The national furor over human cloning is certain to continue for years, regardless of whether or not the U.S. Senate heeds President Bush’s pleas to ban it. The opportunity to create embryonic stem cells that scientists say could generate every cell type in the body-thereby revolutionizing medicine-gives many people pause for ethical reasons.

But in calling for the ban, President Bush raised eyebrows by claiming he had a scientific objection as well: The possible benefits of such research, he said, are “highly speculative.” And yet, eminent life scientists the world over have testified to the extraordinary possibilities of the technology. Even Elias Zerhouni, President Bush’s choice to head the National Institutes of Health, told Popular Science last year that, with proper support, the technology was likely to “crack something really important” and that “it’s not right to have a ban.” So why do the president and his allies contend otherwise?

One reason is David Prentice, a stem cell biologist at Indiana State University. Prentice is a close friend and advisor of Kansas Republican Senator Sam Brownback, who co-sponsored the anti-cloning bill. He has also testified on the issue before Congress and the British and Canadian Parliaments.

“I’ve tried to look at all the published references and especially the science,” he says. And in his opinion, these show little evidence that embryonic stem cells will work as medical treatments. For starters, he claims, James Thomson of the University of Wisconsin at Madison, one of the discoverers of human embryonic stem cells, has “actually said that cloning will not be of any clinical significance.” Moreover, “mouse embryonic stem cells have been around since 1981,” he points out. “But to date, when (scientists) leave the cells in culture, they have not been able to generate every cell type that exists in the body.” Instead of chasing an undeveloped and potentially dangerous Holy Grail, he says, scientists should concentrate on using adult stem cells (a position that, not coincidentally, dovetails perfectly with President Bush’s). Adult stem cells transplanted into small groups of people with Parkinson’s disease and multiple sclerosis have yielded promising results.

But other stem cell scientists seem unimpressed with Prentice’s arguments. “It is a false statement that ‘cloning will not be of any clinical significance,'” retorts James Thomson. “Indeed, understanding reprogramming is one of the central questions of biology today, and could lead to a revolution in what is termed ‘regenerative medicine.'” Another giant in the field, John Gearhart of Johns Hopkins University, responds that though it’s true mouse embryonic stem cells have been around for two decades, they have been used chiefly to create genetically altered mice for research. Substantial efforts to produce different kinds of cells have begun only in the past few years and results have been “very impressive.”

Without disputing the promise of adult stem cell research, Gearhart adds that not all diseases will respond to the same treatment, so both embryonic and adult stem cells are likely to “prove useful, depending on the disease.”

But Prentice and his influential friends are not budging. The research, he insists, is neither “an ethical necessity” nor “will it become a workable type of therapeutic treatment.”

Of course, if the ban is passed, we may never know whether he is right or wrong.

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