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Xenotransplantation: Should we pursue the risk?

An argument against using animals for transplant organs.

Human organ and tissue transplantation (allotransplantation) is common surgery in the United States. The procedure is carried out in order to save the lives of individuals suffering organ failure and serious disease. Examples of this include kidney, heart, liver, and lung transplants. In 1996, the Food and Drug Administration (FDA) in the United States estimated that approximately 48,000 people were on the waiting list for suitable organs for transplantation, and an estimated 3,000 people die each year in the US while waiting for suitable organs or tissue for transplantation. 1 One possible alternative to human organ transplantation is xenotransplantation, using animal organs and tissues for transplantation in humans.

At this time, the US Food and Drug Administration (FDA) in conjunction with the Public Health Service and Center for Disease Control are assessing the need for xenotransplantation and whether or not a balance between public health risk and the potential promise of a suitable organ and tissue source can be found. The main reason to continue xenotransplant research is the overwhelming demand for replacement human organs and tissues. The potential of human lives saved and diminishing human suffering is driving the demand for the research. Opponents of xenotransplantation argue that, although the need for more suitable organs is great, the risks outweigh the need. Arguments against research include scientific reasons and ethical considerations.

The idea of xenotransplantation is not a new concept. Experiments in xenotransplantation date back to 1905, but the majority of the attempts to transplant animal organs into humans have been made since the 1960 s, aided by advances in the understanding of the immune system and the availability of new drugs. At this time possible xenograft candidates are baboons, chimpanzees, and pigs. A total of thirty-one transplants of solid organs from animals into humans were carried out in the US and South Africa between 1963 and 1993, using organs from chimpanzees, baboons, monkeys and pigs. The majority of these have been kidney transplants, but heart and liver transplants have also been carried out. The level of success of these procedures has varied greatly, with patients surviving for between two hours and, in one early case, nine months. The majority of patients receiving cross species transplants do not survive for longer than one month following the operation. In the few cases in which organ failure or rejection did not occur, the patients died as a result of infections which could not be fought by their suppressed immune systems. 2 At current time, there as been no record of a successful xenotransplant. However, recent advances in genetics have made it possible to engineer animals, such as pigs, which have specific combinations of human antigens. This could allow animals to be engineered whose organs have human antigens precisely matching those of a transplant patient. This would allow xenotransplantation to be carried out without the risk of hyperacute rejection. The patient s immune system would not have to be suppressed to the same extent, if at all. This would greatly reduce the risk of infection from immune suppressant drugs.

The risk of induction of new disease and cross species jump of viruses is the main reason to discontinue xenotransplantation research. Many viruses are able to cross the species boundary and infect humans with devastating results. One example of this is HIV a retrovirus which, thought to be carried by primates, was able to cross the species barrier. Retroviruses lying dormant in the genome of the animal may be activated when tissue is transplanted into the human patient. There are over 20 known, potentially lethal viruses that can be transmitted from nonhuman primates to humans including Ebola, Marburg, hepatitis A and B, herpes B, SV40, and SIV. 3 Pigs are also known carriers of disease and viruses that effect people. There are twenty-five known viruses that pigs can transmit to humans, such as leptospirosis (produces liver and kidney damage) and erysipelas (a skin infection). In both primates and pigs there may be more viruses that live harmoniously and undetected within the animals, but are deadly to humans. The threat of new viruses in xenotransplantation is not confined to the patient it is also a threat to public health.

Proponents of xenotransplantation insist that all animals would be screened and carefully raised to diminish the potential for cross species disease. Stock animals would be raised separately from domestic bred animals and that prior to transplantation genetic screening for viruses and diseases would be performed. Opponents believe that since many viruses such as retroviruses can remain dormant and beyond detection so there is no certainty of a disease free animal. In the 1996 report, the Institute of Medicine acknowledged that it is not possible to have completely pathogen-free animals, even those derived by Cesarean section, because some potentially infectious agents are passed in the genome and others may be passed transplacentally. 4 Xenotransplantation would require patient consent to known and inherent risks, and possible quarantine. These risks inherent to the procedure have inherent legal ramifications especially in litigation prone United States.

