CAR T cells were longitudinally monitored in peripheral blood (PB) through multiparameter flow cytometry (MFC) using CD19 CAR detection reagent, as previously described,11 (link) or CD19 CAR FMC63 Idiotype (REA1297) (both from Miltenyi Biotec). CAR T-cell differentiation in infusion product leftovers was assessed by MFC as previously described.11 (link) Antibodies and gating strategies are detailed in supplemental Material. Data were acquired on BD FACSCanto II (BD Biosciences), MACSQuant Analyzer MQ10 or MQ16 (Miltenyi Biotec) and analyzed using FlowJo-v10 and MACSQuantify softwares.