IMMUNOGENICITY OF NEF PROTEIN OF SIVSMM(PBJ14) EXPRESSED IN A LIVE VACCINE STRAIN OF SALMONELLA SPECIES

The nef gene of an infectious molecular clone of SIVSMM isolate PBjl4 was fused to the glutathione S-transferase gene of Schistosoma japonicum to generate plasmid pEMC100. 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 mu g) of fusion protein, apparently because of the transient immunosuppressive effect of live vaccine given by injection. The highest anti-GST-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 mu g 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 SIVSMM-PBj14, one of the most acutely pathogenic primate lentiviruses so far described.