Nasal immunization with the C-terminal domain of BclA3 induced specific IgG production and attenuated disease symptoms in mice infected withClostridioides difficilespores

Clostridioides difficile is a Gram-positive, spore-forming bacterium that causes a severe intestinal infection. Spores of this pathogen enter in the human body through the oral route, interact with intestinal epithelial cells and persist in the gut. Once germinated, the vegetative cells colonize the intestine and produce toxins that enhance a strong immune response that perpetuate the disease. Therefore, spores are major players of the infection and ideal targets of new therapeutic treatments. In this context, spore surface proteins of C. difficile , are potential antigens for the development of vaccines targeting C. difficile spores. Here we report that the C-terminal domain of the spore surface protein BclA3, BclA3 CTD , was identified as an antigenic epitope, over-produced in Escherichia coli and tested as an immunogen in mice. To increase antigen stability and efficiency, BclA3 CTD was also exposed on the surface of B. subtilis spores, a well-established mucosal vaccine delivery system. In the experimental conditions used in this study, free BclA3 CTD induced antibody production in mice and attenuated some CDI symptoms after a challenge with the pathogen, while the spore-displayed antigen resulted less effective. Although dose regimen and immunization route need to be optimized, our results suggest BclA3 CTD as a potentially effective antigen to develop a new vaccination strategy targeting C. difficile spores.