Chagas disease is a chronic and potentially lethal disorder caused by the parasite Trypanosoma cruzi, and an effective treatment has not been developed for chronic Chagas disease. The objective of this study was to determine the effectiveness of a therapeutic DNA vaccine containing T. cruzi genes in dogs with experimentally induced Chagas disease through clinical, pathological, and immunological analyses. Infection of Beagle dogs with the H8 T. cruzi strain was performed intraperitoneally with 3500 metacyclic trypomastigotes/kg body weight. Two weeks after infection, plasmid DNA immunotherapy was administered thrice at 15-day intervals. The clinical (physical and cabinet studies), immunological (antibody and cytokine profiles and lymphoproliferation), and macro- and microscopic pathological findings were described. A significant increase in IgG and cell proliferation was recorded after immunotherapy, and the highest stimulation index (3.02) was observed in dogs treated with the pBCSSP4 plasmid. The second treatment with both plasmids induced an increase in IL-1, and the third treatment with the pBCSSP4 plasmid induced an increase in IL-6. The pBCSP plasmid had a good Th1 response regulated by high levels of IFN-gamma and TNF-alpha, whereas the combination of the two plasmids did not have a synergistic effect. Electrocardiographic studies registered lower abnormalities and the lowest number of individuals with abnormalities in each group treated with the therapeutic vaccine. Echocardiograms showed that the pBCSSP4 plasmid immunotherapy preserved cardiac structure and function to a greater extent and prevented cardiomegaly. The two plasmids alone controlled the infection moderately by a reduction in the inflammatory infiltrates in heart tissue. The immunotherapy was able to reduce the magnitude of cardiac lesions and modulate the cellular immune response; the pBCSP treatment showed a clear Th1 response; and pBCSSP4 induced a balanced Th1/Th2 immune response that prevented severe cardiac involvement. The pBCSSP4 plasmid had a better effect on most of the parameters evaluated in this study; therefore, this plasmid can be considered an optional treatment against Chagas disease in naturally infected dogs.

Chagas Disease (CD) is caused by the protozoan Trypanosoma cruzi . Eight million people are infected in Latin America and 10,000 die annually; because CD has prolonged chronicity is considered the parasitic disease with greater economic burden in Latin America. The 30% to 40% of patients develop chronic chagasic cardiomyopathies and disorders of the gastrointestinal tract. It has not found an effective treatment to cure the chronic disease; nifurtimox and benznidazole in the acute stage offer controversial results. The objective of this study was to test a treatment with plasmid DNA containing T. cruzi genes in dogs with experimental CD and to determine the cellular immune response. Thirty Beagle dogs were divided into 6 groups with 5 dogs each. Dogs from five groups were intraperitoneally infected with 3500 metacyclic trypomastigotes / kg body weight. Two weeks after infection, intramuscular therapeutic vaccinations were administered thrice at 2-week intervals. The plasmids used were: pBCSSP4 (containing a gene encoding an amastigote-specific protein), pBCSP (containing a gene encoding a trans -sialidase protein), pBCSSP4 + pBCSP and pBK-CMV (empty vector); control groups were saline solution mock- treated and non-infected/non-treated dogs. IL-1, IL-6, IL-12, IFN-gamma and TNF-alpha levels were determined by ELISA in each of the serum samples at different times. The proliferative response of spleen cells in vitro at 15 and 30 days after last treatment was studied. IL-6 and IL-12 levels were slightly increased in pBCSSP4 plasmid-treated animals; TNF-alpha and IFN-gamma levels rose after pBCSP plasmid treatment. Treatment with either two recombinant plasmids produced no increase in IL-1 levels. The use of mixed plasmid did not have a synergistic effect. Cell proliferation was induced by DNA plasmid treatment. The highest stimulation index (2.5) was observed in pBCSSP4 plasmid-treated dogs. In conclusion, cellular immune responses are stimulated by therapeutic DNA vaccine; pBCSP plasmid treatment showed polarized type Th1 immune response, while there was a balance in Th1 / Th2 response when pBCSSP4 plasmid was used as treatment. These results support the promising novel therapeutic application with DNA using TcSSP4 and TcSP genes against CD.