Markkula Center of Applied Ethics

Xenotransplantation: Weighing Individual Benefit and Risks to the Public

by Margaret R. McLean

The news is not good: Your heart is failing and you need a transplant, but organs are scarce and the wait is long. It is likely that your heart will wear out before a human replacement can be found. Would you consider a pig heart?

Welcome to the world of xenotransplantation, where healthy animal organs are swapped for failing human organs. The prefix "xeno" refers to something that is strange or different. Xenotransplantation is the transplantation of cells, tissues, or organs from one species to another. Pigs are the most promising "donors" for human organ transplants since they can be genetically modified relatively easily and have similar anatomical structure to humans.

Xenotransplantation research got a shot in the arm in January 2004 when a working party of the Australian National Health and Medical Research Council recommended the initiation of clinical trials in transplanting tissue from pigs to humans. The first of these may be brain cell therapies or skin grafts.

One impetus behind research on animal organs for human transplant is the poor availability of human organs. In 2000, some 50,000 Americans waited for transplants from 5,000 donors. Annually, over 6,000 people die because no donated organs are available.

In addition, the possibility of rejection continues to plague transplant recipients. It may be possible to avoid this complication by genetically modifying pigs so that the human immune system does not recognize the transplanted organ as "foreign." Xenotransplantation came a step closer with the 2002 birth of Goldie, a cloned miniature pig that lacked both copies of a gene responsible for immediate rejection. Cloning is important because it assures that every one of her cells lacks the gene that triggers rejection.

In December 2003, scientists at Massachusetts General Hospital demonstrated that genetically modified pig organs survived for 81 days in baboons, indicating that short-term rejection can be avoided. Slower mechanisms of organ rejection are still a concern.

As deep as the need for transplantable organs is and as promising as recent studies are, there is one ethical issue of such magnitude that many have called for a moratorium on clinical trials-that is the trade-off between benefit to individual patients and the public risk of infection.

All pigs have porcine endogenous retrovirus (PERV) that could potentially infect organ recipients with possibly fatal consequences. Outbreaks of SARS and bird flu serve as sobering reminders that animal viruses can jump to humans. Handling civets and chickens is enough to become infected. How much greater the risk with a pig heart beating inside your chest? Notably, this risk would not only be to the transplant recipient. Animal viruses can modify themselves so that they can spread from person to person-SARS and HIV are notable examples.

One key ethical concern in xenotransplantation is how to weigh compelling individual need against potentially grave, but unknown, risk of public infection. The medical paradigm of the autonomous patient making an informed decision fails us; this is not a risk that affects only the patient. It is a societal risk that requires societal consideration and attention to the common good. We must consider who is helped and who is harmed by moving ahead with xenotransplantion. At this point, it is prudent to confine ourselves to laboratory research. A moratorium on clinical trials is justified because the potential spread of PERV to recipients of pig cells and organs and to the general population is simply too great a risk to take. While scientists study basic mechanisms of viral transmission and quantify risk, we should grab the opportunity to engage in public education and deliberation about patient benefit and public risk associated with xenotransplantation.

Margaret R. McLean is the director of biotechnology and health care ethics at the Markkula Center for Applied Ethics.

Feb 2004

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