Covalent vaccination with Trypanosoma cruzi Tc24 induces catalytic antibody production

Trypanosoma cruzi 24 (Tc24) is a recently described B-cell superantigen (BC-SAg) expressed by all developmental stages of T. cruzi, the causative agent of Chagas disease. BC-SAgs are immunoevasins that interfere with the catalytic response available to a subset of natural antibodies comprising the preimmune (innate) repertoire. Electrophilic modifications of BC-SAgs facilitate the formation of highly energetic covalent reactions favouring B-cell differentiation instead of B-cell downregulation. Therefore, the aim of this study was to convert the inhibitory signals delivered to B-cells with specificity for Tc24 into activating signals after conjugating electrophilic phosphonate groups to recombinant Tc24 (eTc24). Covalent immunization with eTc24 increased the binding affinity between eTc24 and naturally nucleophilic immunoglobulins with specificity for this BC-SAg. Flow cytometric analyses demonstrated that eTc24 but not Tc24 or other electrophilically modified control proteins bound Tc24-specific IgM⁺ B-cells covalently. In addition, immunization of mice with eTc24 adjuvanted with ISA720 induced the production of catalytic responses specific for Tc24 compared to the abrogation of this response in mice immunized with Tc24/ISA720. eTc24-immunized mice also produced IgMs that bound recombinant Tc24 compared to the binding observed for IgMs purified from non eTc24-immunized controls. These data suggest that eTc24 immunization overrides the immunosuppressive properties of this BC-SAg.

Characterization and Stability of Trypanosoma cruzi 24-C4 (Tc24-C4), a Candidate Antigen for a Therapeutic Vaccine Against Chagas Disease

Chagas disease due to chronic infection with Trypanosoma cruzi is a neglected cause of heart disease, affecting approximately 6-10 million individuals in Latin America and elsewhere. T. cruzi Tc24, a calcium-binding protein in the flagellar pocket of the parasite, is a candidate antigen for an injectable therapeutic vaccine as an alternative or a complement to chemotherapy. Previously, we reported that a genetically engineered construct from which all cysteine residues had been eliminated (Tc24-C4) yields a recombinant protein with reduced aggregation and improved analytical purity in comparison to the wild-type form, without compromising antigenicity and immunogenicity. We now report that the established process for producing Escherichia coli-expressed Tc24-C4 protein is robust and reproducibly yields protein lots with consistent analytical characteristics, freeze-thaw, accelerated, and long-term stability profiles. The data indicate that, like most proteins, Tc24-C4 should be stable at -80°C, but also at 4°C and room temperature for at least 30 days, and up to 7-15 days at 37°C. Thus, the production process for recombinant Tc24-C4 is suitable for Current Good Manufacturing Practice production and clinical testing, based on process robustness, analytical characteristics, and stability profile.