T cells increase cell viability of the OCs from human MM PBMCs. Cell viability was measured by MTT assay. MM PBMCs from patients with osteolysis were cultured in the presence (OCs + T cells) or in the absence (OCs – T cells) of T cells for 25, 30, and 35 days. M-CSF and RANKL were added to the T-cell–depleted cultures to allow OC formation. The viability of the OCs generated in the presence of T cells without addition of exogenous cytokines was significantly higher than that of the OCs formed in the absence of T cells.