Xenotransplantation

With approximately 48,000 individuals on the waiting list for organ transplants and only about 4,835 people donating their organs after death each year, there are around 3,000 yearly deaths for those who do not have these organs available to the them (1). Consequently, medicine has turned to an additional yet somewhat controversial source for organ donations: animals. The term xenotransplantation is defined as "the transplantation of living organs, cells or tissue from one species to another..." (2). The obvious and primary benefit of such a procedure is increasing the number of new leases on life that medicine can issue to the thousands waiting for organ transplants. Nevertheless, a variety of ethical issues are raised by such practices, ranging from the treatment of animals to the effects of xenotransplantation in crossing the species border.

Xenotransplantation is by no means a new concept in medicine. Combining parts of different species dates back to Greek lore of over 3,000 years ago in the forms of centaurs (half man and half horse) and the Chimera (a mixture of goat, lion and serpent). In terms of medical procedures, the earliest example of combining man and animal parts was in 1682, when a Russian physician repaired a man's skull using the bone of a dog. After the turn of the 20th century, doctors began grafting tissues from animals to humans, a prime example of this being in 1905, when a French surgeon used slices of rabbit kidney to treat a child suffering from kidney failure. As exploration into xenotransplantation continued with other animals such as pigs, goats, lambs and monkeys, doctors began to notice that these transplants would fail in relatively short amounts of time, lasting for only weeks at best. It wasn't until the 1940's, when the cause for these transplantation failures, and thus the most significant setback within xenotransplantation, was identified as a crucial connection between the immune system and the rejection of a transplanted organ (3).

Two of the most crucial risks involved with xenotransplantation are rejection and xenozoonoses. Rejection primarily involves how the immune system uses several lines of defense against infection from foreign organisms like parasites and bacteria, and specifically when the system attacks transplants. "These defense mechanisms are a double-edged sword...in xenotransplantation, we are walking a fine line between asking the immune system to accept an organ from an animal, but still protect us from other threats, such as infectious disease" (4). To combat this, doctors have been trying various methods of modifying xenotransplantation procedures. One way is to attempt to alter the recipient's immune system to increase transplant tolerance. Another is to utilize genetic engineering to change the organs, cells, and tissues of the donating animal, especially by deleting certain animal genes to be replaced by human genes (2). An example of this transgenic procedure was in 1992, when doctors introduced a human gene that directs the production of a human complement-inhibiting protein into pig embryos, in order to prevent human complement proteins from doing damage (3). While experiments such as these have yet to solve the problem of rejection, the goal is becoming less and less elusive as medicine increases its options for "tricking" the immune system.

The concern of xenozoonoses is centered upon the delicate issue of animal viruses crossing the species barrier and causing human disease, and is also a good place to begin the ethics discussion of xenotransplantation. Not only does it raise questions about the safety of using animal organs in individuals, but it can potentially place the rest of society at great risk as well. The fact that putting living organs into the human body allows pathogens (organisms that cause disease) to bypass natural barriers like skin and the gastrointestinal tract, in addition to the reality that it is difficult to screen animals for these pathogens when we may not even know what they are, makes the spread of deadly infection quite possible (2). While many believe this was the starting point for how AIDS spread through the human race, it is no wonder that the ethical debate over this aspect is concerned with whether or not we have the right to risk the health of so many people by pursuing a procedure that involves significant dangers which we know relatively little