 |
 |
CULTURING NEW LIFE Stem cells lead the way to a new medical paradigm in tissue regeneration. Many killer diseases involve irreversible degeneration of some crucial cell type or tissue: islet cells of the pancreas in diabetes, neurons of the brain in Parkinson's disease, Huntington's disease and other neurological conditions. Researchers have long dreamed of culturing in the laboratory human cells that could colonize and regenerate failing tissue. But biology has been uncooperative. Cancer cells readily grow in a bottle, but healthy, normal ones soon stop propagating outside the body. Recent discoveries point to a solution. Investigators have been able to identify and culture for many months rare "stem cells" from various crucial tissues. These cells, when implanted in the appropriate type of tissue, can regenerate the range of cells normally found there. Stem cells have been discovered in the nervous system, muscle, cartilage and hone and probably exist in pancreatic islet cells and the liver. More remarkable still, unpublished work has convinced moneyed entrepreneurs that special cells derived originally from a fetus could produce a wide variety of tissue-specific cells. A type of human stem cell found in hone marrow, which gives rise to the full range of cells in blood, has been known since Irving L. Weissman of Stanford University discovered it in 1991. A cancer patient whose marrow has been destroyed by high doses of radiation or chemotherapy can be saved by a transplant of bone marrow-derived cells. Stem cells in the transplant establish lineages of all the cells in blood. Researchers have, however, been surprised to learn that stem cells exist in tissues such as the brain, where they can give rise to all three of the common cell types found there: astrocytes, oligodendrocytes and neurons. The discovery "contradicts what is in the textbooks," says Ronald D. G. McKay of the National Institute of Neurological Disorders and Stroke. McKay reports that he has dcmonstrated that central nervous system stem cells grown in his laboratory can engraft in mouse brains and alleviate behavioral abnormalities in animals genetically engineereed to mimic features of Parkinson's disease. Scientific American June 1998 Ken Rowland [log in to unmask]