Testimony before the Senate Appropriations Subcommittee on Labor, HHS and Education by David A. Prentice, PhD

Date: 09/07/2000

September 7, 2000

Mr. Chairman and Members of the Subcommittee, I thank you for this opportunity to appear before you today to talk about this extremely important issue of stem cell research. Your colleague, Senator Brownback, has stated previously his position that federally funded human embryonic stem cell research is “illegal, immoral, and unnecessary”. Others have discussed at length the arguments related to the “illegal” and “immoral” aspects, but not enough has been said regarding the reasons that it is “unnecessary”, and in fact it would appear at times that some of the information which has been brought forth is misleading. Therefore, I would like to spend some time with you today discussing this aspect in terms of an ethical alternative to embryonic stem cells, the so-called “adult stem cells”, and the scientific information which indicates that this alternative actually does make destruction of human embryos completely unnecessary.

Mr. Chairman, while I am certain that you and the other Members of this Subcommittee are by now well aware of the basic information regarding stem cells, for the benefit of those in the audience who are relatively new to this debate I would like to give just a brief background. A stem cell is a cell that can proliferate with almost unlimited potential, maintaining a pool of growing and dividing cells, with the added ability that some of the daughter cells can differentiate into specific cell types. Thus, a stem cell allows for replenishment of itself while providing for specific functional tissues needed by the body. Stem cells have been known for many years, such as the blood stem cells in our bone marrow which continually replenish the red and white cells and platelets in our bloodstream. Embryonic stem cells (ES cells) have been isolated from mice for 20 years. In the fall of 1998, there were two reports on isolation of human embryonic stem cells; in Dr. John Gearhart’s laboratory at Johns Hopkins, the workers actually isolated embryonic germ cells from early human fetuses after elective abortion, while Dr. James Thomson’s laboratory in Wisconsin isolated true embryonic stem cells from human embryos a few days old. Because embryonic stem cells are derived from embryos quite early in the continuum of human development, they should have the ability to form virtually any tissue needed in the body. It is for this reason that many are anxious to use these cells for possible clinical applications in repair of damaged or diseased tissues. As you are also well aware, part of the debate revolves around the requisite destruction of the human embryos for derivation of these embryonic stem cells.

There are, however, some scientific reasons why use of these human embryonic stem cells is less desirable than use of adult stem cells. One is simply the fact that tissues generated by these cells will face transplant rejection, as would any normal organ transplant, and require use of toxic immunosuppressive drugs, perhaps for the lifetime of the patient. While one possible solution to this problem would be to clone the patient and destroy that embryo, the patient’s “twin”, to derive the cells, this complicates the debate even more with an additional controversial technique. Another possible problem may be control of the differentiation of these embryonic stem cells such that they form the desired tissue, and not other tissues or even a tumor.

One concern and potential problem is that while these embryonic stem cells have been termed “pluripotent”, able to form most but not all cell types, published reports indicate that they are actually “totipotent”, able to form all tissues of the developing human, or even the integral human embryo itself. The publications regarding human or primate embryonic stem cell derivation note that, unlike mouse embryonic stem cells, human and primate embryonic stem cells can form not only tissues which become part of the human body, but also trophoblast tissue. Trophoblast is the tissue layer of the early embryo that allows it to implant into the uterine wall, forms part of the placenta, and essentially nurtures early development. It is this layer which is removed in the destruction of the early embryo. Re-formation of this tissue layer in cultures of embryonic stem cells could lead to re-formation of complete human embryos in culture, able to survive if implanted into a womb. This means the possible production and destruction of thousands of new human embryos in culture, created with Federal funds, a direct violation of Federal law and NIH’s own guidelines. The image of a virtual “embryo body shop” springs to mind. This concern certainly impacts the debate again in terms of the legal and moral aspects.

But now turning to the main topic, the ethical alternative of adult stem cells. Let me note for those unfamiliar with the terminology that these cells reside not only in adults but in all of our bodies from birth, one rich source being cord blood from the umbilical cords of newborns. There have been a number of statements critical of this alternative and the abilities of adult stem cells to fulfill the promise of tissue repair. I am somewhat mystified by these statements which malign the capabilities of adult stem cells, and can only assume that the statements have been made without a thorough reading of the scientific literature, especially within the last 1-2 years.

For example, it has been stated that embryonic stem cells will be in clinical use before adult stem cells. To date, there have been no publications regarding the current clinical use of human embryonic stem cells. However, human adult stem cells have already been used successfully for several clinical treatments. There is a wealth of references on the use of stem cells as an adjunct in the treatment of numerous types of cancer, including brain tumors, ovarian cancer, various solid tumors, multiple myeloma, breast cancer, and non-Hodgkin’s lymphoma. The adult stem cells are purified from bone marrow or circulating blood, preferably from the patient, and after treatment to destroy the cancer cells the patient is given back their own purified stem cells (an “autologous” transplant.)

Adult stem cells have also been used successfully to treat several autoimmune diseases such as multiple sclerosis, systemic lupus, juvenile rheumatoid arthritis, and rheumatoid arthritis, as well as anemias. A report in August noted one of the first uses of an adult neural stem cell line for treatment of stroke. This summer there were two reports of the use of corneal stem cells to restore vision to patients with corneal scarring in which normal corneal transplants would not work. Again, in most of the cases, the patient’s own adult stem cells were used. Adult stem cells have been used to treat children with a condition which leads to bone and cartilage deformities. And, in April of this year, “adult” bone marrow stem cells were used in what seems to be the first successful example of human gene therapy, in which infants with a severe immunodeficiency seem to have been cured by giving them their own stem cells with the defective gene replaced.

