There are many examples including CD19 for B cell malignancies (5, 6), CD123 in AML (36), CD7 (24) and carcinoembryonic antigen (CEA) in a range of solid tumors (37).However, in the case where the target antigen may be permanently or transiently expressed on a T cell, this leads to T cell fratricide, which practically translates into a reduced cell yield. The gene discussed is CEACAM5; the disease is acute myeloid leukemia.