Scientists have created human embryos that are genetic copies of living people and used them to produce the cells.
If replicated in other labs, the techniques detailed Wednesday in the journal Cell would allow researchers to fashion embryonic stem cells that are custom-made for patients with Alzheimer's disease, diabetes and other puzzling health problems. Theoretically capable of reproducing themselves indefinitely, these stem cells could be used to grow replacements for a variety of diseased cells - those of the blood, skin, heart, brain, muscles, nerves and more - that would not risk rejection by the patient's immune system.
The report also raises the specter that, with a high-quality donor egg, a bit of skin, careful tending in a lab and the womb of a willing surrogate, humans have cracked the biological secret to reproducing themselves. That is an objective American scientists have squarely renounced as unethical and scientifically irresponsible. At the same time, most acknowledge that such "reproductive cloning" will one day prove too tempting to resist.
In the hope that other researchers will validate and extend their results, the scientists at Oregon Health & Science University provided an exceptionally detailed account of their techniques. But for anyone with a well-equipped fertility lab, the comprehensive guide could be a useful handbook for cloning a baby.
OHSU cell biologist Shoukhrat Mitalipov led a team of 23 scientists who methodically culled the lessons learned from stem cell research on amphibians, mice and rhesus monkeys - as well as from the abundant failures of others in the field. They devised a welter of new techniques to use the DNA of a fully formed skin cell in its most primitive embryonic form.
The approach they used - called somatic cell nuclear transfer - effectively strips an egg of its chromosomes and packs it instead with DNA from a donor.
Nurtured by a stew of nourishing chemicals and zapped with two jolts of electrical current, many of the eggs began to divide and grew for five to six days. At that point, the embryos had 64 to 200 cells, including a dense inner cell mass from which stem cells were extracted.
In past efforts to coax such an assemblage of components to life, researchers have burned through dozens of donor eggs without getting any embryos even to the 16-cell stage at which stem cells become a remote possibility.
This time, the researchers said their methods were so efficient that they could create at least one embryonic stem cell line from each batch of eggs donated by 10 female volunteers. In one case, a single donor produced eight eggs of such exceptional quality that researchers were able to derive four embryonic stem cell lines.
The volunteers, between the ages of 23 and 31, donated their eggs anonymously and were "financially compensated for the time, effort, discomfort and inconvenience associated with the donation process," the study authors wrote.
The success of the experiments rekindled debate among bioethicists, who have long anticipated that human cloning would become a reality. In 2002, a commission of bioethicists established by then-President George W. Bush unanimously urged a ban on reproductive cloning. But the panel was deeply divided about the propriety of "therapeutic cloning" for research and medical treatment.
Though 13 states have passed laws banning reproductive cloning, the United States is one of just a few industrialized countries that has not prohibited the practice. Seven states also have banned therapeutic cloning. Oregon is not one of them.
The OHSU team's success underscores the urgent need for federal rules that spell out consistent national limits on therapeutic cloning and put a clear ban on the technology's use in fertility clinics, said Johns Hopkins University bioethicist Jeffrey Kahn.
Researchers are also likely to step up their demand for donated eggs so they can conduct similar experiments. That lends urgency to the need for standardized practices for compensating women who donate their eggs. Some states have set strict limits on such payments, while others have allowed a market for donated eggs to flourish unregulated, Kahn added.