Xenotransplantation - Nuffield Council on Bioethics

Animal-to-Human Transplants : the ethics of xenotransplantation
Bioengineered organs (see artificial organs)
Brain stem death
Brain stem death is a state in which a person has suffered irreversible brain damage
and cannot breathe without the aid of artificial ventilation. It represents the state at
which a person becomes truly dead, even though the heart is still beating. There are
detailed criteria that enable a reliable diagnosis of brain death to be made. Most
organs for transplantation come from people who are brain dead. These people are
often called heart-beating donors (paragraph 1.7).
Cadaveric organs
Organs obtained from people who have died (paragraph 1.7)
CD59
Cell
CD59 is a human complement regulating molecule. It prevents complement proteins
attacking the body’s cells. (It is called CD59 because it is a member of a group of cell
surface molecules called CD antigens.) (paragraphs 3.13, 3.25 and 3.29).
The cell is the basic unit of any organism. The human body contains 100 million
million cells, each of which is too small to see with the naked eye. Each cell is
surrounded by a cell membrane which has, on its surface, protein molecules. Some of
these protein molecules are complement regulating proteins. Inside the cell is the
nucleus, which contains the genetic material of the cell. Examples of cells are red
blood cells, bone marrow cells and pancreatic islet cells. Cells group together to form
tissues, and tissues group together to form organs (paragraphs 1.9 and 3.8).
Chromosome
The thread-like DNA in a cell is divided into several separate lengths. Each length
forms a structure called a chromosome. There are two copies of each chromosome in
every cell. Human cells contain 23 pairs of chromosomes (paragraph 3.28).
Complement proteins (see complement system)
Complement regulating proteins
Complement regulating proteins are molecules found on the surface of the body’s
cells. They prevent complement proteins attacking the body’s cells. Examples of
complement regulating proteins are DAF, CD59 and MCP (paragraph 3.12 - 3.13).
Complement system
The complement system is a system of twenty complement proteins found in the
blood. It is an important element of the immune response to infectious organisms
or to a transplanted organ or tissue. The immune response starts when antibodies
stick to antigens on the infectious organism or transplant. A reaction is triggered
with one complement protein activating the next, and so on. Ultimately, the
complement proteins at the end of the chain attack the foreign organisms or the cells
of a transplanted organ, punching holes in them and thus destroying them (paragraph
3.12 - 3.13).
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