IL-17–producing MILs increase osteoclastogenesis. (A) BM from normal donors and myeloma patients was incubated for 21 days in medium alone, macrophage colony-stimulating factor and RANKL (MR), MR plus IFN-γ, or MR plus IL-17. Myeloma BM was also incubated with MR plus autologous aMILs (Th1 skewed cells), or MR plus autologous Th17 skewed MILs. OC colonies were scored on day 21 by staining with 23-C6. Data are representative of 10 patients. (B) OC formation is T cell dependent. Ficolled BM from myeloma patients were either CD3 depleted or left unmanipulated and incubated for 21 days in medium alone or with the addition of MR, IL-17, MR/IL-17, MR plus anti–IL-17, or anti–IL-17. Cells were stained with 23-C6 and OCs were scored.