Scientists in California say they have produced embryos that are clones of two men, a potential step toward developing scientifically valuable stem cells.
The newly reported embryos were made with ordinary skin cells. But it's not the first time human cloned embryos have been made.
In 2005, for example, scientists in Britain reported using embryonic stem cells to produce a cloned embryo (see story). It matured enough to produce stem cells, but none were extracted.
The new embryos announced this week did not result in extracted stem cells either, and because of that, experts reacted coolly to the research.
"Only a Matter of Time"
"I found it difficult to determine what was substantially new," said Doug Melton of the Harvard Stem Cell Institute.
He said the "next big advance will be to create a human embryonic stem cell line" from cloned embryos. "This has yet to be achieved."
George Daley of the Harvard institute and Children's Hospital Boston called the new report interesting but agreed that "the real splash" will be when somebody creates stem cell lines from cloned human embryos.
"It's only a matter of time before some group succeeds," Daley said.
Korean scientist Hwang Woo-suk claimed a few years ago that he'd created such cell lines, but that turned out to be a fraud.
(Related story: Cloned Dog Real, Other Hwang Research Not, Study Finds [January 11, 2006])