The lack of human donor organs available for transplantation has "led to an international trade in body parts with Western 'brokers' offering poor people in Latin America, South Asia, Eastern Europe, and Africa money or consumer goods in exchange for their kidneys, corneas, and patches of skin." This scenario is one attempt to remedy the current situation in which 50,000 people in the United States need organ transplants and only a small portion of these people actually receive one. Recent studies point to xenotransplantation as a promising but not yet successful alternative. Doctors have been experimenting with this type of transplantation since 1906 and have yet to be successful. But the recent evidence favoring the use of animal organs for transplantation into humans ignited controversial medical and ethical issues. Xenotransplantation is in its experimental stages and there are many unknowns which need to be solved before its successful implementation is possible. For this problem of the increasing number of donor organs needed and the meager supply of human organs available, with more studying, xenotransplantation seems to be a promising solution.
Pigs are recognized as the most suitable animal for use in xenotransplantation. Initially, primates seemed to be a hopeful choice for this process because their immune systems are most similar to humans, but there are a number of disadvantages with using an animal so closely related to humans. Even though both animals are about the right size for humans, there are more ethical concerns when using a primate which is intelligent and interacts in a social unit. Primates have a long breeding process and they have never been reproduced in large quantities for human exploitation. Pigs, on the other hand, produce litters of offspring at a time, and they are already "farmed" for meat. Finally, it is easier for the public to accept using pigs in xenotransplantation because they do not exhibit human traits. To use these pig organs, recent research shows that the pigs must be genetically engineered to "express human complement-inhibiting protein so that their organs suppress the human immune reaction." The organs of these transgenic pigs could then be transplanted into a human without being destroyed by the human immune system (a process called hyperacute rejection) since they would be recognized as a human organ.
There are many advantages to understanding and using animal organs for transplantation. Xenotransplantation offers hope of an immense supply of organs available for transplantation. With this large supply of organs, recipients could plan their surgery rather than have the procedure done only when an organ becomes available. Experts have also found that there "is evidence that a baboon liver would be resistant to hepatitis B viral infection that destroys many transplanted livers." The differences among species in their disease resistance capabilities could be useful for transplantation. Finally, the Institute of Medicine, and the Food and Drug Administration both recognize the benefits of research on xenotransplantation, but they call for precautions and guidelines for testing and research due to medical and ethical concerns.
These medical and ethical problems have the potential to effect both the individual patient as well as the general population. The spread of new or existing infectious diseases into the human population, and the compatibility of the human and animal organs are medical concerns stemming from xenotransplantation. This type of transplantation generates ethical issues involving animal treatment and cruelty as well. Finally, the problem of performing an operation that benefits an individual but may harm the population as a whole is a moral decision.
The major concern of critics of xenotransplantation is that the procedure will possibly introduce dangerous infectious diseases into the human species. Louisa Chapman notes that:
"The disease-producing potential of an infection is a function of the relation between the host and the infecting agent; the biologic features of both are contributory. Thus, the pathogenic potential of an infection can change in an unpredictable fashion when the infecting microbe is transmitted from its natural host into a new species." Pig retroviruses concern scientists because they are passed from one generation to the next without affecting the pig but these retroviruses may be dangerous for humans. Once these viruses infect the human population, they may be likely to produce major epidemics. Research also shows that when a new species attains such a retrovirus it usually becomes more diverse and persistent in the new host. Another concern is that the xenotransplantation is the perfect scenario for the survival of a virus. During transplantation, the recipient's immune system is repressed which permits the persistence of viruses.
To remedy the problem of transmitting infectious diseases, scientists have tried to create transgenic pigs which are as disease free as possible. The Institute of Medicine has offered the possibility of creating guidelines which would call for testing pigs for disease and tracking the recipients closely to minimize the risks of an epidemic. The problem with these precautions is that research shows that "multiple copies of viruses that can infect human cells are present in pig tissues -implying that it may never be possible to breed pigs from which virus-free organs could be harvested." These researchers also maintain that xenotransplantation is still possible in that more experiments involving primates need to be done in order to test to identify whether the pig viruses will infect human cells.
The compatibility of human and animal organs is another medical concern with xenotransplantation. Biologically, there is no evidence that pig kidneys, livers, and hearts will function appropriately in humans. The human kidney absorbs most of the uric acid while it is expelled in pig kidneys. The pig liver lacks an enzyme which the human liver needs for the immune system. The pig heart is usually at the level of its head, whereas a human heart is below the head. If a pig heart were transplanted into a human, the heart may not be able to produce enough blood flow to sustain the human brain. These anatomical and chemical differences between humans and pigs suggests that a cross-species transplant may not be functionally successful. Another concern is that "nothing is known about how whole xenogeneic organs will perform over the medium and long term. For example, will a human microenvironment be suitable for efficient performance of a porcine organ? Also, what will be the natural lifespan of a xenogeneic organ in a human recipient?" These questions of long term viability of xenogeneic organs are crucial questions but are hard to answer until we come closer to a successful transplantation.
