Successful cloning of embryonic stem cells could open door to creating rejection-free organs, tissues.
A South Korean-led research team scored a scientific coup when it announced earlier this month they successfully created stem cells from a cloned human embryo. While the breakthrough was hailed by many medical professionals and patient advocates as an achievement that could ultimately lead to the development of replacement tissues and organs for transplantation, the feat ignited the wrath of opponents, who called the achievement a "how-to" manual for taking the next fateful step of creating "cloned blastocysts for baby-making."
"Our approach opens the door for the use of these specially developed cells in transplantation medicine," the leader of the research team Hwang Woo Suk of Seoul National University said in a statement. Hwang, who said the research was conducted with strict oversight of an ethics committee, added, "Our inspiration is to treat incurable disease. As scientists, we think it our obligation to do this."
"It would be naive to say this isn't a step closer to irresponsible people attempting reproductive cloning," said Gerald Schatten, an animal-cloning researcher at the University of Pittsburgh School of Medicine, who opposes human cloning but supports the research.
Reporting their breakthrough in the February 13 issue of the journal Science, the researchers described retrieving 242 eggs from 16 unpaid female volunteers (who were informed of the experiments). The scientists then used nuclear transfer technology to remove the nucleus of each egg-the center core that contains most of the genetic material-and replace it with the nucleus of an ovarian cell obtained from the specific egg donor. The cytoplasm within the interior of the eggs reprogrammed the replacement nuclei, deactivating the adult genes and switching on embryo genes.
The eggs were allowed to divide for 5 days, at which point each egg had reached the blastocyst stage and contained about 150 cells. The researchers successfully collected embryonic stem cells from 20 of the cloned blastocysts, and by tweaking the timing of the nuclear transfer and other technical considerations, were able to produce a single embryonic cell line. These cells differentiated into the 3 major types of tissue that appear at the beginning of development, confirming that they were indeed pluripotent stem cells capable of differentiating into every type of body tissue. When the stem cells were transplanted into mice, they morphed into additional cell types, further demonstrating their potential to become any type of cell in the body.
In all, 242 eggs were required to derive just 1 line of embryonic stem cells from a cloned adult cell, an inefficient procedure similar to that encountered in animal cloning.
"It remains to be determined if this low efficiency is due to faulty reprogramming of the [ovarian] cells or subtle variations in our experimental procedures," wrote Woo Suk Hawang of Seoul National University and colleagues. "Further improvement in somatic cell nuclear transfer protocols and in vitro culture systems are needed before contemplating the use of this technique for cell therapy."
Nonetheless, the researchers said that their success "shows the feasibility of generating human embryonic stem cells from a somatic (body) cell isolated from a living person."
The breakthrough reignited the long simmering debate in the US legislating human cloning and embryonic stem cell i.e. therapeutic cloning research and triggered criticism of the Bush Administration's policy banning federally funded scientists from conducting research on new human embryonic stem cell colonies that has been in place since August 2001.
"We call on Congress to follow the common sense conclusion that most Americans have reached-pass legislation that would prohibit reproductive cloning, but allow and encourage this kind of very exciting scientific research," said Sean Tipton, vice president of communications for the Coalition for the Advancement of Medical Research, a Washington-based advocacy group.
Leon Kass, chairman of the President's Council on Bioethics, who has called for federal legislation to ban, or place a moratorium on any human cloning, did not issue a formal response to the research breakthrough. However, the New York Times reported Kass wrote in an e-mail: "The age of human cloning has apparently arrived: today, cloned blastocysts for research, tomorrow cloned blastocysts for babymaking."
The South Korean's breakthrough does not mean other scientists will be able to ride their coattails anytime soon, however.
David Kennedy, editor of Science, said others will not find it easy to reproduce their meticulous work. "It is a recipe only in that catching a turtle is a recipe for turtle soup," Kennedy said.
Rudolf Jaenisch, an expert on the genetics of animal cloning at the Whitehead Institute for Biomedical Research in Cambridge, MA, has published studies that show cloned mice are riddled with abnormalities suggesting that a cloned embryo would have 'little if any potential to ever develop into a normal human being,' the New York Times reported.
As a result, Jaenisch said, the South Korean approach may be "useful therapy, but not useful for cloning."
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|Date:||Feb 29, 2004|
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