Feb. 19 (UPI) -- Scientists in California are working on a way to reduce organ transplants and rejections: Growing embryos in sheep and pigs containing human patients' cells.
In a transplant breakthrough, scientists at the University of California said they have achieved sheep embryos in which around one in every 10,000 cells was human.
The researchers presented preliminary findings Saturday at the American Association for the Advancement of Science's annual meeting in Austin, Texas. Last year, the same researchers introduced human stem cells into early pig embryos, producing embryos with about one in every 100,000 cells being human.
Last year, 34,770 organ transplants were performed in the United States, including 19,849 kidney transplants, and 115,035 people are currently waiting for an organ transplant to save their lives -- so the need for more sources of usable organs is not small.
"We recognize there is a bit of shortage of organs in organ transplants," Dr. Pablo Ross, an associate professor in the Department of Animal Science at the University of California, Davis, told UPI. "Certain conditions are only cured by organ transplant. But only a small small portion get organs. To the extent about 20 people die every day awaiting transplants."
"So science is looking for alternatives to try to procure organs from multiple sources," Ross said.
They have included artificial organs, ones grown in the lab and modifying animals.
"The approach we are pursing involves trying to grow human organs inside an animal," he said. "It turns out its difficult to emulate development of what happens from one embryo to animal."
But Ross said they allowed chimeric embryos to develop for 28 days an estimated 20-30 sheep last year. The team has also used genome editing techniques to produce pig and sheep embryos unable to develop a pancreas.
Past research has been done with other animals and rats, but he said these animals aren't as suitable because they are small.
"Adult sheep and pig have similar size, similar anatomy and specifically grow fast," Ross said.
He noted a sheep can grow from one cell to 200 pounds in 9-10 months compared with one human cell to a nine-pound human baby during the same time. And because the organs are grown from patients' cells, there is less of a chance of rejection.
The U.S. National Institutes of Health currently bans funding of human-animal hybrids but it has been considering lifting the ban. And these so-called chimera studies would undergo an extra layer of ethical review.
But private and public research funds are available. Ross' work includes funding from the California Institute of Regenerative Medicine, which was created in 2004 when California voters approved stem cell research funding of $3 billion.
Although the research is preliminary, Dr. Hiro Nakauchi of Stanford University, who is part of the team, is optimistic humans can receive organs grown in animals.
"It could take five years or it could take 10 years but I think eventually we will be able to do this," he said at the conference in Austin.
And he said animals don't take on human characteristics.
"The contribution of human cells so far is very small. It's nothing like a pig with a human face or human brain," he said. "We have published several papers showing we can target the region, so we can avoid human cells differentiating in to the human brain or human gonads."