The remarkable clinical responses of patients treated with CAR T cells targeting the antigen CD19 expressed on B cell acute lymphoblastic leukemia (B‐ALL) and B cell lymphoma led to FDA approval of two CD19‐targeting CAR T cell products in 2017: Kymriah (tisagenlecleucel) and Yescarta (axicabtagene ciloleucel) [3]. Here, CD19 is linked to acute lymphoblastic leukemia.