Immunization of mice with plasmids containing genes of Trypanosoma cruzi induces protective immunity in the murine model of Chagas disease. A cDNA clone that codes for an amastigote-specific surface protein (TcSSP4) was used as a candidate to develop a DNA vaccine. Mice were immunized with the recombinant protein rTcSSP4 and with cDNA for TcSSP4, and challenged with bloodstream trypomastigotes. Immunization with rTcSSP4 protein makes mice more susceptible to trypomastigote infection, with high mortality rates, whereas mice immunized with a eukaryotic expression plasmid containing the TcSSP4 cDNA were able to control the acute phase of infection. Heart tissue of gene-vaccinated animals did not show myocarditis and tissue damage at 365 days following infection, as compared with control animals. INF-γ was detected in sera of DNA vaccinated mice shortly after immunization, suggesting the development of a Th1 response. The TcSSP4 gene is a promising candidate for the development of an anti-T. cruzi DNA vaccine.

In a murine model of experimental Trypanosoma cruzi (H8 strain) infection, we investigated the induction of protective immunity against the domains [amino (A), repeats (R) and carboxyl (C)] of the surface protein (SP), a member of the trans-sialidase (TS) superfamily. Recombinant proteins and plasmid DNA coding for the respective proteins were used to immunize BALB/c mice, and the humoral response and cytokine levels were analysed. Immunization with the recombinant proteins induced higher levels of anti-TcSP antibodies than immunization with the corresponding DNAs, and analysis of serum cytokines showed that immunization with both recombinant proteins and naked DNA resulted in a Th1-Th2 mixed T-cell response. Mice immunized with either recombinant proteins or plasmid DNA were infected with blood trypomastigotes. The recombinant protein-immunized mice showed a variable reduction in peak parasitemia, and most died by day 60. Only the pBKTcSPR-immunized mice exhibited a significant reduction in peak parasitemia and survived the lethal challenge. DNA-based immunization with DNA coding for the repeats domain of TcSP is a good candidate for the development of a vaccine against experimental T. cruzi infection.

Background: Chagas cardiomyopathy is caused by Trypanosoma cruzi ( Tc ). Two antigenic candidates, TcG2 and TcG4, are recognized by antibodies in naturally infected dogs and humans; and these vaccine candidates provided protection from Tc infection in mice and dogs. Trypanosoma rangeli ( Tr ) is non-pathogenic to mammals and shown to elicit cross-reactive anti- Tc antibodies. In this study, we investigated if fixed Tr (fTr) can further enhance the efficacy of the TcG2/TcG4 DNA vaccine. Methods and Results: C57BL/6 mice were immunized with TcG2/TcG4 DNA vaccine and fTr (delivered as an adjuvant or in prime-boost approach), and challenged with Tc . Serology studies showed that fTr (±quil-A) elicited Tc - and Tr- reactive IgGs that otherwise were not stimulated by TcG2/TcG4 vaccine only, and quil-A had suppressive effects on fTr-induced IgGs. After challenge infection, TcG2/TcG4 -vaccinated mice exhibited potent expansion of antigen- and Tc -specific IgGs that were not boosted by fTr±quil-A. Flow cytometry analysis showed that TcG2/TcG4 -induced dendritic cells (DC) and macrophages (Mφ) responded to challenge infection by expression of markers of antigen uptake, processing, and presentation, and production of pro-inflammatory cytokines. TcG2/TcG4 -induced CD4 + T cells acquired Th1 phenotype and expressed markers that orchestrate adaptive immunity. A fraction of vaccine-induced CD4 + T cells exhibited iTreg phenotype responsible for aversion of self-injurious immune responses. Further, TcG2/TcG4 -vaccinated mice exhibited potent expansion of poly-functional CD8 + T cells with TNF-α/IFN-γ production and cytolytic phenotype post-infection. Subsequently, tissue parasites and pathology were hardly detectable in TcG2/TcG4 -vaccinated/infected mice. Inclusion of fTr±quil-A had no clear additive effects in improving the Tc -specific adaptive immunity and parasite control than was noted in mice vaccinated with TcG2/TcG4 alone. Non-vaccinated mice lacked sufficient activation of Th1 CD4 + /CD8 + T cells, and exhibited >10-fold higher levels of tissue parasite burden than was noted in vaccinated/infected mice. Conclusion: TcG2/TcG4 vaccine elicits highly effective immunity, and inclusion of fTr is not required to improve the efficacy of DNA vaccine against acute Tc infection in mice.

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