Poxvirus Vectors: Mammalian Cytoplasmic-Based Expression Systems
The unique biological characteristics of poxviruses have been exploited for the development of vaccinia virus into a powerful and versatile expression vector with applicability to many areas of research and biotechnology (Moss, 1991). The poxviruses comprise a group of genetically related DNA viruses that are unusual in their ability to propagate in the cytoplasm, rather than in the nucleus, of infected cells. Electron microscopic and autoradiographic examinations have revealed cytoplasmic factories of viral DNA replication and particle assembly. The enzymes and factors required for transcription and replication are encoded within the poxvirus genome, which may contain 200 or more genes. The previous use of vaccinia virus as a live vaccine for the eradication of smallpox, and the potential for recombinant vaccinia viruses containing genes from other microorganisms to serve as live vaccines against current diseases, contributed to the interest in this vector. For these reasons, recombinant vaccinia viruses have been extensively used by immunologists and virologists to determine the targets of humoral and cell mediated immune responses to microbial infections and candidate human and veterinary live recombinant vaccines are currently being tested. Poxviruses encode their own DNA-dependent RNA polymerase and high levels of expression of foreign genes have been obtained by optimizing poxvirus promoter function. Thus, recombinant vaccinia viruses are particularly useful for protein production in cultured mammalian cells. A modified system has been made by importing the bacteriophage T7 RNA polymerase gene into vaccinia virus and using bacteriophage promoters for high level expression. With both systems, the recombinant proteins appear to be properly processed and transported within the mammalian cell.
KeywordsCystic Fibrosis Transmembrane Conductance Regulator Vaccinia Virus Foreign Gene Recombinant Vaccinia Virus Vesicular Stomatitis Virus Glycoprotein
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