In the summer of 2010, Bill Ludwig and Doug Olson were battling an insidious blood cancer called chronic lymphocytic leukemia (CLL). They’d both received numerous treatments, and as remaining options became scarce, they volunteered to become the first participants in a clinical trial of an experimental therapy underway at the Abramson Cancer Center and the Perelman School of Medicine at the University of Pennsylvania. The treatment would eradicate their end-stage leukemia, generate headlines across the globe, and usher in a new era of highly personalized medicine.