T cells that carry tumor-specific chimeric antigen receptors (CAR) have been successfully used to combat B-cell tumors.33 Much effort has been made to optimize CARs to function more efficiently, and cytoplasmic signaling motifs from various immune molecules are important building blocks in the CAR-engineering toolbox.34 Given the Lck-associating nature of the ICOS TMD, we replaced the CD8 transmembrane domain in the standard CD19-reactive FMC63-BBz CAR (BBz CAR) with the ICOS TMD (ICOSTM-BBz CAR) and tested the two types of receptors in Jurkat cells. Here, CD19 is linked to neoplasm.