PREFERRED DONOR ANIMALS: CASE EVALUATIONS

 

With regards to xenotransplantation, the question arises as to which species are most suitable for organ and tissue donation. Through the years, the pig and the baboon have been identified as the animals most compatible with human physiology. The case studies of these two animals are reflective of the overall success and problems xenotransplantation has and continues to experience.

Pig tissue is generally deemed as appropriate for xenotransplantation. This species has both biological compatibility (for example, normal blood glucose range is 70-100 mg/dl for humans, 70-105 mg/dl for pigs) and proven historical efficacy (pig insulin has been administered to humans for nearly 80 years, and thousands of people have already been transplanted with living pig tissue, including islets, hepatic cells, neurons, and skin). Furthermore, it is believed that pigs can genetically be modified to produce organs compatible with the human immunological system.

As mentioned previously, the human immune system distinguishes between native and foreign tissue by the presence of complement-regulating proteins (such as DAF, MCP, and CD59) on the surfaces of bodily cells. In 1991, it was hypothesized that the expression of such proteins by pig organs would inhibit the human complementary response and prevent rejection (Atkinson et al., 1991). Since then, worldwide research has erupted to transform this theory into reality.

 

In a similar concept, rejection of a pig organ transplanted

into a patient ensues after antibodies bind to the

linear sugar chains lining pig blood vessels.

 

But tissues from pigs genetically altered to carry the

angular sugar groups found in human blood

should not elicit such reactions.

Source: Stanford University

 

Some researchers have adopted a somewhat different approach, attempting to modify pig cells so that they no longer carry the antigens that have been identified as the targets of human antibodies.

The evolutionary relationship between humans and primates suggests their suitability as donors. Chimpanzees, for instance, have been identified as among the most suitable of animal donors due to their organ sizes and blood types. The endangered status of many primates, however, raises legal and ethical questions as to their usage. Focus has thus shifted to the baboon, which is not endangered, has an anatomy similar to that of the human, and grows to a weight of approximately 70 pounds. Due to their small size, baboon organs are not viewed as permanent transplants but as bridges to sustain life until more suitable organs become available. The species is also used as a donor of bone marrow cells (Xenotransplants, 1999).