RENO, Nev. — In ancient mythology, chimeras were part animal, part human — imaginary creatures that took many forms. Now scientists are actually creating them. The new creations may look like sheep, but they are part human.
"They're sheep still," says Dr. Esmail Zanjani with the University of Nevada. "But they have significant amounts of human cells in their different organs."
Zanjani creates them at the University of Nevada's agricultural research station outside Reno. The main purpose is to produce a source of organs, especially livers, to transplant someday into humans.
"By putting these organs back into the human, we may be able to allow the humanized portion to regenerate into a full-functioning organ," says Zanjani.
Overcoming organ rejection
To make the chimeras, researchers use stem cells — cells that can develop into many other kinds of cells. Here's how it works: The researchers take stem cells from the bone marrow of adult humans. They put these cells into the sheep while the animals are growing in their mothers' wombs. When the sheep are born, they have millions of human cells in all of their organs. Those cells are genetically identical to the person who donated the bone marrow.
So, in other words, if a patient needed a liver, doctors would take some of the patient’s cells and use a sheep to grow a liver for that patient.
"Your body will vigorously reject the sheep part of the liver, but allow the human part to remain, because it's your own cells," says Zanjani.
The big ethical question is: Could there be a point where these animals have so much human tissue that society finds these experiments objectionable? That’s a concern because the sheep even have human brain cells.
"That's something we have been very sensitive about," says Zanjani. "The level of human cell activity in the central nervous system is rather low. It's less than one percent. And we have not seen these animals talk back to us or behave in any fashion as anything but sheep."
Still, many scientists believe the research will get increasing attention for its medical potential and its ethical dilemmas.
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