Stem Cells From Embryos Still Unproven
WASHINGTON — Despite being touted as the source of miracles for a host of illnesses, embryonic stem cells might never have any direct therapeutic use, according to a surprising authority: one of the scientists who first extracted embryonic stem cells for research in 1998.
John Gearhart, director of research for Johns Hopkins University's Department of Gynecology and Obstetrics, told a National Institutes of Health conference Nov. 14, “I am not sure these cells are going to be used in therapies, but we are going to use the information we get out of this research to get the patient's own cells and work with them to get them to do what we want. This is really where I see the future now.”
Some pro-life observers interpreted Gearhart's statements to mean he had conceded one of the central arguments of embryonic stem cell research opponents — that adult stem cells, which may be obtained from patients without the destruction of “donor” embryos, are the more promising source of future therapeutic applications.
But Gearhart said that interpretation wasn't quite what he meant. In fact, he maintains that, according to current research, embryonic stem cells are far superior to adult stem cells.
He said the goal of research using any stem cell source, however, is to understand better how cells in general work and how they can be engineered to cure diseases.
“What I'm saying is that the information we're going to get out of the embryonic stem cells and how they do their business will then be applied,” he said. “I try to be objective on the adult stem cell story, but as we sit here today and discuss this it is clear that the embryonic stem cell source is far more valuable and has proved to be far more appropriate in generating any of the cell types we would like for therapies.”
Gearhart cited as evidence recent studies indicating that embryonic stem cells can be coaxed to produce insulin or to become dopamine neurons or motor neurons.
On the contrary, however, only adult stem cells have proved useful in actually treating human patients, argues David Prentice, adjunct professor of medical and molecular genetics at the Indiana University School of Medicine.
“What is clear is that as embryonic stem cells have failed to come even close to the hyped promises for potential treatments, proponents are looking for other ways to justify continued research,” he said.
It has been standard procedure for years to use adult stem cells from bone marrow to treat various blood disorders. Gearhart argues these procedures are more akin to transplants and are not indicative of the relative merits of embryonic versus adult stem cells in treating other problems.
Prentice, however, says that in addition to the now-standard uses of bone marrow stem cells in treating blood disorders, researchers in Germany have successfully used bone marrow stem cells to repair heart damage, and in Japan they grew new blood vessels to prevent gangrene in legs. There are also patients who have been successfully treated for Parkinson's disease with adult stem cells.
Apart from the debate on which stem cells are most useful in direct therapeutic applications, there remains the question of which kind is more likely to reveal how cells in general work and therefore how they may be engineered.
Gearhart argues that research on embryonic stem cells is especially necessary for that purpose.
“What we would like to know is, do we have to take [a cell of one tissue type] back … to a point where it represents a very early embryonic cell,” he asked, “and then move it forward in a different direction? Or can you take that cell and immediately, by engineering it in some fashion, convert it to the other cell that you want?”
Prentice counters that because of successful uses of adult stem cells in animals and humans, “the answer already is apparent: that these cells can change directly to other types of cells. This not only makes embryonic stem cells unnecessary for treatments but also gives a direct way to examine these types of changes.”
Apart from which source of stem cells is more promising from a scientific point of view, the ethical issues in the stem cell debate ultimately boil down to the question of whether the embryo should be treated as a human being.
Pope John Paul II and the U.S. bishops have repeatedly condemned stem cell research, which destroys embryos, on the grounds that embryos are full members of the human family.
In his 1995 encyclical Evangelium Vitae (The Gospel of Life), the Holy Father teaches that while some claim that “the result of conception, at least up to a certain number of days, cannot yet be considered a personal human life … in fact, from the time that the ovum is fertilized, a life is begun which is neither that of the father nor the mother; it is rather the life of a new human being with his own growth.”
From fertilization, the embryo is either a boy or a girl, with his or her life expectancy and his or her own DNA.
In November the Ethics Committee of the American Society for Reproductive Medicine issued guidelines for the “donation” of “spare” embryos from in-vitro fertilization for stem cell research.
The committee reasoned that such donations are permissible because “the embryo has a lesser status than adults and children,” and is therefore only a “potential human being.”
The committee adds, however, that the embryo is “worthy of special respect,” and the proposed guidelines for donation are intended to serve this end. Gearhart says this “special respect” is justified on public policy grounds, since some Americans wish to see limits on what can be done with embryos.
Dr. Benjamin Younger, executive director of the American Society for Reproductive Medicine, said in addition to this reason, the embryo merits “special respect” because “this is not just blood or skin or standard human tissue. … The embryo does have the potential to ultimately end up as a new life.”
Still, he says, the embryo “is not the same as a living person. It's somewhere in between.”
Pro-lifers and Catholics object to carrying out research on human subjects without their consent or when the intervention in question is of no reasonable therapeutic value to the subject in question. Some have compared embryonic stem cell research to the Nazi experiments on Jewish concentration camp prisoners during the Holocaust.
Younger says the difference is that embryos are not human beings in the same sense and are not capable of feeling pain.
“The embryos that you use particularly in stem cell research are not to the point that any neurologic tissue or other specially differentiated tissue has ever occurred,” he said.
Supporters of embryonic stem cell research, including Gearhart and the American Society for Reproductive Medicine, agree that the embryo is human, and some admit that it is living, but they argue that in the first 14 days, at least, an embryo cannot be considered an individual, even though, as pro-lifers point out, it has a unique genetic code from conception onward.
One reason for this distinction, Gearhart explains, is until that point the embryo is capable of “twinning” (essentially “cloning” itself, the process by which many twin siblings come into being).
Peter Cataldo, director of research at the National Catholic Bioethics Center in Boston, said this reasoning “is an example of an inadequate philosophical perspective to process the biological data.”
The possibility of twinning, Cataldo says, “is only a potential aspect of the embryo. … The moral status [of the embryo] ought to be determined on the basis of what the embryo really is.”
“I could [theoretically] take a cell from inside of my cheek and clone myself. Does that mean that right now I am not an individual? … Upon death and the disintegration of the body [the chemicals inside of us] return to their original state. Does that mean that while I am living I am not an individual because I am made up of these chemicals, which can take on an independent existence at some point?”
Cataldo also argues that the notion the embryo is merely a “potential human being” because it does not look or function like a fully developed human is based on another misunderstanding of potentiality — the failure to recognize that any potential aspect of a thing is nonetheless a real part of its nature.
“Essentially the early embryo … is a real individual with a rational human nature,” he said. “We can say of an embryo that even though it's not actually exercising rationality it really is rational, because rationality is a part of its [human] nature. The proponents of [embryonic stem cell research] assume that the real is equivalent to actual operation.”
David Curtin writes from Toronto.
- January 5-11, 2003