The science behind the stem cell debate
In the debate over embryonic stem cell research, opponents often cite a list of 65 illnesses that have been treated by adult stem cells, while pointing out that embryonic stem cells have never cured a disease.
They're partly right, but according to a short article published online by the journal Science last week, the vast majority of those 65 treatments are far from being available to the general public, and many of the claims are based on only a handful of observations—some on single patients. What's more, scientists say the comparison between embryonic cells and adult cells is meaningless because research on embryonic stem cells is so new. "Research with adult stem cell therapies has been underway for over 50 years now," says William Neaves, president and CEO of the Stowers Institute for Medical Research in Kansas City and coauthor of the Science article. Embryonic stem cells, on the other hand, were first isolated in only 1998. "One does not turn a laboratory discovery into a new therapy overnight. It requires many years and even decades of research."
Of the nine adult stem cell treatments on the list that have been approved by the Food and Drug Administration, most are for blood diseases and involve transplants of bone marrow, which contains blood stem cells. "These cells are very useful for being able to replace blood cells, to provide a new resource for the production of blood and immune cells for people who have diseases of the blood," says David Scadden, codirector of the Harvard Stem Cell Institute. "In that setting, they are a spectacular advance."
But aside from blood cells, Scadden says, adult stem cells have so far offered only hints of treatments. For example, adult stem cells that can give rise to muscles, bone, cartilage, and fat have been tested in patients after heart attacks but are far from being accepted treatments. Rather than focusing purely on adult stem cells, he says, research should also continue on embryonic stem cells.
While adult stem cells can give rise only to certain types of cells, embryonic stem cells have the potential to develop into any type of cell in the body. Extracting embryonic stem cells destroys a tiny embryo, which is why many people object to the research and why the president has said he will veto the bill passed this week, which would expand federal funding for research on stem cells extracted from leftover embryos created during in vitro fertilization procedures. Currently, scientists can get federal funding for research only on a few embryonic stem cell lines that already existed in 2001.
Both adult and embryonic stem cells offer a tantalizing hint of cures for diseases such as diabetes, for example, if stem cells could be coaxed to turn into new insulin-producing cells, or spinal cord injuries, if stem cells could make new cells of the nervous system. But neither path of research should be followed exclusively, says Kathy Lewis, president of the Christopher Reeve Foundation, which funds research into cures for paralysis. "Why would you not go down all those paths?" she asks. "You would probably learn something on each of those paths that would help you find the cure on the other end."
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