Everything you ever wanted to know about stem cells

From New Scientist Web Site

Why the hoo-ha about stem cells?

In theory, stem cells can grow into replacements for almost any part of your body. If derived from cells taken from you, there'd be no problems with rejection.

So what are they, exactly?

They're cells that can develop into many different types of tissue, such as bone, muscle or brain. There are three basic types. "Totipotent" stem cells - the cells formed when a fertilised egg first divides - can turn into any type of tissue and form a "total" organism. About five days after fertilisation, a hollow ball of about 100 cells called a blastocyst forms. The cells on the outside develop into the placenta, while those on the inside turn into the embryo itself. The 50 or so inner cells are "pluripotent" - they can turn into almost all types of tissue, but not a whole organism. As the embryo develops further, stem cells become "multipotent" - they can give rise only to specific kinds of cells. Totipotent and pluripotent cells are also called embryonic stem cells, and multipotent cells are also known as adult stem cells.

Which ones will doctors use?

If they had their way most doctors would go for pluripotent stem cells because these can give you all the types of tissues you need, but can't turn into a whole human being.

So where would you get them?

There's the rub. At present the only place to get them is from human embryos, which is one reason why pro-life groups are so opposed to stem cell research. Three research groups around the world have found ways to grow potentially limitless supplies of pluripotent cells in the lab - but these did come from embryos in the first place.

Hang on. I'd reject organs grown from these cells.

Well spotted. If you were given organs grown from somebody else's cells, you might have to take immunosuppressant drugs for the rest of your life.

But that's no better than a normal transplant...

Let me finish. You've heard of Dolly the cloned sheep? Well, it might be possible to obtain your very own pluripotent stem cells by the same method. They'd take a cell from you and fuse it with an egg cell emptied of its genetic material. Then they'd let it grow into a blastocyst, from which they'd take the embryonic stem cells. Hence the term therapeutic cloning.

So why don't they get on with it?

It's a thorny issue, ethically and practically. Pro-lifers say it is immoral to end the blastocyst's potential for life. Also, they're worried that people might be tempted to clone themselves.

Is there another way?

Researchers think it might be possible to "rewind" adult cells to get pluripotent cells without having to make a viable embryo. Lifting bans on government researchers working on human stem cells and embryos might speed up progress.

From New Scientist, 19 August 2000

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