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The technique represents an important step towards growing human organs for transplant, say researchers
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A team at the Salk Institute has grown the first living embryos containing cells from both human beings and pigs.
To create the human-pig chimeras, the researchers injected human stem cells – master cells that can develop into any type of tissue – into pig embryos. The stem cells survived and began to integrate with the pig tissue to form a chimeric human-pig embryo. These embryos were implanted in sows and allowed to develop for up to four weeks.
“This is long enough for us to try to understand how the human and pig cells mix together early on, without raising ethical concerns about mature chimeric animals,” said lead investigator Juan Carlos Izpisua Belmonte.
However, the process is currently very inefficient – out of the 2,075 embryos created, just 186 stayed alive for the full four weeks.
“It’s like when you try to duplicate a key. The duplicate looks almost identical, but when you get home, it doesn’t open the door. There is something we are not doing right,” said Izpisua Belmonte. “We thought growing human cells in an animal would be much more fruitful. We still have much to learn about the early development of cells.”
Though they sound disturbing, human-animal chimeras may someday provide a means of growing human tissues and organs for transplant – potentially saving thousands of lives.
“The ultimate goal is to grow functional and transplantable tissue or organs, but we are far away from that,” said Izpisua Belmonte. “This is an important first step.”
The next step is to guide the stem cells into forming specific human organs within the pigs. The team has previously used CRISPR genome editing tools to
delete specific genes involved with organ development in fertilised mouse egg cells and replace them with rat stem cells. As the organism matured, the rat cells filled in where mouse cells could not, forming the functional tissues of the organism’s heart, eye or pancreas.
The researchers are now working on reproducing this effect in the human-pig embryos.
“WE STILL HAVE MUCH TO LEARN ABOUT THE EARLY DEVELOPMENT OF
ABOVE: The work of the Salk Institute team, led by Juan Carlos Izpisua Belmonte, could pave the way for lab-grown