DEAR DOCTOR K: People have been talking about stem cells as a revolutionary technique for a long time. Has anything come of it? And why has it been so controversial?
DEAR READER: You're right; people have been excited about stem cells for nearly 25 years. Yet progress was quite slow, and some people had major ethical concerns. But in the past eight years, progress has accelerated and the ethical issues largely have been circumvented. Theoretically, stem cells could be used to replace cells that are killed by disease -- heart cells killed in a heart attack, or brain cells killed by Alzheimer's disease. But to explain the exciting potential of stem cells, I need first to define some terms and concepts.