Enhancement of Immune Responses to an HIV env DNA Vaccine by a C-Terminal Segment of Listeriolysin O

An effective vaccine against AIDS should induce both cellular and humoral immune responses. Here we report that immunization of mice with a DNA plasmid encoding a chimeric protein consisting of HIV89.6 Env gp140 and the listeriolysin O (LLO) C-terminal segment (59 amino acids) significantly enhanced both humoral and cellular immune responses against the HIV89.6 Env protein. Plasmid DNA expression vectors with genes codon-optimized for mammalian expression were synthesized for HIV89.6 gp140 as well as for chimeric protein gp140-LLO, in which the coding sequence for the C-terminal 59 amino acids of LLO were fused in frame to the 3′ end of the codon-optimized gene for gp140. All plasmid vectors produced high levels of protein expression, and the gp140-LLO chimeric protein was cleaved and secreted as efficiently as gp140. Analysis of humoral immune responses by ELISA showed that the chimeric gp140-LLO construct induced higher antibody responses than the gp140 construct in immunized mice, more notably in the I...