By Anthony L. Komaroff, M.D.
Brigham and Women's Hospital

Most diseases are caused by the death of healthy cells in a particular organ. For example, Alzheimer's disease is caused by the death of brain cells (neurons) that are important in thinking and memory; diabetes is caused by the death of insulin-producing cells in the pancreas (an organ that lies beneath the stomach); Parkinson's disease is caused by the death of brain cells that produce a chemical called dopamine; and heart attacks cause the death of heart muscle cells. Almost all the organs in our bodies cannot, on their own, replace the cells that die (the liver is an exception). Nor have we discovered medicines that prompt our bodies to replace dead cells.

Stem cells have the capability to replace cells that have died, in different organs. In mice, stem cells have in fact replaced dead cells, and cured the mice of particular diseases (including heart muscle damage). That is why there is such excitement about using stem cells for what is called "cell therapy."

Anthony L. Komaroff, M.D., is professor of medicine and editor-in-chief of Harvard Health Publications at Harvard Medical School. Dr. Komaroff also is senior physician and was formerly director of the Division of General Medicine at Brigham and Women's Hospital. Dr. Komaroff has served on various advisory committees to the federal government, and is an elected Fellow of the American Association for the Advancement of Science.