Human cloning has been used to produce early embryos, marking a "significant step" for medicine, say US scientists. The cloned embryos were used as a source of stem cells, which can make new heart muscle, bone, brain tissue or any other type of cell in the body.
The study, published in the journal Cell, used methods like
those that produced Dolly the sheep in the UK, reports Reuters. However,
researchers say other sources of stem cells may be easier, cheaper and less
controversial. Campaigners opposed to the use of embryonic stem cells argue
that all embryos, whether created in the lab or not, have the potential to go
on to become a fully-fledged human, and as such it is morally wrong to
experiment on them.
They strongly advocate the use of stem cells from adult
tissue. Stem cells are one of the great hopes for medicine. Being able to
create new tissue might be able to heal the damage caused by a heart attack or
repair a severed spinal cord. There are already trials taking place using stem
cells taken from donated embryos to restore people's sight. However, these
donated cells do not match the patient so they would be rejected by the body.
Cloning bypasses this problem. The technique used - somatic cell nuclear
transfer - has been well-known since Dolly the sheep became the first mammal to
be cloned, in 1996.
Skin cells were taken from an adult and the genetic
information was placed inside a donor egg which had been stripped of its own
DNA. Electricity was used to encourage the egg to develop into an embryo.
However, researchers have struggled to reproduce the feat in
people. The egg does start dividing, but never goes past the 6-12 cell stage.
A South Korean scientist, Hwang Woo-suk, did claim to have
created stem cells from cloned human embryos, but was found to have faked the
evidence.
Now a team at the Oregon Health and Science University have
developed the embryo to the blastocyst stage - around 150 cells - which is
enough to provide a source of embryonic stem cells.
Dr Shoukhrat Mitalipov said: "A thorough examination of
the stem cells derived through this technique demonstrated their ability to
convert just like normal embryonic stem cells, into several different cell
types, including nerve cells, liver cells and heart cells. “While there is much
work to be done in developing safe and effective stem cell treatments, we
believe this is a significant step forward in developing the cells that could
be used in regenerative medicine."
Chris Mason, a professor of regenerative medicine at
University College London, said this looked like "the real deal". "They've
done the same as the Wright brothers really. They've looked around at where are
all the best bits of how to do this from different groups all over the place
and basically amalgamated it. "The Wright brothers took off and this has
actually managed to make embryonic stem cells."
Embryonic stem cell research has repeatedly raised ethical
concerns and human eggs are a scarce resource. This has led researchers to an alternative
route to stem cells. The technique takes the same sample of skin cells but
converts them using proteins to "induced pluripotent" stem cells. However,
there are still questions about the quality of stem cells produced using this
method compared with embryonic stem cells.
Prof Mason said the field was leaning towards induced
pluripotent stem cells: "It has got a lot of momentum behind it, a lot of
funding and a lot of powerful people now."
Dr Lyle Armstrong at Newcastle University said that the
study "without doubt" marked an advance for the field.
But he warned: "Ultimately, the costs of somatic cell
nuclear transfer-based methods for making stem cells could be
prohibitive."
Dr David King, from the campaign group Human Genetics Alert,
warned that: "Scientists have finally delivered the baby that would-be
human cloners have been waiting for: a method for reliably creating cloned human
embryos.
"This makes it imperative that we create an
international legal ban on human cloning before any more research like this
takes place. It is irresponsible in the extreme to have published this
research."
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