TKT and neoplasm: Previously, we have shown that insertion of the foreign marker gene expression cassettes into the F14.5L, J2R (encoding thymidine kinase, TK), and A56R (encoding hemagglutinin, HA) loci of the VACV LIVP genome disrupted the open-reading frames (ORFs) F14.5L, J2R, and A56R, resulting in the recombinant VACV GLV-1h68 with enhanced tumor colonization specificity as well as reduced virulence in mice [10,11].