Predominance of CD4 Th1 and CD8 Tc1 cells revealed by characterization of the cellular immune response generated by immunization with a DNA vaccine containing a Trypanosoma cruzi gene

Immunization with a plasmid DNA containing the gene encoding the catalytic domain of trans-sialidase (TS) elicits protective immune responses against experimental Trypanosoma cruzi infection. As several studies provided stron g evidence that during infection CD4 Th1 and CD8 T cytotoxic type 1 (Tc1) c ells are important factors in host resistance, the present study was design ed to evaluate which T-cell types were activated in DNA-vaccinated BALB/c m ice. We found that bulk cells from DNA-immunized mice had CD4 and CD8 T cel ls that produced gamma interferon (IFN-gamma) but not interleukin-4 (IL-4) or IL-10. To characterize the TS-specific T cells at the clonal level, we g enerated CD4 and CD8 clones. We obtained cytotoxic CD4 clones of the Th1 ty pe that secreted large amounts of IFN-gamma but not IL-4 or IL-10. Unexpect edly, we obtained other CD4 clones with a Th2 phenotype, secreting IL-4 and IL-10 but not IFN-gamma. All CD8 clones were cytotoxic and produced IFN-ga mma. IL-4 and IL-10 were not secreted by these cells. Using synthetic pepti des, we determined a CDS epitope recognized by several clones as being repr esented by amino acids IYNVGQVSI. The antiparasitic activity of a CD4 Th1 a nd a CDS Tc1 clone was assessed in vitro. CD4 or CD8 T cells significantly inhibited T. cruzi development in infected macrophages or fibroblasts, resp ectively. We concluded that DNA vaccine efficiently generates potentially p rotective CD4 Th1 and CD8 Tc1 cells specific for a T. cruzi antigen, theref ore reinforcing the possibility of using this strategy for developing a pre ventive or therapeutic vaccine against Chagas' disease.