the subject:
- Infectious risks with the transfer of diseases from the donor to the recipient.
- Risk of rejection, either very soon after grafting, or on the longer-term.
2 – Immuno-suppression strategies and treatments to reduce the risk of rejection
Cellular compatibility tests are conducted prior to any graft. The treatment intended to improve the graft, based on immuno-suppressants, is effective but involves a certain toxicity. According to INSERM, "In the long term, such medicines cause virtually inevitable acute or chronic kidney failure". Moreover, such treatments make patients more vulnerable to other infections.
In the case of xenografts, there is an additional risk of zoonosis: the transmission of viruses from animals to humans. According to the document by the Pontifical Academy, even if the genetic modifications quoted above are intended to reduce the risks, it cannot be excluded that an unknown pig virus could exist representing no danger for pigs but which is pathogenic for humans.
III. The ethical aspects of xenotransplants
The ethical questions raised by this practice are necessarily dependent on a vision of humankind and animals. The document by the Academy recalls the biblical vision of the position of humankind on earth, its responsibilities and its relations with other living beings. In that approach, Mankind has a unique dignity, including the ability to use the earth and its resources, including living resources, and the responsibility of caring for them. This vision is in opposition to other so-called ‘anti-speciesist’ currents which do not recognise the essential differences between humans and animals.
The raising of animals for food has been a human practice throughout history. From that point of view, the raising of animals to provide organs intended to save human lives does not represent any major ethical difficulty. Slightly provocatively, a Revivicor official, interviewed by the media claimed: “I consider that for a pig to be used for its organs for xenograft purposes, is a far more noble cause than to end up as pieces of meat".
However, other ethical questions remain, and need to be examined.
According to the published document, biotechnological research is an example of the high human creativity characteristic of its personality. The Academy nevertheless underlines the need to apply the safety-first principle in all such research. This includes not seeking to breakdown the barrier between species, in particular not modifying the appearance, nor the brain, and to refrain from attempting to modify germinal cells (reproductive cells).
The document indicates "That it is essential that xeno-transplants minimise any risk of alteration or influence of the human genome". Similarly, the implantation of animal cerebral cells in a human brain must not modify the personal identity of the patient.
Moreover, regarding animal experimentation, the "3 R rule" should be applied.
- Replace, if possible, the use of animals by alternative models;
- Reduce the number of animals used;
- Refine the experiments by minimising the pain subjected to animals.
The means must therefore be in proportion to the specified objectives. Finally, the rearing of genetically modified pigs requires precautionary measures in order to maintain the barrier with wild species related to pigs. Strict monitoring is required of farming for medical purposes.
Xenotransplantation must respect the identity of the person: their genetic identity, their appearance and behaviour (psychological identity). An animal-sourced organ must not modify its characteristics. However, the recipient may justifiably have doubts and psychological support, as well as detailed information, must be provided. Furthermore, a xenotransplant must not be imposed: any patient must be free to make a decision.
The current cultural context focuses more on the question of animal well-being. For that reason, the Academy recalls the benefit of continuing research for alternative solutions to xeno-organs.
The health risks must be carefully considered. According to the principle already established by Blaise Pascal in the 17th century, risk analysis must include two aspects: the probability of occurrence, and the damage caused in the event of occurrence of the risk. Frequently, the risk analysis is limited to considerations on the probability of occurrence alone. Regarding the health of patients, that would be a serious mistake. The document stresses the importance for research scientists to properly circulate the results of their work, in order to help the entire scientific community to refine their risk analysis.
There remain many unknowns in the research on xenografts, among which the risk of zoonosis mentioned above, the long-term impact of immuno-suppressant treatments on patients. These unknowns affect the life of patients: increased risks of infection, possible extension of the hospital isolation period etc. All of this has an impact on patients and their entourage, which calls for appropriate psychological and spiritual support.
Of course, enlightened consent based on detailed information, including on the risks and unknowns, must be sought from the patient. The ethical committees must be consulted on the subject in order to avoid any exploitation of vulnerable patients, and to ensure that the teams have the necessary skills, and the free consent of patients.
For all these reasons, the document by the Academy repeats the need to proceed in small stages, for the clinical tests (tests on living people).
Without going into details, the Academy finally mentions the issue of patenting the techniques used. It will be necessary, according to the Academy, to find an equilibrium between the hope of profit by private companies and access to xeno-organs to save human lives. In the USA, Revivicor has mentioned the price of a million dollars for a liver, once the research is complete. The price has been based on the cost of 10 years of dialysis in that nation.
Conclusion
Research into animal organs transplantable to humans has made considerable progress in recent years, leading to a few clinical tests on patients. This practice is not incompatible with respect for human dignity. In particular, the research aims to reduce the disease and suffering of patients, and to improve their chance of a better life. They do however demand compliance with numerous ethical rules:
- Progress prudently, in small steps,
- Maintain the barriers between species, and the personal identity of the recipient patient,
- Provide adequate support and ensure the enlightened consent of potential recipients,
- Remember to share the results with the scientific community for the benefit of all,
- Be concerned for animal well-being.
This contribution by the Pontifical Academy for Life comes at a time when according to certain research scientists, we are approaching a future when xeno-grafts will be able to contribute to lessen the shortage of organs.