Research on adult stem cells has generated a great deal of excitement. Scientists have found these groundbreaking cells in many more tissues than they once thought possible. Because of this, clinicians and researchers alike have begun to ask if these cells can be used for transplants. Adult hematopoietic, or blood-forming, stem cells from bone marrow have been used in transplants for more than 40 years. If the differentiation of adult stem cells can be controlled or manipulated, then these cells could possibly become the basis of transplantation-based therapies.
Research on adult stem cells dates back to the 1950’s, when researchers discovered that there were at least two kinds of stem cells present in bone marrow. One population, called hematopoietic stem cells, is responsible for forming 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. This second population of stem cells makes 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.
In the 1960s, scientists studying rats discovered regions of the brain containing dividing cells that ultimately became nerve cells. This finding came contrary to popular belief that the adult brain was incapable of generating new nerve cells. It was not until the 1990s that scientists agreed that the adult brain does contain stem cells able to generate the brain’s major cell types.