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鈥檇 be no problems with
rejection.
So what are they, exactly?
They鈥檙e cells that can develop into many different types of tissue, such as
bone, muscle or brain. There are three basic types. 鈥淭otipotent鈥� stem
cells鈥攖he cells formed when a fertilised egg first divides鈥攃an turn
into any type of tissue and form a 鈥渢otal鈥� 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
鈥減luripotent鈥濃�攖hey can turn into almost all types of tissue, but not a
whole organism.
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As the embryo develops further, stem cells become 鈥渕ultipotent鈥濃�攖hey
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鈥檛 turn
into a whole human being.
So where would you get them?
There鈥檚 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鈥攂ut these did come from
embryos in the first place.
Hang on. I鈥檇 reject organs grown from these cells.
Well spotted. If you were given organs grown from somebody else鈥檚 cells, you
might have to take immunosuppressant drugs for the rest of your life.
But that鈥檚 no better than a normal transplant . . .
Let me finish. You鈥檝e heard of Dolly the cloned sheep? Well, it might be
possible to obtain your very own pluripotent stem cells by the same method.
They鈥檇 take a cell from you and fuse it with an egg cell emptied of its genetic
material. Then they鈥檇 let it grow into a blastocyst, from which they鈥檇 take the
embryonic stem cells. Hence the term therapeutic cloning.
So why don鈥檛 they get on with it?
It鈥檚 a thorny issue, ethically and practically. Pro-lifers say it is immoral
to end the blastocyst鈥檚 potential for life. Also, they鈥檙e worried that people
might be tempted to clone themselves.
Is there another way?
Researchers think it might be possible to 鈥渞ewind鈥� 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.