A self-initiating eukaryotic transient gene expression system based on contransfection of bacteriophage T7 RNA polymerase and DNA vectors containing a T7 autogene.

A novel cytoplasmic gene expression system has been developed. This system differs from other expression systems in that it relies on the co-delivery of plasmid DNA and T7 RNA polymerase (RNAP) during transfection. The plasmid contains a T7 RNAP gene driven by the T7 promoter (T7 autogene) and a functional/reporter gene driven by another T7 promoter (T7T7/T7-gene construct). Once this DNA-enzyme complex is introduced into eukaryotic cells, the transcription of the T7 RNAP and the functional/reporter genes is initiated by the co-delivered T7 RNAP. The T7 RNAP, which is responsible for the initiation and maintenance of expression of both T7 and functional/reporter genes, is replenished by translation of newly synthesized T7 mRNA. This T7 system was designed in such a manner that the expression of the functional/reporter genes can occur in the cytoplasm and does not require any nuclear involvement. When transfected by either a pT7T7/T7Luc or a pT7T7/T7hGH plasmids with the cointroduced T7 RNAP, mouse L cells were found to express high levels of luciferase immediately after transfection, apparently due to the cytoplasmic gene expression; the expression of human growth hormone (hGH) could be sustained for at least 6 days. Both T7 and hGH mRNA were expressed by the cells transfected with pT7T7/T7hGH. These results suggest that this cytoplasmic expression system may be used for certain targets of somatic gene therapy.