| 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
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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/
0/07B8521C2D5C38E2CA256BCD008272F3?Open
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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