Organ transplantation: the road ahead
Angie Sutalo

While advances in physiology and immunology have successfully enabled organ transplantation, unfortunately many patients still die waiting for organs. Some scientists suggest that xenotransplantation, the transplantation of animal tissues and organs into humans, can alleviate this shortage.

Despite national advertising campaigns, the number of organs donated by Australians is low by international standards: just one suitable organ per 100,000 people.¹ This figure means that only 350 organs are available for transplant, resulting in a four-year waiting period for many potential recipients. Organ donation from living donors is usually not an option, even though a family member can donate one kidney or a piece of liver – subject to a good tissue match. Most organs are sourced from those recently deceased from natural causes and car accident fatalities – making the widespread harvesting of animal organs an attractive option.

In the future, will xenotransplantation be the solution to human organ shortage? Photo: Pam Roth

In 2002, PPL Therapeutics, the first company to clone pigs, genetically engineered pigs specifically for xenotransplantation purposes with the aim of minimising the risk of organ rejection in humans. They found that the presence of a particular sugar (alpha-1,3-galactose) on the cell surface triggers immune rejection, leading to rejection of foreign tissue. Scientists removed from the pig’s genome the gene for the enzyme that transfers this sugar to the cell surface, alpha-1,3-galactosyl transferase. This will reduce the likelihood that a human body will reject the organ from the pig.

Theoretically, at least, modified pigs could provide a limitless supply of organs for transplant. In the future, people could have their own tissue-compatible pig raised and waiting until needed. Several problems must be addressed before this service becomes a reality, even for a select few who can afford it. Altered pig organs will still trigger immunological responses in the human body. Whether anti-rejection drugs will suffice here remains to be seen. Using pig organs could also expose the patient (and ultimately the rest of the human population) to pig-borne diseases, such as PERVs (Porcine Endogenous RetroVirus), that would not otherwise infect humans.

Professor Robert White of Case Western Reserve University, Ohio, is a pioneer of full body transplants and has been a strong advocate of xenotransplantation as an adjunct to his research. Once president of the American Neurological Society, White has managed to transplant the head of a rhesus monkey onto the body of another. He has achieved this feat of vivisection by cooling the brain down to 10-15 degrees Celsius, reducing its oxygen use, and temporarily suspending circulation within the brain while the head is removed from one body and reconnected to the other. Once the operation is completed, the monkey is conscious and can smell, taste and hear – indicating that the body is capable of supporting the attached head. However, the brain cannot control bodily functions since the damage to the spinal nerves is currently irreversible.² White kept the animal alive for several weeks and is prepared to trial the approach on humans who are willing to undergo the $2 million procedure.³

There are clearly dangers associated with xenotransplantation, though it is a potential solution to organ shortages when other avenues have been exhausted. Ultimately, the availability of xenotransplantation will depend not only on being able to successfully engineer organs that are accepted by the human body, but also acceptability of the procedure by the public at large and by the patients themselves.


References

1. Australian Bureau of Statistics (2003) Australian Social Trends 2002 - Health Related Actions: Organ donation. Australian Bureau of Statistics. http://www.abs.gov.au/ausstats/abs@.nsf/
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2. BBC News – Health (6 April, 2001) ‘Frankenstein fears after head transplants’. BBC News. http://news.bbc.co.uk/1/hi/health/1263758.stm

3. Chang, G. (9 September, 1999) ‘Head Transplants in the Near Future’. EXN.ca – Discovery Channel. http://www.exn.ca/Stories/1999/09/09/52.asp

4. Penman, D. (22 August, 2002) ‘Modified pigs are a transplant breakthrough’. NewScientist.com. http://www.newscientist.com/news/news.jsp?id=ns99992711

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