The presence of RPMI8226-CXCR4-GFP myeloma cells altered the BM milieu in favor of osteoclast genesis, inducing mRNA levels of murine osteoclast specific factors Rankl, Gpnmb, Oscar, Ctsk, Calcr, Rank and Nfatc1. In comparison, significantly reduced expression of osteoclast activation factors was observed in the BM of animals inoculated with CXCL13-silenced MM cells (Fig. 6G). The gene discussed is GPNMB; the disease is plasma cell myeloma.