Clostridium difficile PSI polysaccharide: synthesis of pentasaccharide repeating block, conjugation to exotoxin B subunit, and detection of natural anti-PSI IgG antibodies in horse serum

Characteristics of the Clostridium difficile cell envelope and its importance in therapeutics

“…Glycans are T cell‐independent antigens, although when conjugated to a carrier protein, these molecules can elicit a T‐cell memory response (Berti and Adamo, ). Anti‐PS‐I antibodies can be detected in sera from healthy horses and chemically synthesized PS‐I has been fused to a subunit of C. difficile toxin B to form a potential dual conjugate vaccine (Jiao et al ., ). These preliminary studies demonstrated the potential of cell wall polysaccharides as vaccine candidates.…”

Vaccines againstClostridium difficile

“…This result suggests that the glycosyl phosphate and the polymeric nature of PSI could be immunologically important to develop a vaccine. 146 Antibodies against the third isolated glycan structure, named PSIII, have been detected in the blood of infected patients. 147 Intraperitoneal or subcutaneous immunizations of Balc/C mice or rabbits, respectively, with either intact or de-O-acylated LTA fraction of PSIII conjugated to the genetically inactivated P. aeruginosa exoTcdA protein (ExoA) or HSA revealed that it was possible to elicit IgG antibodies recognizing PSIII on C. difficile cells 148 rendering this molecule a potential target for vaccine development.…”

The potential for emerging therapeutic options forClostridium difficileinfection

“…[128][129][130][131][132] Adamo et al noted that mice, hamsters, as well as farm animals had elevated levels of anti-PSII antibodies in response to vaccines containing the polysaccharide. 129,132 Interestingly, due to exposure to C. difficile, humans also carry anti-PSII IgA and IgG antibodies.…”

“…Jiao et al further studied the importance of C. difficile PSI polysaccharide as a basis for the development of anti-C. difficile vaccines. 128 It is apparent that while PSII is found on the cell surface of biofilms of C. difficile, PSI and PSIII are expressed stochastically. The pentasaccharide moiety of PSI, chemically synthesized and fused to an exotoxin B subunit could be an effective vaccine with 2 separate antigens to mount an immune response.…”

“…Importantly in the study, anti-PSI IgG antibodies were found in sera of horses in response to both the native PSI polysaccharide, as well as the chemically synthesized non-phosphorylated PSI repeating block, thus highlighting the potential for such an approach in vaccine development. 128 Novel chemical synthesis protocols to generate large quantities of the pentasaccharide repeating unit and oligosaccharide structures were optimised by Martin et al to overcome problems with lowlevel expression of natural PSI. 133 Using mouse models, the authors demonstrated that a chemically synthesized PSI repeating unit CRM197 conjugate elicited an immune response.…”