Although we injected some of the eggs with nuclei from skin fibroblasts as usual, we injected others with ovarian cells called cumulus cells that usually nurture developing eggs in the ovary and that can be found still clinging to eggs after ovulation. Cumulus cells are so small they can be injected whole. In the end, it took a total of 71 eggs from seven volunteers before we could generate our first cloned early embryo. Of the eight eggs we injected with cumulus cells, two divided to form early embryos of four cellsand one progressed to at least six cellsbefore growth stopped.
Although mature eggs and sperm normally have only half the genetic material of a typical body cell, to prevent an embryo from having a double set of genes following conception, eggs halve their genetic complement relatively late in their maturation cycle. If activated before that stage, they still retain a full set of genes.
They would not be identical to the individuals cells because of the gene shuffling that always occurs during the formation of eggs and sperm.
Such cells might also raise fewer moral dilemmas for some people than would stem cells derived from cloned early embryos. Under one scenario, a woman with heart disease might have her own eggs collected and activated in the laboratory to yield blastocysts. Scientists could then use combinations of growth factors to coax stem cells isolated from the blastocysts to become cardiac muscle cells growing in laboratory dishes that could be implanted back into the woman to patch a diseased area of the heart.
Using a similar technique, called androgenesis, to create stem cells to treat a man would be trickier. But it might involve transferring two nuclei from the mans sperm into a contributed egg that had been stripped of its nucleus. Researchers have previously reported prompting eggs from mice and rabbits to divide into embryos by exposing them to different chemicals or physical stimuli such as an electrical shock.
As early as , Elizabeth J. Robertson, who is now at Harvard University, demonstrated that stem cells isolated from parthenogenetic mouse embryos could form a variety of tissues, including nerve and muscle. In our parthenogenesis experiments, we exposed 22 eggs to chemicals that changed the concentration of charged atoms called ions inside the cells.
After five days of growing in culture dishes, six eggs had developed into what appeared to be blastocysts, but none clearly contained the so-called inner cell mass that yields stem cells.
Currently our efforts are focused on diseases of the nervous and cardiovascular systems and on diabetes, autoimmune disorders, and diseases involving the blood and bone marrow. Once we are able to derive nerve cells from cloned embryos, we hope not only to heal damaged spinal cords but to treat brain disorders such as Parkinsons disease, in which the death of brain cells that make a substance called dopamine leads to uncontrollable tremors and paralysis.
Alzheimers disease, stroke and epilepsy might also yield to such an approach. Besides insulin-producing pancreatic islet cells for treating diabetes, stem cells from cloned embryos could also be nudged to become heart muscle cells as therapies for congestive heart failure, arrhythmias and cardiac tissue scarred by heart attacks. Autoimmune disorders such as multiple sclerosis and rheumatoid arthritis arise when white blood cells of the immune system, which arise from the bone marrow, attack the bodys own tissues.
Preliminary studies have shown that cancer patients who also had autoimmune diseases gained relief from autoimmune symptoms after they received bone marrow transplants to replace their own marrow that had been killed by high-dose chemotherapy to treat the cancer.
Infusions of blood-forming, or hematopoietic, cloned stem cells might "reboot" the immune systems of people with autoimmune diseases. But are cloned cellsor those generated through parthenogenesisnormal? Only clinical tests of the cells will show ultimately whether such cells are safe enough for routine use in patients, but our studies of cloned animals have shown that clones are healthy. In the November 30, , issue of Science, we reported on our success to date with cloning cattle.
Of 30 cloned cattle, six died shortly after birth, but the rest have had normal results on physical exams, and tests of their immune systems show they do not differ from regular cattle. Two of the cows have even given birth to healthy calves. The cloning process also appears to reset the "aging clock" in cloned cells, so that the cells appear younger in some ways than the cells from which they were cloned.
In we reported that telomeresthe caps at the ends of chromosomesfrom cloned calves are just as long as those from control calves. Telomeres normally shorten or are damaged as an organism ages. Therapeutic cloning may provide "young" cells for an aging population. Imprinting is a type of stamp placed on many genes in mammals that changes how the genes are turned on or off depending on whether the genes are inherited from the mother or the father.
The imprinting program is generally "reset" during embryonic development. They saw them return to the pronuclear state, which is only found in fertilised eggs. The nuclei then proceeded to divide into six cells, just as a normal fertilised human egg would do. The company has not said whether it has made the next move, to isolate stem cells for potential use in medical therapy from the cloned embryo.
Dr West said that the stem cells could have exciting applications, given that the company's earlier work in animals had shown that cloned embryonic cells can start their lifespan again. Scientists were concerned that Dolly the sheep and other animals cloned from adult cells suffered from premature ageing - the clock began ticking at the age of the cells from which they were cloned.
ACT reported that it had overcome the problem in six calves born earlier this year. This would allow us to supply young cells of any kind, identical to the patient, that could be used to address the tidal wave of age-related disease that will accompany the aging of the population. Scientists hope the embryonic cells may regenerate damaged parts of the brains of the sufferers of Parkinson's disease or Alzheimer's.
Mary Ann Liebert, the publisher of e-biomed, called it "a milestone in therapeutic cloning". Vivienne Nathanson, head of ethics at the British Medical Association, said that the development underlined the need for strong regulation so that therapeutic cloning to extract embryonic stem cells for life-saving medical treatment, which most of the public supports, can go ahead while reproductive cloning which most of the public opposes, cannot. This would have to include the inspection of all labs involved in therapeutic cloning to ensure the work was done ethically and to a high standard.
But there was alarm from John Smeaton, national director of the Society for the Protection of Unborn Children, who said: "This appears to be a very disturbing and deplorable development. It underlines the need for the government's bill to be fundamentally changed so that all forms of human cloning, both experimental cloning and cloning for child birth, are completely banned. Harvesting the cells from an embryonic clone of a patient would mean the transplant tissue was perfectly matched.
The work is legal in the US because ACT is a private company, not receiving federal government funds. However, President George W Bush had planned to outlaw cloning before the 11 September attacks and is likely to revive the proposed legislation.
Most scientists oppose reproductive cloning producing babies , but are in favour of therapeutic cloning producing transplant cells and so will hope that any new laws in the US or UK will be able to separate the two. The researchers from ACT, with colleagues at Duncan Holly Biomedical, used two different techniques to produce the embryos. Both have been successful in previous animal experiments, but had not been performed on human embryos.
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