Date of Award

2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Abstract

Vaccines represent the most outstanding success story of modern medicine. In addition to pathogen-derived antigen(s), immune adjuvants are crucial for the development of efficacious new generation vaccines. Most modern vaccines are comprised of purified recombinant proteins, peptides or polysaccharides, which are weakly immunogenic. The incorporation of adjuvants in vaccine formulations not only enhances the immunogenicity of the antigen but also activates various innate and adaptive immune parameters. New-age adjuvants become particularly important in the development of vaccines against some challenging pathogens, such as Staphylococcus aureus, for which vaccines are not yet available or are inadequate. S. aureus has proven exceptionally difficult to control with subunit vaccines, warranting the development of novel approaches. The use of multivalent antigens and new generation adjuvants that can counter immune imbalances induced by S. aureus virulence factors have been viewed as potential methods. The broad antigenic diversity among S. aureus strains also limits vaccine efficiency. In this study, we therefore sought to answer the following questions: 1) Can phytol-derived isoprenoid immunoadjuvants enhance vaccine efficiency against different S. aureus strains, such as laboratory strain ATCC 25923 and methicillin-resistant strain (MRSA) MW2? 2) How do the phytol derivatives compare with alum (an inorganic mineral salt adjuvant) and the small intestinal submucosa or SIS (an extracellular matrix derived adjuvant) in orchestrating immune responses to S. aureus? 3) How do these adjuvants affect S. aureus induced immune signaling, such as antibody production, T-cell activation, TLR and NLR signaling, cytokine-chemokine generation and granulocyte-monocyte migration? Our results indicated that: 1) The phytol derivative, phytanol (PHIS-01) could induce protective immunity against both strains of S. aureus. Alum did not confer protection against the laboratory strain; however, it significantly reduced the bacterial burden upon live challenge with MRSA. 2) SIS did not show potential as an effective S. aureus vaccine adjuvant, since it down-regulated the expression of a number of genes known to play key roles in S. aureus defense, such as Cxcl1 or KC, GM-CSF, MIG, I-TAC and TECK. 3) Both alum and the phytol derivatives induced potent CD11b+ cell infiltration. Chemokines such as, Ccl3, Ccl4, Ccl5, Ccl7, Ccl12, Cxcl1 and Cxcl3 were upregulated by both phytol derivatives and alum. Furthermore, both alum and PHIS-01 efficiently induced the expression of T-cell effector functions, analyzed by the expression of transcription factors, T-bet (Th1), Gata-3 (Th2), Foxp3 (T-reg) and RORγt (Th17). Interestingly, S. aureus by itself was found to selectively enhance Foxp3 expression, indicating its ability to induce immune suppression. There were marked differences between the expression patterns in cytokine profile elicited by alum and the phytol derivatives. Unlike alum, the phytol derivatives induced potent expression of IL-17 and IL-1β, key cytokines for host defense against S. aureus. In summary, our studies highlight the potential use of phytol derivatives as new generation adjuvants in S. aureus vaccine design.

Download

Share

COinS