Xenotransplantation Flashcards
Xenotransplantation
The process of grafting or transplanting organs or tissues between members of different species.
Organ statistics
•The total number of people on the Organ Donor Register is 19,320,264.
•Up to 1,000 people die every year due to a shortage of organs for transplant, that is 3 people every day.
•There are currently 7,410 people on the national waiting list for an organ transplant.
•There are currently 139 children on the national waiting list for an organ transplant.
•Although 90% of people say they support organ donation, just 30% of the UK population are on the NHS Organ Donor register
Regans Kantian position
-Regan’s position is Kantian (though Kant himself did not apply it to non-humans), namely that all subjects-of-a life possess inherent value and must be treated as ends-in-themselves, never as a means to an end.
-He also argues that, while being the subject-of-a-life is a sufficient condition for having intrinsic value, it is not a necessary one: an individual might not be the subject-of-a-life yet still possess intrinsic value.
What can xenotransplantation involve ?
-Xenotransplantation can also involve the infusion or transplantation of body fluids, tissues or cells that have been in contact with the tissues or cells of another species outside the recipient’s body.
-For example, a person might be treated for liver failure by having their blood passed through an artificial device containing pig liver cells.
-Some non-living animal devices, such as pig heart valves, have been used in humans for many years.
-Xenotransplants differ from these devices in that they are alive and can perform the same functions as the organ, tissue or cells that they replace.
Why is xenotransplantation being considered?
-very successful way to treat a variety of illnesses.
-very few human tissues and organs are available for transplantation, so that many patients who could benefit from a transplant wait in vain for a suitable donor.
-Transplant specialists are therefore considering animals as a possible source of organs and tissues for human transplantation.
-The greatest benefit of xenotransplantation would be a potentially unlimited supply of cells, tissues and organs for use in humans.
-Recent advances in technology have increased the possibility of successful xenotransplantation and stimulated research in this area.
-For example, genetic engineering has allowed human genes to be inserted into pigs so that their cells, tissues and organs are less likely to be rejected when transplanted into humans.
What sort of diseases could it help?
-Xenotransplantation has the potential to treat a wide range of life-threatening or debilitating conditions.
-For example, it is possible that isolated cells could be transplanted to treat diseases such as diabetes, Parkinson’s disease, Huntingdon’s disease or strokes.
-Another possibility is that xenotransplantation could be used to ‘buy time’ while potential transplant patients wait for a suitable donor.
-There have been promising results from overseas trials in which isolated pig liver cells contained in a bioreactor were used to treat acute liver failure.
What does xenotransplantation research involve?
In order for xenotransplantation to become an option for human therapy, research is needed that includes:
• animal-to-animal studies (preclinical studies) - in which proposed xenotransplantation
procedures are tested on animals (eg pig-to-baboon kidney transplant); and
• animal-to-human trials (clinical trials) - in which animal products are used for xenotransplantation procedures on human beings (eg pig-to-human brain cell transplants).
Animal-to-animal studies are covered by existing regulations for research involving animals.
Why use pigs?
Pigs are considered the most suitable species as a source of material for xenotransplantation for several reasons:
• they reproduce quickly and have large litters;
• their organs are similar in size to those of humans;
• they are easy to rear in conditions free of particular pathogens (disease-causing organisms);
• the risk that they will carry pathogens that can infect humans is smaller than with nonhuman primates (apes and monkeys); and
• they can be genetically manipulated to reduce the risk of rejection.
Risks of xenotransplantation to participant
-The main risk to the recipient of a transplant is rejection due to the patient’s immune response.
-In human-to-human transplantation (allotransplantation), rejection has been largely overcome by tissue matching of donors and recipients, and by giving the recipient drugs that suppress their immune response.
-The risk of rejection in xenotransplantation is more severe because the differences between the donor and the recipient are much greater.
-The most promising approach at this stage is to genetically modify the source animals so that they do not cause such a strong immune response.
-Scientists have already produced several genetically modified strains of pig that show promising results.
Risks of xenotransplantation to wider community
-Xenotransplantation carries some risks for the wider community.
-The major concern for public health is that xenotransplantation might transmit an infectious agent (such as a virus) from animals to humans.
-Retroviruses are the chief concern, because there are many examples of such viruses moving from one species to become infectious in another.
-However, retroviruses do not always cause obvious signs of disease initially.
-If a retrovirus present in a xenotransplant were to infect the recipient of the transplant, it may spread to close contacts, carers and even the general population before it became obvious that an infection had occurred.
PERV
-PERV is present in almost all strains of pigs and cannot be removed by raising pigs in sterile conditions.
-Although PERV is inactive, and therefore harmless, in pigs, there are concerns that transplantation into humans may activate the virus, creating a new human disease that could spread to those close to the transplant recipient and eventually to the wider community.
-PERV can infect human cells in the laboratory, suggesting that it could infect humans through xenotransplantation.
-However, studies of around 150 people worldwide who have been transplanted with pig tissue or had their blood pass through pig cells have shown no evidence of infection with a virus or any other infectious agent originating from pigs.
-Approval of an animal-to-human trial would depend on there being an appropriate policy for testing the xenotransplant recipient and their close contacts for PERV and any other organisms that may emerge as a result of the transplant.
For xenotransplantation
-It increases the number of organ sources. A human organ transplant takes time because the procedure would depend on available resources. Pigs are readily available and have been used widely in xenotransplantation experiments.
-new infectious agents are less likely with pigs because humans have domesticated them for generations.
-The shortage of organs for transplantation results all around the world accounts for 20-35% of deaths of patients on the waiting list.
-The breeding of genetically modified pigs as well as new cloning techniques may be used to reduce the risk of organ rejection.
Against xenotransplantation
-There have been no successful xenotransplantation trials to date because of problems that arise from the response of the immune system of the patient. The responses are more extreme compared to human-to-human transplants and eventually leads to the rejection of the xenograft.
-There is a high risk of transferring diseases and viruses from animals to humans. For example, human contact with chimpanzee blood possibly transmitted an immune deficiency from chimps to humans, where it mutated into HIV and then to AIDS – now a global pandemic.
- Animals are sentient intelligent beings and cannot consent to being harvested for their organs.
-cruel and diminishes the quality of life of the animal.
AIDS
human contact with chimpanzee blood possibly transmitted an immune deficiency from chimps to humans, where it mutated into HIV and then to AIDS – now a global pandemic.
