Current Human Clinical Applications Using Adult Stem Cells

David T. Scadden, MD

Stem cell therapies are a reality in the clinic today, however, the diseases they are used to treat are limited to very specific types of disorders. Some who oppose embryonic stem cell research have provided a list of 69 conditions putatively treated by adult stem cells. The implicit message is that adult stem cell therapies are sufficient and that scientists underemphasize the power of adult stem cells in order to justify embryonic stem cell research. This proposition is profoundly cynical about the motivation of scientists and because of its use to inform the public, is a claim that deserves careful scrutiny.

What are the diseases where adult stem cell therapies have been shown to be beneficial in responsibly conducted clinical trials? The range of diseases is still extremely restricted, largely limited to blood disorders and specific cancers. Inherited disorders of the blood and immune system and acquired loss of bone marrow function can be cured with stem cell transplantation.

In cancer, intensive use of chemotherapy or radiation destroys normal bone marrow along with tumor cells and replacement of blood forming stem cells can be lifesaving. Most of the cancers for which this approach is successful are childhood tumors or blood cell-derived cancers in adults (leukemia, lymphoma, multiple myeloma). Despite breast cancer being among the list of conditions currently treated by adult stem cells, it is not a disease where stem cell transplantation has conclusively been shown to be of use.

Another type of adult stem cell, the mesenchymal stem cell, has entered the scene as a developing therapy. This cell type can become muscle, bone, cartilage or fat and has some ability to modify immune function in certain experimental models. It has therefore become a cell of intense interest for treating musculoskeletal abnormalities, cardiac disease and some abnormalities of immunity (such as graft-versus-host disease after bone marrow transplant). There are ongoing studies to test the role of this cell type, some of which have been quite encouraging. However, mesenchymal stem cell therapy has not yet been shown to have a clear- cut advantage over existing therapies, is not considered a standard of care for any condition and does not have regulatory approval for the routine treatment of any disease. Some specific uses of these cells may eventually emerge, however it is incorrect to state that it is a current clinical therapy in any context other than a clinical research study.

Beyond those stated above, diseases that are listed as “current clinical applications” of adult stem cells include a broad range of problems from spinal cord injury to Parkinson’s disease to coronary artery disease. While it is true that adult stem cells have been tested in these and other desperate situations, it is not true that the results have been compelling enough to consider stem cells a current therapy. Reports of success are generally anecdotal and often without appropriate control groups. These reports may be helpful for encouraging further, more in-depth research, but they should not be regarded as definitive evidence of current therapy. To imply such is misleading and may be hurtful to patients and ultimately to the goal shared by those on both sides of this debate: to define the most effective ways to reverse debilitating disease.

Adult stem cell therapies are powerful, but they are not as wide-ranging as claimed. They have a narrow record of disease types for which the therapy is extremely valuable, a success story that is enormously encouraging evidence for stem cell research leading to methods of positively affecting people’s lives. It took approximately 25 years between discovery and routine clinical application of adult stem cell therapy. It is not known how long it will take for embryonic stem cells to become a useful therapy or whether they will ever directly do so. However, it would be unwise to ignore the potential for either adult or embryonic stem cells to result in a meaningful new approach. Adult and embryonic stem cells are complementary subjects of research and studying them side by side offers the greatest potential to rapidly generate new therapies.

Posted August 14, 2006

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