Systemic and mucosal immune responses after intranasal administration of recombinant Mycobacterium bovis bacillus Calmette-Guerin expressing glutathione S-Transferase from Schistosoma haematobium

A major goal of current vaccine development is the induction of strong immu ne responses against protective antigens delivered by mucosal routes. One o f the most promising approaches in that respect relies on the use of live r ecombinant vaccine carriers. In this study, Mycobacterium bovis BCG was eng ineered to produce an intracellular glutathione S-transferase from Schistos oma haematobium (Sh28GST). The gene encoding Sh28GST was placed under the c ontrol of the mycobacterial hsp60 promoter on a replicative shuttle plasmid containing a mercury resistance operon as the only selectable marker. The recombinant Sh28GST produced in BCG bound glutathione and expressed enzymat ic activity, indicating that its active site was properly folded. Both intr aperitoneal and intranasal immunizations of BALB/c mice with the recombinan t BCG resulted in strong anti-Sh28GST antibody responses, which were enhanc ed by a boost. Mice immunized intranasally produced a mixed response with t he production of Sh28GST-specific immunoglobulin G1 (IgG1), IgG2a, IgG2b, a nd IgA in the serum. In addition, high levels of anti-Sh28GST IgA were also found in the bronchoalveolar lavage fluids, demonstrating that intranasal delivery of the recombinant BCG was able to induce long-lasting secretory a nd systemic immune responses to antigens expressed intracellularly. Surpris ingly, intranasal immunization with the BCG producing the Sh28GST induced a much stronger specific humoral response than intranasal immunization with BCG producing the glutathione S-transferase from Schistosoma mansoni, altho ugh the two antigens have over 90% identity. This difference was not observ ed after intraperitoneal administration.