Genetics and Biology of Retroviral Vectors

Publisher Summary This chapter discusses retroviral vectors, based on the Moloney murine leukemia virus, as a method for delivering genes into target cells. This vector system offers the advantages of highly efficient gene transfer and stable gene expression in the target cell by virtue of the integration of the vector genome into the host chromosomal DNA. Retroviral vectors have a wide host range, both in terms of species and cell types, but can infect only dividing cells. The chapter details the genomic organization and life cycle of retroviruses. Retroviruses are single-stranded RNA viruses encoding a characteristic RNA-dependent DNA polymerase. These viruses transform cells by expression of viral oncogenic sequences originally transduced from host-cell genomes or by integration near a cellular oncogene and its subsequent activation. A large body of evidence indicates that viral replication, integration, and production of progeny virus depend on host cell progression through the cell cycle. Retroviruses that contain oncogenic sequences lead to a rapid induction of tumor formation and are termed “acutely transforming retroviruses”. Integration of a retrovirus near a cellular proto-oncogene may drive its transcription under the influence of viral promoter or enhancer elements. Retroviral vectors may be either replication-competent or replication- defective. RSV is an example of a replication-competent vector that carries the src oncogene in addition to viral genes. Virions containing replication-defective vectors are generated in packaging cell lines carrying helper provirus. Retroviral vectors provide a highly efficient method to transfer and stabily express genes in target cells. Their limitations include difficulties in obtaining high titer producer lines, the time involved in establishing a stable clonal producer cell line, and gene inactivation due to a high rate of mutation per replication cycle.