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Xenotransplantation is basically the transplant of organs and tissues from one species to a different species i.e. animal to human. There has been a long history of this dating back to 1682. It is not a new procedure that is being researched. Pigs and primates, mostly chimpanzees and baboons, are most often used in experiments concerning Xenotransplantation.
In 1682 a bone from a dog was used in Russia in an attempt to repair an injured skull. It was reported successful, but the Russian had the bone removed soon after the procedure was complete due to pressure from his church.
In the late 1800s, frog skins were often used as a way of healing burns or skin ulcers by grafting the affected skin
In 1905, a French surgeon grafts kidney tissues from a rabbit into a child. However the child died two weeks later.
In 1963-64, Thomas Starzl grafts baboon kidney into six patients. All six patients died, only surviving between nineteen and ninety-eight days.
Also in this year, Dr. Keith Reemtsma gave twelve patients chimpanzee kidneys. Most failed within two months of surgery. However one patient lived for nine months which is the longest time for a Xenotransplantion patient to live up to now.
In 1977, a twenty-five year old woman receives a baboon heart but dies only six hours after surgery. About the same time, a sixty year old man receives a chimpanzee heart to assist his own heart but died four days later.
More recently in 1995, immune cells from a baboon were used for an AIDS patient. The patients' condition improved though the cells died quickly.
In 1997, pig fetal nerve cells used in patients with Parkinson Disease. Pig cells survived in one patients' for seven months.
One of the most famous Xenotransplantation cases is the 'Baby Fae Case'. Stephanie Fae Beauclair was born on October 14 1984. She was born with hypoplastic left heart syndrome. This is where the left side of heart is severely underdeveloped. She underwent a procedure to give her a baboon heart. The procedure was carried out by Leonard L. Bailley at Loma Linda University Medical Centre in California. It was thought that she would have been an ideal patient for this procedure as she was so young that her immune system would not have been fully developed therefore theoretically eliminating the risk of organ rejection. She died twenty-one days despite the use of immunosuppressive drugs. It has been suggested that the baboon heart was too large for her body to handle. However organ rejection is more likely to have occurred. There was huge ethics and legal rights surrounding this case which will be discussed later. 75 complaints were received in regards to cruelty to baby Fae whereas 13,000 complaints were received with regards to cruelty to the baboon.
Is Xenotransplantation being used today?
Pig and cow heart valves have been used to replace human heart since 1975. They are still commonly used however they only last 10-15 years. They are referred to as biological valves. The pig heart is like the human heart and therefore it makes the best anatomical fit if the valves need replaced. Mechanical valves are now also available. However with this type of valve an anticoagulant is needed to stop blood clots from forming on or around the valve. The use of biological valves does not require the need for anticoagulant drugs. The valve is first examined and must be of a high quality before it is then treated with a solution to preserve and stiffen it. Glutaraldehyde is used to do this process. In bovine heart valves, leaflets are sewn onto a metal frame made from a cobalt nickel alloy. A wire is used to make three U-shaped prongs. Biological valves are better suited for elderly patients as they have a durability of ten to fifteen years, and in elderly patients they will probably only have to endure this procedure once.
Advantages of Xenotransplantation
There are many advantages of xenotransplantation.
Once xenotransplantation becomes available, there will be no shortage of organs and it will be possible to offer transplantation to all patients in need. There are huge waiting lists for organs and many people die whilst waiting for an organ. Xenotransplantation has the potential to save lives.
With access to pig organs, more liberal age limits could be applied making it possible to accept elderly patients who are not accepted today.
Using pig organs, the transport procedure can be prescheduled allowing for the pre-treatment of the recipient with immunosuppressive agents.
Pig organs would make it possible to alleviate graft rejection by modifying the donor tissue through genetic engineering therefore making the outcome dependent on recipient treat with immunosuppressive drugs.
Pigs are already slaughtered on a daily basis.
What are immunosuppressive drugs?
Immunosuppressive drugs are taken in order for a patient who has received an organ or a tissue, human or animal, immune system not to attack the organ or tissue. In xenotransplantation, immunosuppressive drugs will be taken to stop the immune system recognising the new organ or tissue as foreign i.e. non-self and start to destroy it. They suppress the activity of the lymphocytes which are responsible for anti-body production.
What is genetic engineering?
