Xenotransplantation - Nuffield Council on Bioethics
Xenotransplantation - Nuffield Council on Bioethics
Xenotransplantation - Nuffield Council on Bioethics
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<str<strong>on</strong>g>Xenotransplantati<strong>on</strong></str<strong>on</strong>g> : progress and prospects<br />
Chapter 3<br />
<str<strong>on</strong>g>Xenotransplantati<strong>on</strong></str<strong>on</strong>g> : progress and prospects<br />
3.1 A key questi<strong>on</strong> raised by xenotransplantati<strong>on</strong> is whether or not the technique will<br />
work. In this chapter the scientific background to xenotransplantati<strong>on</strong> is set out to<br />
provide a basis for the discussi<strong>on</strong> of the ethical issues that follows in subsequent<br />
chapters.<br />
3.2 Table 3.1 gives examples of the main xenotransplantati<strong>on</strong> procedures involving<br />
human recipients that have occurred to date. A wide range of procedures has been<br />
used. Some of them are now routine, such as the use of pig heart valves to replace<br />
the patient’s own defective valves. Far more ambitious and, to date, unsuccessful are<br />
attempts to replace defective human organs, such as the heart, liver or kidneys, with<br />
transplanted animal organs. There are two major practical problems that have to be<br />
faced.<br />
3.3 First, there is the problem of organ rejecti<strong>on</strong>. When a human organ is transplanted<br />
from <strong>on</strong>e individual into another, the recipient’s immune system attacks the organ<br />
because it is seen as foreign (the sole excepti<strong>on</strong> is transplantati<strong>on</strong> between identical<br />
twins). If the immune resp<strong>on</strong>se is extreme, the organ will be rejected and the<br />
transplant will fail. This is why human d<strong>on</strong>or organs are matched with those of<br />
transplant patients as closely as possible. Even with closely matched organs, however,<br />
immunosuppressive drugs have to be used to subdue the resp<strong>on</strong>se of the patient’s<br />
immune system to the transplanted organ.<br />
3.4 Organ rejecti<strong>on</strong> becomes much more of a problem with xenografting, because of the<br />
greater difference between human and animal tissues. The more distantly related, in<br />
a biological sense, the human recipient and the source animal, the str<strong>on</strong>ger the<br />
immune reacti<strong>on</strong>. For this reas<strong>on</strong>, attempts have been made in the US to use organs<br />
from primates, such as babo<strong>on</strong>s, for xenotransplantati<strong>on</strong>. Biologically speaking,<br />
primates are closely related to human beings so that problems of organ rejecti<strong>on</strong> may<br />
not be much more severe than those seen with human transplants. As discussed in<br />
Chapter 4, however, ethical c<strong>on</strong>cerns are raised by the use of primates for<br />
xenotransplantati<strong>on</strong>. So efforts have been made to develop animals other than<br />
primates for use in xenografting. Attenti<strong>on</strong> has focused in particular <strong>on</strong> the pig for<br />
several reas<strong>on</strong>s. Pig organs are comparable in size and, to a lesser degree, physiology<br />
to those of human beings, and they reproduce quickly and produce large numbers of<br />
offspring. The use of pigs as a domestic animal that is farmed and eaten is l<strong>on</strong>g<br />
established and many would have fewer c<strong>on</strong>cerns about their use for xenotransplantati<strong>on</strong><br />
as compared with the use of primates (discussed further in Chapter 4).<br />
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