Chimeric antigen receptor (CAR) T cells are an effective therapy for relapsed or refractory pediatric B cell leukemia. Analysis of the starting material, the T cells collected from the patient prior to CAR manufacture, reveals possible biomarkers of cells destined to perform poorly in patients. Long-term follow-up shows that long periods of B cell aplasia, a marker of in vivo CAR activity, are associated with longer remission but also a higher chance of antigen-negative relapse. The role of transplantation as consolidative therapy is unclear in this nonrandomized data, but clearly warrants further study.
