There remains an ‘off-tumor and on-target’ limitation of targeting CS1 on hematopoietic cells: the potential for inducing a state of prolonged immunodeficiency due to high CS1 expression on CD8 T, NK, and probably also invariant NKT cells (iNKT) that may be clinically consequential. The gene discussed is SLAMF7; the disease is Immunodeficiency.