Will Stem Cells Finally Deliver?

By Scadden, M. D. David T.; Komaroff, Anthony L. | Newsweek, December 15, 2008 | Go to article overview

Will Stem Cells Finally Deliver?


Scadden, M. D. David T., Komaroff, Anthony L., Newsweek


Major breakthroughs are propelling the field. Science becomes medicine.

Many diseases involve the death of cells that the body cannot naturally replace. Sometimes cell death comes suddenly, as in a heart attack. Other times it is slow and inexorable, as in Alzheimer's disease. The great promise of stem cells--the body's equivalent of renewable energy--is that they could be coaxed into becoming and then replacing cells lost to disease.

But daunting scientific challenges, ethical concerns and even politics have slowed progress for more than a decade. In the past two years, however, a series of remarkable breakthroughs has advanced the field: suddenly, it appears possible to create cells with all the potential of embryonic stem cells without using embryos, eliminating most of the ethical concerns surrounding stem-cell research.

Embryonic stem cells have two extraordinary properties that make them, potentially, the most medically useful. First, they are "pluripotent," with the capacity to become any type of specialized cell in the body--a heart-muscle cell that pumps blood, an acid-producing cell in the stomach, a cell in the retina of your eye that sees light, or a brain cell that stores memories. Second, embryonic stem cells can keep dividing and making unlimited copies of themselves--an important property, since huge numbers of new cells may be needed to replace cells lost to disease.

Scientists have also been studying adult stem cells, work that doesn't raise the ethical questions posed by em-bryonic-stem-cell research because it doesn't involve the use of human embryos. Bone marrow and organs like the heart and liver all naturally contain adult stem cells. These cells have the potential to develop into most of the cells in their specific organ. Adult stem cells help replace specialized cells that have been killed, since most specialized cells cannot naturally reproduce themselves. However, adult stem cells in most organs cannot naturally repair the massive injury caused by many diseases, although scientists are working on ways to change that. Also, adult stem cells are not pluripotent: unlike embryonic stem cells, they cannot be turned into any cell in the body.

The remarkable properties of embryonic stem cells, however, are difficult to exploit. Ideally, a patient in need of stem cells would want his own genetically identical stem cells because they would not be attacked as foreign by his immune system. But embryonic stem cells exist only briefly, within the first two weeks after conception. And stem cells from embryos produced for in vitro fertilization programs would be genetically different from the patient, raising the risk that they would be rejected by the immune system and would therefore require potentially toxic treatments to suppress the immune response.

Such cells also raise ethical questions, since some people believe an embryo with the potential to be implanted and develop into a baby has the moral status of a person and should not be destroyed, no matter how great the human benefit. In 2001, President George W. Bush restricted federal funding to existing lines of embryonic stem cells; government money could not be used for research that involved the further destruction of embryos. (President-elect Obama has pledged to reverse that policy.)

A possible solution to these daunting obstacles came from a team of Japanese researchers who asked a simple, if fanciful, question: is it possible to turn a specialized cell back into an embryonic stem cell, or at least into a cell with the same remarkable properties as an embryonic stem cell? It's the genes within every cell that determine how that cell acts and looks. While all of our specialized cells and our embryonic stem cells share exactly the same set of genes, very different genes are "turned on" in each type of cell. In other words, an embryonic stem cell turns into a specialized cell because certain genes are turned on, and others turned off. …

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