With the breakthrough of cellular immune therapies, such as CAR+ T, flow cytometry became a critical platform, not only for the clinical laboratories, but also for drug developers and manufacturers. Indeed, flow cytometry plays a crucial role in the production process of CAR+ T cells where it is used for assessing transduction efficiency, purity and characterization of the CAR+ T product before infusion. But also after manufacturing, when CAR+ T cells are infused into the patients, flow is used in clinical laboratories to assess CAR+ T expansion, efficiency and persistency and to monitor minimal residual disease (MRD).