What's Xenotransplantation?

The use of live nonhuman animal cells, tissues, and organs in human patients. These cells can be implanted or enclosed in a device that is used outside the body ("ex vivo perfusion").

-The United States Food & Drug Administration, 20 September 1996

The past few decades have witnessed an increasing worldwide acceptance of transplantation as a method of treating patients with end-stage organ failure. As of 1999, the procedure had been performed with some 25 different organs and tissues, including bone and cartilage, bone marrow, skin, cornea, heart, kidney, liver, lung, and pancreas. This rising trend has been in no small part due to improving survival rates; for instance, 80 percent of kidney transplant recipients live for at least one year, and over 60 percent live for at least five years. Indeed, the number of transplant recipients in the United States alone increased by 49 percent within the past decade. Unfortunately, the length of the waiting list for transplants increased even more greatly during the same period of time (Xenotransplantation, 1999).

There is no doubt that widespread donor organ shortage exists. In the United States alone, nearly 4,000 people die each year while awaiting transplants. Various solutions have since been proposed to breach the gap between organ supply and demand. Currently, organ procurement in the United States is regulated by the Uniform Anatomical Gift Act. The method used is known as "required consent," which mandates that hospitals and medical staff must inform patients or their next of kin as to the possibility of organ donation. Until recently, most European countries used presumed consent. Physicians could presume that patients have consented to donate their organs if they have not specifically objected to doing so. There are some who have argued that the United States could alleviate its procurement gap by adopting the European model. Yet, there is no established relationship between presumed consent and high donation rates, and most European nations still face organ shortages at least as severe as that in the U.S. Perhaps most indicative of all, most European countries have recently abandoned presumed consent in favor of more voluntary methods of procurement.

Some scientists believe that even if all conditions for optimal organ procurement were met, the potential donor pool would still be insufficient to fulfill existing waiting lists (Miranda et al., 1996). With the seeming inability of human donors to remedy the procurement problem, there has been increasing attention focused on a re-emerging technique, xenotransplantation.