Chagas disease (ChD) is a devastating neglected tropical illness caused by the protozoan parasite Trypanosoma cruzi. It is estimated that 8-11 million people are chronically infected in Latin America, representing a substantial social and economic burden. Owing to the extensive global migration of asymptomatic, chronically infected individuals from endemic regions, ChD now affects thousands of people in nonendemic regions like the U.S. and Europe. The two available drugs for ChD chemotherapy have limited efficacy in the chronic phase of the disease and are rather toxic. Moreover, there is no preventive or therapeutic vaccine for human ChD, despite numerous experimental efforts targeting almost entirely parasite proteins. Although glycoconjugates are the major surface molecules of the infective trypomastigote stages (from both insect vector and host cells), they remain completely unexplored as vaccine targets. We recently employed the ?3-galactosyltransferase-knockout (?3GalT-KO) mouse model, which closely mimics the human humoral immune response against T. cruzi. As vaccine, we used the synthetic trisaccharide Gal?3Gal?4GlcNAc (Gal?N), which is one immunodominant epitope in T. cruzi, covalently linked to bovine serum albumin (BSA) as carrier protein. Gal?N-BSA-immunized mice showed very high levels of protective anti-?al antibodies, much lower parasitemia, and very low parasite levels in the heart, as compared to control BSA-immunized animals. Although not sterile, the protection induced by the Gal?NBSA vaccine was long lasting and dependent on CD4+ (helper) T cells. Based on these results, we hypothesize that the ideal vaccine for ChD should induce both humoral (B cell) and cellular (T cell) immune responses, since both lytic antibodies and T cells play a decisive role in controlling T. cruzi infection.
Aimi ng at the generation of a ChD vaccine that provides sterile protection against T. cruzi mediated by both B and T cells, here we plan to synthesize a series of neoglycopeptides (NGPs) consisting of a well-characterized major histocompatibility complex class II (MHCII)-binding peptide, i.e., tetanus toxoid peptide (TTp) or ovalbumin peptide (OVAp), covalently linked to the immunodominant Gal?N epitope. These synthetic NGPs will be employed for the immunization of ?3GalT-KO mice and the B and T cell-mediated immune responses will be examined.
Three specific aims are proposed:
Specific Aim 1 : Chemical synthesis of ?3-Gal-containing neoglycopeptides.
Specific Aim 2 : Vaccination of ?3GalT-KO mice with synthetic ?3-Gal-containing neoglycopeptides and evaluation of the protective B cell-mediated immune response.
Specific Aim 3 : Elucidation of T cell-dependent immune mechanisms by synthetic T. cruzi glycan epitopes. We anticipate that high levels of protective anti-?al antibodies will be achieved following immunization with the synthetic NGPs. In addition, we will learn which NGP architecture(s) will be ideal for achieving long-term, sterile protection against T. cruzi, dependent on both B and helper T cells. We strongly believe that this project will establish the basis for development of the first synthetic glycoconjugate vaccine able to induce a long-term, sterile protection against T. cruzi.
Chagas disease is a devastating neglected tropical illness caused by the parasite Trypanosoma cruzi. Millions of people are chronically infected in Latin America, representing a substantial social and economic burden. Due to the widespread global migration of chronically infected individuals from endemic countries, Chagas disease now affects thousands of people in nonendemic countries like the U.S., Canada, Spain, Japan, and Australia. Drug treatment for Chagas disease has limited efficacy in the chronic phase of the infection and the two available drugs cause serious side effects. Moreover, there is no preventive or therapeutic vaccine for Chagas disease, despite numerous experimental efforts over the years. Although glycoconjugates like glycoproteins and glycolipids are the major surface molecules of the parasite, these molecules remain completely unexplored as potential vaccine candidates for Chagas disease. In that regard, we recently employed a mouse model that closely mimics the human immune response against T. cruzi to test a novel synthetic glycoconjugate vaccine. Mice vaccinated with this vaccine showed very high amounts of antibodies that destroy the parasites and, consequently, had very low levels of parasite in the heart, which is the main organ affected in Chagas disease. This current project aims at the generation of an improved Chagas disease glycoconjugate vaccine that provides full, long-lasting protection. To achieve this goal, we will synthesize four glycoconjugates that have great potential to strongly activate both arms of the immunological defenses against the parasite. We anticipate that high amounts of protective antibodies will be produced in mice after vaccination with the synthetic glycoconjugates and a long-term protection against T. cruzi will be achieved. We strongly believe that this project will establish the basis for development of the first synthetc glycoconjugate vaccine able to prevent and, perhaps, treat Chagas disease.
