A Study of Fludarabine Dosing in Children and Young Adults With B-cell Acute Lymphoblastic Leukemia

The researchers are doing this study to find out whether PK-targeted fludarabine is an effective Lymphodepletion (LD) chemotherapy approach for people with relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL) who will receive tisagenlecleucel CAR T-cell therapy. The researchers will compare PK-targeted fludarabine dosing with standard fludarabine dosing to see which treatment approach is more effective. The researchers will also look at whether PK-targeted fludarabine dosing is feasible (practical), the side effects of the study treatment, and how the study treatment affects people's quality of life. The researchers will measure quality of life by having participants complete questionnaires.