Xenotransplantation - Nuffield Council on Bioethics

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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). 136
Annex E : Glossary Concordant xenotransplantation This refers to xenotransplantation between closely related species, where the immune response is not too extreme (paragraph 3.18 - 3.19). DAF DAF (decay accelerating factor) is a human complement regulating molecule present on the body’s cells. It prevents complement proteins attacking the body’s cells (paragraphs 3.13, 3.25 and 3.29). Dialysis Dialysis of body fluids is used for patients with kidney failure. A synthetic membrane, or the peritoneum, is used as a dialysing medium across which the blood can be freed of toxic waste products normally excreted by the kidneys. Patients spend several sessions a week having dialysis, and can live relatively normal lives between treatments, which is not the case when most other organs fail (paragraph 2.13). Discordant xenotransplantation <strong>Xenotransplantation</strong> between distantly related species, where the immune response is extreme (paragraph 3.23). DNA DNA (deoxyribonucleic acid) is the biochemical substance that genetic material is made of. DNA has a thread-like structure. A gene is a short length of DNA containing the information needed to make one protein. The DNA in a cell is in several long lengths each of which contains many genes. Each length of DNA forms a structure called a chromosome. Elective ventilation Elective ventilation involves placing patients for whom death is inevitable on a ventilator so that their breathing is artificially maintained. This keeps their organs in a suitable state for transplantation (paragraph 2.9). Endogenous retroviruses Retroviruses are RNA viruses that infect cells and then become inserted into the genetic material of the host cells. Some retroviruses will then start to reproduce. Endogenous retroviruses, however, remain in the genetic material of the host cells in a dormant state. If the retrovirus is inserted into the germ cells (eggs or sperm) it may be passed down from parent to offspring. A procedure such as transplantation might reactivate endogenous retroviruses in a pig organ, leading to the production of new retroviruses in the human recipient and their insertion into the genetic material of the human cells (paragraph 6.9). Foamy virus A form of retrovirus that can infect white blood cells (paragraphs 6.10 and 6.28). Galactosyl -1,3-galactose (see -gal) 137
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NUFFIELD COUNCIL ON BIOETHICS Anima
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Preface Preface Since the N
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Table of contents Table of contents
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Working Party on Xenografts Working
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Summary of recommendations Summary
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Summary of recommendations Effects
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The promise and the problems Chapte
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Alternatives to xenotransplantation
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Xenotransplantation</strong
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Transmission of infectious diseases
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Xenotransplantation - Nuffield Council on Bioethics

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