New Guidelines for Xenotransplantation

Although transplants of hearts or lungs from pigs should not be permitted at the present time, clinical trials of such transplants would be justified when researchers achieve acceptable results in animal studies and have determined there is little risk of spreading animal viruses to humans. This is one of a number of recent recommendations made by a group of leading scientists, doctors, and surgeons assembled by the International Society for Heart and Lung Transplantation (ISHLT) to review the status of cross-species transplantation and its potential for treating patients with end-stage heart and lung diseases. Their review is published in the December issue of Journal of Heart and Lung Transplantation.

The pig is considered to have the best potential as a donor, say the authors, but because of its genetic differences to humans, researchers must devise strategies to overcome the rejection of pig organs. Rejection and other hurdles must be overcome before testing can be permitted to evaluate xenotransplantation in patients. Several strategies show promise, such as humanizing pig organs by introducing certain human proteins into the pig.

Lung transplantation using a pig organ is far from becoming a reality. Continued advancements, however, could make pig-to-human heart transplants feasible within a few years, note the authors. The authors recommend that laboratory evidence would need to indicate that the transplanted pig heart could support a good quality of life for at least six months. This would need to be achieved in the absence of complications from the immunosuppressive drugs required to control rejection. The longest a nonhuman primate has survived supported by a pig heart has been 39 days.

Patients considered for an initial clinical trial should be those who are either currently excluded from receiving a human heart or are unlikely to survive the wait for a human heart and cannot qualify for mechanical heart support.

All xenotransplant trials should be regulated by national bodies that have far-reaching government-backed control, including the authority to halt them if deemed necessary. An international body, such as the ISHLT, should monitor the trials and serve as a registry of information and data.



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