The potential for oncolytic viruses to induce a tumor-specific immune response has led to the engineering and clinical testing of oncolytic viruses designed to enhance this response, in particular through insertion of genes that encode cytokines [e.g., granulocyte-macrophage colony-stimulating factor (GM-CSF) [23–26], Flt3L [27, 28]] or chemokines (e.g., CCL3 [27], CCL5 [29, 30]). The gene discussed is CSF2; the disease is neoplasm.