This was based on the detection of clonotypic somatic mutations in the CDRs (complementarity determining region) of immunoglobulin heavy- and light-chain genes in myeloma cells and peripheral-blood B-cells and is compatible with evidence that MMSCs do not express the classic myeloma marker, CD138, on the cell surface, express less CD38 than conventional or “bulk” myeloma cells [22, 23], exhibit a CD19+CD24+CD27+ memory B-cell phenotype [24, 25], and are enriched in the B-cell fraction of the myeloma SP [26, 27]. Here, CD27 is linked to plasma cell myeloma.