Led by George Daley of Children's Hospital in Boston, the researchers began their process by culturing mouse embryonic stem cells to form globular clusters called embryoid bodies.

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While cloning stem cells is a technical breakthrough, there's already a method of deriving embryonic-like stem cells that doesn't require the use of embryos at all: induced pluripotent stem (IPS) cells, said Dr. George Daley, who is director of the Stem Cell Transplantation Program at Children's Hospital Boston and an international expert in stem cells.

CNN: Cloning stem cells: What does it mean?

Former President George Bush joined Chicago Mayor Richard Daley and other dignitaries at a news conference announcing the reopening of the tallest skyscraper in the United States.

CNN: Sears Tower observatory reopening