Genetic engineering means altering the genes in an organism to produce an organism with a new genotype. It is also known as recombinant DNA technology.
Isolate the desired gene
Insert it in a host using a vector
Produce as many copies of the host as possible
Separate and purify the product of the gene
This is a basic overview of how genetic engineering works. It could play a major part in Xenotransplantation and making it a successful procedure because a patient could be less dependent on drugs.
Stem cell use in Xenotransplantation
Stem cells, an already hot topic, have a high role to play in xenotransplantation. The animal stem cells would perform the same function as human stem cells or hoped to assume, and because of the fact that these stem cells would not come from human embryos scientists hope to gain more support in their research. Organ transplants have been the main theme in xenotransplantation for the most part as can be seen in the history of xenotransplantation. There are a couple of different ways these organs can be used. The most common is to replace the original organ with the animal organ. Another idea is to actually add the animal organ as a helper to the human organ as both a permanent and temporary fix. One of the more obscure, but still important uses of xenotransplantation is the delivery of genes for therapeutic purposes. The idea behind this is the hope that certain animal sources might be genetically engineered to better express a gene under regulated conditions.
Disadvantages of Xenotransplantation.
There are also many disadvantages to Xenotransplantation.
Pigs are distantly related to humans therefore diseases can be transmitted and rejection is more likely to occur
Primates are slow-breeding and due to the potential threat of extinction that could result from the extremely large practice of using primates for transplant outweighs the potential benefits
It is not known how animal organs could affect humans
It is unknown how this will impact on the human race- should a new infection be introduced for which there is no cure
The most common issue of xenografts is that it could be seen as doing something unnatural
Some already see human-human transplants as wrong
Some believe that man has no right to interfere with natural life
There are also many animal rights that come into the argument - why should animals be killed even for food?
It could be argued that the bible allows animals to be killed for food and some would say xenotransplantation could come into this as it would save human life
Many believe that xenograft technology is just another way for biotech companies to make money and they are not concerned with the welfare of the animals or mankind.
The emotional impact on a person who has an animal organ or tissue inside their body.
Are we creating our own subclass of human? Patients who underwent a xenograft would be genetically and anatomically different from the rest of our species.
Dispute would also arise from those of a Judaism and Islam background. They believe that swine are unclean and are forbidden to eat it therefore I doubt they would be willing to allow their organ to be replaced with a pig organ.
The future for Xenotransplantation.
Xenotransplantation needs to be perfected in such a way that there is no need for a replacement human organ or extensive therapy after the procedure has been carried out. The largest barrier which needs to be overcome in a xenotransplant is to genetically alter the donor organ, either by gene therapy or gene splicing, in order for the organ to be acceptable to human antibodies to eradicate the problem of organ rejection. It is becoming more apparent that a new breed of pigs and/or baboons would be need to be developed solely for harvesting their organs.
It is very clear to say that the history of xenotransplantation is not very convincing. Practically all of the patients have died after the procedure where a major organ has been replaced. However with the use of biological heart valves, it does prove that animal tissues can successfully be used in humans. I do believe we are closer than ever before to perfecting the xenotransplantation because of techniques such as genetic engineering. However I believe that the mountain to climb with regards to the science behind xenotransplantation is just as big as public attitudes towards it. In 1998, the National Kidney Foundation releases results from a survey which they had conducted regarding attitudes towards xenotransplantation. The results were very interesting.
50% of healthy persons would accept organs from other species
62% of those in the survey agreed that xenotransplantation is an option due to the short supplies of human organs
75% would consider xenotransplantation for a loved one if no human organs were available.
However, I have to question to these results. They are published to show that public attitudes are more for xenotransplantation. The first bullet point states that half of those surveyed would accept animal organs. Obviously the other half would not accept it. Also, it is very easy to say you would accept an animal organ or would want a loved to accept one, but if they were really in that situation would their feelings be the same?
It is obvious that a lot more research is needed in this field. It could take many more years to perfect this procedure and some would argue that it is unnecessarily killing animals for this research.
I am somewhere in the middle of this topic. I do believe that it should be researched because it could save lives. However, we will not know how this will affect a patient in 1 year, 5 years or 10 years because it is a new procedure and we will not know the long term effects. And also, all the research in the world would not show if a new strain of a virus or disease would arise to which there would be no cure for. I also believe that is will cause a lot of controversy from animal activists and from religious groups.