Vaccinia virus can accommodate more than 30 kb of foreign DNA. Foreign genes can be stably integrated into the viral genome, resulting in efficient and long-term gene expression. The deletion of the viral genes of thymidine kinase (TK) and vaccinia growth factors (VGF) results in enhanced tumor-selectively and antitumor activity, and reduced virus virulence. https://www.creative-biolabs.com/oncolytic-virus/category-pre-made-oncolytic-vaccinia-virus-291.htm