Could a pig save your life?

Human genes injected into a pig's ovum ... can breed pigs with hearts that ... can be transplanted into humans; A doctors' group opposed to animal-human organ transplants was launched yesterday. Tom Wilkie examines a medical and moral controversy

What is "xenotransplantation"? Your kidneys are failing. If you are lucky and young you may have the option of dialysis. Another possibility might be to have the kidneys of a specially reared pig transplanted into your body. Which would you go for? This is xenotransplantation: the use of organs taken from an animal to treat a human being with terminal disease. No one in Britain has been treated in this way, although it has been tried in the US.

Is human organ transplantation worth it?

Transplanting organs from human to human saves thousands of lives in Britain each year. The number of operations has risen and the outlook for the recipients has been getting better. This is not because surgeons have become better at stitching new organs into the body but because better drugs are available to suppress the immune system's attempts to reject the organ as "foreign". The most notable advance was the drug cyclosporin which became available at the start of the 1980s. But as the success rate improved, it opened the way for new demand for the operation and that in turn created a chronic shortage of organs to transplant.

In 1978, 765 kidney transplants were performed in the UK and Ireland, but 1,274 people remained on the waiting lists. In 1994, the number of transplants had increased to 1,744, but the waiting list had risen to nearly 5,000. One estimate for the US is that the unmet demand for organs for transplant is running at about 100,000 a year.

Do transplants work?

Yes. More than 70 per cent of recipients of human kidneys are still alive five years after the transplant. World-wide there are patients whose lives have been considerably extended by transplant: by 23 years after a liver transplant and 20 years after a heart transplant.

Are there alternatives to transplants?

Kidney dialysis requires lengthy sessions of treatment each week and restrictions in diet and travel, yet it cannot prevent a general decrease in health. Various devices are under development to help heart patients, but these are unlikely to do better than supplement rather than replace the real thing.

Are transplants cost-effective?

Transplants are cheap, compared to the alternatives. A kidney transplant costs about pounds 10,000. The recipient has to take drugs thereafter to stop the immune system from rejecting the (human) transplant. This costs about pounds 3,000 a year. Dialysis costs pounds 18,000 a year in hospital and pounds 11,000 a year at home.

Why is there a shortage of human organs?

Frankly, because not enough young people are dying in road traffic accidents anymore. Improved road safety has reduced the number of sudden deaths and thus of organs suitable for transplant. When we die of old age or disease, our organs are unlikely to be fit for transplantation.

So is there no way of increasing supply?

Opinion polls show that 70 per cent of the adult population are in favour of donating their organs but only 25 per cent carry a donor card. Close relatives turn down one out of every three requests by a doctor to remove organs for transplantation from someone who has just died. In Belgium and Singapore the law presumes that everyone is a donor unless they have registered their refusal to donate. But the Department of Health believes that such a law would be too intrusive in the UK.

Surely animal organs would not work?

The human immune system rejects "foreign" tissues. If the transplant comes from a different species the reaction will be hyperacute and can destroy the organ in minutes. But the closer an animal is to humans on the evolutionary scale, then the less likely the human immune system is to have a hyperacute reaction to the grafted organ. So the ideal animal to supply organs to humans would be the chimpanzee, from which humans differ by less than 2 per cent of our DNA. One American in 1964 survived for nine months with a chimpanzee's kidney, taking the immuno suppressive drugs necessary for human-to-human transplants.

Aren't chimpanzees an endangered species?

Yes, so attention is switching to other animals. In the US, researchers are investigating baboons. In Britain, a company called Imutran is working with pigs. Imutran is genetically engineering the pigs so that the human immune system will be fooled into thinking that the pig's organ is human.

Is rejection the only risk?

No. Animals may harbour viruses or bacteria which are harmless to the animal but which, transplanted into a human who is receiving drugs to suppress their immune system, might cause disease. The patient may then unwittingly infect other people - at the extreme, there is the risk of creating a global pandemic. The risk of viruses jumping species is particularly high with animals which are close together on the evolutionary scale. Disease cross-over from one species to another is well known. The Aids epidemic is believed to result from the transmission of a monkey virus into humans. Malaria, one of the most devastating diseases to afflict humanity, appears to have originated thousands of years ago as a cross- over from an infection in birds.

Can this risk be eliminated?

Perhaps by ensuring that organs are taken from animals that have been raised under conditions that are so far as is practicable disease free. But baboons, like us, are social animals - if they had to be raised in isolation for quarantine purposes, it might be psychologically cruel. Unlike chimpanzees, baboons are not endangered in the wild although their habitat is under threat. They breed very slowly, with a female producing one offspring every 15 months. Yet with a demand for 100,000 organ transplants a year in the US, the need to capture wild baboons to establish breeding colonies for transplantation could tip them into extinction.

So it's genetically engineered pigs for us?

The risk of disease is smaller than with baboons. And we are accustomed to farming pigs for their meat, so moral objections to using them for organs are less acute. They breed faster, so demand for organs would be met more quickly.

Will organs from animals "work" in humans?

No one has yet proved that an animal's organ will grow and function properly within a human. A pig's heart might work - because the heart is basically a pump - whereas a liver or pancreas might not, because these organs carry out complex biochemical functions where slight differences may be very important. Pigs have another advantage: their organs are about the same size as a human's.

Who will decide whether these transplants should go ahead?

In March, the authoritative independent Nuffield Council on Bioethics published a meticulously researched but readable report on the ethics of xenotransplantation. The council ruled out the use of baboons and recommended strict controls, warning that for years to come any such transplants would be experiments with human beings, rather than treatment of proven efficacy. The Department of Health has an Advisory Group working on the issue too. Just last week, it organised a meeting of many of the country's leading experts to consider the risks of infectious diseases from xenografting. Its report in June should lay the basis for legislation. There is no specific legal prohibition against transplants but it is inconceivable that doctors would go ahead with such a treatment without legal safeguards.

'Animal to Human Transplants - the Ethics of Xenotransplantation' is available from the Nuffield Council on Bioethics, 28 Bedford Square, London WC1B 3EG, price pounds 10.