Scientists in California say they have produced embryos that are clones of two men, a potential step toward developing scientifically valuable stem cells.
The new report documents embryos 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. It matured enough to produce stem cells, but none were extracted.
Stem cells weren't produced by the new embryos either, and because of that, experts reacted coolly to the research.
"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."
Dr. 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.