Pediatric patients with relapsed leukemia can now be enrolled in the CCTL019B2202 study. This multicenter phase II study investigates the efficiency and saftety of CTL019 (CAR-T-Cells) in pediatric patients with refractory or relapsed acute lymphoblastic B-Cell-Leukemia. Children and adolescents at the age of 3-21 years with CD19-positive relapse after allogeneic stem cell transplantation can be enrolled. They should not have received Blinatumomab before.