TKT and neoplasm: In our previous work, we characterized several recombinant variants of the oncolytic VV, deficient in the viral thymidine kinase (TK) gene and encoding red fluorescent protein tagRFP and cytokines, as a potential anti-tumor OV in several syngeneic murine tumor models, such as melanoma (B16), colon cancer (MC38, CT26), and breast cancer (EO771) models [12].