Exploring BCG to deliver avidin fusion antigens from Schistosoma mansoni

BACKGROUND Bacillus Calmette-Guérin (BCG) is one of the most successful vaccines in the world and evidence suggests it can be used as a bacterial vector to deliver heterologous antigens. OBJECTIVES We evaluated whether BCG could be biotinylated and used as a carrier of Schistosoma mansoni antigen tetraspanin-2 (TSP-2) fused with rhizavidin, an avidin analog. METHODS BCG was grown and biotinylated. The recombinant protein Rzv:TSP-2 was produced and purified from Escherichia coli. The biotinylation and antigen coupling was analysed by flow cytometry, enzyme-linked immunosorbent assay (ELISA) and Western blot. Vaccine immunogenicity was tested in immunised mice by the assessment of lung and splenic T cells. FINDINGS BCG can be biotinylated, which in turn, can be coupled with Rzv:TSP-2. After a series of optimisations which involved molarity of the biotin, ratio of BCG:reagent and the concentration of Rzv:TSP-2 used, almost 50% of the bacteria were biotinylated and 35% coupled with antigen. Although a clear adjuvant effect of BCG was observed, evaluation of immune response in immunised mice demonstrated an overall low immunogenicity of the BCG-Rzv:TSP-2. MAIN CONCLUSION These results demonstrated the use of BCG as a carrier of avidin-tagged antigens. Further optimisations are needed in order to strengthen the stability of tagged proteins in order to produce antigen-specific immune responses.