Animal treatment is a factor in the ethical concerns of critics of xenotransplantation. Linda Lange, a member of the People for the Ethical Treatment of Animals, noted that "To put it most simply, animals are not spare parts." These activists think it is not morally correct for animals to die to keep humans alive. Some of these activists views are stiffled by the notion that pigs are already farmed for their meat and these organs should just be taken from these pigs which would be sacrificed anyways. Another ethical issue is raised when scientists try to produce disease-free pigs. Some people think that "the pigs must be raised and live under special--and some would argue, cruel--conditions in a sterile, pathogen-free environment with little light and no natural material for bedding and rooting." These disease-free pigs may also produce concern over whether they are safe to eat. Other activists argue that genetically altering pigs can eventually damage their immune system.
A final ethical concern is whether to perform xenotransplantation on an individual even though there are potential concerns for the human population as a whole. In a study of Australian's attitudes toward xenotransplantation, Mohacsi found that 78% of dialysis patients would accept a transgenic organ from a pig. Only 17% would not accept the organ but their decisions were mostly due to religion and animal rights views. This study indicates that people are willing to accept pig organs knowing the possible problems. The issue of whether it is morally right to perform this surgery with the risk of creating an epidemic in the general public should be a decision of the general public because "nothing could be worse than if in trying to save our lives we inadvertently engineered a plague." Even though recipients would choose a pig organ if they had that option, the public needs to be informed of the potential harm this could produce.
On a societal level, there is concern that there is a discrepancy between the public and the expert view on the issue of transplantation. The public view on the potential danger of xenotransplantation has to do with how familiar, how controllable, and how disastrous this procedure seems to be to people. "Fears and values play a key role in the way" the general population views the potential danger, but on the other hand, the expert view is one which involves the practicality of xenotransplantation and the likelihood that the procedure will save lives. To bring these two views closer together, experts must inform the public of the benefits of the procedure as well as warn them of the potential dangers.
Another ethical concern for society involves the individual recipient. After receiving a pig organ, the individual must be tracked for most of their lives to ensure that a disease does not persist in the recipients body. Patients could not refuse to be followed for life. This infringes upon their individual rights but is important to ensure that an epidemic does not start. The people who are in contact with this person should be followed as well to make certain that the disease, if there were one, had not spread to other people. Another concern is confidentiality for the patient. The question arises of whether some people should be informed that the patient has a xenogeneic organ. Should the co-workers be informed they could be at risk? This knowledge would violate the confidentiality of the patient but might be ethically necessary for the general public. There is also the potential for keeping the patient isolated if a disease is transmitted, which again has ethical concerns in whether this type of treatment is humane. These issues must be made known to the public as well as the individual to ensure an informed decision about xenotransplantation.
Xenotransplantation offers new hope to those in need of organ donors but there is much research which still needs to be done to ensure the safety and practicality of the procedure. One must also consider the effects on the human being psychologically. The recipients become a mixture of two different species, because when an animal organ is transplanted, the animal cells flow throughout the entire body. In a sense, "the borderline between 'animal' and 'human' is thus modified, bringing the very identity of the 'human' patient into question." These medical, ethical and psychological concerns are legitimate, but more and more the experimentation that is being done is providing hope and promising benefits for xenotransplantation. With more research these transgenic pig organs could "usher in a golden era of tissue and organ transplantation."
1. Koechlin, Florianne, "The Animal Heart of the Matter", The Ecologist 26, 93-97 (1996).
2. "Xenotransplantation, The Mayo Clinic Website", <http://www.mayohealth.org/mayo/9812/htm/xenotransplant.htm>.
3. Dorling, A., Riesbeck, K., Warrens, A., Lechler, R., "Clinical Xenotransplantation of Solid Organs", The Lancet 349, 867-871 (1997).
4. Abdulla, Sara, "Xenotransplantation Debate Boils On", The Lancet 350, 868 (1997).
5. Skolnick, Andrew, "Transplantation Pioneer Predicts Successful Xenotransplantation Soon", JAMA 269, 2951-2958 (1993).
6. "Xenotransplantation-Caution, But No Moratorium", Nature Medicine 4, 372 (1998).
7. Chapman, Louisa, "Sounding Board, Xenotransplantation and Xenogeneic Infections", The New England Journal of Medicine 333, 1498-1501 (1995).
8. "IOM Backs Cautious Experimentation", Science 273, 305-306 (1996).
9. Mitchell, Peter, "Xenotransplantation Prospects Thwarted", Lancet 350, 1148 (1997).
10. "The Uncaged Campaigns Website", <http://www.uncaged.co.uk/XenoFour.html>.
11. "Animal to Human Transplants: Mad Science or Medical Miracle?, The Fox News Archive Website", <http:/www.foxnews.com>.
12. Allen, W. H., "Farming for Spare Body Parts, The BioScience Website", <http://www.albs.org/biosciencelibrary/vol45/farming.html>.
13. Ward, E., "Attitudes to Xenotransplantation", Lancet 349, 1775 (1997).
14. "A Double-edged Sword ", New Scientist 159, 3 (1998).
15. Bach, F. H., "Uncertainty in Xenotransplantation: Individual Benefit Versus Collective Risk", Nature Medicine 4, 141-144 (1998).