Long-term protective immunity induced against Trypanosoma cruzi infection after vaccination with recombinant adenoviruses encoding amastigote surface protein-2 and trans-sialidase.

Protection against protozoan parasite Trypanosoma cruzi has been shown to be dependent on the induction of type 1 immune responses. Replication-deficient human type 5 recombinant adenoviruses have an unsurpassed ability to induce type 1 immune responses. Thus, we constructed two type 5 recombinant adenoviruses encoding parasite antigens trans-sialidase (rAdTS) and amastigote surface protein-2 (rAdASP2). Both antigens were genetically engineered to secrete recombinant products in order to induce both optimal antibody and T cell responses. Immunizations of mice with rAdASP2 and rAdTS induced high levels of serum antibodies specific for their recombinant products. In addition, both recombinant viruses were able to elicit a biased helper T cell type 1 (Th1) cellular immune response and a substantial CD8+ T cell-mediated immune response. Moreover, individual immunization with rAdASP2 or rAdTS induced high levels of protection against a challenge with live parasites. CD8+ T cells mediated, at least in part, such protection. Furthermore, when combined in the same inoculum, rAdTS plus rAdASP2 induced complete protection in all animals tested, even when challenges were performed 14 weeks after the last immunization. Taking together, these results show that recombinant adenoviruses expressing TS and ASP-2 antigens of T. cruzi are interesting candidates for the development of a vaccine against Chagas' disease.