CD27 and plasma cell myeloma: To evaluate myeloma memory B cells, we identified clusters of memory B cells that were either unswitched (UM1–4 clusters; CD19+, IgM+, IgDhet, CD20+, CD22+, and CD27+) or switched (SM1–3 clusters; IgM+, IgD–, CD27het, IgG+, and IgA+).