In work that observers call both remarkable and inevitable, scientists in Korea have produced an embryonic stem (ES) cell line from cloned human cells--an advance that holds promise for replacing cells damaged by diseases such as Parkinson's and diabetes. In doing so, the team has apparently overcome some of the obstacles that to date have hampered human and monkey cloning, and the work is likely to reignite the smoldering debate over how such research should be regulated.
Scientists have hoped to create ES cells with genes that match those of a patient, an idea called therapeutic cloning or "cloning for stem cells." As published online in Science this week, a team led by veterinary cloning expert Woo Suk Hwang and gynecologist Shin Yong Moon of Seoul National University in South Korea shows that the technique can work in humans.
The secret to their success may be the gentle way in which they removed the nucleus from a human egg. Then they added the nucleus from a Cumulus cell, a kind of cell that surrounds the developing eggs in an ovary. After prompting the reconstructed egg to start dividing, the team allowed it to develop for a week to the blastocyst stage, when the embryo forms a hollow ball of cells. They then isolated the inner-cell mass, which would develop into the fetus. When these cells are grown in culture, they can become ES cells, which reproduce indefinitely and can form all the cell types in the body. The ES cell line the team derived seems to form bone, muscle, and immature brain cells, for example.
Calling the work an important step forward, Rudolf Jaenisch of the Massachusetts Institute of Technology points out one potential drawback. Because both the egg and the cumulus cell came from the same person, the researchers can't completely prove that the cells developed from the inserted cumulus cell nucleus.
Nevertheless, the evidence that cloned human embryos can develop to the blastocyst stage is likely to reinvigorate debates in the U.S. Congress and the United Nations over a ban on human cloning. Members of both bodies agree that cloning to produce a human child should be banned, but debate continues about the kind of research described this week. The Bush Administration, for example, objects to the idea that human embryos would be deliberately created and then destroyed to derive stem cells.