Success! Human stem cells cloned

Stem cells viewed on a computer screen at the University of Connecticut's Stem Cell Institute.

STORY HIGHLIGHTS

(TIME.com) -- It's been 17 years since Dolly the sheep was cloned from a mammary cell. And now scientists applied the same technique to make the first embryonic stem cell lines from human skin cells.

Ever since Ian Wilmut, an unassuming embryologist working at the Roslin Institute just outside of Edinburgh stunned the world by cloning the first mammal, Dolly, scientists have been asking -- could humans be cloned in the same way?

Putting aside the ethical challenges the question raised, the query turned out to involve more wishful thinking than scientific success. Despite the fact that dozens of other species have been cloned using the technique, called nuclear transfer, human cells have remained stubbornly resistant to the process.

Until now. Shoukhrat Mitalipov, a professor at Oregon Health & Science University, and his colleagues report in the journal Cell that they have successfully reprogrammed human skin cells back to their embryonic state.

The purpose of the study, however, was not to generate human clones but to produce lines of embryonic stem cells. These can develop into muscle, nerve, or other cells that make up the body's tissues. The process, he says, took only a few months, a surprisingly short period to reach such an important milestone.

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Nuclear transfer involves inserting a fully developed cell -- in Mitalipov's study, the cells came from the skin of fetuses -- into the nucleus of an egg, and then manipulating the egg to start dividing, a process that normally only occurs after it has been fertilized by a sperm.

After several days, the ball of cells that results contains a blanket of embryonic stem cells endowed with the genetic material of the donor skin cell, which have the ability to generate every cell type from that donor.

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Success! Human stem cells cloned