A Plasmid-Based Self-Amplifying Sindbis Virus Vector

Sindbis virus was used as a self-amplifying eukaryotic expression vector. A recombinant cDNA genome of this (+)-strand RNA virus was placed under the transcriptional control of a Rous sarcoma virus LTR (RSV) promoter. Transfection of this plasmid construct into mammalian cell lines (3T3, HepG2, and 293 cells) resulted in expression of the luciferase reporter gene. High-expression levels were also measured after transfection into primary rat myoblasts. In differentiated myotubes, expression levels generated by the Sindbis virus vector were up to 200 times higher than those obtained with a conventional RSV expression vector. In vivo expression was detected after injection of plasmid DNA into mouse quadriceps. In vivo expression was transient and undetectable by day 16. This self-amplifying expression vector can be used for generating high-level expression of transgenes in vitro and in vivo. Its transient nature in vivo could allow for safe, short-term delivery of gene products in gene therapy protocols. It should facilitate the study of Sindbis and other RNA viruses.

In transfection experiments, expression levels are related to promoter strength and the number of transfected plasmid molecules. To improve expression levels, a self-amplifying vector was developed. This plasmid-based vector consists of a cDNA copy of the Sindbis virus under transcriptional control of the RSV promoter. Transfection of this vector into mammalian cells resulted in much higher levels of cytoplasmic mRNA as compared to a conventional expression vector.