Adoptive cellular immunotherapy utilizing tumor-reactive T cells has proven to be a promising strategy for cancer treatment. However, we hypothesize that successful treatment strategies will have to appropriately stimulate not only cellular immunity, but also humoral immunity. We previously reported that B cells in tumor-draining lymph nodes (TDLNs) may function as APCs. In this study, we identified TDLN B cells as effector cells in an adoptive immunotherapy model. In vivo primed and in vitro activated TDLN B cells alone mediated effective (p < 0.05) tumor regression after adoptive transfer into two histologically distinct murine pulmonary metastatic tumor models. Prior lymphodepletion of the host with either chemotherapy or whole-body irradiation augmented the therapeutic efficacy of the adoptively transferred TDLN B cells in the treatment of s.c. tumors as well as metastatic pulmonary tumors. Furthermore, B cell plus T cell transfers resulted in substantially more efficient antitumor responses than B cells or T cells alone (p < 0.05). Activated TDLN B cells conferred strong humoral responses to tumor. This was evident by the production of IgM, IgG, and IgG2b, which bound specifically to tumor cells and led to specific tumor cell lysis in the presence of complement. Collectively, these data indicate that in vivo primed and in vitro activated B cells can be employed as effector cells for cancer therapy. The synergistic antitumor efficacy of cotransferred activated B effector cells and T effector cells represents a novel approach for cancer adoptive immunotherapy.