Evaluation of a novel Poly-Staphylococcal Superantigen-like Fusion Vaccine for Staphylococcus aureus

Abstract

Staphylococcus aureus is a globally important pathogen and a major causative agent of opportunistic infection in nosocomial and community settings. No vaccines for S. aureus are currently available despite intense efforts invested in the search for a vaccine. In the face of a dearth in new antibiotics and rapid spread of antibiotic-resistant strains, research into new vaccine candidates is critical. This thesis aimed to develop and evaluate a novel Poly-Staphylococcal Superantigen-Like (SSL) fusion vaccine to investigate SSLs as potential vaccine targets and the efficacy of a Poly-SSL fusion vaccine in protection against a peritonitis model of S. aureus infection. SSL3, SSL7 and SSL11 are the best-studied proteins in the SSL family with specificity for Toll-like receptor 2, complement component C5, immunoglobulin A and glycosylated receptors on granulocytes respectively. Past studies have elucidated the active binding sites and mutants for the three proteins to enable the creation of a Poly-SSL vaccine. Two recombinant constructs, Poly-SSL7-11 and Poly-SSL7-3-11 (Poly-SSL) were produced for use as potential vaccines and characterised for binding to human IgA, C5, TLR2 and PSGL-1 using established binding assays. Three neutralising assays (SSL3-TLR2, SSL7-IgA and neutralising C5b-9) were developed to examine downstream functions of SSL3 and SSL7 after neutralisation with anti-SSL sera from vaccinated mice. Immunisation of mice with either of the constructs was found to induce 100 % seroconversion in vaccinated animals to produce high titres of antigen-specific IgG. Serum from vaccinated mice was found to effectively neutralise SSL7’s ability to bind IgA and C5 in-vitro. A pilot immunisation study analysing formulation of Poly-SSL vaccine with different adjuvants (AdjuPhos, Alhydrogel and AddaVax) revealed higher humoral and splenocyte proliferative responses in animals vaccinated with Poly-SSL-AdjuPhos and Poly-SSL-AddaVax. The two formulations were further evaluated in a peritonitis model using S. aureus. Mice immunised with Poly-SSL-AddaVax demonstrated faster recovery from intraperitoneal challenge and possessed significantly lower S. aureus load in the liver post-challenge. Immunisation with Poly-SSL was observed to drive IL-6, TNF, and IFN-γ production in splenocytes of challenged mice. The current study revealed SSLs to be viable candidates for an effective S. aureus vaccine with protection partially originating from humoral responses.