Safety and immunogenicity of a recombinant vaccine against Trypanosoma cruzi in Rhesus macaques.

Chagas disease, caused by the protozoan parasite Trypanosoma cruzi is one of the most important neglected parasitic diseases in the Americas. Vaccines represent an attractive complementary strategy for the control of T. cruzi infection and pre-clinical studies in mice demonstrated that trypomastigote surface antigen (TSA-1) and the flagellar calcium-binding (Tc24) parasite antigens are promising candidates for vaccine development. We performed here the first evaluation of the safety and immunogenicity of two recombinant vaccine antigens (named TSA1-C4 and Tc24-C4) in naïve non-human primates. Three rhesus macaques received 3 doses of each recombinant protein, formulated with E6020 (Eisai Co., Ltd.), a novel Toll-like receptor-4 agonist, in a stable emulsion. All parameters from blood chemistry and blood cell counts were stable over the course of the study and unaffected by the vaccine. A specific IgG response against both antigens was detectable after the first vaccine dose, and increased with the second dose. After three vaccine doses, stimulation of PBMCs with a peptide pool derived from TSA1-C4 resulted in the induction of TSA1-C4-specific TNFα-, IL-2- and IFNγ-producing CD4+ in one or two animals while stimulation with a peptide pool derived from Tc24-C4 only activated IFNγ-producing CD4+T cells in one animal. In two animals there was also activation of TSA1-C4-specific IL2-producing CD8+ T cells. This is the first report of the immunogenicity of T. cruzi-derived recombinant antigens formulated as an emulsion with a TLR4 agonist in a non-human primate model. Our results strongly support the need for further evaluation of the preventive efficacy of this type of vaccine in non-human primates and explore the effect of the vaccine in a therapeutic model of naturally-infected Chagasic non-human primates, which would strengthen the rationale for the clinical development as a human vaccine against Chagas disease.

Expression, purification, immunogenicity, and protective efficacy of a recombinant Tc24 antigen as a vaccine against Trypanosoma cruzi infection in mice.

The Tc24 calcium binding protein from the flagellar pocket of Trypanosoma cruzi is under evaluation as a candidate vaccine antigen against Chagas disease. Previously, a DNA vaccine encoding Tc24 was shown to be an effective vaccine (both as a preventive and therapeutic intervention) in mice and dogs, as evidenced by reductions in T. cruzi parasitemia and cardiac amastigotes, as well as reduced cardiac inflammation and increased host survival. Here we developed a suitable platform for the large scale production of recombinant Tc24 (rTc24) and show that when rTc24 is combined with a monophosphoryl-lipid A (MPLA) adjuvant, the formulated vaccine induces a Th1-biased immune response in mice, comprised of elevated IgG2a antibody levels and interferon-gamma levels from splenocytes, compared to controls. These immune responses also resulted in statistically significant decreased T. cruzi parasitemia and cardiac amastigotes, as well as increased survival following T. cruzi challenge infections, compared to controls. Partial protective efficacy was shown regardless of whether the antigen was expressed in Escherichia coli or in yeast (Pichia pastoris). While mouse vaccinations will require further modifications in order to optimize protective efficacy, such studies provide a basis for further evaluations of vaccines comprised of rTc24, together with alternative adjuvants and additional recombinant antigens.

Aluminium phosphate potentiates the efficacy of DNA vaccines against Leishmania mexicana.

DNA vaccines have been able to induce partial protection against infection with Leishmania in mice, but it is still necessary to increase their efficacy. In the present study we evaluated aluminium phosphate as an adjuvant of different formulations and doses of DNA vaccines against L. mexicana in BALB/c mice. Aluminium phosphate had no effect on the humoral response induced by a high dose (100 microg) DNA vaccine, but slightly increased the cellular response and the protection against infection. It also allowed a non-immunoprotective low dose (20 microg) DNA vaccine encoding L. mexicana GP63 and Leishmania donovani NH36 to become protective. Aluminium phosphate may thus be an effective, low cost and safe adjuvant for DNA vaccines, and the vaccine formulation described here may be an excellent candidate for further vaccine development against Leishmania.