GM pigs raise hopes for human organ transplants

Herbert Rhodes
August 14, 2017

Growing human transplant organs in pigs has become a more realistic prospect after scientists used advanced gene editing to remove threatening viruses from the animals' DNA.

This is the first time researchers have been able to demonstrate they were able to inactivate PERV and open the way for xenotransplantation (the act of transplanting animal organs to humans) without cross-species contamination.

Cloning often fails; most of the embryos and fetuses died before birth, and some piglets died soon after they were born.

"I'm a strong believer that science can help us improve health care if we look holistically for a solution", says Yang, lead author on the paper and chief science officer of eGenesis, the biotechnology company funding advancements in the research.

Yang believes that CRISPR can accomplish what previous approaches have not: make multiple, simultaneous changes in pig DNA so that the animals' organs work, and work safely, in people. More than 117,000 people are on the waiting list for organ transplants in the USA, according to the Department of Health and Human Services. But in the late '90s, the discovery of a type of retrovirus in pig DNA complicated matters. For one thing, tissue from a different human-let alone a different animal-is enough to freak out our immune systems and cause them to attack. A team of worldwide science is able to genetically modify the piglets so that their organs are more compatible for transplants in humans.

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In 2015, eGenesis announced they had used the revolutionary gene-editing technology CRISPR-Cas9 to target a record-breaking 62 genetic copies in a number of cloned pig embryos. Porcine retroviruses (PERVs) are now one of the big safety barriers preventing us using pigs as organ donors. "This is a great step forward for xenotransplantation", says Joachim Denner of the Robert Koch Institute in Germany. In a lab dish the pig viruses infected human cells, and those infected cells were able to infect other human cells that had not been directly exposed to pig cells. However, other researchers argue that it could be years before scientists even know if pig organ transplants are safe.

From about 200-330 embryos per sow transferred across to 17 sows, they produced 37 piglets, of which 15 remained alive up to four months.

As it is now, receiving an organ transplant in many cases requires waiting for a donor to die.

Scientists pursuing this goal argue that the few thousand pigs grown for their organs would represent just a small fraction of the estimated 100 million pigs killed in the USA each year for food. Just last week, USA scientists were able to demonstrate they could successfully CRISPR out a faulty heart gene mutation in human embryos. Pig heart valves already are routinely transplanted into patients.

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