Chicago Tribune (KRT) via NewsEdge Corporation :

Jun. 7--Outside the bruising politics of stem cell research, scientists are rapidly moving beyond the black-and-white contrasts that have fueled the moral battle over their work.

Conservatives have staked out a position opposed to all stem cell research that involves the destruction of human embryos, championing methods that derive stem cells in other ways.

Advocates of embryonic stem cell research, on the other hand, argue that only embryo-derived cells can form any type of tissue, offering unique hope for diseases such as Parkinson's and diabetes.

Yet researchers who work with stem cells increasingly describe the different types not as rival therapies, but as tools with distinct strengths and weaknesses.

An example of the complicated research picture arose on Wednesday, when teams from the U.S. and Japan published studies showing they could reprogram skin cells from adult mice to behave like embryonic stem cells.

Some critics of embryonic research hailed the reports as proof that embryonic stem cells are obsolete. But the researchers themselves rejected that conclusion, saying that applying the work to humans will require far more research on many kinds of stem cells.

The new research added a wrinkle to the most recent effort to overturn President Bush's restrictions on funding for embryonic stem cell research. On Thursday, House Democrats hope to pass a bill that would lift those limits; the president has vowed to veto it.

The political fray has obscured quiet efforts in recent months to compare stem cells from many different sources. Experts doing the research say some cells may be best for treating certain diseases, while others are easier to grow in the lab. The upshot is likely to be an array of trade-offs that lack the clarity of the moral debate.

"You can't say one cell type is better than another," said Dr. Anthony Atala, director of Wake Forest's Institute for Regenerative Medicine, who is leading one stem cell comparison study. "Each cell has its own properties. We won't know what the properties are unless they're studied and we find out which cells do best for certain applications."

Embryonic stem cells are prized as the body's primordial kernels, able to grow without limit into about 220 different tissue types. Researchers usually get the cells by taking apart 5-day-old embryos made for couples undergoing fertility treatment. Concern over the destruction of embryos spurred Bush's policy, which has banned funding for stem cells extracted from human embryos since 2001.

One stem cell researcher complained that activists and lawmakers treat the science as an election, with only one possible winner. In reality, the results of stem cell research often don't favor any specific policy conclusion.

This year, for example, Atala published a paper detailing a novel method of obtaining stem cells from amniotic fluid. Critics of embryonic research cheered the method as a replacement for embryonic stem cells, but Atala says it is not that simple.

So far, Atala said, it seems that his cells may be more stable than embryonic cells and less prone to produce tumors in patients--but they also appear to be less versatile.

In another study, published in March, researchers found that embryonic stem cells and so-called "adult" stem cells derived directly from the human nervous system performed equally well in treating mice with a degenerative brain disease.

The success of the adult stem cells does not mean embryo-derived cells are outmoded, said study author Dr. Evan Snyder, director of the stem cell research center at the Burnham Institute for Medical Research in California.

For one thing, Snyder said, the embryonic stem cells were easier to grow into the quantities needed for the therapy. And though the other cells technically were at an adult stage, his team actually derived them from the nervous systems of aborted human and mouse fetuses.

In the studies published Wednesday in the journals Nature and Cell Stem Cell, scientists activated a set of genes in mouse skin cells that normally function only during embryonic development. The reprogrammed skin cells were "pluripotent," meaning they could form any kind of tissue--like embryonic stem cells.

But the procedure could carry risks in humans, in part because it requires activating known cancer-causing genes.

"This provides just one alternative," said co-author Konrad Hochedlinger, a researcher at the Harvard Stem Cell Institute. "We simply don't know which approach will work the best."

To help justify Bush's policy, the White House Domestic Policy Council released a report in April that touted Atala's method along with other stem cell techniques that do not require the destruction of embryos. The report concluded that compared with embryonic stem cells, the new cell types appear "more stable to grow, safer to use in therapies, and free of the ethical violations of embryo destruction."

Yet Atala is more cautious in describing his work.

Though it might seem good that Atala's cells do not become genetically unstable and form tumors, that could also be a drawback of sorts, he said.

Part of the value of embryonic stem cells is the genetic flexibility that lets them develop into different cell types. Left unchecked, the cells can form a kind of benign tumor called a teratoma, which contains many kinds of tissue. In fact, the ability to form teratomas is part of the scientific definition of embryonic stem cells.

Because amniotic-derived stem cells do not form tumors, "it stands to reason that they will not be as nimble" as embryonic stem cells, Atala said.

The need to understand such subtle differences is a major reason for the collaboration between Atala and Robert Lanza, vice president of research and development at California-based Advanced Cell Technology.

By running the tests in the same labs under the same conditions, the groups hope to make consistent measurements of the cells' immunogenic traits and their potential for growth.

Snyder said such tests can ensure that policy decisions are guided by facts rather than hype.

"I think what you'll find is in some diseases one cell type is preferred, for others another type is preferred, and with some diseases different cells may work equally well," Snyder said. "Rather than say what we think is going to work, we should just fund the work and let the data dictate the next step."

jmanier@tribune.com

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