This is a two cohort, open-label, pilot study to describe the efficacy of administration
timing of tocilizumab on CART19 (CTL019) associated cytokine release syndrome safety events
in pediatric patients with CD19 expressing relapsed and refractory B-cell acute lymphoblastic
leukemia with high versus low pre-infusion tumor burden following redirected autologous T
cells transduced with the anti-CD19 lentiviral vector (CART19/CTL019).