Osteoblastic niche supports the growth of quiescent multiple myeloma cells

The heterogeneity of multiple myeloma (MM) contributes to variable responses to therapy. In this study, we aim to correlate the heterogeneity of MM to the presence of quiescent cells using the PKH26 dye. We tracked the rare quiescent cells in different niches of the bone marrow by allowing the cells to cycle in vivo. Surprisingly, quiescent PKH⁺ MM cells prefer to reside within the osteoblastic niches of the bone marrow (PKH⁺/OS) rather than the vascular (VS) niches or the spleen. These cells (PKH⁺/OS) displayed enhanced stemlike properties by forming colonies in semisolid medium. PKH⁺ cells were highly tumorigenic compared with PKH^- cells and were resistant to a variety of drugs. However, the levels of drug resistance were somewhat similar regardless of where the PKH⁺ cells were isolated. Our data indicate that osteoblastic niches support the growth of quiescent PKH⁺ cells and allow them to have stemlike functions.