It has previously been shown that the SLAM receptor CD229/LY9 is a potential target for CAR T cell therapy in MM due to its strong and homogenous expression on the bulk of tumor cells, as well as chemotherapy-resistant myeloma progenitors, its absence from most normal cells, and dependence of MM cells on CD229 for their survival5–8. This evidence concerns the gene LY9 and plasma cell myeloma.