Fresh hope for transplant patients
Hearts from genetically modified pigs could soon be transplanted into cardiac patients after an organ implanted into a baboon survived for more than two and a half years.
Scientists hope the procedure, known as xenotransplantation, could combat the dire shortage of organs from human donors, which often leads to patients dying before they receive a transplant.
Using a technique described as ‘immunomodulation’, researchers say they have overcome the natural rejection that occurs when tissue from another species is implanted into a body.
Normally the immune system attacks organs and tissue that it does not recognise.
But scientists based at the National Heart, Lung and Blood Institute in Maryland, used hearts from pigs that had been genetically modified to make the organs more tolerable to baboons.
They were then transplanted into five baboons, which were given a combination of drugs to alter their immune systems so it would not attack the organs.
While the idea of using organs from animals such as pigs for human transplants has been around for some time, developments in stem cell cloning techniques has opened up the possibility of a new approach.
Animal organs, like many human organs, will be rejected by the immune system of recipients without powerful supression drugs.
But by using the stem cells taken from patients, scientists believe it may be possible to grow organs that are a perfect match for them, reducing the risk of rejection.
It relies upon a cutting-edge fusion of technologies, including recent breakthroughs in stem-cell biology and gene-editing techniques.
By modifying genes, scientists can now change the DNA in pig or sheep embryos so they are genetically incapable of forming a specific tissue.
Then, by adding stem cells from a person, they hope the human cells will take over the job of forming the missing organ, which could then be harvested from the animal for use in a transplant operation.
Dr. Muhammad Mohiuddin, a chief of the transplant section of the cardiothoracic surgery research program at the National Heart, Lung and Blood Institute, said the breakthrough was a big step towards delivering xenotransplantation in humans.
He said: ‘It is very significant because it brings us one step closer to using these organs in humans.
“Xenotransplants – organ transplants between different species – could potentially save thousands of lives each year that are lost due to a shortage of human organs for transplantation.”
The researchers, whose work is published in the journal Nature Communications, used pigs that had undergone three genetically modifications so they organs appeared less alien to the recipient animal’s immune system.
In a previous study, researchers had shown that using organs from these pigs alone had allowed them to survive for up to a year in a baboon.
But in the new work, the researchers also used a cocktail of antibodies and drugs that allowed them to fine tune the immune response in the baboons so they did not reject the transplant.
Five of the animals were given the modified pig hearts, which were connected to the baboon’s circulatory system alongside their own original heart.
While the implanted pig organ did not replace the baboon’s heart, they were found to continue beating for up to 945 days with the help of the antibody and drug treatment.
On average the implanted hearts kept beating for 298 days.
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