Study Identifies Current and Future Benefits and Possible Barriers

June 21, 2004…Washington, D.C. The Council for Agricultural Science and Technology (CAST) is releasing a new issue paper that examines benefits from, and concerns about, the use of animals as organ and tissue donors (xenotransplantation). Written by Jeffrey L. Platt, Mayo Clinic, Rochester, Minnesota, and Randall S. Prather, University of Missouri, Columbia, Animal Organ Donors: Human Health Applications is the second in a nine-part series on “Animal Agriculture’s Future through Biotechnology.” The paper addresses head-on the critical elements of this timely, often controversial issue.

In recent decades, the ethical barriers to transplanting human organs have been overcome, but the demand far exceeds the supply. For example, although transplantation is the preferred treatment for severe chronic failure of the heart, only 5% of hearts needed for transplantation in human patients become available. “Because of a shortfall in available organs, transplantation does not begin to achieve its full potential for the treatment of human disease,” coauthor Platt says. “Even if the animal organ does not function perfectly, that organ may function better than the failing organ in the afflicted person. And many medical professionals continue to view animals rather than humans as the best source of organs, maintaining that by using animals as a source, the full needs of society can be met.”

Benefits of xenotransplantation include:

• Increased supply of replacements for failing human organs.
• Potential means to preempt diseases that afflict humans but not animals.
• Opportunity to identify new and emerging infectious agents.
• Technology that could be applied widely if needed to address an epidemic or environmental catastrophe.
• Use of animal organs as a “bridge” to transplantation with a human organ.
• Possibility that sometime in the future, animals might be used as a system in which human cells and organs can be grown.

According to Platt, “If the potential applications of xenotransplantation are substantial, the barriers to application are equally so. Certainly the ethics of xenotransplantation must be considered, although those discussing the subject often have concluded that societies that countenance the use of animals for labor or as a source for food could not as matter of policy abjure the use of animals as a source of transplants.”

Other barriers to the use of xenotransplantation include:

• Immune and inflammatory reactions of the human recipient to the animal graft
• Failure of certain animal organs to function well in humans
• Possibility of infection transferred from animal source to human recipient
• Possibility of new human/animal disease development and spread

“One aspect of xenotransplantation that has stimulated much excitement and discussion is genetic engineering,” says Teresa A. Gruber, CAST Executive Vice President.  According to the coauthors, genetic engineering is viewed at present as a way to modify a line of animals so that their organs and cells would be less likely to provoke an immune response, making those organs or cells more acceptable to a human recipient.

“The two technologies that came together to make a genetic modification to an existing gene in swine are homologous recombination and nuclear transfer, also known as cloning,” says coauthor Prather. “Thus it is now possible to consider multiple genetic modifications to overcome the various immune and inflammatory reactions stimulated by the graft.”

Additional possibilities include:

• Using animal cell transplants as a way of delivering genes for treating disease.
• Modifying or adding genes to confer new physiological properties to the transplant or to avert physiological limitations.
• Eradicating an endogenous virus or viral genes to permit safer application of xenotransplantation in humans.

The full text of the paper Animal Organ Donors: Human Health Applications (Issue Paper No. 26) may be accessed on the CAST website at www.cast-science.org, along with many of CAST’s other scientific publications, and is available in hardcopy for $5.00 (includes shipping) by contacting the CAST office at 515-292-2125. This paper is the second in a series on the topic “Animal Agriculture’s Future through Biotechnology.” CAST is an international consortium of 37 scientific and professional societies. It assembles, interprets, and communicates science-based information regionally, nationally, and internationally on food, fiber, agricultural, natural resource, and related societal and environmental issues to its stakeholders—legislators, regulators, policymakers, the media, the private sector, and the public.