Stem cell limits worry scientists
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By Paul Recer
Aug. 10, 2001 | WASHINGTON (AP) --
President Bush's decision to limit embryonic stem cell studies to existing sets -- whether it's 60 or a dozen -- could be a "cruel compromise" excluding people from medical miracles promised by the new science, researchers say.
They said that only by studying stem cells from many different embryos can science be sure that treatments developed would be universally available. By limiting the number, they said, there is the risk of creating two biological classes -- those who can be treated with stem cell therapy and those who cannot.
And they questioned whether there are actually 60 usable stem cell lines, as the president said. Before his Thursday night speech, scientists had estimated there were 12 stem cell lines, including some that would not meet strict research guidelines.
Bush said he would permit federal funding but with a major restriction: Researchers could use only cells from existing embryonic stem cell lines. This restriction, he said, would mean that no more embryos would be killed to advance federally funded research. Extracting the stem cells kills the embryo.
Federal health officials said Bush's statement about the existence of more than 60 stem cell lines was based on a survey of international laboratories and includes "proprietary information" not generally available. They said the labs are in the United States, Sweden, India, Israel and Australia.
"All of the stem cell research currently being done on mice is being done on only five stem cell lines," White House counselor Karen Hughes said on NBC's "Today" show. "We're talking about 60 stem cell lines here. I think there's enough work to keep the scientific community very busy and we hope certainly to produce cures."
But most researchers say that even 60 is not enough and that it could well take hundreds of embryonic cell lines to harvest the full benefit of cell therapy.
An embryonic cell line starts as a cluster of cells, each able to evolve into any tissue in the body. The cells have the ability to divide virtually forever -- sort of like endlessly cutting out identical paper dolls from a basic pattern. In effect, the cell "line" is endless.
Properly cultured with special proteins, the new cells could evolve into heart, muscle, liver, brain and other tissue. Researchers believe these fresh cells could be injected into patients to boost or repair ailing organs.
But not all embryonic stem cell lines are the same. Since they come from different embryos, they have fundamental genetic differences. As with organ transplants, therapeutic stem cells would have to be compatible with the immune system of the receiving patient. Without this compatibility, the body rejects the curative cells, just as an incompatible kidney or heart can be rejected in an organ transplant.
For this reason, said Dr. Harold Varmus, a Nobel laureate and former head of the National Institutes of Health, limiting embryonic cell lines could be a "cruel compromise" for some people.
"We're going to have to have a sufficiently large repertoire of cell lines to treat patients who have very different" types of immune sensitivities, he said.
Limiting the cell lines "would be a very poor investment and a very cruel investment" if science ended up with stem cells that would not be compatible to many patients, he said.
Larry Goldstein, a University of California, San Diego, stem cell researcher, said, "We know that different embryonic stem cell lines have different properties. So why do we think that the very first lines to be derived have the best properties?
Dr. James Thomson, the University of Wisconsin researcher who first isolated human embryonic stem cells, said researchers do not now know the minimum number of cells lines needed to get the maximum benefit.
Thomson estimated the number could be 100 or more, "but until we start working with the cell lines we really won't know."
Limiting the number of cell lines also discourages creation of new cell lines, the purpose of the Bush restriction.
"Right now, the number of cell lines is small, dangerously small," Thomson said. "If a fire broke out in my lab, it would knock out a major part of the cell lines. That would be a disaster for public policy." |
