CONSTRUCTION AND CHARACTERIZATION OF REPLICATION-COMPETENT SIMIAN IMMUNODEFICIENCY VIRUS VECTORS THAT EXPRESS GAMMA-INTERFERON

We report the construction and characterization of several replication -competent simian immunodeficiency virus (SIV) vectors with a deletion in the viral nef gene (Sn-Delta nef that express gamma interferon (IF N-gamma). The expression of the cytokine gene was controlled either by the simian virus 40 early promoter or by the SIV 5' long terminal rep eat regulatory sequences, utilizing the nef gene splice signals. To en hance the expression of IFN-gamma, the two in-frame nef start codons w ere mutated without altering the Env amino acid sequence (SIVHyIFN). P lasmids containing full-length proviral genomes were used to obtain hi gh-titer stocks of each recombinant virus in cell cultures. Expression of IFN-gamma by STVHyIFN reached levels as high as 10(6) U/ml after 1 1 days in culture. The IFN-gamma gene was unstable and sustained delet ions after serial passage of SIVDelta nef 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-gamma. Only one virus, SIVHyIFN, expressed detectable levels of IFN-gamma up to the sixth passage. Pro spects for the use of IFN-gamma and other lymphokines to enhance the s afety and efficacy of live attenuated vaccines are discussed.