Using an approach to isolate endosteal niche populations reported by Nakamura et al.15, we sorted osteoprogenitors (ALCAM+Sca1−), stromal progenitor cells (Sca1+ALCAM−15,16), and endothelial cells (CD31+) from the bone-lining, and GFP+ myeloma cells from the bone-lining and central bone marrow using multi-colour fluorescence-activated cell sorting (Fig. 1a and Supplementary Fig. 1). This evidence concerns the gene PECAM1 and plasma cell myeloma.