Addressing the crucial issues of stem-cell research

The Stem Cell Controversy: Debating the Issues, 2nd Edition. Michael Ruse and Christopher A. Pynes, eds., Amherst, N.Y.: Prometheus Books, 2006. ISBN: 978-159102-404-0. 367 pp. $22, softcover.

Parkinson's disease results from the death of nigral neurons, the dopamine-producing brain cells that facilitate signal transmission between nerve cells. Neuroscientists have successfully grafted fetal neurons into the brains of Parkinson's patients, dramatically relieving some sufferers' symptoms. But six fetuses are needed to treat just one patient, in part because transplanted cells perish at a rate of 90 percent shortly after grafting. As such, there will never be enough fetal tissue to treat all of the people who need it, and, according to science writer Marcia Barinaga, that is precisely why researchers are "pinning their hopes on cultured stem cells" that could potentially produce an unlimited supply of nigral cells for more than one million American Parkinson's patients.

But the use of stem cells has raised many questions and stimulated much debate in recent years. How do different kinds of stem cells compare? What are the scientific challenges, ethical implications, and political realities that complicate proposed research? And what medical progress has already been made? In The Stem Cell Controversy, a manageable but refreshingly balanced anthology, philosophers Michael Ruse and Christopher Pynes relay recent commentaries, official decrees, and, most important, expert analyses addressing each of these crucial issues.

The limitations of adult stem cells (ASCs) have been well documented by many, including the National Institutes of Health. ASCs are difficult to isolate and, in fact, have never been isolated in many tissue types. When located, they are often present only in small quantities, and they quickly lose the ability to divide and differentiate in cultures. ASCs are also more likely than embryonic stem cells (ESCs) to contain genetic errors or blemishes resulting from disease or the unavoidable hazards of daily living. And, although certain varieties of ASCs--bone-marrow and umbilical-cord blood stems in particular--might be more versatile than others, there is no evidence to suggest that any ASCs are pluripotent (capable of producing almost any type of cell in the human body).

But some of these concerns are largely unwarranted, argues neurobiologist Maureen Condic. That ASCs are difficult to locate and grow is a mere technical problem that science will likely solve given sufficient time and effort. The scarcity issue is trivial, because autologous transplants, involving stems extracted from one's own tissue, require fewer cells than would be necessary to treat groups of patients. Diseased donor tissues, as a practical matter, affect ASCs and ESCs equally, because injuries or foreign agents are responsible for most illnesses. On the other hand, genetically based diseases are not usually relevant, because they typically occur only later in life.

And, assuming the successful isolation, maintenance, and transplantation of sufficiently numerous ASCs, adds neurologist Sidney Houff, their proliferative limitations might actually offer clearly practical advantages. After all, as stem cells or more advanced progenitor cells become further differentiated, fewer things can go wrong. Prior commitment is an especially attractive attribute in the context of central-nervous-system cell transplants where phenotype control is crucial. In addition, ASCs and progenitors are likely to be more responsive than ESCs to signals in niches, where stems typically reside. In fact, ESCs might require signals that are simply not available in adult tissues.

But ESCs are uniquely pluripotent, supplying scientists and patients with the greatest hope for wide-ranging success, everything else being equal. ESCs possess vast potential with respect to cell and tissue therapies, despite the very iniquitous menaces of immune rejection and teratoma formation. But they can also help us to better understand the processes by which the most perilous diseases--cancers and birth defects, for example--are created. In other words, a more sophisticated comprehension of cellular activity at the executive level, and therefore of life itself, may hang in the balance.

But at what moral cost? Most people are familiar with the standard permissive argument--generally, that the barely visible, 150-cell blastocysts from which inner cell masses and ESCs are extracted do not display the attributes of personhood. But philosopher Don Marquis finds this position ethically dubious, even from a purportedly objective and nonreligious perspective. Moral agency, for example, cannot be the standard, because neither infants nor the mentally retarded can be considered moral agents. Sentience and consciousness cannot be considered elemental to personhood either, because every person drifts into unconsciousness, albeit temporary, on a regular basis--during sleep. ESC research, Marquis concludes, is nothing more than age discrimination.