Immunogenicity of Nef Protein of SIV SMM-PBj14 Expressed in a Live Vaccine Strain of Salmonella Species

The nef gene of an infectious molecular clone of SIV_SMM isolate PBj14 was fused to the glutathione S-transferase gene of Schistosoma japonicum to generate plasmid pEMCl00. The recombinant plasmid was placed in an aroA live vaccine Salmonella dublin strain, and the production of GST-Nef protein was induced by exposure to IPTG. The fusion protein was purified and administered as vaccine to BALB/c mice by i.p. injection. Several doses of the purified fusion protein produced an earlier anti-GST-Nef response, without an anti-GST response, than did IPTG-induced Salmonella live vaccine containing an equal amount (0.1 μg) of fusion protein, apparently because of the transient immunosuppressive effect of live vaccine given by injection. The highest antiGST-Nef titers were obtained by a third immunization schedule in which mice were treated with a priming inoculum of induced live vaccine followed, after the predicted immunosuppressed interval, by two i.p. doses of 1 μg of purified GST-Nef protein with Ribi adjuvant. The data presented here demonstrate that SL5928 aroA, an attenuated S. dublin strain, can be used as a live vaccine carrier to express Nef protein of SIV_SMM.PBj14, one of the most acutely pathogenic primate lentiviruses so far described.