We have focused our attention on B-cell maturation antigen (BCMA) as the primary specificity, because this molecule is expressed by mature normal and neoplastic B cells, including MM, plasma cell leukemia (PCL), as well as some differentiated diffuse large B-cell lymphomas (DLBCLs), but is mostly absent from other tissues [7,8]. Here, TNFRSF17 is linked to plasma cell leukemia.