Development and Applications of Retroviral Vectors

Excerpt

The ability of retroviruses to integrate efficiently into the genomic DNA of animal cells and be stably replicated and transmitted to all of the progeny of these cells provided a strong incentive for the development of retroviral gene transfer vectors. The discovery that acutely oncogenic retroviruses often arise as the result of acquisition of sequences derived from cellular proto-oncogenes provided an additional stimulus. It was clear from many studies that retroviral genomes could accommodate extensive alterations, and even though these changes often resulted in defects in replication, the altered viruses could be propagated in the presence of replication-competent or “helper” virus. Indeed, early synthetic retroviral vectors were produced by using helper virus (Shimotohno and Temin 1981; Wei et al. 1981; Tabin et al. 1982). However, the presence of helper virus precluded many types of experiments where viral spread after infection was unacceptable, especially for many genetic studies or for human gene therapy.

A major advance in retroviral vector design came with the development of retroviral packaging cells that provide all of the retroviral proteins in trans but did not produce replication-competent virus (Mann et al. 1983; Watanabe and Temin 1983). Many of the first generation of packaging cell lines produced helper virus as a result of recombination events, especially after the introduction of retroviral vectors or after prolonged cultivation, but evolution in design has greatly reduced this frequency. The host range of vectors produced by packaging cell lines has also been extended by the development of packaging cell lines based on a variety of mammalian and avian retroviruses.