Cloning discovery may kill ethical objection
Posted by Richard Linney on Apr 23, 2002 at 04:00
A key ethical objection to "therapeutic" cloning could be undermined if the results of experiments on abnormal cloned frog embryos are repeated in humans.
Therapeutic cloning involves the harvesting of embryonic stem cells from cloned embryos. Scientists hope the stem cells will provide powerful treatments for disease. But collecting them destroys the embryo - which is destroying a potential life, in some people's view.
However, this ethical problem would be avoided if healthy cells could be extracted from abnormal human embryos doomed to die anyway, and researchers have shown this is possible in frogs.
"If an embryo is certain to die, I can't see why anyone would object to someone taking cells and working with them," says John Gurdon, head of the team at the Wellcome Cancer Research Institute in Cambridge, which experimented on the cloned frog embryos. "If it's destined to die within days, it's not a potential human," he says.
However, some pro-lifers disagree, saying they would only be satisfied that the procedure was ethical if the cells could be harvested without killing the defunct embryo. "It's a question of whether it curtails the life expectancy of the embryo," says Josephine Quintavalle of the UK's Pro-Life Alliance. She says that the principle of not killing an embryo is the same, whether its life expectancy is three days or three months.
Couples undergoing treatment at fertility clinics almost invariably generate spare embryos that are visibly abnormal and doomed to die within two to three days. Now, through his work on frogs, Gurdon has shown that even if an abnormal embyro's fate is sealed, it contains cells which are completely normal and which develop normally into many tissue types.
To demonstrate this, Gurdon created genetically engineered frogs whose cells were equipped with a gene to make the green fluorescent protein (GFP) produced by some jellyfish.
Next, he took gut cells from the frogs and made them into cloned embryos by fusing them into normal frog eggs emptied of their own genetic material.
Half the embryos Gurdon created were complete duds, failing to divide at all. Another quarter developed into "partial embryos" which were clearly and visibly abnormal, with normal cells developing in only one half of the embryo, for example. These embryos all died a day later.
But before they did, Gurdon extracted normal cells and grafted them into normal frog embryos. As the embryos developed, Gurdon could spot all tissues that came from the grafted cells, because they carried the GFP gene and so glowed green.
"The surprising result was that some of the cells from the cloned embryos did well and grew for months in the new host embryo," says Gurdon.
If the same was true of defunct human embryos, it might be possible to extract cells from them for crafting into tissues for patients. At the very least, says Gurdon, the cells could be used for research to find out how to fast-forward their development into any type of tissue.
Journal reference: Proceedings of the National Academy of Sciences (vol 99, p 6059)
Article from NewScientist.com
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