1. Leukapheresis: following registration, participants will undergo an unstimulated leukapheresis, which will be used for the manufacture of the IL-15/06B5 CAR T cells.
2. Ommaya reservoir (or similar catheter)insertion: Participants will have an intracerebroventricular catheter placed following enrolment and prior to IL-15/06B5 CAR T cell infusion to allow monitoring, and treatment, if necessary, of increased intracranial pressure(ICP) and, if eligible, for IL-15/06B5 CAR T cell administration (on Theme 2).
3. Lymphodepletion: Prior to the 1st IV CART cell infusion, participants will receive fludarabine 30mg/m2 (on days -6 to-3) and cyclophosphamide 500mg/m2 (on days -4 to -3).
4. IL-15/06B5 CAR T cell infusion: The IL-15/06B5CAR T cells will be given in two themes. All participants will receive treatment on Theme 1 (intravenous infusion) of CAR T cells at a dose assigned to the participant by TMG/CTC.
The following dose levels will be tested:
• Dose Level 1: 10 x10^6 CAR T cells/m2
• Dose Level 2: 30 x10^6 CAR T cells/m2
• Dose Level 3: 100 x10^6 CAR T cells/m2
Participants whose disease does not respond to this intravenous infusion (or comes back (relapses) later) and in the absence of significant and/or persistent toxicity, may receive a second flat dose of 10x10^6 CART cells infusion in theme 2 (intracerebroventricular infusion delivered into the brain using Ommaya reservoir or similar catheter).