What Is Xenogeneic Transplant?

Xenogeneic transplants, or xenotransplantation, is a transplant of body tissue between two different species of animals. Humans already use the tissues of various animal species to replace certain human hormones and body parts, but successful total organ transplants are not yet a reality.

History

• Experimentation on xenotransplation has been carried out since the 1960s and has met with only limited success. Currently, some animal tissues are routinely used by humans including bovine hormone and thyroid extract and pig heart valves (replacing defective human valves). However, there has not been a successful full organ transplant between species as of yet, due largely to immune rejection issues. The most widely publicized attempted xenotransplant involved a newborn baby, who lived for 20 days after receiving a baboon heart in a transplant in 1984. Most recently, in 1993, a patient received bone marrow and a kidney from a baboon but lived for only 3 weeks afterward.

Benefits

• According to the Department of Health and Human Services, each day in the United States 17 people die while waiting to receive an organ transplant. There is a serious shortage of organ donors, and that number drops even lower when considering that not all causes of death allow for transplantation of the deceased's organs. Xenotransplantation could save many of these lives, if only by providing a temporary reprieve while waiting for a human organ transplant. Organs are not the only types of tissues that could help save lives, however, as evidenced by the fact that many humans are now alive only because of the pig valves that replaced their own defective heart valves.

Ethical Issues

• As with many issues regarding animal testing and the use of animals in medicine, there are ethical and moral objections from some regarding the topic of xenogeneic transplants. Animal rights groups are concerned that animals, unlike humans, are unable to object to having their organs transplanted, and that doing so means that they are killed. They also express concerns that there is excessive testing in this area, exposing numerous animals to pain and early deaths, while little to no progress has been made towards successful xenotransplantations. Various religious groups are also opposed to xenogeneic transplantation.

Warning

• The primary impediment to successful xenogeneic transplantation is the issue of immunologic rejection. Both human and non-human animal's immune systems are set up to fight against potentially harmful foreign substances, leading to rejection of the transplanted organ or tissue. Although there are drugs that suppress this reaction somewhat, they also lower the body's defenses against disease to dangerously low levels, and may not be a long-term solution. Another great concern of scientists is the potential for xenozoonosis, the transmission of disease from species to species.

Definition

• "The Dictionary of Cell and Molecular Biology" states that the word "xenogeneic" translates literally as being "of foreign genetic stock" and refers to cells or tissues of a different species. Thus, a xenogeneic transplant involves taking the cells, tissue or organs from an animal of one species and putting them in the body of an individual of another species. Transplants have the best chance of success when the donor tissue comes from an animal with structural and physiological similarities in the tissue in question.