MONKEY embryos have been cloned for the first time and used as a source of embryonic stem cells. Researchers should now be able to test stem cell therapies on non-human primates, before testing on humans.
Ever since 1997, when the world learned of Dolly the sheep, researchers have been trying to clone non-human primates. Then in February a South Korean team made headlines when they cloned a human embryo using a new, gentler method that involved coaxing embryos to develop to the blastocyst stage (91av, 21 February, p 6). Embryos at this stage can yield embryonic stem cells (ESCs), which are universal precursors to all the cell types in the body and thus the holy grail for clinicians hoping to repair damaged organs and tissues. But cloning human embryos is fraught with ethical problems, besides the practical problem of obtaining donor egg cells.
Cloning non-human primate embryos had remained elusive, despite the success with human embryos. Experiments by Gerald Schatten’s group at the University of Pittsburgh in Pennsylvania showed that cloned monkey embryos had many genetic abnormalities. This was presumably because the technique of sucking out the nucleus of an egg with a micropipette was destroying some of the molecules needed for cells to divide properly.
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Now Schatten’s team has collaborated with the South Korean researchers to apply their “gentle-squeeze” technique to macaque monkeys. Of 49 cloned embryos, three became blastocysts and yielded ESCs, the team reported at an American Society for Cell Biology meeting in Washington DC this week. None survived beyond the blastocyst stage, suggesting a viable cloned primate is still a long way off.
The team has not yet established permanent cultures from any of the stem cells, but their study does suggest that experiments using cloned ESCs will be possible in non-human primates. One important goal is to find out whether replacement tissues or organs could be created from the recipient’s own ESCs.
“Success fusing eggs with adult cells taken from unrelated individuals suggests males, too, could be cloned in this way”
Such experiments in non-human primates will be crucial to test the safety of stem cell therapies before they are tried in people, says Judith Vaitukaitis, the director of a National Institutes of Health division in Bethesda, Maryland that helps to manage human stem cell lines.
The Korean team had the most success when an egg was fused with the nucleus of an adult cell from the same woman. But Schatten’s team had equal success fusing eggs with cells taken from unrelated adults, which suggests males, too, could be cloned in this way. “This is important for those of us who carry a Y chromasome,” says Schatten