updated 2/12/2004 5:51:04 PM ET 2004-02-12T22:51:04

The procedure Korean scientists used to create the first human stem cells from cloned embryos is a mix of standard and unusual lab techniques, and it’s not clear yet what steps were critical to success.

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Those methods must be improved, however, before they can be used to supply cells for medical treatment, the Korean researchers said.

Basically, the goal was this: to take human eggs, insert DNA from other cells, get the eggs to grow into early embryos in the lab, and then destroy the embryos to remove their stem cells. The stem cells are a genetic match of the person who donated the DNA.

In theory they can be spurred to become specialized cells and transplanted into the donor to replace faulty tissue without fear of rejection. The hope is that one day these cells can be used to treat a variety of ailments from spinal cord injuries to diabetes.

Large supply of fresh eggs
One key advantage the Koreans enjoyed was a large supply of fresh human eggs: 242 obtained from 16 volunteers who donated them specifically for the study. In contrast, researchers normally get leftover eggs from fertility clinics, so they are not only aged but potentially of less than top-notch quality, said stem-cell researcher Gerald Schatten of the University of Pittsburgh.

The Korean scientists used a new method to remove the DNA from the eggs. Normally, the DNA is sucked out with a fine needle. The Korean researchers instead created a tiny hole in the egg membrane and squeezed the DNA out. That appears to remove less of the cell material surrounding the nucleus.

Another unusual step was replacing each egg’s DNA with genetic material from the same woman who donated the egg. In animal work, most scientists take the DNA from a different individual, because that makes it easier to prove the resulting embryo is using the donated DNA.

'A spectacular achievement'
But maybe taking the egg and the DNA from the same individual gives an advantage, Schatten said. When the DNA is inserted, it carries along material from the cell it came from, so maybe the Korean procedure gets around some incompatibility problem when inserted material from one individual mixes with an egg taken from another, he said.

That doesn’t necessarily mean that the benefits of stem cells would be limited to women of child-bearing age, Schatten said, but it’s an issue for further investigation.

Once the DNA was inserted into the egg, the Koreans experimented with how long to wait until they spurred the egg to grow. Rather than proceeding right away, as is done in pig cloning, they got better results by waiting a couple hours to let the DNA reprogram itself to drive development of an embryo. That’s what scientists do when they clone cows.

The scientists also focused on the ingredients of the chemical “soup” in which the embryos grew, using the sugar fructose rather than the more commonly used glucose, for example.

Schatten said it’s not clear which, if any, of the steps the Koreans chose made a crucial difference in the outcome. But in any case, he said, “this is a spectacular achievement.”

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