Scientists in South Korea have succeeded in obtaining stem cells from cloned human embryos. A report published online today by the journal Science describes the work, in which 30 embryos of about 100 cells were created and used to harvest stem cells that later differentiated into a variety of tissue types. The findings offer hope for treating disease through so-called therapeutic cloning but are sure to revive ethical debates.

The list of successfully cloned animals includes sheep, mice, horses and cats, among others, but primates have proved difficult. In the new work, a team of researchers led by Woo Suk Hwang of Seoul National University collected 242 eggs from 16 unpaid volunteers who knew their eggs would be used for scientific experiments. The scientists transferred the nucleus of a somatic, or nonreproductive, cell into an egg from the same donor that had had its nucleus removed. The researchers used a slightly different technique to extract the contents of the eggemploying gentle extrusion instead of the more commonly used suction methodwhich, together with careful timing and the freshness of the donated eggs, may have aided their success.

Still, even with these improvements, the researchers could culture only 30 hollow balls of cells called blastocysts, which yielded just one embryonic stem cell line. The resulting stem cells differentiated into three tissue types, the researchers report. Furthermore, when transplanted into mice, the cells became more specialized, turning into cartilage, muscle and bone. "Because these cells carry the nuclear genome of the individual, after differentiation they could be expected to be transplanted without immune rejection for treatment of degenerative disorders," Hwang says. "Our approach opens the door for the use of these specially developed cells in transplantation medicine."

Such applications remain a long way off, however. "Were years away from any human use, of course," comments bioethicist Laurie Zoloth of Northwestern University, "but this is proof of principle." The researchers stress that they are opposed to reproductive cloning of any kind and are pursuing only potential medical applications of the technology. According to Donald Kennedy, editor-in-chief of Science, "the generation of stem cells by somatic cell nuclear transfer methods involving the same individuals may hold promise for advances in transplantation technology that could help people affected by many devastating conditions."