Replication-deficient vaccinia virus encoding bacteriophage T7 RNA polymerase for transient gene expression in mammalian cells

The vaccinia virus/bacteriophage T7 hybrid transient expression system employs a recombinant vaccinia virus that encodes the T7 RNA polymerase gene, a plasmid vector with a gene of interest regulated by a T7 promoter, and any cell line suitable for infection and transfection. Although high expression in a majority of cells is achieved, the severe cytopathic effects of vaccinia virus and the safety precautions required for use of infectious agents are undesirable features of the system. Here, we report the construction of a highly attenuated and avian host-restricted vaccinia virus recombinant that encodes the T7 RNA polymerase gene (MVA/T7 pol) and demonstrate the use of the virus for transient expression in mammalian cells. MVA/T7 pol has reduced cytopathic effects compared to the previously used replication-competent vaccinia virus, while providing a high level of gene expression in multiple mammalian cell lines.