Xenotransplantation

Xenotransplantation (xeno- from the Greek meaning "foreign") is the transplantation of living cells, tissues or organs from one species to another such as from pigs to humans (see Medical grafting). Such cells, tissues or organs are called xenografts or xenotransplants. The term allotransplantation refers to a same-species transplant. Human xenotransplantation offers a potential treatment for end-stage organ failure, a significant health problem in parts of the industrialized world. It also raises many novel medical, legal and ethical issues. A continuing concern is that pigs have different lifespans than humans and their tissues age at a different rate. Disease transmission (xenozoonosis) and permanent alteration to the genetic code of animals are also a cause for concern.

Because there is a worldwide shortage of organs for clinical implantation, about 60% of patients awaiting replacement organs die on the waiting list. Recent advances in understanding the mechanisms of transplant organ rejection have brought science to a stage where it is reasonable to consider that organs from other species, probably pigs, may soon be engineered to minimize the risk of serious rejection and used as an alternative to human tissues, possibly ending organ shortages.

Other procedures, some of which are being carefully investigated in early clinical trials, aim to use cells or tissues from other species to treat life-threatening and debilitating illnesses such as cancer, diabetes, liver failure and Parkinson's disease. If vitrification can be perfected it could allow for long-term storage of xenogenic cells, tissues and organs so they would be more readily available for transplant.

There are only a few published successful xenotransplant procedures.

Xenotransplants are transplants of organs from one species to another, such as an animal organ to humans. They are cutting edge of medical science and could save thousands of people’s lives who are waiting for an organ donation. The animal organ, probably from a pig or baboon could be genetically altered with human genes to trick a patient’s immune system into accepting it as apart of its own body. They have re-emerged because of the lack of organs available and the constant battle to keep immune systems from rejecting the organs. Xenotransplants are thus hopefully able to provide a way of transplants which are safe and effective.

Acceptance

Xenografts have been a controversial procedure since they were first attempted. Many, including animal rights groups, strongly oppose killing animals in order to harvest their organs for human use. Medical concerns exist about possible disease transfer between animals and humans, such as the porcine endogenous retrovirus found in pig tissues. Religious beliefs, such as the Jewish and Muslim prohibition against eating pork, have been sometimes thought to be a problem, however according to a Council of Europe documentation both religions agree that this rule is overridden by the preservation of human life.

In general, however, the use of pig and cow tissue in humans has been met with little resistance, save some religious beliefs.

Some of the main and biggest biological/human health problems involved with Xenotransplants are that of transmitting animal diseases to humans, the unknown certainty of an outbreak of infectious diseases and the probability of rejection of donor organs. Baboons and pigs carry myriad transmittable agents which are harmless in their natural host but extremely toxic and deadly in humans. HIV is an example of a disease which was believed to be transmitted to humans by monkeys. Scientists and researchers also do not know if an outbreak of infectious diseases could occur and if they could contain the outbreak even though they have measures for control. Another obstacle for Xenotransplants is that of the body’s rejection of foreign objects by it immune system. These antigens (foreign objects) are often treated with powerful drugs which may in turn make the patient vulnerable to other infections and actually aid the disease trying to be cured. This is the reason the organs would have to be altered to fit with the patients DNA. In 2005, the Australian National Health and Medical Research Council declared a eighteen-year moratorium on all animal-to-human transplantation, concluding that the risks of transmission of animal viruses to patients and the wider community have not yet been resolved . The main ethical issues associated with Xenotransplants are that the animals which would be commonly used for their organs, such as pigs and baboons are killed or sacrificed. Baboons are very similar to humans with human-like hands, faces and a developed social structure. For this reason pigs could be used more as their anatomies are similar to humans and are a lot easier to breed than baboons that only produce one offspring at a time. Pigs are also a lot healthier and carry less disease than primates as well. There are less moral objections to the killing of pigs as they are already killed for food and are already being produced.