Immunization with irradiated tumor cells engineered to secrete granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulates potent, specific and long lasting anti-tumor immunity in clinical and preclinical settings. Efforts to further increase immunotherapy efficacy with immune-modulatory agents are under evaluation. Based on the immune-modulatory properties of 4-1BB (CD137), it has been postulated that agonistic 4-1BB antibodies may add additional anti-tumor efficacy to GM-CSF-secreting tumor cell immunotherapy. The combination of GM-CSF-secreting tumor cell immunotherapy and anti-4-1BB monoclonal antibody (mAb) treatment resulted in rejection of established tumors in the B16 melanoma model. These anti-tumor effects correlated with persistent tumor-specific CD8(+) T cell responses. In addition, early tumor infiltration of functional CD8(+) T cells and a greater expansion of antigen-specific memory T cells were found in mice treated with the combination therapy. In summary, an agonistic anti-4-1BB mAb combined with GM-CSF-secreting tumor cell immunotherapy may provide a novel and potent treatment strategy for patients with cancer.