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WASHINGON, Feb 13: South Korean and US researchers said on Wednesday they had cloned a human embryo and extracted from it medically important stem cells.
It is the first published report of cloned human stem cells. Here is a chronology of some of the major developments resulting from embryo cloning experiments since 1998:
1998: US researchers with the biotech company ACT fuse genetic material from a human skin cell with eggs from cows and retrieved stem cells from the mixed embryos. South Korean researchers also reported successes in cloning, but did not produce any evidence.
2000: A Chinese researcher says she began cloning human embryos for medical purposes. In subsequent years she claimed to have grown stem cells from cloned embryos.
2001: The first scientific report on true human cloning appears in The Journal of Regenerative Medicine. ACT researchers used eggs from women between 24 and 32 years old and inserted genetic material from cells of adults. Several cloned embryos developed beyond the first three cell divisions, resulting in eight cells, but the researchers didn't isolate any stem cells.
2002: South Korean researchers say they inserted human genetic material into the egg of a cow with the goal of retrieving stem cells from the resulting embryos for medical purposes.
2003: Chinese researchers report in the journal Cell Research the extraction of human stem cells from an embryo created through the fusion of rabbit egg cells and human genetic material.
2004: The journal Science publishes the first scientific report about the extraction of stem cells from cloned human embryos that reached the stage of blastocysts, which contain hundreds of cells. -DPA
