Researchers have been able to create genetically modified piglets that are cleaned of the viruses that could causes diseases in humans. This could open up new avenues in organs transplants from pigs to humans. The process of transplanting organs or tissues from animals to humans is called xenotransplantation. The report was published this Tuesday in the journal Science.
If successful this could pave the way for organ transplants such as livers, hearts and other organs from pigs into humans. According to Dr. David Klassen, chief medical officer at the United Network for Organ Sharing – which is a private, nonprofit organization that manages the nation’s transplant system, this could be a “real game changer”. Dr. Klassen was not involved in this study but he explained that there were 33,600 organ transplants last year and the waiting list was almost four times as long at 116,800 patients. The gap between the demand and supply is huge he said.
Dr. George Church, a geneticist at Harvard who led this new study said that transplants from pigs to humans can become a reality in two years. Two new techniques have been utilized in this study – gene editing and genetic cloning. There have been speculations regarding use of pig organs for humans for years now. The size is just about right and functions are also similar. Although animal welfare questions remain as manufacturers are anticipating a huge rise in demands for pig organs. On the other land long term safety or other issues with these transplants is also not known.
Dr. Jay Fishman, co-director of the transplant program at Massachusetts General Hospital has said that major religious groups have concluded that pig organs may be used in lifesaving transplants. Scientists have assured that if pigs were to be used for transplants, they would be anesthetized and killed humanely. Also the numbers needed for the transplants to meet the waiting lists is far less than the number of pigs killed each year for food.
It was Dr. Fishman who in 1998 found that hidden in pig DNA were genes for viruses that mimiced those causing leukemia in monkeys. These are called porcine endogenous retroviruses (PERVs). When these pig cells grew in the laboratories, next to human embryonic kidney cells, these viruses spread to the human cells. The viruses are retroviruses and once the human cells became infected, they infected other healthy cells as well. This brought the research to an end since these viruses could mean deadly outcomes among transplant recipients. But this new study shows that these viruses could be worked around using genetic editing of the pig DNA. Genetic editing is being done by CRISPR that has revolutionized gene therapy.
For examples patients who have type 1 diabetes have damaged pancreas cells. The pig pancreas cells can be transplanted using a sheath to prevent the immune system from attacking it. Pig skin could also be used as skin grafts among burn patients. Dr. A. Joseph Tector, a transplant surgeon at the University of Alabama at Birmingham added that pig retroviruses can be treated with drugs used against HIV AIDS virus. Dr. Fishman said the risk of transplanted organs spreading the virus to others is low.
Dr. Church and his colleagues took up this challenge as used CRISPR to cut out the viral DNA from the pig cell DNA. Then the scientists cloned the edited cells. The cells were brought back to their earliest developmental stage and then inserted into an egg. Then the genetic material was inserted and the egg was allowed to develop into an embryo. The embryos were implanted in sows. These grew into piglets that were genetically identical and did not have the viruses. Many of the embryos and piglets were lost in the process of this complex cloning. Dr. Church and his colleagues ended up with 15 living piglets with the oldest being 4 months of age. None of them have the viruses.
Dr. Church’s company eGenesis, would be selling the genetically altered pig organs. Further the pigs would be engineered to carry human genes so that those getting the transplants do not need to take anti-rejection medications.
References
Mayo Clinic researchers advocate for comprehensive TPMT genotyping across ancestries