Along with scientific objections, the issue of xenotransplantation raises ethical objections as well. Most religions believe in life being sacred and unique, and by altering the genetic code of the donor organ with human DNA, we might be doing more harm than good. Animals have been altered through selective breeding techniques for thousands of years in order to obtain livestock with desirable characteristics. This has always been accepted, and few people are likely to object to the to the breeding of animals specifically for transplant purposes when the lives of transplant patients could be saved. However, some people feel strongly about altering animals through the use of more direct genetic techniques. Some people feel that it is too much like playing god , that humans do not have the right to interfere with life at such a fundamental level. They see the alteration of tissue type by replacing a portion of the animal s genome with the human equivalent to be unethical. It is unlikely that adverse opinion about the genetic engineering of animals will prevent the development and use of engineered animals for xenotransplantation in the future.

Another ethical consideration is whether we should take the lives of animals in order to save human lives. Some people believe that animals have an equal right to life, and that we should not interfere with that. Certain groups within society view the killing of animals for the benefit of humans (food or otherwise) as cruel. Most people do not believe that animals are spare parts for humans. It is argued that the idea of killing animals for the benefit of humans is a form of speciesism and that it is wrong to assume that the lives of humans are in some way more valuable than the lives of other animals. Although people argue that the families and patients suffering outweigh any right the animal has to life.

Another alternative to xenotransplantation is an aggressive campaign to solicit more human organ donors. Currently only 20% of those individuals who die healthy have arranged to donate their organs, even though 85% of the public supports organ donation. Organ availability quadrupled in Austria when its presumed consent law was enacted, and similar results prevail in other European countries. The law assumes that everyone is an organ donor unless they specify otherwise. If presumed consent legislation were enacted in the US, 75% of the adult US population might become committed potential organ donors. 5 The US adult population could alleviate the need for xenotranplantation all together.

Aside from the arguments pro or con concerning xenotransplantation, prevention of disease should be the first and foremost priority. Heart disease is the top cause of death in the United States. A disease caused mainly by lifestyle choice and practice. Although, there are many cases of a person s genetic disposition leading to illness and organ failure requiring organ and tissue transplants; these people are the minorities of transplant cases. A large majority of heart, liver, and kidney transplants could be prevented if people reduced their meat, alcohol, and tobacco consumption. Federal health authorities should be encouraging Americans to take responsibility for their health by eating properly, exercising, and avoiding cigarettes and alcohol. 6

There are many reasons research for xenotransplantation should be halted and safety analysis researched before continuing. The potential risk of new diseases and viruses coupled with a potential world health crisis is enough to halt research until further testing and safety analysis can be conducted. Also, at this time, xenotransplantation has not been successful because of animal organ rejection within the human body. Not enough has been done to examine alternatives to using animals for organ and tissue transplants.


Dept. of Health and Human Services, Draft Public Health Service Guideline on Infectious Disease Issues in Xenotransplantation; Notice, Sept. 23, 1996

Dorling, Anthony, et al, Clinical Xenotransplantation of Solid Organs, The Lancet 349, March 22, 1997, p. 867-715

Fano, Alix; Cohen MD, Murry; Cramer MD, Marjorie; Greek M.D., Ray; Of Pigs, Primates, and

Plagues , Medical Research Modernization Committee, 1997.2, 6

Michler, Robert, Xenotransplantation: Risks, Clinical Potential, and Future Prospects

EID Volume 2, January-March 1996.3

Morse, S.S., Emerging Viruses: The Evolution of Viruses and Viral Diseases, Journal of Infectious

Diseases 162, Institute of Medicine 1990.4

Robbins, John, Diet for a New America. New Hampshire: Stillpoint, 1987, p. 73-81.

Xenotransplantation , www.geocities.com1

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