The first human stem cell was isolated and cultured.  Stem cells are cells that can form more than one type of cell.  There are three types of stem cells, unipotent, pluripotent, and totipotent.  Unipotent stem cells can only form one type of cell, whereas pluripotent stem cells can differentiate to form different types of cells.  Totipotent cells, cells that can make any other cell in the body,  have never been isolated from a human being, and it is questionable if one even exists.
 Research into therapeutic cloning is one of the major uses for stem cells.  Also known as “regenerative medicine”, this field involves slowing the effects of age by repairing any damage to tissue or organs at the cellular level.  It works by essentially making an aging cell younger again, turning a cell back into its original state as an embryonic stem cell.  By repairing an ailing person’s own cells, there is no risk of the body rejecting the tissue, as it sometimes does in procedures such as transplants from another body.

*Pictures from Microsoft Electronic Encarta Encyclopedia Standard Edition 2002

Sources:
West, Michael D. The Immortal cell : one scientist's quest to solve the mystery of human aging. New York: Doubleday, 2003 (primary)

“Stem Cell”. Microsoft Electronic Encarta Encyclopedia Standard Edition 2002.

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