By Lilly Manske, Body1 staff
May 8, 2000
Currently, more than 62,000 people in the U.S. are waiting for organ transplantations—nearly 4,000 of these people die each year. Xenotransplantation, an experimental procedure involving organ transplants between closely related species, offers an alternative for these people. However, numerous issues set xenotransplantation apart from other experimental treatments.
Xenotransplantation uses animal parts to save human lives through the transplantation of whole organs, parts of organs, or small numbers of cells from certain animals. Such a transfer or grafting of tissue from an animal of one species into an individual of another species has been considered a possible way to meet the needs of those whose life depends on an organ transplant.
Xenotransplantation has come a long way since doctors first transplanted kidneys from chimps to humans nearly 30 years ago. Since then, scientists have made at least 55 attempts at taking whole organs from animals and transplanting them into humans. In 1972, the introduction of cyclosporin, a powerful drug that minimizes the rejection of foreign tissue, has dramatically expanded the possibilities of successful transplants.
Xenotransplantation still faces formidable challenges. One such challenge is hyperacute rejection in which the new host rejects its donor organ. The host's immune system responds to the graft as foreign and starts attacking the organ in several stages. As reported in Genetic Engineering News, major medical companies such as Imutran, Nextran, and Genzyme are using a range of technologies to combat the risk of hyperacute rejection. These technologies include nuclear transfer, transgenic animal development (adding human genes to animals), gene knockout, antibodies, and thymokidney to combat hyperacute rejection. Other medical concerns include proper functioning of the xenotransplant and risk of infection.
Scotland-based PPL Therapeutics recently announced that it successfully cloned five healthy piglets—a milestone on the road to developing transgenic-cloned pigs. Researchers believe that pigs are the best option for xenotransplantation with humans because of the similarity in size and function of their organs.
As of now, there are no human trials with whole animal organs. In developing clinical trials, patient recruitment remains a major issue because of fear of infection. Furthermore, questions remain about whether animals may be infected with viruses from other animals. The FDA also tightened its monitoring and overseeing of xenotransplant trials because of recent deaths in gene therapy trials. They proposed a tier-review system of xenotransplantation procedures and products, which categorizes or ranks the risks associated with certain procedures.
Xenotransplantation also intensifies other issues such as informed consent, community consent, intimate contact without putting others at risk, and the welfare and use of animals. For this reason, many feel xenotransplantation compels the need for further public review and discussion.
