A strange and confused chapter in the history of American medical research ended Monday morning, when President Obama signed an executive order ending a ban on federal funding for embryonic stem cell lines that were developed after August 9, 2001.

The ban has been roundly denounced as hypocritical and destructive, stunting advances in one of the most exciting fields of medical research. Some restrictions will still apply, and whether research will provide much-anticipated cures is an open question — but at least the question will be answered by science, with the government's full weight behind it.

"This is a momentous occasion for anyone who believes in the pursuit of biomedical knowledge for the betterment of human health," said Harvard Stem Cell Institute researcher George Daley.

Embryonic stem cells may be used to replace diseased and failing tissues, and treat now-incurable diseases, from cancer to Parkinson's. Though most stem cell–based treatments are probably a decade away, some advances, like universal blood made from stem cells, could become available much sooner. And now, with the ban lifted, money from the the National Institutes of Health's

$29 billion budget is likely to pour into the coffers of stem cell scientists across the nation, speeding up the pace of the research.

Over the last seven years, as the therapeutic promise grew, research on embryonic stem cells became a front in the culture wars, with lines drawn between religious fundamentalists and everyone else. Thirteen states established state-funded stem cell research institutes like the mammoth $3 billion California Institute for Regenerative Medicine, but they couldn't provide the same level of backing as the national government.

"This marks a new era for stem cell research. It will not only impact research in the laboratory, but perhaps more importantly, it finally lifts the black cloud that has hovered over this research for so long. We have been operating for the last decade with one hand tied behind our back," said Robert Lanza, science director of Advanced Cell Technologies. "For the first time in almost a decade, we can now apply for government grants to use our cells to treat human diseases. Rather than keeping the cells in the freezer, now we can use them to help people."

Though President Bush's ban has received most of the attention, the political battle over embryo destruction and stem cell research actually dates to the Clinton administration, when Congress passed the little-known Dickey-Wicker amendment. The law denies taxpayer money for research that creates or destroys embryos.

Creating and destroying embryos is central to a procedure called somatic-cell nuclear transfer, or therapeutic cloning: A nucleus is taken from one cell and put inside a hollowed-out embryo, which is allowed to divide for several days, producing embryonic stem cells that can become any other type of cell in the body.

Under Dickey-Wicker, however, the federal government could still fund research on the resulting cells — just not the original embryo creation and destruction. President Bush banned government support for all therapeutic cloning research, from inception to application, and prevented research on cells manufactured in other ways. Scientists could not use embryos discarded by fertility clinics, or from cells taken from embryos without destroying them.

This restricted government-funded research to exactly 21 embryonic stem-cell lines developed in the field's early days. Few are useful for anything but basic research.

Obama's decision was criticized by opponents of embryonic stem cell research, who say that the cells' medical promise is overhyped, and made unnecessary by advances in research on adult stem cells. These develop into one cell type rather than a full range, and are relatively better understood than their embryonic counterparts.

"Human embryonic-stem cell-research is now passé," said James Sherley, a

Boston Biomedical Research Institute biomedical engineer. In 2007,

Sherley was denied tenure at the Massachusetts Institute of Technology, a decision resulting, he alleged, from his scientifically unpopular opposition to ESC research. "The most advertised property of human embryonic stem cells, their potential to produce any tissue type in the body, is also their worst failing. The tissue types that they always produce are tumors."

President Obama's decision, he said, "will not promote human embryonic stem cell research. However, it will put more resources in the hands of scientists who have been selfishly promoting dead-end research since 2001."

But most scientists and medical experts say that research is justified on all types of stem cells: The insights generated in one type can inform another, just as breakthrough cell reprogramming research — driven, in part, by concerns over embryo destruction — required the identification of genes activated in embryonic stem cells. Different diseases may also require different treatments; a single type of stem cell may not suffice.

Comparing adult and embryonic stem cell research is also unfair, wrote University of Pennsylvania bioethicist Art Caplan in an MSNBC editorial.

"After eight years of zero-budget funding of embryonic stem cell research, it is hardly fair and completely disingenuous for critics to point to the practice and wonder why it lags four decades behind government-funded adult stem cell research," he wrote.

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