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Vaccinia viruses may serve a useful viral vector since large genes can be incorporated stably into the genome, resulting in efficient replication and gene expression. Vaccinia recombination plasmids are used for placing a foreign gene into a nonessential region of the parental wild-type vaccinia virus. The plasmids contain a cloning site for insertion of the gene of interest, a selectable marker gene (eg, LacZ) or antibiotic resistance gene, and flanking portions of a nonessential vaccinia virus DNA. Co-transfection of the recombinant plasmid and a wild-type vaccinia virus into susceptible cells in culture leads to homologous recombination between the plasmid and the vaccinia genome. Selection of recombinant viruses is possible using the selectable markers found only on the recombinant plasmid. The recombinant viruses can then be purified and characterized for gene expression. Attenuated vaccinia virus (i.e. MVA, Wyeth) have also been developed for use as vaccines, are less pathogenic than wild-type virus, and are useful for human vaccination.
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