Protective immunity induced by a recombinant BCG vaccine encoding the cyclophilin gene of Toxoplasma gondii

The investigation of Toxoplasma gondii virulence factors can elucidate the immunopathology of T. gondii infection and identify potential candidates for effective human vaccines. The adjuvant is an important component of an effective vaccine. In this study, attenuated Mycobacterium bovis was used as a live vaccine vector with both antigen and adjuvant characteristics. Following amplification of the T. gondii cyclophilin gene, the shuttle expression plasmid pMV261-TgCyP and integrative expression plasmid pMV361-TgCyP were constructed, and their expression was stimulated after transfection into BCG. Both recombinant plasmids were highly immunogenic. Greater proliferation of CD4⁺ and CD8⁺ T cells was observed in the rBCG-vaccinated groups compared to the control groups. The levels of Th1-type IFN-γ, IL-2 and IL-12 were significantly increased following immunisation with the rBCG vaccines via the i.v. or oral route, which indicated that catalytic activity against T. gondii infection was generated in the mice. rBCGpMV361-TgCyP i.v. inoculation resulted in a higher protection efficiency, as demonstrated by the increased survival time and survival rate (17%) of BALB/c mice. The present study demonstrates that a BCG vector expressing a target antigen, TgCyP, represent an alternative system for the production of effective vaccines to prevent toxoplasmosis.