RNA virus vectors: Where are we and where do we need to go?
- Department of Microbiology, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029
The ability to genetically engineer animal viruses has dramatically changed our understanding of how these organisms replicate and has allowed the construction of vectors to direct the expression of heterologous proteins in different systems. The small DNA-containing viruses were in the forefront of the recombinant DNA revolution, which started in the 1970s. In fact, transfected DNA molecules of SV40 (approximately 5,000 bp in length) allowed the first rescue of defined viral mutants (1). Subsequently, the molecular engineering of herpes simplex viruses (genome of approximately 150 kbp) and of vaccinia viruses (genome of approximately 190 kbp) represented major breakthroughs for modern virology (2–4). After this seminal work in the early 1980s, techniques were developed to specifically alter the genomes of adenoviruses, adeno-associated viruses (5), and many other DNA-containing viruses. Most recently, it has become feasible to rescue human cytomegalovirus (6) and Epstein–Barr virus (7) by cotransfecting into cells cosmids containing overlapping fragments of the respective viral genomes. Thus, extraordinary progress has been made in harnessing the genomes of DNA viruses to (i) help us understand the structure function relationships of the viral components and to (ii) generate mutants and recombinant viruses expressing foreign proteins. Similar success was brought to the retrovirus field by the study of myriads of novel constructs of RNA tumor viruses. In addition, retrovirus-based vectors have been shown to express foreign genes in animals over periods of weeks and months (5).
Equally exciting has been the progress in the development of genetic engineering methods for nonretroviral RNA viruses. The paper by Rice and coworkers in this issue of the Proceedings (8) is the most recent example of a highly imaginative approach to using RNA viruses (or components of RNA viruses) to express foreign genes. The foundation of the system described here goes back to 1987 …
