These viruses are engineered to express therapeutic transgenes (e.g. granulocyte macrophage colony stimulating growth factor GM-CSF) to enhance host immune response against the cancer, to synergize with drug or radiation therapy (e.g. cytosine deaminase, herpes simplex virus thymidine kinase (HSV-TK), sodium iodide symporter (NIS) or reporter genes to permit noninvasive nuclear imaging of sites of viral gene expression (HSV-TK, NIS) [12-15]. Here, TKT is linked to cancer.