Enhancement of cellular and humoral immune responses to Trypanosoma cruzi infection using genetic vaccines augmented with cytokine-expressing plasmids

Immunity to the protozoan parasite Trypanosoma cruzi requires the elicitation of humoral and cell mediated immune responses to extracellular trypomastigote forms and CD8⁺T cell mediated responses to intracellular amastigotes. In this study, the ability of genetic vaccines encoding T. cruzi surface antigens TSA-1, ASP-1 or ASP-2 to generate protection against T. cruzi infection was investigated. All three of these molecules had previously been shown to induce both humoral and CTL responses in T. cruzi infected mice. Mice immunized with vectors encoding TSA-1 ,ASP-1 or ASP-2 individually or in combination exhibited moderate levels of cytotoxic T lymphocyte (CTL) activity and no apparent antibody production. However, when challenged with blood-form trypomastigotes, all mice immunized with nucleic acid vaccines (plasmid CMVI.UBF3/2 containing TSA-1, ASP-1 or ASP-2) exhibited lower parasitemia compared to controls injected with vector alone. Further, 50% of mice immunized with CMVI.UBF3/2.ASP-1 or CMVI.UBF3/2.TSA-1 and 75% of mice immunized with CMVI.UBF3/2.ASP-2 survived the challenge infection, while all the mice injected with vector alone succumbed to infection. The enhancement of host immune response which can provide protective immunity to T. cruzi infection was attempted by co-immunization with antigen-encoding vectors and vectors containing interleukin 12 (112) and granulocyte macrophage-colony stimulating factor (GMCSF). Co-delivery of IL12 and GMCSF expression cassettes with genetic vaccines for T. cruzi resulted in splenomegaly, significant antigen-specific stimulation of CDS⁺T cells and secretion of Th1/Tc1 type cytokines. Most importantly, we observed a dramatic increase in the specific antibody and CTL response in mice immunized with antigens and cytokines encoding vectors when compared to the group of mice immunized with antigen encoding vectors only. The ability of the enhanced B and T cell responses observed in mice receiving both antigen and cytokine encoding plasmids to increase protection to T. cruzi infection will be determined.