Ten years ago, Tom and Kari Whitehead came to Children’s Hospital of Philadelphia (CHOP) looking for a miracle. Their 6-year-old daughter, Emily, had relapsed in her battle with acute lymphoblastic leukemia (ALL), after many months of unsuccessful chemotherapy and a disease that had progressed so rapidly that she was ineligible for a bone marrow transplant to treat it. Her family came to CHOP in the hopes that Dr. Stephan Grupp, a pioneer in the field of cellular immunotherapy, could provide the miracle they were looking for.