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> Amniotic fluid a promising stem cell source
cerebral
post Jan 08, 2007, 01:17 AM
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Congress is once again drawing the political spotlight to human embryos as House Speaker Nancy Pelosi, D-San Francisco, leads a new attempt this week to expand federal grants for stem cell research.

Scientists are all for that. At the same time, they keep moving in other directions. They are looking for different sources of stem cells perhaps more practical in the long run than the controversial, days-old embryos getting all the attention on Capitol Hill.

On Sunday, researchers offered new evidence that stem cells, very much like those derived from embryos, can be obtained from ordinary amniotic fluid, the liquid that bathes the fetus during pregnancy.

Although such cells had been found before, a report in the journal Nature Biotechnology suggests they can be isolated from the fluid more easily than previously thought and coaxed into developing into muscle, bone, liver, brain and other major cell types in the search for new treatments for diabetes, paralysis and many other maladies.

"It's a plentiful source," said Dr. Anthony Atala, senior author of the research paper and director of the regenerative medicine institute at Wake Forest University in Winston-Salem, N.C.

Now, it appears the birth fluid may be a repository of all sorts of valuable biological material.

The study is one of many recent examples of scientists pushing the boundaries in the search for stem cells -- driven partly by scientific interest and partly by practical necessity.

Moral objections to embryonic stem cell research prompted the Bush administration in 2001 to limit federal backing for the work. Scientists are opposing those limits but simultaneously exploring other sources, noting that human embryos for research would be rare even in ideal circumstances. And some of the alternatives may have valuable properties not seen in the embryonic cells.

"Scientists are opportunistic," said Dr. Evan Snyder, a stem cell researcher and physician at the Burnham Institute in San Diego, a co-author of the new report. "They will use whatever works."

Moral critics of embryonic stem cell research say alternative sources of stem cells like amniotic fluid undercut the need to use embryos, which typically must be destroyed to yield their core nugget of stem cells.

Sunday's report "is one in a line of studies showing very versatile stem cells can be obtained from a number of different products after live birth -- amniotic membrane, amniotic fluid, cord blood, placenta, even umbilical cord tissue," said Richard Doerflinger, deputy director of the U.S. Conference of Catholic Bishops Secretariat for Pro-Life Activities. "There is no reason why the amniotic fluid couldn't be obtained, raising no moral problem whatever. So, we welcome this further advance in expanding the known sources of potentially useful stem cells."

Scientists insist they need access to all sources.

Stem cells derived from early embryos are by definition the most versatile -- they give rise to all the cell types that make an organism -- and so they remain the gold standard against which all other stem cells are compared. Bush's restrictions limit researchers to only those few cell lines already created before the 2001 policy was announced. "The government has forced stem cell research through the eye of a needle defined by the federal lines," said Susan Fisher, co-director of the UCSF Human Embryonic Stem Cell Center. "What we need is a broad comparative assessment of as many different cell types from as many different sources as possible."

That's also one of the goals of California's Proposition 71 stem cell program, created largely to get around the federal financing restrictions on embryonic research. The program expects to issue a draft list of its first research grant awards in early February. Although embryonic stem cells are the main focus, Prop. 71 program leaders also recognize the value of finding alternative sources, tentatively targeting $12 million in initial grants for that purpose starting next year.

Previous congressional attempts to overturn the president's restrictions ran aground on a presidential veto. Now, Pelosi and her Democratic colleagues are trying again, emboldened by the results of the 2006 fall election, which put Democrats in the majority.

Even if the federal grant restrictions are erased, there is a limited number of human embryos available to researchers, and their use requires special procedures to ensure informed consent on the part of donors. The embryos are generally leftovers donated by couples undergoing in vitro fertilization.

Attempts are under way to produce stem cells in other ways, such as by reprogramming adult cells or cloning. But those experiments also are controversial, and in some cases have yielded disappointing results.

By contrast, amniotic fluid can be easily obtained during or right after any typical pregnancy -- and there are roughly 4.5 million births a year in the United States. The fluid can be withdrawn through a needle for a diagnostic procedure known as amniocentesis. The same fluid is routinely discarded when a woman's "water breaks."

"It really is the baby's bathwater -- and everything from the fetus gets sloughed into that from the earliest stage of development," Snyder said. "It's not unexpected that among all the thousands of different kinds of cells, some would be these very early cells that helped put the fetus together."

The scientists used elaborate sorting methods to find the stem cells, "like panning for gold," Snyder said, and then did separate tests to find out how flexible the cells really were.

Results showed the stem cells derived from amniotic fluid aren't identical to stem cells derived in the classic manner, from the "inner cell mass" of an embryo four or five days after fertilization. Further studies may be needed to prove the versatility of the fluid-derived cells.

So far, the cells appear to have many of the hallmarks of their embryo-derived relatives, including one of the defining traits of a stem cell: the ability to make high-fidelity copies of itself without losing its flexibility.

The amniotic cells didn't need to be grown on layers of "feeder" cells, as is the case for cell lines taken from embryos. Unlike embryonic stem cells, the fluid-derived cells showed no apparent tendency to develop into cancerous tumors.

That may be because the amniotic cells lack true "stemness" -- the ability to turn into different cell types, a feature known as "pluripotency" -- but it's clearly a plus as far as reducing the cancer risk of any stem cell therapy.

Because the cells are so immature, they lack immune system flags that could start rejection if the cells are ever fashioned into replacement parts for patients. Atala calculated that only about 100,000 specimens would be needed to create a stem cell bank to cover 99 percent of the U.S. population.

But that still won't eliminate the need for embryos, he said, citing the unique powers of that handful of cells that form at the earliest stages of life.
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cerebral
post Jan 08, 2007, 01:18 AM
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clearly, it's too early to get overly-excited about this result, but it's something to keep an eye on.
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