NUCLEAR TRANSFER, the first step in creating a clone, involves inserting the nucleus from an adult somatic, or differentiated, cell into the emptied cytoplasm of an egg cell. The egg cell then reprograms the adult cell's genes so that it behaves like an all-purpose stem cell.

PLURIPOTENT STEM CELLS, first isolated in humans last November, can be transformed into any other type of cell, making them the ideal raw material for fashioning replacement parts. By reactivating telomerase, an enzyme that reknits the frayed ends of genes in older cells that have undergone many divisions, scientists can extend the life span of the new parts.

STEM CELL-DERIVED TRANSPLANTS can be made in a variety of tissue types. Moreover, when they are created using the genes from a patient's adult cells, they make a perfect tissue match, described by scientists as histocompatible.