Development of an oral spore vaccine to Clostridium difficile infection

Summary 

Clostridium difficile infection (CDI) is one of the leading causes of nosocomial antibiotic-associated diarrhoea. Although CDI is usually considered a disease restricted to HIC, recent data suggests that rates in LMIC are similar to that of Europe or USA. Importantly, the primary method of control is by the use of antibiotics yet this pathogen acquires AMR as well as multidrug resistance and so developing a prophylactic is a priority. Parenteral vaccines have failed. Overarching evidence suggests that to prevent CDI an approach that prevents spore germination of the pathogen and colonization of the host GI-tract is required. Thus, mucosal vaccination that induces secretory IgA responses is a rational approach. Recently, a recombinant spore vaccine expressing the C-terminus of toxin A (TcdA26-39) has been shown to protect against CDI, induce mucosal responses and has been taken to Phase 1 studies. Nevertheless, this vaccine should be improved to ensure higher levels of protection and to overcome downstream regulatory hurdles arising from the use of GMOs. In the current project, we will develop a vaccine candidate using the oral spore (Bacillus subtilis) vaccine approach with a revised vaccine formulation that delivers additional C.difficile antigens constructed utilising a novel cloning system (THY-X-CISE™) that allows the creation of spores that are unable to proliferate in the environment. This latter point is essential for addressing biological containment of genetically modified organisms (GMOs) and ultimately facilitating regulatory approval of the vaccine candidate. 

Project Outcome

Bacterial spores from Bacillus subtilis were engineered to produce a protein derived from the spore of Clostridium difficile known as CotE.  This protein is involved in host colonization, has enzymatic properties, and is a putative protective antigen.  Expression of the protein was achieved on the surface of the Bacillus spores enabling these spores to be used in an oral vaccination approach. 

These recombinant spores were tested for oral immunization in mice and hamsters either alone or in combination with recombinant spores (known as PP108) previously obtained by Dr. Cutting’s group. The later spores express another antigen from C. difficile, namely the C terminus of toxin A (TcdA_26-39). The elicitation of systemic and mucosal humoral immune response (specific antibodies in serum and fecal extracts) was tested in both animal species. At the end of the immunization plan, hamsters were challenged with viable C. difficile by the oral route. Specific antibodies could not be detected in either mice or hamsters from any immunization group. However, a trend to increased survival and decreased disease after C. difficile challenge was observed in hamsters immunized with spores expressing CotE (but not in the group receiving PP108 or the combination of both spores).