When One Body Can Save Another

Now the long quest was ending. The surgeons bent over the grail: a 14-month- old girl named Marissa Ayala.

She lay anesthetized upon an operating table in the City of Hope National Medical Center in Duarte, Calif. A surgeon inserted a 1-in.-long needle into the baby's hip and slowly began to withdraw bone marrow. In 20 minutes they removed about a cup of the viscous red liquid -- the stuff of resurrection.

The medical team then rushed the marrow to a hospital room where Marissa's 19-year-old sister Anissa lay waiting. Through a Hickman catheter inserted in the chest, the doctor began...