For decades, stem cells have attracted the attention of medical researchers and others because they have the capacity to develop into specialized cells that make up a variety of organ and other tissues. These so-called "building blocks of nature" can literally transform into any other type of cell in the body, making them potentially invaluable in treating many diseases and injuries.
There are two basic kinds of stem cells: those found in certain adult tissues and those found in the cells of three-to five-day-old embryos. Adult stem cells, found in brain, bone marrow, muscle, skin, blood and liver tissue, can change into a limited number of cell types. The stem cells found in embryos, on the other hand, are pluripotent, that is, they have the unique ability to develop into any of the 220 cell types in the human body.
In addition to their versatility, embryonic stem cells are easier to grow in the laboratory than adult stem cells. Adult stem cell lines proliferate only for a limited time, while embryonic stem cells potentially can continue dividing forever.
The first and best-known success in adult stem cell research is the bone marrow transplant, in which stem cells from a donor's bone marrow are used to regenerate healthy bone marrow in patients with leukemia and other blood diseases. This therapy is still used today.
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