OK, so now we know the problem. There are certain genes needed to make a cell turn into an ES cell. Since these genes are presumably off in a skin cell, we need to turn them on again. And have all of the skin cell genes shut off too.

The way the scientists decided to do this was to add back whatever genes are needed to erase the pattern in the skin cell. (These genes are off in a skin cell.) This is a lot easier than specifically turning on this small set of genes.

The way they decided to add back the genes was with a virus. A lot of gene therapy gets done this way.

Many viruses work by sticking themselves into a cell's DNA. What the scientists planned to do was to take out some of the nonessential virus DNA and put in the necessary genes.

We're all set except we don't yet have the genes. Scientists had figured out through various means that if they added 24 different genes to a skin cell, it would turn into an ES cell. Yikes!

That is way too many to do gene therapy. So they started taking one away at a time to find the really key ones. They finally settled on 4 genes. This is still an awful lot but it is at least doable.

Last year they added back these genes and got some promising results. The skin cells took on many of the properties of ES cells but not all of them. This is encouraging but not good enough.

To fix this, they changed the skin cells to make selecting the most ES-like ones easier to do. When they did this, they were able to grow cells that essentially looked like an ES cell.

As a final test, they added some of these cells to an early mouse embryo. The embryo grew into a pup that contained different cell types derived from the original embryo and the skin cells (a chimera). This test proved these cells had been turned into something that could be used as ES cells.

Cool. But it is not a slam dunk to get this to work in people. We don't know if these same 4 genes are the ones that work in people too. And around 20% of the mice died from cancers caused by one of the added genes.

But these are problems we can deal with. Of course we'll have to continue to use "real" ES cells to figure out the genes needed to turn skin cells into ES cells. In other words, we need to destroy embryos now to stop destroying them in the future.

This research will progress very quickly. Because the experiments are easier to do than cloning, little labs all over the world can tackle these kinds of questions with no government interference. Personalized medicine may be here sooner than we think.

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Embryonic stem cells from skin cells | Understanding Genetics