Gene editing spurs hope for transplanting pig organs into humans

Harvard geneticist George Church

Harvard geneticist George Church

Pig organs are similar in size and function to our own, and people are less squeamish about harvesting body parts from an animal raised for meat than they would be about a primate's.Yet one major hurdle that has continued to vex any such cross-species transplants, or xenotransplants, has been the threat of transmitting viruses that can infect people and pigs alike: The latter's genome includes 25 so-called retroviruses that apparently do nothing to porkers but might transmit diseases to people-especially immune-compromised transplant patients.

An alternative method being developed includes injecting human stem cells into pig embryos, so they grow human organs. Between 2012 and 2016, there was a almost 20 percent increase in the number of transplants that happened in the United States, and that number is only expected to increase as the population grows older, according to the United Network for Organ Sharing.

In 2015, Church and other scientists involved in today's research showed that they could eliminate all 62 copies of a PERV gene in pig cells using CRISPR. That means their organs wouldn't risk infecting humans if transplanted. These are known as endogenous retroviruses which, although normally silent, can be activated to become fully infectious for human cells when pig cells carrying these retroviruses are co-incubated with human cells.

To overcome this, researchers used the CRISPR-Cas9 gene-editing technique to inactivate all the PERVs in a porcine primary cell line and generated PERV-inactivated pigs through somatic cell nuclear transfer.

"The problem is that all pig cells carry cancer viruses embedded in their DNA". With only a few more gene editing breakthroughs, we might start seeing pig organs saving thousands of lives in only a few years.

And Professor Ian McConnell, from Cambridge University, said: "The safe use of pig organs such as kidneys in xenotransplantation has been seen as an approach which could be used to overcome the shortage of donor organs in human transplantation".

The team then implanted the PERV-free embryos into surrogate sows and demonstrated the absence of PERV re-infection, initially in fetuses and finally in recently born piglets. In any event, said Dr. A. Joseph Tector, a transplant surgeon at the University of Alabama Birmingham, pig retroviruses are very sensitive to the drugs used to treat HIV.

Through their private company called eGenesis, Harvard researchers, together with Chinese and Danish collaborators, have created genetically engineered piglets that are free of viruses that might harm humans.

Fears that pig organs would infect humans with freaky retroviruses brought the research to a halt.

They successfully transplanted hearts and kidneys from those pigs into monkeys and baboons. "Our study highlights the real concern and the significance of addressing this issue", study co-author Luhan Yang, the co-founder of biotech company eGenesis, tells The Verge.

An estimated 100 million pigs are killed in the United States each year for food, The New York Times reported.

"About 22 people a day die waiting for a transplant", he said.

From those cells you can clone pigs that grow up, at which point you can take the organs from them.

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