PhD to be confirmed after 6 months of lab rotations

Clostridium difficile has been recognised as the leading cause of hospital-acquired infection associated with severe diarrhoea, pseudomembranous colitis, toxic megacolon, and bowel perforation. In up to 15% of hospital patients, C. difficile infection (CDI) arises as a result of antibiotic treatment causing changes in the balance of the microbiota, enabling pathogenic C. difficile to colonise. This is particularly prevalent in the aged and immunocompromised. These conditions account for significant morbidity and mortality across the world, with many cases resulting in death within 30 days of initial diagnosis. The emergence of hypervirulent strains and antibiotic resistant strains have further contributed to the spread of CDI worldwide. The CDC reports half a million cases of CDI in the United States each year and around 30, 000 deaths, costing healthcare institutions $4.8 billion each year. CDI is most commonly transmitted by the ingestion of clostridial spores which have been released into the environment by infected individuals and The pathology of CDI is mediated by production of the clostridial toxins TcdA and TcdB.

Current therapies for CDI all have limitations. Antibiotic treatment with metronidazole and vancomycin are the mainstay of therapy, however, the probability of recurrent CDI (rCDI) is between 20%-60%. Antimicrobial resistance to metronidazole and vancomycin is a growing concern, especially as prolonged treatment with vancomycin can be nephrotoxic. Faecal microbiota transplantation provides another alternative, but uptake by patients is low and long-term side-effects are not yet known.

Pfrizer, Valneva, and Sanofi Pasteur have all developed vaccines based on full-length clostridial toxins TcdA and TcdB. These vaccines have proved to elicit antibody-specific responses in vivo. However, in December 2017 Sanofi Pasteur announced discontinuation of their phase III clinical trial of their vaccine.

TcdA and TcdB are exotoxins, meaning they are secreted from the cell body. Antibody responses raised against the toxins will prevent symptoms, but will leave the colonising pathogen relatively untouched. This would effectively produce asymptomatic carriers, who are still able to release clostridial spores into the environment and contribute towards transmission. For this reason, Sanofi Pasteur discontinued their Phase III trial, and it is predicted that Pfizer and Valneva's vaccines will also fail as they share a mechanism of action.

This project aims to address the above issues by developing a spore-based mucosal vaccine against C. difficile. Mucosal vaccines have significant advantages when compared to their parenteral counterparts. This includes the stimulation of secretory IgA which persists in the mucosal tissues and provides protection by blocking entry to host cells. However, mucosal tolerance and safe delivery of vaccines to mucosal surfaces pose significant barriers to the activation of a mucosal immune response . Spores are a promising delivery vehicle due to their robust nature, and should allow ease of both storage and administration.

Using CRISPR-Cas9 technology, auxotrophic spores will be created and recombinant toxin and cell-wall antigens will be fused to proteins expressed on the exosporium layer of C. difficile. These spores will then be assessed for their immunogenicity and ability to elicit an antibody-specific immune response in vivo.