A novel dual promoter DNA vaccine induces CD8+ response against Toxoplasma gondii sporozoite specific surface protein “SporoSAG” through non-apoptotic cells

Toxoplasma gondii is a protozoan parasite that can infect all warm blooded animals including humans. During natural course of T. gondii infection, bradyzoites or sporozoites invade the intestinal cells and turn into tachyzoite form in 12–18 h. Therefore, a vaccine against toxoplasmosis is required to induce protective immune response initially in intestines against bradyzoites or sporozoites. The present study aimed to generate a DNA vaccine containing a sporozoite specific surface antigen “SporoSAG”. To increase antigen specific-CD8+ T lymphocyte response, anti-apoptotic Bcl-xL gene was inserted to vaccine as a molecular adjuvant.For the construction of DNA vaccine, SporoSAG gene was inserted after CMV promoter and Bcl-xL gene was inserted in frame with EGFP after IRES promoter (pSporoSAG/Bcl-xL). Bcl-xL expression and functionality as well as humoral and cellular immune responses were demonstrated by Western blotting and flow cytometer.Western blotting and flow cytometer analyses rationalized Bcl-xL expression that impedes apoptotic cell death. The ratio of pSporoSAG/Bcl-xL transfected cells were significantly higher than empty pEGFP control plasmid (P < 0.05). Analysis of sera obtained from vaccinated mice showed strong anti-SporoSAG specific IgG response. The ratio of CD8+ T lymphocytes secreting IFN-γ significantly increased compared to controls (P < 0.0001), indicative of protection against toxoplasmosis.The results of this study reveal the ability of SporoSAG protein to induce CD8+ T lymphocyte response for the first time. Overall, SporoSAG protein can be included to multivalant vaccine formulations in future studies to increase the protection in infections acquired through T. gondii oocysts.