One of the common criticisms leveled against adult stem cells is that there are only a few types, and they are not pluripotent, lacking the range of ability to differentiate into all tissues which is claimed for embryonic stem cells. In point of fact, human embryonic stem cells also have not been shown at this time to be able to generate all tissues in the body; nonetheless, it is presumed that they have pluripotent potential.

For adult stem cells, however, in June of this year a group in Sweden performed an experiment with mice using adult neural stem cells which shows that these adult cells are pluripotent. The study replicates an experiment done in 1984 using mouse embryonic stem cells, an experiment which has not been done–and ethically should not be done–with human embryonic stem cells. The Swedish group’s results confirm that adult neural stem cells are pluripotent–the cells were able to participate in formation of heart, lung, intestine, liver, nervous system, muscle, and other tissues. The authors state that “these studies suggest that stem cells in different adult tissues may be more similar than previously thought and perhaps in some cases have a developmental repertoire close to that of ES cells.”

Other reports note that adult neural stem cells can be stimulated to grow even while still within the brain if given sufficient signal. Several sites with the human brain have been found to contain neural stem cells, and that these cells can be used in animals to repair spinal cord damage and other neural damage. One report notes that these human adult neural stem cells can be multiplied in culture, established as continuous cell lines, and are “similar to human embryonic stem cells.” The authors of this study also note that “The fact that this revolutionary strategy uses autologous neuronal material means that it has all of the advantages of biosafety, histocompatibility, and neurophysiological efficiency. Furthermore, it does not raise the ethical and moral questions associated with the use of embryonic or heterologous material.”

Other adult stem cells identified include those in muscle, and these cells also appear capable of reprogramming to form different cell types including blood, bone, and cartilage. Just 2 days ago a report in the Journal of Cell Biology announced purification of adult stem cells from muscle of a mouse model of Duchenne’s muscular dystrophy. The cells were intravenously injected back into the dystrophic mice, and resulted in muscle regeneration and partial restoration of dystrophin expression in the mice. Transplantation of these cells engineered to secrete a bone protein resulted in the cells changing from muscle to bone cells, and accelerated healing of a skull defect in mice.

Diabetes is one of the leading killers in the United States. There have recently been reports of successful treatment using adult pancreatic stem cells from cadavers. Again, if a patient could use their own stem cells, there would be a distinct advantage. In this respect, in March of this year adult pancreatic stem cells from mice were used to reverse diabetes in these animals, employing their own stem cells. After treatment, the mice no longer needed insulin shots to survive.

Other criticisms of adult stem cells are that they are hard to access, and that they do not multiply well in culture. One of the most versatile and accessible adult stem cell populations is in bone marrow. In August researchers showed that these human adult bone marrow stem cells can take up a “new job description” and be changed into neurons. The authors noted that this source could provide “a virtually limitless supply” of nerve cells. According to reports, the cells “grow rapidly in culture”, “are readily accessible”, and “provide a renewable population.” They also add that “Autologous transplantation overcomes the ethical and immunological concerns associated with the use of fetal tissue.”

In July, two groups, one in the U.S. and one in the U.K., found that human adult bone marrow stem cells could form liver. In considering the promising potential of these stem cells, one researcher noted, “We could avoid problems with current liver transplants where the patient’s body rejects the foreign organ.” Another said “This would suggest that maybe you don’t need any type of fetal stem cell at all–that our adult bodies continue to have stem cells that can do this stuff.”

Others have found that human adult bone marrow stem cells can be reprogrammed to form bone, cartilage, muscle, and fat cells. You might ask, “Why would I want fat cells?” Such tissues have significant applications in reconstructive surgery. Numerous reports in the last year demonstrate the significant proliferative capacity of adult stem cells in culture when given the proper signals.

And one more note on the tremendous potential of adult stem cells in terms of tissue engineering and reconstructive repair. There are now numerous reports where adult stem cells have been seeded onto polymer matrices. Testing these constructs in a sheep model system, autologous adult heart cells have been used to form heart valves and aorta.

Some have urged that research on both adult and embryonic stem cells should go forth. However, the President’s own National Bioethics Advisory Commission has said that because human embryos deserve respect as a developing form of human life, destroying them “is justifiable only if no less morally problematic alternatives are available for advancing research.” Senators, the scientific literature overwhelmingly demonstrates that adult stem cells are already fulfilling the goals only hoped for with embryonic stem cells, making destruction of human embryos completely unjustifiable.

Mr. Chairman, respected Members of this Subcommittee, it has been said that these human embryos targeted for destruction to derive embryonic stem cells will die anyway, and so we should get some good out of them, possibly to benefit those with life-threatening diseases. If we follow this path, devaluing human life and sacrificing one set of lives for the potential benefit of others, how long might it be before those patients with life-threatening diseases will hear the same phrase–“they’re going to die anyway, let’s get some good out of them”? To whom will we choose to assign value, and who will dare to make those choices? I implore you not to follow this path.

Thank you once again for this opportunity to discuss this extraordinarily important topic with you, and I would be pleased to respond to any questions you might have.

{
Adult/73
|
Embryonic/0
}