7. The Interests of Animals

In this discussion we have been talking about using animal tissues, cells and organs in medical procedures involving humans. As we have seen, there are an enormous variety of possible uses for xenotransplantation, utilising a range of different animals. Before looking at the ethical aspects of using animals for xenotransplantation it will be worthwhile to see which animals are likely to be used and for what reasons.

Animals likely to be used in xenotransplantation

Non-human primates

Researchers, research sponsors and the wider community generally agree that non-human primates (such as baboons and other monkeys) are not a suitable source for any of the proposed animal therapies (external therapies, cell therapies or organ transplants) because of the risk of infections to the recipient and the wider community. The US Food and Drug Administration has effectively prohibited the use of non-human primates in animal-to-human xenotransplantation since 1999.

The use of non-human primates in medical research also raises serious ethical issues. Non-human primates are highly intelligent animals with complex behavioural and social needs that are difficult to meet in a medical research environment. However, baboons are considered the most suitable species for animal-to-animal studies (such as pig to baboon) to obtain important information on the effectiveness of a procedure before it can be tested in an animal-to-human trial.

Pigs

At present, pigs are considered to be the most likely and appropriate non-human source of organs and tissues. The anatomy and functioning of pigs are very similar to those of humans. Pigs are domesticated animals that are easy to breed, and, importantly, pigs are suitable for genetic modification.

Other animals

Animal-to-animal transplantation studies would use a variety of animal species in the early stages of the research (such as mice, rats and rabbits). If these studies show promising results, researchers will need to trial the procedure in an animal study that is as much like the future clinical use of the therapy as possible. This will usually involve the use of non-human primates (specifically baboons) as transplant recipients, as noted above, but fish and cattle might also be used for some procedures, such as helping to grow skin. Researchers are also considering the use of other species (such as cattle, fish and mice) for cellular transplants.

Genetic modification of animals

Researchers predict that immune rejection of animal-to-human transplants may be avoided by genetically modifying the source animals, as well as by treating the human recipient with drugs to suppress their immune response (immunosuppressant drugs). Genetic modification of source animals involves inserting some human genes into the animals to make their cells, tissues and organs behave more like human-to-human transplants.

This raises some difficult ethical issues about the rights and welfare of the animals, such as whether the insertion of human genes may make the animal in some way 'human', or whether inserted genes cause unexpected side-effects in the animals. One view may be that these issues need to be considered case by case to ensure that the proposed modification does not alter the animal in any other significant way. The aim would be to ensure that the animals retain the essential characteristics of their species.

Animal welfare and ethics

Virtually everyone believes that mammals, at least, have some ethical significance, in that it is wrong to hurt or kill them, especially if this has no benefit to humans. People who believe that human benefits outweigh the harm caused to animals often argue that these benefits are potentially very large, in terms of lives saved and suffering alleviated. This argument is often based on the belief that humans in some sense have a moral status superior to that of animals, and that therefore the needs of humans outweigh the rights of animals.

Some think it is wrong to cause suffering to or kill animals even if this has major benefits. Such an argument might be based on the belief that humans and animals have the same moral status, but it is not necessary to take this position to argue against the exploitation of animals. Some opposing the exploitation of animals maintain that the benefits to humans of xenotransplantation are often overstated and the suffering of animals understated. In this view, many animals will have to die or suffer in research for gains that are purely speculative.

It is a matter of controversy how much suffering xenotransplantation experiments and rearing would cause. For example, some types of xenotransplantation involve killing young pigs under anaesthesia, whereas others involve the destruction of a chimpanzee's immune system through chemotherapy and radiation. To minimise the risk of cross-species infection, source animals for xenotransplantation would probably need to be bred and raised in monitored, biosecure facilities. The adverse effects on animals could give rise to particular concern, especially since these source animals would need to be raised in isolation.

The Animal Welfare Act 1999 regulates the use of animals for research or testing through Institutional Animal Ethics Committees, each of which includes a representative of an animal welfare organisation. It is likely that the physical care and health of source animals would be high, because of the need to minimise the risks relating to transplantation, but as we have seen this does not eliminate ethical concerns about the treatment of animals. The Animal Welfare Act provides no guidance on balancing the harm to animals against the human benefits of the research.

The primary question seems to be how we ought to weigh the interests of animals against those of humans. The answer to this could depend on the animal in question - whether apes, pigs or mice - and how much the animal suffers in rearing and experimentation. It may also depend on the benefits to humans, in terms of exactly how safe and effective xenotransplantation will be.

Xenotransplantation involving genetic modification

One of the reasons there has been renewed scientific interest in xenotransplantation is the possibility that genetic modification will greatly reduce the immune response that is currently a major barrier to the use of animal-to-human transplants.

Pigs have a molecule on the surface of their cells called the Gal antigen, which triggers an acute immune response in humans. Genetic modification has made it possible to 'knock out' the Gal gene that produces this molecule in pig cells. Cloned piglets have now been born with the Gal gene deleted, which removes the molecule that causes the human immune system to reject pig cells, tissues and organs. Research is still being carried out on this and other aspects of the human immune response to pigs to see to what extent genetic modification can solve the problem of rejection. While immunosuppressant drugs may still be needed, the genetic modification of pigs to deactivate or delete molecules that trigger human immune reactions significantly improves the chances of successful xenotransplantation.

People with strong objections to genetic modification may accept the transfer of an animal organ or animal tissue if it has not been genetically modified, but oppose the use of xenotransplantation if it involves genetic modification of the source animal.

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