Prospective Evaluation Of Delayed Effects Of Pediatric Car T Cell Therapy

Inclusion Criteria: * Participants must have received an initial systemically-administered CAR T cell infusion within the last 1-3 months (+/- 14 days). * Initial infusion is defined as the first administration of a CAR T cell product the participant has not previously received OR receipt of a CAR T cell product previously received after an interval allogeneic HSCT. * Age ≤ 30 years at CAR T cell infusion. Exclusion Criteria: * Active malignancy other than the disease under study. * Planned consolidative HSCT within 3 months post CAR T cell infusion. * Received or planned additional disease directed therapy post CAR T cell infusion. * Inability or unwillingness of research participant or legal guardian/representative to give written informed consent.