Straight talk: Adult and embryonic stem cells and the future of research

July 13, 2003

At an American Association for Cancer Research forum designed to provide straight talk on what's known -- and what isn't known -- about the primitive precursor cells that act as a reservoir of new cells in the body, Johns Hopkins' Curt Civin, M.D., will lead a discussion about stem cell research and policy and their relation to cancer research. The forum is scheduled for July 13 at the Washington, D.C., meeting.

While stem cells found in the blood and bone marrow, so-called hematopoietic stem cells, have been studied for 20 years, more primitive stem cells obtained from embryos have revolutionized stem cell research, says Civin, professor of oncology at the Johns Hopkins Kimmel Cancer Center.

Previewing the discussion, Civin says that "until 1998, 'stem cells' were hematopoietic stem cells; no other kind was known in people. Now, the potential of stem cells from embryos to shed light on basic biology, human development and genetic diseases, and to someday offer ways to treat incurable and fatal diseases has made us re-examine what we think we know about stem cells from the blood and other tissues."

Blood-forming stem cells and other more specialized stem cells from specific tissues or organs are known as "adult" stem cells even if found in newborns or children. Darwin Prockop, from the Gene Therapy Center at Tulane University Medical Center, will recap advances with adult stem cells, which seem to be capable of becoming more cell types than once thought. Irving Weissman, from Stanford University, will discuss the current status of embryonic stem cell research and where it is heading.

"Right now, scientists are just learning about the biology of human embryonic stem cells and how to grow them reliably -- things we've known about hematopoietic stem cells for 20 years or longer," says Civin. "But embryonic stem cells are ahead of adult stem cells in making a wide variety of different cell types on demand."

People's opinions differ widely on whether using leftover in vitro fertilization embryos to gather embryonic stem cells is acceptable, particularly on whether obtaining the stem cells is destroying a "life." Cells from newborns or more grown-up humans don't pose the same dilemma, prompting a repeated question, says Civin.

"People always ask if the new finding -- whatever it is -- means that scientific and medical goals could be accomplished by researching only 'adult' stem cells to avoid the ethical debate," he says. "The bottom line is that we don't know enough to answer that question, and we won't for some time."

One hurdle to understanding the differences between embryonic and adult stem cells is political indecisiveness, says Civin, who will open the AACR session by describing a current effort in the Maryland legislature. A proposed bill would try to make Maryland an attractive place for research using human embryonic stem cells, in part by setting up framework for research on somatic cell nuclear transfer techniques with human cells, widely known as therapeutic cloning.

Among other things, proponents say developing the technique -- far from a "gimmee" -- could help unravel the processes that lead directly to many genetic diseases, including cancers. By creating a line of embryonic stem cells from a person with such a condition, scientists could study how that genetic change affects cells in early development -- currently impossible to examine -- and farther along the path from embryonic cell to a particular type of cell (mammary cell, prostate cell, ovary cell, etc.).

"How does the genetic change affect the signals that tell cells to divide or stop dividing, or what type of cell to become? In cancer, a disease of abnormal cell growth, that's an extremely important question, and it's hard to think of a more direct way to investigate it," says Civin.

Criticizing policies that would limit study to only stem cells from "adult" tissue, or from embryonic tissue, Civin says the key to making progress scientifically, which eventually improves medicine, is to approach a question from a number of angles. Limiting the approaches slows discovery and prevents validation of results, he says.

"What if 20 years ago the government had decided that computed tomography should be set aside and work should only continue on magnetic resonance imaging, say, because it doesn't involve radioactivity?" asks Civin. "At the time, no one knew if one would turn out to be better, and as fate would have it, each has its niche, even today."

Similarly, he says, pursuing research with both embryonic stem cells and adult stem cells is the most reasonable way to learn what scientists and doctors don't know about stem cells.

"Stem cells from all sources have potential to reveal answers to biology's great mysteries and someday to impact medicine," he says, "and the constant cry to try to use stem cells from only one source is counter to how science is done best."
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