Flow cytometry is used for the accurate quantification of CAR expression, T-cell subsets (such as CD4+ and CD8+) and activation or exhaustion markers, which is crucial for product validation – safety and efficacy for CBTs. Multiparametric analysis allows the purity, viability and functional status of the CAR-T cells to be assessed simultaneously. This ensures that the final product meets strict quality and safety requirements before it is clinically administered, and it is therefore important that analysts are trained in this technology and its validation.