In order to establish the method of generating powerful γδ T cells for anti-tumor immunotherapy, we investigated the effects of monocyte-derived dendritic cells (mo-DCs) on anti-tumor cytotoxicity of expanded γδ T cells. Activation of γδ T cells co-cultured for 2-3 days with immature or mature mo-DCs was evaluated by CD69 expression and anti-tumor cytotoxicity using two assays : the 5- (and 6-) carboxyfluorescein diacetate, succinimidyl ester-based cytotoxicity assay and the calcein-AM-based Terascan assay. γδ T cells were used as effector cells and myeloma cell line (RPMI8226) or chronic myelogenous leukemia blastic crisis cell line (C2F8) were used as target cells. CD69 expression on γδ T cells was enhanced by co-culture with both immature and mature mo-DCs in a cell-number-dependent fashion. CD69 expression was enhanced after addition of mo-DCs of either autologous or allogeneic origin. Activation of γδ T cells with mo-DCs enhanced anti-tumor cytotoxicity of γδ T cells against RPMI8226 and C2F8 in an effector-to-target ratio-dependent manner. Activation of γδ T cells by mo-DCs was associated with the enhancement of anti-tumor cytotoxicity of γδ T cells. Potent γδ T cells activated by mo-DCs were considered to be applicable to an efficient γδ T cell-mediated immunotherapy for tumors. [J Clin Exp Hematopathol 47(2) : 61-72, 2007]