Protective immune response against Toxoplasma gondii elicited by a recombinant DNA vaccine with a novel genetic adjuvant

Previous immunological studies from our laboratory have demonstrated the potential role of Toxoplasma gondii antigens SAG1 and GRA2 as vaccine candidates. To further evaluate the vaccine's effects, a series of recombinant DNA vaccines pVAX1–SAG1, pVAX1–GRA2 and pVAX1–SAG1–GRA2, termed pSAG1, pGRA2 and pSAG1–GRA2, respectively, were constructed. A plasmid pVAX1–S/PreS2, termed pSPreS2 encoding hepatitis B virus (HBV) surface antigen (HBsAg) S and PreS2 as a novel genetic adjuvant, was also constructed. The expression abilities of those DNA plasmids were examined in HFF cells by Western blotting. Then BALB/c mice were intramuscularly immunized with DNA plasmids and followed by challenging with the highly virulent T. gondii RH strain. The results demonstrated that the recombinant DNA vaccine pSAG1–GRA2 was capable of eliciting high levels of antibodies, a Th1 type of immune response with significant production of IFN-γ and low levels of IL-4 or IL-10 in BALB/c mice, and partial protection against the acute phase of toxoplasmosis as compared to pSAG1, pGRA2 and controls. In addition, the adjuvant pSPreS2 formulated with DNA vaccine induced a Th1 type of immune response and therefore might be a novel genetic adjuvant to DNA vaccine for further investigation.

► DNA vaccine encoding T. gondii SAG1 and GRA2 increased distinct antibodies in mice.
► DNA vaccine pSAG1–GRA2 elicited Th1 type of immune response.
► The Th1 response was enhanced by a novel genetic adjuvant from HBsAg.
► DNA vaccine pSAG1–GRA2 improved the survival time against acute toxoplasmosis.
► These findings may shed light on the production of new vaccine against T. gondii.