Vaccinia virus expression vector for selective replication in a tumor cell and introduction of exogenous nucleotide sequence into a tumor cell

A method of introducing an exogenous nucleotide sequence into a mammalian tumor cell, comprising:

• providing a composition comprising a vaccinia virus expression vector with a negative thymidine kinase phenotype and a negative vaccinia virus growth factor phenotype, wherein the vector selectively replicates in the tumor cells but is substantially incapable of replicating in non-dividing cells and wherein the vector has enhanced safety;
• contacting said mammalian tumor cell with said composition;
• and
• expressing said exogenous nucleotide sequence in the tumor cell, thereby producing an amount of an expression product.