In order to verify the efficacy of mAb-sCT conjugates, we employed in vitro osteoclast-like cell cultures. It is well established that osteoclasts are derived from cells of the monocyte/macrophage lineage and are formed after the cellular fusion of their mononuclear precursors (33) . Hence, we utilized the RAW 264.7 cell line that can be differentiated in vitro into osteoclast-like cells after exposure to M-CSF and RANKL cytokines. RANKL is the essential factor necessary for osteoclast differentiation, whilst M-CSF (also known as CSF-1) has also been identified as an essential factor necessary to initiate osteoclastogenesis (34) . The main role of M-CSF is to act as a survival factor for osteoclast precursor cells and to induce the expression of the RANK receptor for stimulation by the RANKL.