[Multiple Myeloma Stem Cell]

Multiple myeloma (MM) is characterized by the clonal expansion of malignant plasma cells. MM patients harbor phenotypic CD19+ B cells expressing the immunoglobulin gene sequence and the idiotype unique to the individual myeloma clone. However, in most MM patients CD19+ clonotypic B cells do not reconstitute MM disease upon transplantation into immune-deficient mice. In the SCID-rab and SCID-hu models, which enable engraftment of human MM in vivo, CD19-CD38++ plasma cells engrafted and rapidly propagated MM. These results indicate that MM-initiating cells are derived from plasma cells, which are terminally differentiated cells. It should be now clarified whether all MM plasma cells can exert as MM-initiating cells when located in the appropriate niche or only distinct myeloma stem cells can propagate MM.