ORLANDO, Fla. - Chimeric antigen receptor T (CAR T) cells have proved to be a major advance in treating patients with refractory B-cell malignancies so far. But, often, in approaching those issues "we solve one and we create another," Stephen Schuster, a doctor at the Abramson Cancer Center at the University of Pennsylvania in Philadelphia, told reporters at the 61st American Society of Hematology (ASH) annual meeting Saturday.