Full length SIV nucleocapsid mutant DNA vaccine: immunization and challenge

To evaluate a novel vaccine strategy in the SIV system, we have constructed a mutant virus with alterations in nucleocapsid protein (NC) zinc finger (ZF) motifs essential for infectivity. Transfection of cells with the mutant provirus results in authentic expression of virion proteins and production of ultrastructurally intact progeny virions which can bind to target cells and initiate the viral life cycle. These particles are deficient in packaged viral genomic RNA and are not detectably infectious. Five macaques were inoculated intramuscularly with a NC protein mutant (D2ZF CWNC) SIV proviral DNA. Anti-SIV serum antibody was detected in two of these animals, consistent with in vivo expression of the inoculated DNA. Four control animals received vector plasmid DNA lacking the SIV proviral insert. All animals were challenged with infectious (wild type) SIVmne. All 4 control animals became persistently infected with high plasma virus loads (10(5)-10(6) RNA copy equivalents/mL); virus was readily isolated and 3 of 4 control animals show markedly declining levels of CD4+ cells. Following challenge, only 1 of the SIV DNA inoculated animals showed virus levels comparable to controls. In the other 4 SIV DNA inoculated animals, virus was either undetectable or was present at levels 2-3 logs lower than in controls and CD4+ cell counts are still in the normal range. Current status of the challenge study will be presented. Initial studies of strategies to increase expression from future constructs appear promising and should facilitate further evaluation of this novel vaccine approach.

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