ABSTRACT
Expression systems based on single-stranded RNA viruses offer exciting prospects for their application as vaccines. The relatively recent development of cDNA-based genetic systems for a substantial number of these viruses has made possible the directed manipulation of RNA virus genomes, the discovery of substantial genomic plasticity in these virus systems, and their reconfiguration as vaccine vectors. While not directly germane to a discussion of vaccines, pioneering work with infectious clones of poliovirus [1], positive-strand RNA plant viruses [2,3]), and rabies virus [4] was key in guiding the subsequent development of analogous reverse genetic systems for other RNA viruses and vaccine vectors derived from them.
