Distant metastasis is the major cause for therapeutic failures in Clinical oncology. Active immunotherapy in the adjuvant setting of patients with low tumor volume would contribute to further reduction of the remaining tumor and establish long-lasting immunity that could protect the patient from recurrence of disease. Studies employing rodent tumor models with little or no intrinsic immunogenicity have shown that genetically modified tumor cell preparations consisting of irradiated tumor cells transduced with and expressing cytokines, such as interleukin-2 (IL-2), IL-6, interferon-gamma (IFNgamma), or granulocyte-macrophage colony stimulating factor (GM-CSF), or co-stimulatory molecules, such as B7-I, were capable of inducing the regression of preexisting tumors and cure animals from their disease. Moreover, in some instances, the cured animals have retained immunological memory, as indicated by the fact that animals have resisted a second challenge with the parental tumor cells. Induction of potent immune responses in tumor-bearing animals against nonimmunogenic or weakly immunogenic tumors supports the view that active immunization of cancer patients deserves consideration despite lack of demonstrable immunogenicity in many human tumors.