We report the construction and characterization of several replication- competent simian immunodeficiency virus (SIV) vectors with a deletion in the viral nef gene (SIV(Δnef)) that express gamma interferon (IFN-γ). The expression of the cytokine gene was controlled either by the simian virus 40 early promoter or by the SIV 5' long terminal repeat regulatory sequences, utilizing the nef gene splice signals. To enhance the expression of IFN-γ, the two in-frame nef start codons were mutated without altering the Env amino acid sequence (SIV(Hy-IFN)). Plasmids containing full-length proviral genomes were used to obtain high-titer stocks of each recombinant virus in cell cultures. Expression of IFN-γ by SIV(HyIFN) reached levels as high as 106 U/ml after 11 days in culture. The IFN-γ gene was unstable and sustained deletions after serial passage of SIV(Δnef) vectors in CEM-X-174 cells. The degree of instability appears to depend on size and orientation of the insert and the expression of IFN-γ. Only one virus, SIV(HyIFN), expressed detectable levels of IFN-γ up to the sixth passage. Prospects for the use of IFN-γ and other lymphokines to enhance the safety and efficacy of live attenuated vaccines are discussed.
ASJC Scopus subject areas
- Insect Science