Gina Kolata explains in the New York Times:

Two teams of scientists are reporting today that they turned human skin cells into what appear to be embryonic stem cells without having to make or destroy an embryo — a feat that could quell the ethical debate troubling the field.

All they had to do, the scientists said, was add four genes. The genes reprogrammed the chromosomes of the skin cells, making the cells into blank slates that should be able to turn into any of the 220 cell types of the human body, be it heart, brain, blood or bone. Until now, the only way to get such human universal cells was to pluck them from a human embryo several days after fertilization, destroying the embryo in the process.

The reprogrammed skin cells may yet prove to have subtle differences from embryonic stem cells that come directly from human embryos, and the new method includes potentially risky steps, like introducing a cancer gene. But stem cell researchers say they are confident that it will not take long to perfect the method and that today’s drawbacks will prove to be temporary.

Researchers and ethicists not involved in the findings say the work should reshape the stem cell field. At some time in the near future, they said, today’s debate over whether it is morally acceptable to create and destroy human embryos to obtain stem cells should be moot.