Induction of a Specific Humoral Immune Response by Nasal Delivery of Bcla2ctd of Clostridioides difficile.

Clostridioides difficile, formerly known as Clostridium difficile, is a spore-forming bacterium considered as the most common cause of nosocomial infections in developed countries. The spore of C. difficile is involved in the transmission of the pathogen and in its first interaction with the host; therefore, a therapeutic approach able to control C. difficile spores would improve the clearance of the infection. The C-terminal (CTD) end of BclA2, a spore surface protein of C. difficile responsible of the interaction with the host intestinal cells, was selected as a putative mucosal antigen. The BclA2 fragment, BclA2CTD, was purified and used to nasally immunize mice both as a free protein and after adsorption to the spore of Bacillus subtilis, a well-established mucosal delivery vehicle. While the adsorption to spores increased the in vitro stability of BclA2CTD, in vivo both free and spore-adsorbed BclA2CTD were able to induce a similar, specific humoral immune response in a murine model. Although in the experimental conditions utilized the immune response was not protective, the induction of specific IgG indicates that free or spore-bound BclA2CTD could act as a putative mucosal antigen targeting C. difficile spores.

Characterization of Bacillus anthracis Spore Proteins Using a Nanoscaffold Vaccine Platform.

Subunit vaccines are theoretically safe and easy to manufacture but require effective adjuvants and delivery systems to yield protective immunity, particularly at critical mucosal sites such as the lung. We investigated nanolipoprotein particles (NLPs) containing the Toll-like receptor 4 agonist monophosphoryl lipid A (MPLA) as a platform for intranasal vaccination against Bacillus anthracis. Modified lipids enabled attachment of disparate spore and toxin protein antigens. Intranasal vaccination of mice with B. anthracis antigen-MPLA-NLP constructs induced robust IgG and IgA responses in serum and in bronchoalveolar and nasal lavage. Typically, a single dose sufficed to induce sustained antibody titers over time. When multiple immunizations were required for sustained titers, specific antibodies were detected earlier in the boost schedule with MPLA-NLP-mediated delivery than with free MPLA. Administering combinations of constructs induced responses to multiple antigens, indicating potential for a multivalent vaccine preparation. No off-target responses to the NLP scaffold protein were detected. In summary, the NLP platform enhances humoral and mucosal responses to intranasal immunization, indicating promise for NLPs as a flexible, robust vaccine platform against B. anthracis and potentially other inhalational pathogens.