Adult cells are behind much of
stem cell success so far
By Jean Peduzzi-Nelson
Posted: Sept. 2, 2006
The great potential moral controversies and political party alignments associated with stem cell issue makes the subject a hot topic.
Human stem cells can be obtained from human embryos, produced either by in vitro fertilization of human eggs or cloning via somatic cell nuclear transplant, or adults.
The often stated advantages of embryonic stem cells are 1) their great promise, 2) their potential to form every cell type, 3) their rapid proliferation, 4) their lack of rejection and finally, 5) their usefulness in drug testing and disease models.
However, from a scientific and medical point of view these advantages are less clear.
The "great promise" of embryonic cells is often stated by scientists that either hold key patents or are strongly supported by biotech companies pursuing embryonic cells commercially.
Every type of stem cell may be useful for injuries but are unlikely to cure most diseases, as underlying causes of uncured diseases are often not known. Stem cells may alleviate the symptoms for several years but not affect the disease process. Other areas of research are actively being studied on disease processes so stem cells are not the magic silver bullet in diseases.
The "potential of embryonic stem cells to possibly form every cell type" in the body is amazing but is of little clinical relevance. As long as a stem/progenitor cell is capable of forming the cell types needed for a particular injury or disease, the capability to form every cell type is a moot point.
Furthermore, there are numerous supporting studies that stem cells derived from adults have the same potential. Sources of adult stem cells include the skin, fat, bone marrow stromal cells, umbilical cord and many other sites in the body.
The "rapid proliferation of embryonic stem cells" is rather ironic claim in that the quality cited for the superiority of embryonic stem cells is actually responsible for causing serious problems. Rapid growth is not always a desirable quality, as clearly seen with weeds in a garden or cancer in the body.
In an animal model of Parkinson's disease, rats injected with embryonic stem cells showed a slight benefit in about 50% of the rats, but one-fifth of the rats died of brain tumors caused by the embryonic stem cells.
The "lack of rejection of embryonic stem cells" is a clever twist of words. It is true that embryonic cells are not rejected. However, to be useful as a therapy, the cell must mature into a particular cell type. When the cell matures, it is recognized by the immune system as foreign and is rejected. However, it has also been argued that this is the reason for the great need for human cloning (somatic cell nuclear transplant) so the problem of rejection of embryonic stem cell can be avoided.
This field is in its infancy, and only a very few studies have been done to even demonstrate the feasibility of this in experimental animals. Pursuing this extreme measure when the human body is full of stem/progenitor cells that would not be rejected is one of the most absurd directions ever observed in the history of science that is supposedly being promoted to help people.
"Usefulness in drug testing and disease models" is not a reasonable claim because tissue models and drugs need to be tested on mature tissue, not embryonic cells. There are numerous tissue cultures model systems of muscle, skin, etc., that are routinely used in drug and disease models. The advantages of stem cells derived from adult stem cells are virtually unknown to the American public. The most profitable, not the best, treatment for people is not surprisingly getting the most publicity.
The greatest advantage of adult stem cells is that it's usually possible to use a person's own stem cells, which is the safest stem cell option for people. This avoids the problems of rejection, disease transmission, chromosomal abnormalities and uncontrolled growth.
One problem with embryonic stem cells that is rarely mentioned is that methods have yet to be developed to grow these cells in a manner that does not induce significant chromosomal abnormalities. If one looks at the human clinical trials or research using experimental animals, the record for adult stem cells compared to embryonic stem cells is extremely impressive. In examining only the scientific evidence, one wonders why the controversy even exists.
Parkinson's disease: When a transplant consists of embryonic/fetal tissue, the stem/progenitor cells are the only cells that survive. In two clinical trials using embryonic/fetal tissue, devastating deterioration at one year after treatment occurred in about 15% of these patients that was believed to result from cellular overgrowth or from rejection of the foreign cells/tissue derived from embryo or fetus.
These results are in striking contrast to the report on a patient who received his own adult stem cells, who had almost full recovery for several years after the transplant.
In a recent animal study, human embryonic stem cells not only did not cause improvement in an animal model of Parkinson's disease but also caused tumor formation. Another direction of hope for Parkinson's disease is the use of growth factors.
Diabetes: Diabetes, like Parkinson's disease, is a disease, so it may not be possible to cure diabetes with any type of stem cells but only dissipate the symptoms for several years. Recently, insulin independence was reported in a person after receiving cells from her mother.
Also encouraging were results found in animal studies that blocking the autoimmune reaction can reverse diabetes in mice. There are also several reports that adult stem cells can develop into insulinsecreting cells.
Spinal cord injury: The comparison of results with adult and embryonic stem cells is even more dramatic. Although mice receiving embryonic stem cells made the front page of many newspapers and extensive web coverage, a paper published by Zurita and Vaquero found almost total recovery from complete paralysis in rats using adult stem cells from bone marrow. Transplants of tissue containing one's own stem cells is safe and causes some improvement in people with severe, chronic spinal cord injury.
Heart disease: Several recent studies patients with heart attacks report benefit from adult stem cells derived from bone marrow. Clinical trials have also shown improvements in some patients with heart failure after using one's own adult stem cells in treatment.
Similar comparisons can be made for a variety of diseases and injuries. But the successes with adult stem cells will never make headlines or be heard by the majority of the American public.
Although it may take years for these adult stem cell treatments to be commonly available, the results with adult stem cells will eventually end a controversy that should never have existed in the first place. The controversy may end even sooner than that with last month's report of embryonic stem cells can be derived from sperm, as reported in the most recent edition of "Nature."
Jean Peduzzi-Nelson is an associate professor in the department of anatomy and cell biology Wayne State University School of Medicine in Detroit.
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