Chagas disease is a major health problem in Latin America, and an emerging infectious disease in the US. Previously, we have screened the Trypanosoma cruzi sequence database by a computational/bioinformatics approach, and identified antigens that exhibited the characteristics of vaccine candidates.
We investigated the protective efficacy of a multi-component DNA-prime/protein-boost vaccine (TcVac2) constituted of the selected candidates and cytokine (IL-12 and GM-CSF) expression plasmids in a murine model. C57BL/6 mice were immunized with antigen-encoding plasmids plus cytokine adjuvants, followed by recombinant proteins; and two-weeks later, challenged with T. cruzi trypomastigotes. ELISA and flow cytometry were employed to measure humoral (antibody isotypes) and cellular (lymphocyte proliferation, CD4+ and CD8+ T cell phenotype and cytokines) responses. Myocardial pathology was evaluated by H&E and Masson's trichrome staining.
TcVac2 induced a strong antigen-specific antibody response (IgG2b>IgG1) and a moderate level of lymphocyte proliferation in mice. Upon challenge infection, TcVac2-vaccinated mice expanded the IgG2b/IgG1 antibodies and elicited a substantial CD8+ T cell response associated with type 1 cytokines (IFN-γ and TNF-α) that resulted in control of acute parasite burden. During chronic phase, antibody response persisted, splenic activation of CD8+ T cells and IFN-γ/TNF-α cytokines subsided, and IL-4/IL-10 cytokines became dominant in vaccinated mice. The tissue parasitism, inflammation, and fibrosis in heart and skeletal muscle of TcVac2-vaccinated chronic mice were undetectable by histological techniques. In comparison, mice injected with vector or cytokines only responded to T. cruzi by elicitation of a mixed (type 1/type 2) antibody, T cell and cytokine response, and exhibited persistent parasite burden and immunopathology in the myocardium.
TcVac2-induced activation of type 1 antibody and lymphocyte responses provided resistance to acute T. cruzi infection, and consequently, prevented the evolution of chronic immunopathology associated with parasite persistence in chagasic hearts.
Trypanosoma cruzi, a parasitic protozoan, is the etiologic agent of Chagas disease. Chagas disease is the most common cause of congestive heart failure related deaths among young adults in the endemic areas of South and Central America and Mexico. Vaccine development against Chagas disease has been dramatically limited because of extensive debate on the mechanisms involved in this pathology. It is now accepted that the presence of parasites in cardiac tissue is necessary to initiate and maintain the inflammatory responses and that therapeutic treatments or vaccines aimed at eliminating T. cruzi would limit or prevent the progression of chronic chagasic cardiomyopathy. In the present study, we have tested the protective efficacy of a multi-component heterologous DNA-prime/protein-boost vaccine TcVac2 in a murine model of T. cruzi infection. Immunization of mice with TcVac2 induced potent antibody, CD8+ T cell and cytokine responses that provided protection from acute parasitemia and chronic parasite persistence and immunopathology in chagasic mice in comparison to unvaccinated mice.