Determination of immune response and protection elicited by adjuvanted multivalent recombinant protein vaccine using toxoplasma gondii specific vaccine candidate antigens

Toxoplasma gondii is an obligate intracellular parasite that can infect almost all warm-blooded animals, avian species and humans. Toxoplasmosis is asymptomatic in healthy individuals, whereas may lead to death in immune suppressed or deficient patients. For these reasons, a vaccine against T. gondii is important to prevent consequences of the infection. The aim of this thesis is to generate a multivalent recombinant protein vaccine against T. gondii. For this purpose, 49 antigenic proteins of T gondii which were determined by protein microarray screening are analyzed by the bioinformatics approaches as well as expressed and purified in small scale. Among them, six vaccine candidate proteins were selected to generate a six-valent adjuvanted recombinant protein vaccine formulation for the first time [6-Valant (+) Montanide]. Mice were vaccinated two times at three week intervals and then humoral immune response was analyzed by Western blot and Rec-ELISA, cellular immune response was detected by flow cytometry and cytokine ELISA. Mice were infected intra-peritoneally with a lethal dose of the T. gondii Ankara strain tachyzoites to determine protection conferred by vaccination. Results show that 6-Valant (+) Montanide vaccine induced strong total IgG response compared to controls (P<0,0001). Analysis of IgG1 and IgG2a responses displayed that polarization was significantly towards TH1 direction (P<0,001). IFN-γ secreting CD4 T-Helper and CD8 T-Cytotoxic lymphocyte ratios increased 1,45 to 2 and 1,6 to 2 times compared to the controls. In addition, 6-Valant (+) Montanide induced significantly higher extracellular IFN-γ level secretion from lymphocytes compared to the controls (P<0,001). These results show that 6-Valant (+) Montanide vaccine induced strong protective TH1 immune response. The survival time of the vaccinated mice was increased to 8,38 ± 2,13 days which was significantly higher than controls (P<0,01). Overall, this study showed that vaccine candidate antigens selected from a protein microarray screening data induced strong humoral and cellular immune response as well as conferred some protection against lethal toxoplasmosis. In addition, multivalent recombinant protein vaccines containing six or more antigenic proteins can be generated and used against toxoplasmosis. Thus, future studies can develop multivalent recombinant protein vaccines and use more antigenic proteins in their formulations to confer full protection against toxoplasmosis.