The risk of reactivity against healthy tissues: Novel CARs demand testing for overlooked binding properties.

A rapidly growing number of chimeric antigen receptors (CARs) is being translated into cell therapy for malignant and autoimmune diseases. While cancer cell-selective CAR targeting is undergoing continuous refinement, specific testing for overlooked recognition of healthy tissues is commonly not performed, which potentially results in underestimating of the risk of severe tissue damage upon CAR T cell application. Using the FcμR/IgM receptor/FAIM3/TOSO-specific CAR, designed to target chronic lymphocytic leukemia cells, we exemplarily outline a screen to uncover reactivities to healthy tissues and discuss the value of such pre-clinical testing to improve safety in CAR T cell application.