By Rick Weiss
Washington Post Staff Writer
Friday, May 20, 2005
Scientists in South Korea reported making nearly a dozen cloned human embryos that are genetic twins of patients with various medical problems and have isolated from those embryos batches of stem cells with the potential to replace failing tissues in those patients.
The experiments mark a significant advance in therapeutic cloning, the fast-paced but controversial field that aims to make customized heart tissues for heart attack patients, nerves for patients with spinal cord injuries, and a host of other laboratory-grown spare parts genetically tailored to the patients who need them.
The single previous claim that stem cells had been derived from a cloned human embryo, reported last year by the same team at Seoul National University's College of Veterinary Medicine, left some scientists doubting the results. Moreover, the process appeared to be hopelessly inefficient, requiring almost 250 human eggs extracted from female donors to get just one cloned embryo with its precious cache of stem cells.
In the new experiments, described in yesterday's online version of the journal Science, the team needed only 17 eggs on average to make each batch of stem cells, which have the capacity to develop into any type of tissue. That means a single egg-retrieval procedure of the sort used routinely in fertility clinics is now adequate to produce a colony of personalized cells with the potential to treat a wide spectrum of diseases.
If therapeutic cloning can indeed be achieved with the same efficiency as such a widely accepted medical procedure, it would deeply undercut one of the major ethics arguments against it: that it would require egg donations by countless women -- at some risk -- to make enough embryos and stem cells to be medically useful.
"I think this paper will have enormous impact on the political discussion," said Rudolf Jaenisch, a stem cell researcher at the Whitehead Institute for Biomedical Research in Cambridge, Mass.
The report comes at a delicate time in the escalating U.S. battle over funding of embryonic stem cell research. Within the next week, a closely divided House is expected to vote on legislation that would, for the first time, loosen the restrictions that President Bush imposed on federal funding for the field in 2001.
That legislation would not allow funding of cloning research like that done in South Korea -- a kind of research the House has twice voted to ban and which the Senate has deadlocked over for years. Rather, it would facilitate the less contentious use of frozen embryos about to be discarded by fertility clinics.
Unknown at this point is whether the Korean advance will bolster the bill's opponents -- who have painted the legislation as a step down a slippery slope that could lead to cloned babies -- or strengthen the bill's supporters by making the pending bill look relatively modest by comparison and by heightening concerns that the United States is falling behind in one of the hottest arenas of biomedical research.
Several countries, including South Korea, Singapore and Britain, not only support research on unused fertility clinic embryos but also have given their blessings to research on cloned human embryos and promulgated ethics rules for such work.
The new research was led by Woo Suk Hwang, a cow-cloning expert whose recent rise to international fame for his stem cell work has made him somewhat of a folk hero in Korea.
A cloned embryo is made from a single cell -- often a skin cell -- taken from the person or animal to be cloned, which is then fused to an egg from a donor. In the latest experiments, the team started with 185 eggs donated by 18 women. The women underwent a month-long series of hormone shots followed by the extraction of about a dozen ripened eggs from their ovaries. None of the women was paid.
Each egg had its own DNA removed and then was fused to a single skin cell taken from one of 11 patients. The patients, ages 2 to 56, had either a spinal cord injury, diabetes or an inborn disease of the immune system.
Of those 185 treated eggs, 31 grew into early embryos in laboratory dishes. The team was able to extract stem cells from 11 of them. Each of the resulting colonies of stem cells is a genetic and immunological match to the patient who supplied the original skin cell.
The overall efficiency was 11 self-perpetuating colonies -- or cell lines -- from 185 eggs, or about one cell line for every 17 eggs. But the procedure was even more efficient with eggs from the youngest donors. For eggs retrieved from women under age 30, one cell line was obtained for every 14 eggs.
In another major advance, the Koreans said they are cultivating the stem cell lines in dishes without any animal cells. Virtually all other human embryonic stem cell lines to date have been grown for at least a while on mouse cells, which secrete a cocktail of hormones that support the growth of finicky stem cells.
By growing the stem cells on a bed of human support cells instead of mouse cells, the team does not have to worry that animal viruses or other contaminants may prevent transplantation of the stem cells, or tissue grown from them, into patients -- the ultimate goal.
"We want to find a way to cure devastating diseases, and one of the big points of our research is patients [now] have immune-matched, cloned, embryonic stem cells," Hwang said in a telephone interview.
The team is now working to transform the cells into various kinds of tissues -- a process at which scientists are becoming increasingly adept -- but has no current plans to put them into patients, Hwang said.
Several experts said they were extremely impressed and predicted that the first therapeutic cloning treatment would come more quickly than they had imagined.
"They have increased the efficiency tenfold over what their paper was a year ago, and this is very important," said John Gearhart, a stem cell researcher at Johns Hopkins University. "It's kind of remarkable. It tells you how quickly things are moving."
Judy Norsigian of the Boston Women's Health Book Collective, who supports stem cell research but has warned against therapeutic cloning's potential to exploit egg donors, said she was relieved that the process would need fewer eggs but still had concerns because the ovarian stimulation used to mass-produce the eggs can lead to complications.
"Young women would still be providing eggs to treat men, children and older women. We need to make sure that those women aren't put at unnecessary risk," she said.
Others voiced greater concerns.
"You're placing the woman at risk to create an embryo that has a 100 percent risk of death, to attempt to treat patients who themselves will face significant risks," said Richard Doerflinger, deputy director of the Secretariat for Pro-Life Activities of the U.S. Conference of Catholic Bishops.
"To say something was initially impossible but is now possible is not enough," Doerflinger said. "We have to make moral decisions about whether we should do this."