WHAT ARE ADULT STEM CELLS?*
An adult stem cell is an undifferentiated cell, found among differentiated cells in a tissue or organ that can renew itself and can differentiate to yield some or all of the major specialized cell types of the tissue or organ. The primary roles of adult stem cells in a living organism are to maintain and repair the tissue in which they are found. Unlike embryonic stem cells, which are defined by their origin (cells from the preimplantation-stage embryo) the origin of adult stem cells in some mature tissues is still under investigation.
Research on adult stem cells has generated a great deal of excitement. Scientists have found adult stem cells in many more tissues than they once thought possible. This finding has led researchers and clinicians to ask whether adult stem cells could be used for transplants. In fact, adult hematopoietic, or blood-forming, stem cells from bone marrow have been used in transplants for 40 years. Scientists now have evidence that stem cells exist in the brain and the heart. If the differentiation of adult stem cells can be controlled in the laboratory, these cells may become the basis of transplantation-based therapies.
The history of research on adult stem cells began about 50 years ago. In the 1950s, researchers discovered that the bone marrow contains at least two kinds of stem cells. One population, called hematopoietic stem cells, forms all the types of blood cells in the body. A second population, called bone marrow stromal stem cells (also called mesenchymal stem cells, or skeletal stem cells by some), were discovered a few years later. These non-hematopoietic stem cells make up a small proportion of the stromal cell population in the bone marrow, and can generate bone, cartilage, fat, cells that support the formation of blood, and fibrous connective tissue.
WHERE ARE ADULT STEM CELLS FOUND, AND WHAT DO THEY NORMALLY DO?*
Adult stem cells have been identified in many organs and tissues, including brain, bone marrow, peripheral blood, blood vessels, skeletal muscle, skin, teeth, heart, gut, liver, ovarian epithelium, and testis. They are thought to reside in a specific area of each tissue (called a “stem cell niche”).
Typically, there is a very small number of stem cells in each tissue, and once removed from the body, their capacity to divide is limited, making generation of large quantities of stem cells difficult. Scientists in many laboratories are trying to find better ways to grow large quantities of adult stem cells in cell culture and to manipulate them to generate specific cell types so they can be used to treat injury or disease. Some examples of potential treatments include regenerating bone using cells derived from bone marrow stroma, developing insulin-producing cells for type 1 diabetes, and repairing damaged heart muscle following a heart attack with cardiac muscle cells.
*Source: National Institutes of Health
WHY ARE ADULT STEM CELLS IMPORTANT?
Adult stem cells offer the possibility of a renewable source of replacement cells and tissues to treat a myriad of diseases, conditions and disabilities. Adult stem cells are relatively quiescent (inactive) cells, particularly in organisms where cell turnover is low, yet they can mount a rapid and strong response to tissue stress and injury.
Adult stem cell transplants (bone marrow transplants) have been used for over 40 years in successfully treating cancers such as leukemia, multiple myeloma and lymphomas, and research has now opened the doors to regenerative and reparative therapeutics. There has been an increase in adult stem cell therapy clinical trials which are showing great promise in the areas of skin and wound healing, orthopedics, and in treating diseases including peripheral vascular disease, scleroderma, diabetes, congestive heart failure, myocardial infarction, and much more.