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AAMC Therapeutic Cloning |
Cloning is the creation of multiple copies of a single molecule, cell, or virus. There are many different kinds of cloning, most of which are now commonplace in science. Cloning has allowed scientists to develop powerful new drugs and to produce insulin and useful bacteria in the lab. It also allows researchers to track the origins of biological weapons, catch criminals and free innocent people, and produce new plants and livestock to feed an undernourished world population.
Somatic Cell Nuclear Transfer
(SCNT) or therapeutic cloning
involves removing the nucleus
of an unfertilized egg cell, replacing it with the material from the nucleus
of a "somatic cell" (a skin, heart, or nerve cell, for example), and stimulating
this cell to begin dividing.
Once the cell begins dividing, stem cells can be extracted 5-6 days later and used for research.
The AAMC supports on-going research into SCNT and has endorsed legislation that would allow such research to flourish.
Reproductive cloning, on the
other hand, is intended to create human beings by cloning human embryos.
The AAMC and the National Academy of Sciences recommend a ban on all forms
of this type of cloning.
Hope for therapeutic cloning despite hype and fraud
01 July 2006
JUST a year ago, the prospects for "therapeutic" cloning seemed bright. The idea is to create an embryo by inserting the nucleus of a patient's cell into a human egg stripped of its own genetic material. The embryo, genetically matched to the original patient, would be grown for a few days to create a hollow ball of cells called a blastocyst. Embryonic stem cells (ESCs), which have the potential to turn into any type of tissue in the body, would then be extracted from it.
So in May 2005, when Woo Suk Hwang of Seoul National University in South Korea claimed that he had created 11 different lines of cloned human ESCs in this way, the goal of treating patients with tissues genetically matched to their own cells seemed to be within reach. Now, with Hwang revealed as a fraud, we are back to square one: no one has yet created a single line of cloned human ESCs. But for groups that are planning to try there are some reasons for optimism.
Two research teams,
one led by Rudolf Jaenisch of the Massachusetts Institute of Technology,
the other by Teruhiko Wakayama of the RIKEN Center for Developmental Biology in Kobe, Japan,
have found that, while cloned mouse embryos may grow into abnormal adults (see page 10), stem cells extracted from these cloned embryos seem to be perfectly normal, calming fears that tissues grown from cloned human ESCs would be inherently unsafe. The likely explanation is that a minority of cells within a cloned embryo are normal, and that the process of culturing ESCs selects for these.
The second hopeful sign is that
Don Wolf of the Oregon National Primate Research Center in Beaverton
has grown cloned monkey blastocysts.
He has yet to extract ESCs from these blastocysts, but sees no fundamental obstacles facing groups interested in therapeutic cloning. Indeed one human blastocyst - aside from those claimed by Hwang - has already been created by Alison Murdoch and her colleagues at Newcastle University in the UK.
The big difficulty, Murdoch says, is the shortage of human eggs for cloning experiments. "In animals, you have opportunities to try lots of different ways, and play around, but with such a small number of human eggs available, you have to be a lot more careful," she says.
For the past six months, the company
Advanced Cell Technology (ACT)
has been trying to recruit egg
donors, with little success.
Other teams hope to get round the problem by using eggs that failed to become fertilised during IVF procedures, rather than asking women to donate eggs specifically for cloning experiments. "It makes sense to begin with resources that are not as precious as fresh eggs," says Arnold Kriegstein, who heads the stem cell programme at the University of California, San Francisco.
But some specialists doubt it will be possible to derive cloned ESCs using these eggs, as they are likely to be sub-standard. "You're not going to get anything, other than frustrated," Wolf contends. And researchers hoping to recruit donors of fresh eggs admit that they are unsure of their chances of success. "We are hopeful but uncertain as to whether or not women will participate," says Kevin Eggan of Harvard University.
Given the logistical difficulties, many researchers doubt therapeutic cloning will ever live up to its billing as a means of growing tissues to replace those lost to disease or injury. And looking back on the past decade of controversy, some wonder whether its main legacy has been to muddy the wider debate over stem cell research. In reality, most of the excitement about using stem cells in medicine does not concern therapeutic cloning, but rather ESCs derived from "spare" embryos left over from IVF procedures, or the less-flexible "adult" stem cells taken from a patient's own tissues.
“Therapeutic cloning may never live up to its billing. Its main legacy may be to muddy the wider debate over stem cells.” "Pro-life" activists oppose all ESC research, and have been particularly successful in the US, where severe restrictions have been placed on government funding. Their arguments also seem to have had a strong influence on mainstream opinion partly because the public and political debate has become inextricably linked with human cloning - which many people remain uneasy about.
Anne McLaren, a developmental biologist at the
Gurdon Institute in Cambridge, UK,
wishes in retrospect that Dolly's birth had followed the first creation of human ESCs, rather than coming the year before. This might have allowed the stem-cell debate to mature without getting mired in concerns about cloning. "There would have been hype, but not hype about cloning," she says.
Even if therapeutic cloning never becomes part of clinical practice, there is still good reason to try and create cloned ESCs from patients with serious genetic diseases, as they could be used to study how the disease affects development, and to develop and test drug treatments.
Dolly's creator Ian Wilmut, now at the University of Edinburgh, UK, aims to create cloned ESCs to study motor neuron disease. If too few human eggs are available, he may try rabbit or cow eggs, borrowing a technique pioneered by Hui Zhen Sheng of the Shanghai Second Medical University in China. "The group clearly has blastocysts," says Wilmut. "Whether you can get normal embryonic stem cells out I don't know, but if it can be made to work, it removes the biggest block."
From issue 2558 of New Scientist
magazine, 01 July 2006, page 11
Therapeutic Cloning
What exactly is therapeutic
cloning? Better described as somatic cell nuclear
transfer (SCNT), therapeutic cloning is the transplanting of a patient's
DNA into an unfertilized egg in order to grow stem cells that could cure
devastating diseases. The promise of SCNT is that the patient's body would
accept these cells after transplantation. Therapeutic cloning produces
stem cells, not babies. NO sperm is used in this procedure. The cells are
not transplanted into a womb. SCNT aims to treat or cure patients by creating
tailor-made, genetically identical cells that their bodies won't reject.
In other words, SCNT could allow patients to be cured using their own DNA.
-- Stem Cell Action Network
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