On July 14, the Senate Commerce, Science, and Transportation Subcommittee on Science, Technology, and Space held a hearing on the scientific potential of adult stem cell research.
In his opening statement, Chair Sam Brownback (R-KS) stated, “Today’s hearing is about miracles and prayers answered.” Explaining that there is no controversy concerning adult stem cell research, he expressed his hope that Congress would “aggressively” fund this type of research in the future.
Sen. Ron Wyden (D-OR) agreed that studies have shown that adult stem cell research can help “some” individuals, but argued, “People deserve more.” He pointed out the National Institutes of Health website states that there are a number of limitations to adult stem cells, including their presence in minute quantities, which makes them difficult to isolate and purify; their structure, which often consists of DNA abnormalities; and their limited capacity to multiply in the same manner as embryonic stem cells.
Dr. Michael Levesque, a physician, neuroscientist, and neurosurgeon at Cedars-Sinai Medical Center in Los Angeles, California, detailed the differences between adult stem cells and embryonic stem cells in medical research. He explained that neural stem cells “are formed after a cascade of sequential events activates genes within embryonic cells during development. They are derived from a specific layer of the embryo and can only become, under normal conditions, precursors of cells found only in the central nervous system…In the adult brain, these cells cannot on their own trigger repair responses. However, if placed in experimental laboratory conditions stimulating certain genes, these neural stem cells can be ‘awakened’ and begin to divide and replicate events of normal development.” In examining the potential for adult stem cell therapy to treat Parkinson’s disease, Dr. Levesque stated, “Our animal studies showed that human adult neural stem cells do not divide once differentiated, do not form aberrant tissue or tumors after chronic transplantation, and have normal karyotypes (number of chromosomes),” adding, “Autologous adult neural stem cells represent a new source of cell replacement with identical genetic material to the patient, and mitigate the risks of immune rejections and transmittable diseases generally associated with tissue transplants from a source external to the patient such as HIV, Encephalitis, Hepatitis, and Creutzfeld-Jacobs Disease.”
Dr. Levesque said that embryonic stem cells “have the potential to generate any type of cells and presumably can be guided in their differentiation to generate an unlimited number of dopamine neurons. One of the problems is to understand the proper steps to guide the gene expression along the formation of neural stem cells and then to achieve proper differentiation. In addition, there remain risks of unstable phenotypic expression, possible transdifferentiation into other types of tissues causing tumors, immune reactions in the host brain and questionable functional benefits.” He also noted that embryonic stem cell therapy “has yet to be scientifically proven as safe, if even effective, in human patients.”
Stating that his field of research is in adult tissue stem cell biology, Dr. Irving Weissman, director of the Institute for Cancer/Stem Cell Biology and Medicine at the Stanford University School of Medicine, explained that there are limitations to his research because “adult tissue stem cells…can lead to robust regeneration, but only of the tissue from which they came.” He referred to President Bush’s decision in August 2001 to allow the use of federal funds for only 78 existing embryonic stem cell lines and legislative proposals to ban embryonic stem cell research, warning, “Before one enacts the first (that I know) ban on biomedical research in US history based on ideology, not safety, we should realize what will be lost, and think deeply about the political, medical, societal, commercial, and moral consequences of such a ban. To do so we need to know what experiments and therapies today cannot be accomplished with adult tissue stem cells or the allowed human embryonic stem cell lines.”
Dr. Weissman demonstrated the limitations of the existing embryonic stem cells: “The genetic diversity of the usable 9-64 lines currently available is that of the population that in the US undergoes in vitro fertilization; they are largely white, well to do, and always infertile. There is no doubt that the wide variety of racial and ethnic populations that characterize America are not represented in these cell lines, and of course, it would be extremely unlikely if any had the genetically determined diseases such as sickle cell anemia, thalassemia, and adult onset diabetes, to name a few, prevalent in black, Mediterranean, and native American populations resident in the US.” He noted that nuclear transfer (NT) research, which also would be banned in legislative proposals, could be used in cancer research, explaining, “All cancers differ that play a role in their progress from a normal cell to a cancer cell that can spread and kill a person. There are, to date, no exceptions. It is therefore likely that NT research could make available pluripotent cell lines made from real patients’ cancers capable of evolving the particular cancer, and these lines should be susceptible to the same kinds of research to define the dangerous genes, and how to attack them.” Dr. Weissman concluded, “Adult tissue stem cells, embryonic stem cells, and NT stem cells each have important and unique properties to allow the biomedical and clinical community the opportunity to pursue the understanding of human development, the regeneration of damaged tissues, the development of human genetic diseases, and the broadest possible approaches of translating those discoveries to the treatment of patients. In my view it is irresponsible to fail to pursue all such avenues in parallel to stop or ameliorate the tragedies our families endure because of these diseases.”
Dr. Jean Peduzzi-Nelson, a professor in the Department of Physiological Optics at the University of Alabama, argued that the research community supports embryonic stem cell research because it is more profitable than adult stem cell research, explaining, “Cloned stem cells derived from embryos with genetic defects represent the possibility of millions in patentable stem cell lines. Adult stem cell therapies are much better for people with diseases or injuries but generate an inferior business plan. In the case of adult stem cells where, in most cases, a person’s own cells can be used, one can only develop a procedure that is generally not patentable according to new patent laws. However, the embryo/fetal/cloned stem cells can lead to tremendous profits in the short run.” Dr. Peduzzi-Nelson also contended that there are not an unlimited number of frozen embryos in fertility clinics, as supporters of embryonic stem cell research have indicated. “To use even one of these embryos would require legal release from the parents that in most states is not easily accomplished,” she stated, adding, “Many of the frozen embryos are also not viable. Despite the impressive results with in vitro fertilization, recent studies suggest that these children have a higher rate of congenital anomalies and human overgrowth syndrome.” Dr. Peduzzi-Nelson concluded by summarizing the “tremendous progress” in adult stem cell research: “Adult stem cells transplanted into mice with liver injuries helped restore liver function within two to seven days. Transplantation of stem cells from [an] adult human brain causes myelination to occur in a focally demyelinated spinal cord of the rat. Demyelination is common in spinal cord injury and disease states such as Multiple Sclerosis, and interferes with signal conduction between the neurons. Human cells from adults have been used to treat animal models of disease states. For example, human cells led to function improvement in animal models of Parkinson’s disease using human bone cells or neural stem cells.”
Testifying on behalf of the Juvenile Diabetes Research Foundation International, Chief Scientific Officer Dr. Robert Goldstein explained that the foundation provides funding for both embryonic and adult stem cell research “because no one can predict what area of research will produce new therapies or a cure for juvenile diabetes.” Explaining that the research community “believes that embryonic stem cells offer more promise in the area of diabetes,” he stated, “Recent studies have demonstrated the ability to coax embryonic stem cells into insulin-producing cells in the lab. We have good reason to believe that embryonic stem cells will one day be able to grow large amounts of insulin-producing beta cells for transplant, but more work needs to be done. Unfortunately, adult stem cells have not shown the same promise when it comes to diabetes. Last month, Harvard University researcher Douglas Melton published a paper in Nature pointing out that in mice, new beta cells in the pancreas are formed through the replication of existing beta cells rather through the differentiation of adult stem cells. This finding indicates that adult stem cells in the pancreas do not contribute to beta cell formation, and that embryonic stem cells may prove to be the only stem cells that will be useful to generate beta cells for the treatment of Type 1 diabetes.”
