Transplantation is the best available treatment for many serious health problems including diabetes, kidney failure and heart disease. These conditions affect millions of people worldwide and the cost of treatment, loss of productivity and reduced quality of life are enormously expensive to society.
Although transplantation offers a lifeline to these patients, there is far greater demand for organs and tissues than can ever be met using human donors. Even with the government-driven push to increase the donation rate in Australia, many patients will become too sick to receive a transplant or will die while on the waiting list.
Some scientists believe that stem cells will ultimately provide a solution to this pressing medical problem, but growing a highly complex organ from stem cells remains in the realms of science fiction, at least for now.
A treatment that is much closer to reality, and indeed has already entered early clinical trials, is the transplantation of animal organs, tissues or cells into humans. This is called xenotransplantation.
Which species?
Humans are primates, so the obvious choice of donor animal for xenotransplantation would appear to be another member of the primate family (chimpanzees and baboons, for instance) because of their physiological similarity. But non-human primates have been ruled out as donors for several compelling practical and ethical reasons.
One of the risks to transplant recipients is infection by viruses transmitted by the transplanted organ. As our closest cousins in the animal kingdom, primates are more likely than other animals to carry viruses capable of infecting humans; HIV, the virus responsible for AIDS, originated in chimpanzees.
This “relatedness” also poses ethical problems, with the public understandably reluctant to exploit animals that share many features with humans. And even if you discount the ethical question, it’s hard to imagine being able to breed enough primates to meet the increasing demand for donor organs.
Pigs, on the other hand, tick many of the boxes. They can be raised in a clean environment, so the risk of infection from pig donors may actually be lower than that from human donors. They are already widely bred for the food industry, solving the supply issue and, provided they are treated humanely, present less of an ethical dilemma.
Material from pigs has been routinely and safely used for medical purposes for decades, with heart valves the best known example. The evidence from animal models suggests that most pig organs will work properly in human recipients.
On the downside, the evolutionary distance between pigs and humans means that the human immune system mounts a very strong response to pig organs. The drugs that are used to prevent rejection of human transplants are simply not powerful enough when it comes to pig transplants.
One solution for this problem is to genetically modify pigs so that their organs will not be recognised as foreign when transplanted into humans. Several groups around the world, including in Australia, have produced GM pigs for xenotransplantation research. These pigs are still in the testing phase, but the progress that has been made over the last 10 years suggests that the move to the clinic is not too far away.
Treating diabetes with pig islets
Pigs may also be the key to future treatment of diabetes. Insulin, the hormone that controls the level of sugar in the blood, is made by clusters of cells in the pancreas called islets. People with type 1 diabetes have abnormally high blood sugar because their islets are destroyed by the immune system. While regular insulin injections restore some control, the long term prospects are poor, with complications including renal failure and blindness.
Transplantation with human islets is an option open to only a handful of patients. Pig islets are an attractive alternative, because pig insulin is 98% identical to human insulin and was used to treat patients before recombinant human insulin became available.
In a clinical trial currently taking place in New Zealand, pig islets contained within microcapsules have been injected into the abdomen of 11 patients with diabetes. The microcapsules allow nutrients to get in and insulin to get out, but importantly they also protect the pig islets from the recipient’s immune system so that no anti-rejection drugs are needed. Early results suggest that the microcapsule treatment will not be a complete cure, but may benefit patients with severe diabetes.
In the meantime, many other strategies are being explored. Results from animal models showing islets from GM pigs can reverse diabetes for many months are particularly encouraging.
Future xenotransplantation
A recent review in the prestigious medical journal The Lancet is carefully optimistic that clinical xenotransplantation may soon become a reality, particularly for cellular grafts such as islets. Will this be, as suggested by the authors of the review, the “next medical revolution”? We’ll have to wait and see.
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Comments (7)
Peter Cowan
(Co-director of the Immunology Research Centre at St Vincent's Hospital Melbourne)
Nick, following on from Anthony's comments: I wasn't trying to say that there are no ethical issues with using pigs. I realise that those people who object to the use of pigs for human purposes, whether it be for meat production or as a source of heart valves, are unlikely to support xenotransplantation.
Regarding the opt-out system, you're correct that it is not employed here, although I should point out that there is considerable debate over whether it actually increases donation rates. Whatever the case, even the most optimistic scenario for improved human donation doesn't see a complete fix of the problem. Another important point is that xenotransplantation may provide a treatment for many patients who (for a variety of reasons) are unsuitable candidates for human transplantation.
Nick Pendergrast
(PhD Candidate in Sociology at Curtin University)
Australia has a ridiculously low organ donation rate:
http://www.smh.com.au/lifestyle/diet-and-fitness/how-to-mend-a-broken-heart-20100818-12f97.html
I think very few people would opt out of being an organ donor and certainly a lot less than currently don't bother becoming one - there would be many, many more organs available if this law would change.
I agree that if we accept the idea that pigs can be killed simply for our enjoyment (we like the taste) then obviously we wouldn't reject to xenotransplantation. But I obviously reject both uses.
Humane slaughter is an oxymoron that does very little for the animals who still have their lives tragically cut short well before would be the case if they were from exploitation by humans.
Nick Pendergrast
(PhD Candidate in Sociology at Curtin University)
*sorry, that is 'if they were FREE from exploitation by humans'
Nick Pendergrast
(PhD Candidate in Sociology at Curtin University)
I don't see why this article accepts there are ethical issues with using primates, but doesn't see these same problems with using pigs. Pigs and primates are both sentient animals who feel pain and desire to avoid suffering and death - I don't believe there is any meaningful difference between using pigs and primates.
This is a human problem, so why not find a human solution, rather than going down the usual route of dragging in other animals to solve our problems without considering better alternatives. If the law was changed so people had to opt out of organ donation, rather than having to opt in, that would address this issue. I believe that this is where we should be putting our efforts, not promoting the further exploitation of other animals - whether primates or pigs.
Anthony Park
(logged in via Facebook)
As noted in the article, there is a big effort by the government to increase human organ donation however, this is not sufficient, hence the focus on xenotransplantation.
As a society we eat pigs for sustenance so it is hardly hypocritical to use pigs for a more worthy purpose such as curing disease. I'd also note the objections of pain and suffering that you raise are not necessarily the case, xeno-pigs would presumably be well cared for while they are raised (the are expensive after all). My understanding is that they are raised in pathogen free environments so would never get sick from microbiological disease. Also, if best practice industry standards are applied the pigs will be slaughtered humanely with little suffering.
In short I think this idea is quite defensive from an ethical viewpoint.
matt nunney
National Search Director (logged in via email @hotmail.com)
Nick,
Your narrow-mindedness and self -righteous responses to this article amazes me. Type 1 diabetes is a terrible disease that is not only relentless, stressful and depressing for anyone unlucky enough to have it but also extremely destructive and ultimately deadly. Type 1 diabetes often leads to blindness, loss of limbs, cardio vascular problems and a host of other nasty medical problems. If you can honestly put your hand on your heart and say you don’t consume any animal products what so ever…
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Nick Pendergrast
(PhD Candidate in Sociology at Curtin University)
Matt,
I'm not advocating that we do nothing to help people who suffer from diabetes, just arguing that this can be done without harming other animals.
The author himself admits there are ethical issues with using primates for this purpose - if we accept this, I don't see any rational reason why these same ethical issues don't apply to pigs.
I do not consume any animal products and do not currently take any medication. However, unfortunately all medication is currently tested on animals, and I don't think the solution is to not take this medication, but to support those in the medical community who are developing alternatives to animal testing.