WEDNESDAY, June 6, 2007 (HealthDay News) -- A pair of stem cell discoveries announced Wednesday may one day surmount both the ethical and technical hurdles confronting such research, setting the stage for medical advances, researchers say.
In the first study, scientists at the Harvard Stem Cell Institute managed to create stem cells from non-viable mouse embryos, potentially opening a new source of cells for experiments and research.
In the second study, investigators at the Whitehead Institute for Biomedical Research in Cambridge, Mass., succeeding in creating cells identical to embryonic stem cells from adult skin cells in mice, bypassing both the need for eggs and the need to destroy early embryos.
"This group of papers is in a very exciting area of nuclear reprogramming and advance the field substantially in a number of ways," Kevin Eggan, senior author of the first paper and a principal faculty member at the Harvard Stem Cell Institute, said during a press conference.
Because the advances involved mouse cells, not human cells, the investigators noted that much work needs to be done before the processes can be applied to humans.
Embryonic stem cells are pluripotent, meaning they have the ability to develop into virtually any cell type in the body. The hope is that these cells may one day yield treatments or cures for diseases such as diabetes, liver failure, spinal injury, stroke, Alzheimer's disease and heart disease.
But, harvesting stem cells involves destroying a viable embryo, and embryonic stem cell research in the United States has been severely limited since August 2001, when President George Bush placed limits on federal funding of the field. Now, federal funds can only be used to study stem cell lines derived from embryos that had been destroyed before that date.
Somatic cell nuclear transfer, or "therapeutic cloning," involves creating customized embryonic stem cell lines with a patient's own DNA, by transferring DNA from an unfertilized egg to a "somatic" cell or a cell from the patient's body, then coaxing that somatic cell to begin dividing.
The advantage of this technique is that the cell lines have the same genetic make-up as the patient's own cells.
But unfertilized eggs aren't easy to come by.
For the first study, Eggan's team showed that researchers could use cells from very early fertilized embryos to accomplish the same things as unfertilized eggs.
"The practical payoff is that our experiments in mice suggest that you might be able to use very large numbers of fertilized embryos routinely discarded in IVF clinics to do human somatic cell nuclear transplantation to try to generate embryonic stem cell lines," Eggan said.
Routinely discarded embryos are those that are abnormally fertilized and could never go on to become a human -- about 3 percent to 10 percent of the 500,000 eggs that go into in vitro fertilization clinics every year.
"They are set aside or discarded at the one-cell stage, because they can never make a child," Eggan said. "There are up to 50,000 one-cell embryos that can be used for this research. That's a considerable resource."
For the second paper, scientists used a retrovirus to activate four specific transcription genes in mouse skin cells. Transcription genes regulate groups of other genes. The four cells had previously been identified by Japanese researchers.
"The cells we reprogrammed were remarkably similar to embryonic stem cells," said Marius Wernig, lead author of this study and a postdoctoral researcher at the Rudolf Jaenisch Lab at the Whitehead Institute. "We can basically reverse development in a culture dish."
Not only were the reprogrammed cells identical to embryonic stem cells, including the ability to be pluruipotent, they were also able to give rise to live mice and their DNA that could be transmitted to succeeding generations. In other words, they could do everything a traditional stem cell could do.
"This opens up a new field in stem cell research," said Konrad Hochedlinger, co-author of the paper, previously a member of the Jaenisch lab and now with the Harvard Stem Cell Institute and Massachusetts General Hospital. "There should be no fear of epigenetic reprogramming [passing on flaws, such as cancer] in using these cells. This provides just one alternative to somatic nuclear transfer."
But there remains one big caveat. "A human is not a mouse," said Wernig. "It's important to continue, if not intensify, our research on human embryonic stem cells. The method we used to reprogram the mouse cells would not be safe to use in human cells. A lot more work needs to be done."
Eggan's paper is published online June 6 in the journal Nature. The other papers are published in the inaugural issue of the journal Cell Stem Cell.
More information
The U.S. National Institutes of Health has more on stem cell research, including current official policy.
