Abstract 47: Treatment With a DNA Vaccine in Experimentally Trypanosoma cruzi -infected Dogs Modulates Cellular Immune Response

Abstract

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.