US Scientists With Cloning Techniques Created Human Embryonic Stem Cells

The landmark discovery by an Oregon Health & Science University team involved taking a skin cell from an 8-month-old child with a rare inherited disease and replacing the nucleus of a donated human egg cell with it.

Stem cells have been a research focus for more than a decade because they can morph into any type of cell, potentially leading to treatments to replace damaged cells and organs. But along with the promise of the technology has come ethical questions and worry over human clones.

Until now, the best human stem cells were made using a different method and have not been truly identical. The new method could prove more valuable for treatment, said Natalie DeWitt, a cell and molecular biologist for the California Institute for Regenerative Medicine. “It's a big deal,” she said.

A similar process was used to clone a well-publicized sheep, named Dolly, in 1996. But while the process had been done in animals, many scientists had concluded it was impossible to replicate in humans.

“It's been really challenging: many people have tried,” DeWitt said. “From a...