When I read news stories about stem cells I wonder if the general populace realizes that our bodies are full of stem cells, known as adult stem cells? That adult stem cells are an established and vital part of our treatment of cancer? And that adult stem cells are being tested in a large number of clinical trials to test their use against diseases as varied as epidermolysis bullosa, heart disease, and diabetes? I doubt it. The ignorance surrounding stem cells is astounding, especially considering the important role they play in treating cancer victims and more.
Some definitions first: Stem cells are progenitor cells that give rise to differentiated cells. Most references to stem cells are for those cells that specifically give rise to a lineage of cells found in a specific tissue to replace cells lost to aging (wear and tear), disease or injury. They are known as adult stem cells and they are multipotent, able to only become a limited number of tissues. Pluripotent cells are stem cells that can become any tissue type. Pluripotent stem cells are also distinguished by their ability to replicate indefinitely. Multipotent adult stem cells divide for a very long (though still finite) time, and differentiated cells only divide for a limited number of divisions. I think of this as nature’s “planned obsolescence” program.
The stem cells that most people are familiar are blood (haematopoietic) precursor stem cells from bone marrow, which divide to become red and white (immune) blood cells. However they are not the only adult stem cells: dermal stem cells are the source of the different cell types present in skin, and hepatic stem cells divide to become the different cells in a liver, and so on throughout the body. Another source of haematopoietic stem cells is umbilical cord blood. Although it is taken from the umbilical cord of a baby, the baby is a fully differentiated human, and therefore the stem cells are adult stem cells, committed to making blood and immune cells like the adult stem cells from bone marrow.
The use of adult stem cells in medicine is wide spread, with bone marrow stem cells the most frequently used clinically. The high levels of chemotherapy or radiation therapy used to eradicate cancer can additionally kill the stem cells present in a person’s bone marrow, depriving them of their immune system and the ability to make red blood cells. In these cases the use of their own stem cells (an autologous transplant of cells taken prior to the radiation or chemotherapy) or stem cells from another person (an allogeneic transplant) are used to restore the patient’s immune system and red blood cells. In allogeneic transplants the donor must have similar immune system markers, known as the histocompatibility complex.
How common is the use of adult stem cells in medicine? ClinicalTrials.gov is a registry of federally and privately supported clinical trials conducted in the United States and around the world. Using “stem cell” in the search field yields 3275 clinical trials. My interest is in the number and kind of clinical trials being conducted consequently these numbers are all inclusive: clinical trials enrolling patients, active trials (not recruiting), terminated and suspended trials.
Narrowing down the search by using “autologous stem cells” yields 976 clinical trials. Of the first 100 trials listed, 85 trials were of cancer patients receiving their own bone marrow stem cells following chemotherapy or radiation therapy. Of the other 15 clinical trials, 14 investigate the use of blood marrow stem cells in the treatment of non-haemotopoietic diseases: seven trials were investigating the use of blood marrow stem cells to treat heart disease, two trials of blood marrow stem cells for the treatment of brain injury, two trials of blood marrow stem cells for the treatment of amyloidosis, one trial of blood marrow stem cells for the treatment of Crohn’s disease (inflammatory bowel disease), and one trial of blood marrow stem cells for the treatment of diabetes. There was one clinical trial using stem cells derived from the patient’s own fat cells (lipoasperates) for the treatment of anal fistula. Recent research has indicated that adult stem cells are more pluripotent than originally thought and these 15 clinical trials are examining this hypothesis. I would like to emphasize that these are not the only clinical trials investigating the use of adult blood marrow stem cells for treatment of non-cancerous diseases, they are 15 out of the first 100 of 976 clinical trials in my search of the ClinicalTrials.gov website.
Another search of the ClinicalTrials.gov website using “umbilical stem cells” in the search field results in 150 clinical trials. What is surprising about the clinical trials listed is the amazing diversity of diseases for which the umbilical cells are being tested as a treatment. This is not a complete list but it gives an idea of the surprising variety of diseases in which the pluripotent potential of multipotent cells is being investigated: liver cirrhosis, ulcerative colitis, diabetes, critical limb ischemia, idiopathic dilated cardiomyopathy, bronchopulmonary displasia, epidermolysis bullosa, osteopetrosis, cartilage injury, cerebral palsy, inherited metabolic diseases, sickle cell anemia, and cytomegalovirus and adenovirus infection.
The dogma of adult stem cells being committed to certain cell lineages is being challenged with surprising results. I look forward to reading about the outcomes of these trials, and benefiting from the positive effect they will have on the treatment of disease in the future.
For more information about stem cells follow this link: http://www.isscr.org/public/adultstemcells.htm