Six commercial CAR T-cell therapies have been approved by the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) since 2017; four of them are designed to bind the B-lymphocyte antigen CD19 (Cluster of Differentiation 19) expressed on the cell surface of different types of lymphoma and leukemia, whereas the other two approved CAR T-cell therapies target the multiple myeloma-expressed B-cell maturation antigen BCMA (Supplementary Table 1). The gene discussed is TNFRSF17; the disease is leukemia.