Trans-Sialidase Recombinant Protein Mixed with CpG Motif-Containing Oligodeoxynucleotide Induces Protective Mucosal and Systemic Trypanosoma cruzi Immunity Involving CD8+ CTL and B Cell-Mediated Cross-Priming

Abstract

The Trypanosoma cruzi trans-sialidase (TS) is a unique enzyme with neuraminidase and sialic acid transfer activities important for parasite infectivity. The T. cruzi genome contains a large family of TS homologous genes, and it has been suggested that TS homologues provide a mechanism of immune escape important for chronic infection. We have investigated whether the consensus TS enzymatic domain could induce immunity protective against acute and chronic, as well as mucosal and systemic, T. cruzi infection. We have shown that: 1) TS-specific immunity can protect against acute T. cruzi infection; 2) effective TS-specific immunity is maintained during chronic T. cruzi infection despite the expression of numerous related TS superfamily genes encoding altered peptide ligands that in theory could promote immune tolerization; and 3) the practical intranasal delivery of recombinant TS protein combined with a ssDNA oligodeoxynucleotide (ODN) adjuvant containing unmethylated CpG motifs can induce both mucosal and systemic protective immunity. We have further demonstrated that the intranasal delivery of soluble TS recombinant Ag combined with CpG ODN induces both TS-specific CD4+ and CD8+ T cells associated with vaccine-induced protective immunity. In addition, optimal protection induced by intranasal TS Ag combined with CpG ODN requires B cells, which, after treatment with CpG ODN, have the ability to induce TS-specific CD8+ T cell cross-priming. Our results support the development of TS vaccines for human use, suggest surrogate markers for use in future human vaccine trials, and mechanistically identify B cells as important APC targets for vaccines designed to induce CD8+ CTL responses.

Swimming against the current: genetic vaccination against Trypanosoma cruzi infection in mice

“…In a few cases, some of the mechanisms of induction of protective immunity were investigated. Following intranasal immunisation with (TS) in the presence of the TLR-9 activator CpG ODN, B cells are critical to inducing type I immune response mediated by CD4 + and CD8 + T cells (Hoft et al 2007). In this same model, the absence of CD4 + or CD8 + T cells also renders the vaccinated animals completely susceptible to infection.…”

“…This hypothesis was tested once following vaccination with TS in the presence of CpG ODN. Parasites isolated from immune mice did not show any increase in resistance to anti-TS immune responses, indicating that antigenically distinct forms of the parasites were not selected by the strong protective immune response (Hoft et al 2007). The question as to whether the absence of selectively imposed variations has an effect on CD8+ T cell immune evasion should be evaluated in more experimental models.…”

Long-Term Immunity to Trypanosoma cruzi in the Absence of Immunodominanttrans-Sialidase-Specific CD8+T Cells

“…A recent study (57) showing that T. cruzi's flagellum is shed early during host cell invasion and is a source of protective T cell epitopes demonstrates the potential utility of assessing the biological relevance of a pathogen's antigenic mole- T. cruzi's TS family exhibits considerable intra-and interstrain variability in sequence (17,(58)(59)(60) and expression patterns (25), which impacts the generation of CD8 ϩ immunodominance hierarchies (14,15). We and others (21,(23)(24)(25)(26)(27)61) hypothesize that variant TS genes function as a means of immune evasion, and it has been suggested that immunodominance by TS epitope-specific CD8…”

“…We previously analyzed the importance of immunodominant TS-specific CD8 ϩ T cells during T. cruzi infection and observed that mice tolerized against either TSKB20 or TSKB74 (a crossreactive peptide recognized by TSKB18-specific CD8 ϩ T cells [14]) alone, or simultaneously, exhibited modest increases in parasite load during the peak of acute infection, though ultimately they were similar to control-treated mice with respect to control of the acute infection (21). Since the TS gene family is dramatically and selectively expanded in T. cruzi (22) and TS gene sequences exhibit considerable intra-and interstrain variability (14,17), it is hypothesized that this gene family is involved in immune evasion (21,(23)(24)(25)(26)(27). The observation that immune control is generated independent of CD8 ϩ T cell recognition of the identified immunodominant TS-derived epitopes indicates that the described TSfocused CD8 ϩ responses are not necessary and may even inhibit the generation of alternative CD8…”

Immunodominance: a new hypothesis to explain parasite escape and host/parasite equilibrium leading to the chronic phase of Chagas' disease?

“…Whether dominant immune responses select for T. cruzi mutants has never been pursued in depth and should be evaluated in different experimental models and chagasic patients. However, a single recent report was unable to detect the presence of mutant parasites following vaccination of BALB/c mice with a T. cruzi trans-sialidase recombinant antigen (16).…”