To test for potential cytotoxic effects of our mAb and/or mAb-sCT conjugate, we tested RAW 264.7 cell viability using the MTT assay. Anti-RANK monoclonal antibody, mAb-sCT conjugate and sCT showed no demonstrable cytotoxicity at the concentrations tested (up to 200 nM), as measured by the absorbance of formazan solution formed after 4 h incubation (Fig. 9) . Thus, the viability of these cells was not perturbed by our mAb and/or conjugate treatments.