Structural Biochemistry/Adult Stem Cells
Long after our embryonic stem cells have differentiated, we all still harbor other types of multitalented cells, called adult stem cells. These cells are found throughout the body, including in bone marrow, brain, muscle, skin, and liver. They are a source of new cells that replace tissue damaged by disease, injury, or age.
Researchers believe that adult stem cells lie dormant and largely undifferentiated until the body sends signals that they are needed. Then selected cells morph into just the type of cells required. Like embryonic stem cells, adult stem cells have the capacity to make identical copies of themselves, a property known as self-renewal. But they differ from embryonic stem cells in a few important ways. For one, adult stem cells are quite rare. In addition, adult stem cells appear to be slightly more “educated” than their embryonic predecessors, and as such, they do not appear to be quite as flexible in their fate.
However, adult stem cells already play a key role in therapies for certain cancers of the blood, such as lymphoma and leukemia. Doctors can isolate from a patient’s blood the stem cells that will mature into immune cells and can grow these to maturity in a laboratory. After the patient undergoes high-dose chemotherapy, doctors can transplant the new infection-fighting white blood cells back into the patient, helping to replace those wiped out by the treatment. Although researchers have been studying stem cells from mouse embryos for more than 20 years, only recently have they been able to isolate stem cells from human embryos and grow them in a laboratory. In 1998, James A. Thomson of the University of Wisconsin, Madison, became the first scientist to do this. He is now at the forefront of stem cell research, searching for answers to the most basic questions about what makes these remarkable cells so versatile. Although scientists envision many possible future uses of stem cells for treating Parkinson’s disease, heart disease, and many other disorders affected by damaged or dying cells, Thomson predicts that the earliest fruits of stem cell research will be the development of powerful model systems for finding and testing new medicines, as well as for unlocking the deepest secrets of what keeps us healthy and makes us sick.