Researchers have successfully grown sheep embryos that contain human cells, a breakthrough that may someday save the lives of many patients who need an organ transplant.

Pablo Ross, from the University of California, Davis, and colleagues announced at this week's meeting of the American Association for the Advancement of Science in Texas that they have grown sheep embryos with human cells.

Growing Sheep Embryos For Organ Transplant

Researchers have been using genome editing technique to produce animal embryos that do not develop pancreas. The objective is that human cells introduced to these embryos would grow to replace the missing organ.

Researchers have already worked on pig embryos but there are several advantages for using sheep embryos, one of which is that these can be easily produced by IVF. Fewer sheep embryos are also required for an experiment.

"For a pig we typically transfer 50 embryos to one recipient," said Ross. "With the sheep we transfer four embryos to one recipient."

Sheep also have heart and lungs that are similar to those of humans. They also produce organs that are about the right size for the human body. Depending on the organ a patient needs, organs are typically matched using characteristics, which include the size of the organ needed.

"The sheep is a good model for many human conditions," Ross said. "The size of the sheep organs is similar to human size, some of the organs are physiologically similar between sheep and humans and a lot of cardiovascular research is done in sheep because it has some similarities to humans in terms of heart shape."

Ross and colleagues transplanted human stem cells into the preimplantation embryos of sheep. The embryos are then allowed to grow for a week before these were implanted into a surrogate sheep. The researchers are currently allowed to let these chimeric embryos develop for 28 days so the surrogate animal is slaughtered after 21 days.

About one in 10,000 cells in the sheep embryos that the researchers developed are human. Nonetheless, they said that more work is needed to raise the proportion of humans cells in the chimera.

Thousands On The Organ Transplant List

Growing the human organs inside animals offers hope of revolutionizing organ transplantation by increasing the supply of organs and possibly develop genetically tailored organs that can significantly reduce odds of transplant rejection.

More than 76,000 individuals in the United States are on the organ transplant list. It will take years for them to get to the top of this list. According to the United Network for Organ Sharing, more than 7,000 patients who needed an organ transplant died in 2016. Some patients who were lucky to receive transplants see organs rejected.

To date, more donated organs come from deceased donors.

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