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The Stem Cell Controversy
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Researchers think human embryonic stem cells could be a boon to medical research and treatment. "Embryonic stem cells could serve as replacement cells for those that have been lost or destroyed because of disease," says Robert Goldstein, Chief Scientific Officer of the Juvenile Diabetes Research Foundation. "If we can discover the biological cues that make an embryonic stem cell develop into a specialized cell -- like an insulin-secreting cell in the pancreas -- we could try to reproduce these signals in the lab and create a source of replacement cells for many afflictions."
Embryonic stem cells have other potential uses: as tools for studying early events in human development (shedding light on birth defects), as test systems for new drug therapies, to screen potential toxins, and as vehicles or "vectors" to deliver genes that could correct defects. These applications remain theoretical -- the field is too new for any of these treatments to have reached human stages. But various animal studies have demonstrated "proof of principle" -- that these approaches can work. For example, mouse embryonic stem cells have been converted into
specialized cell types and transplanted into animals to relieve symptoms of spinal cord injury and Parkinson's disease.
The Controversy
The isolation of human embryonic stem cells in 1998 thrust stem cell research into a volatile national debate tied to the fight over abortion. Deriving embryonic stem cells, and destroying an embryo in the process, raised profound ethical questions. Most revolve around the question of when life begins. Is an embryo a person? Should we forego embryonic stem cell research to protect the embryo? Is it right to negate a potential life for benefits that are unproven? Should researchers avoid this ethical minefield and redouble their efforts with adult stem cells?
The Case Against Using Embryonic Stem Cells
Objections to deriving human embryonic stem cells arise from the contention that human embryos are nothing less than individual beings in the earliest stages of life. As some members of a bioethics council appointed by President Bush put it in 2002, "We find it disquieting, even somewhat ignoble, to treat what are in fact the seeds of the next generation as mere raw material for satisfying the needs of our own."
Those opposed to using embryonic stem cells contend that the benefits from the cells are speculative today, while the medical applications of adult stem cells have been shown for years. "Embryonic stem cells have not helped a single human patient or demonstrated any therapeutic benefit," reads a statement by the United States Conference of Catholic Bishops. "By contrast, adult stem cells and other ethically acceptable alternatives have already helped hundreds of thousands of patients, and new clinical uses expand almost weekly."
Many on this side of the argument cite the recent studies suggesting that adult stem cells can change type, or transdifferentiate. If researchers could isolate enough adult stem cells, couldn't they, instead of embryonic stem cells, be used as replacement tissue? Some scientists even think it might be possible to "reprogram" adult stem cells back to an embryonic-cell-like state -- again providing a source for replacement tissue without the moral objections. An added benefit of this technique would be that the cells come from the patient's own body and thus are less likely to be rejected.
Another issue with using embryonic stem cells concerns their ability to divide indefinitely. Studies in animals have shown that embryonic stem cells sometimes form tumors called "teratomas" or develop into a mixed collection of partially formed tissue. This could make injecting them into human patients risky. Adult stem cells, on the other hand, are not thought to pose such risks.
The Case for Using Embyronic Stem Cells
Many scientists do not think adult stem cells offer the same therapeutic and research potential as embryonic stem cells. Adult stem cells are difficult to isolate, and they do not proliferate well in culture. There's little proof, researchers argue, of a wide array of human adult stem cells that can differentiate into multiple tissue types. Some studies that appeared to show adult stem cells transforming into other cell types have been called into question by more recent findings, and evidence seems to indicate that adult stem cells may not possess the same capacity to give rise to any cell type as embryonic stem cells do.
But despite the questions, the consensus among most scientists is that research on both stem cell types should continue on parallel tracks. Even those who have made their mark working with adult stem cells, such as Catherine Verfaillie of the University of Minnesota, hold this view. "We will not know which stem cells, adult or embryonic, are most useful in treating a particular disease without side by side comparison of adult and embryonic stem cells," Verfaillie wrote on February 4, 2002 in a letter submitted to Pennsylvania Senator Arlen Specter.
And in 2001, a letter from 40 Nobel Laureates to President Bush stated: "It is premature to conclude that adult stem cells have the same potential as embryonic stem cells -- and that potential will almost certainly vary from disease to disease ... Therefore, for disorders that prove not to be treatable with adult stem cells, impeding human pluripotent stem cell research risks unnecessary delay for millions of patients who may die or endure needless suffering while the effectiveness of adult stem cells is evaluated."
Many disease sufferers consider embryonic stem cells to be their only lifeline. Karen Miner, 52, has been paralyzed from the shoulders down after her car went into a ravine during a rainstorm 11 years ago. In 1998, she co-founded Californians for Cure, which advocates for spinal cord and embryonic stem cell research in California. Miner doesn't understand why "pro-life" forces are aligned against her cause.
"They really don't understand that it's not destroying a life, it's saving a life," she says. "I do not believe these cells are children. Blood cells are alive, and so are skin cells. We cut into them during surgery, but no one considers that murder. They make it sound like there are people growing out in warehouses that we take body parts from."
Finally, in answer to those who consider destruction of an embryo unjustified even if it saves a life, those favoring embryonic stem cell research point out that IVF-created embryos often get discarded, so they should be put to use rather than wasted.
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Regenerating nerve cells (in green) grown from transplanted stem cells (in red). |
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We'd like to know.
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Joy Veron received a transplant of her own nasal stem cells in Portugal. |
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