Years later, then, it was nothing less than thrilling—mesmerizing—to watch the cellular revolution unfold in humans. When I first met Emily Whitehead, in a fluorescent-lit corridor outside the auditorium at the University of Pennsylvania, it was as if she had allowed me to enter a portal that linked the future and the past. I trained as an immunologist at first, then a stem cell scientist, and, finally, a cancer biologist before I became a medical oncologist.
