All five got pregnant. Researchers terminated the pregnancies of three of them to test the fetuses for chimerism, and they found it. Soon after, the remaining two monkeys delivered twins (named Roku and Hex for the Japanese and Greek words for "six") and a singleton, Chimero. All appear male, though testing on their cells reveals that they also contain individual female genomes.
Growing up chimeric
The monkeys were delivered by C-section. Their mothers rejected them, probably in response to the nonnatural method used to deliver them, so now they are being raised by a foster mama.
Researchers aren't yet sure whether Roku, Hex and Chimero will be able to reproduce. It takes rhesus macaques four to five years to reach sexual maturity.
There are no plans to create human chimeras and no need to, Mitalipov emphasized. This research by itself should help scientists in conducting biomedical research more relevant to humans, he said.
Chimeric mice, for instance, are used to produce genetically engineered "knock-out" mice that carry deletions of important genes. In that way, researchers can see firsthand what genes do or don't do.
The results may be useful in stem cell therapy, Mitalipov said. Researchers believe that stem cells cultured in Petri dishes could be transplanted into adult patients to treat conditions such as paralysis or Parkinson's disease.
"But this is based on mouse models," Mitalipov said. "We didn't know whether primates have this capacity."
The chimeric monkey study, reported today (Jan. 5) in the journal Cell, shows that primate cultured stem cells probably have some potential to differentiate, but they aren't comparable to in-vivo stem cells, or stem cells produced in the body, Mitalipov said.
"We cannot model everything in the mouse," Mitalipov said. "If we want to move stem cell therapies from the lab to clinics and from the mouse to humans, we need to understand what these primate cells can and can't do. We need to study them in humans, including human embryos."
Even though the researchers found success without culturing, cultured cells shouldn't be written off, said Richard Behringer, a geneticist at MD Anderson Cancer Center in Houston. The reason the cells didn't work in monkeys may be due to something in the laboratory process, not because of the cells themselves, Behringer told LiveScience.
"We know so little about the early embryology of our cells," Behringer said. "We know about the fertilization to the blastocyst stage because you can do that in vitro, but after that there's very little known about human embryology — this is when a woman may not even know she's pregnant. Having the monkey model is useful to understand the early embryonic development, where the monkey can stand in for the human."
- Top 10 Wacky Animal Stories of 2011
- The History and Future of Birth Control
- Blossoming Body: 8 Odd Changes That Happen During Pregnancy