Cyclophosphamide potentiates the antitumor activity of v-p97NY

Previous work has demonstrated that a recombinant live vaccinia virus-based tumor vaccine, v-p97NY, induces an immune response in mice which can lead to the rejection of transfected lines of mouse melanoma cells expressing the human melanoma antigen p97 (S.-L. Hu et al., J. Virol. 62, 176, 1988; C. D. Estin et al., Proc. Natl. Acad. Sci. USA 85, 1052, 1988). We now show that the ability of v-p97NY to induce delayed-type hypersensitivity to p97 improved if the vaccinated mice were given cyclophosphamide (Cy) on the day of vaccination. Likewise, treatment of vaccinated mice with Cy increased the antitumor activity of vaccination so that tumor colony formation in the lungs was inhibited even when v-p9NY plus Cy was not given until 7 days after intravenous injection of tumor cells.