TO: THOMAS. YOU ARE THE BEST LITTLE BROTHER! I -- On a sign posted in Thomas Tatem's hospital room. DURHAM, N.C. When a nurse finally delivered the bag of deep-red liquid to Lisa Tatem, she cradled it like the most fragile piece of glass. She stood motionless in the hospital hallway and stared. "My God," Tatem whispered. "That's really it." Inside the pouch decorated with a "Finding Nemo" sticker were cells from her daughter's bone marrow, the soft tissue that makes blood cells needed to fight disease. Those cells, invisible to the eye, could heal her two other children -...
