The theory - and the expectation - is that stem cells will turn out to be the ultimate repair kits of the human body, able to grow into any of the body's more than 200 cell types to reverse disease or replace damaged tissue.
But scientists who have only begun to explore the potential for these blank slate cells are caught in an ethical and political crossfire over whether their research should include cells obtained from human embryos.
President Bush is expected to decide soon whether federal money can be used for embryonic stem cell research, and if so, under what terms. He may also act to impose guidelines or restrictions on the research in privately funded labs.
Bush's decision probably won't be the last word on the research, since many in Congress also want to intervene, but the White House focus on the issue has given it so much visibility that every scientific development involving stem cells has come to have political implications.
"We're all responsive to the debate, all waiting to see how the guidelines fall to determine the environment we'll need to work in," said Dr. William Gibbons, spokesman for the Jones Institute for Reproductive Medicine. The private fertility clinic in Norfolk, Va., reported earlier this month it has been producing embryonic stem cells from paid egg and sperm donors.
The facility also assisted in the creation of the nation's first test-tube baby 20 years ago. Affiliated with Eastern Virginia Medical School, it is believed to be the first to create embryos specifically to harvest stem cells.
Gibbons said the announcement of the research in a medical journal wasn't timed to affect the research on the debate, but "we were certainly aware that it would become part of the discussion."
Likewise, opponents who say the destruction of embryos for stem cells is abortion have been quick to tout accomplishments of research into stem cells obtained from adults, saying this approach could make embryonic stem cell research needless.
Yet scientists have repeatedly stressed in reports and forums over the past several months that they simply don't know enough about the relative merits of stem cells obtained from adult tissue, embryonic stem cells or aborted fetuses to rule any type of study in or out.
"To date it is impossible to predict which stem cells - those derived from the embryo, the fetus, or the adult - or which methods for manipulating the cells - will best meet the needs of clinical applications. The answers clearly lie in conducting more research," said scientists at the National Institutes of Health, in a report summarizing recent stem research prepared at the request of the White House and released earlier this week.
"Because we do not know... the door should be left open to conduct research on both," Lana Skirboll, director of the NIH's office of science policy, told a Senate hearing.
The situation has prompted many adult stem cell researchers to emphasize doubts about their work.
"At face value (the scientific literature) says adult stem cells can do everything, but if you look more critically, many of us really doubt the major conclusions," said Margaret Goodall, a Baylor College of Medicine researcher who reported a study two years ago that seemed to suggest muscle stem cells could morph into blood cells, but has since concluded they probably cannot.
While his own lab work strongly suggests that adult stem cells derived from bone marrow can become new brain cells, Darwin Prackop, a researcher at Tulane University Medical Center, said recently: "We are simply not ready for a moon-shot like strategy in which we place all our bets on adult stem cells."
Even if Bush decides to allow some limited federally funded embryonic stem cell research to go forward, scientists in the field are also at odds over how the cells should be obtained.
Most advocates have assumed that the technique of obtaining stem cells from frozen embryos created for assisted pregnancies but instead donated by consenting parents would prevail, since they allow the ethical argument that the embryos would have been destroyed anyway.
Geron Inc., a California biotechnology company, has taken the lead in obtaining stem cells with this technique. While some samples of the cells have been shipped, chief executive Thomas Okarma told a forum at the National Academy of Sciences last month that many institutions have held back obtaining stem cells for fear they could jeopardize government funding if Bush rules against the research.
Nonetheless, he predicted that "the work will go on, one way or another."
Gibbons of the Jones Institute said having embryos specifically donated for stem cell studies is a more open process that allows better monitoring and screening for genetic mutations conditions. "This way the donors know what's going on up front," he explained.
And scientists working for Advanced Cell Technologies, in Worcester, Mass., revealed last week that they're trying to use cloning technology to create embryos for stem cell production.
Michael West, the head of the company, said the technique would not be used to clone people, but that it would allow the custom culturing of stem cells for therapeutic purposes with material taken from the intended patient, reducing the risk of immune system rejection.
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