Activation and expansion of T cells are important in disease resolution, but tumors do not usually satisfy these immune requirements. Therefore, we employed a novel strategy whereby dual-specific T cells were generated that could respond to both tumor and influenza virus, reasoning that immunization with influenza virus would activate and expand tumor-specific cells, and inhibit tumor growth. Dual-specific T cells were generated by gene modification of influenza virus-specific mouse T cells with a chimeric gene-encoding reactivity against the erbB2 tumor-associated antigen. Dual-specific T cells were demonstrated to respond against both tumor and influenza in vitro, and expanded in vitro in response to influenza to a much greater degree than in response to tumor cells. Following adoptive transfer and immunization of tumor-bearing mice with influenza virus, dual-specific T cells expanded greatly in numbers in the peritoneal cavity and spleen. This resulted in a significant increase in time of survival of mice. However, tumors were not eradicated, which may have been due to the observed poor penetration of tumor by T cells. This is the first demonstration that the potent immunogenic nature of an infectious agent can be utilized to directly impact on T-cell expansion and activity against tumor in vivo.