Thesis (Ph.D.) - University of Queensland, 2004. / Includes bibliography.

Thesis (Ph.D.) - University of Queensland, 2004. / Includes bibliography.

Thesis (M.Phil.) - University of Queensland, 2005. / Includes bibliographical references.

Thesis (M.S.)--Northern Michigan University, 2009. / Bibliography: leaves 35-36.

Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (M.Phil.) - University of Queensland, 2005. / Includes bibliography.

Thesis (M. Med. Sc.)--University of Hong Kong, 2006.

The innate immune response mediates immediate control of the pathogen and is followed by the acquired immune response which is slower but ensures comprehensive elimination of the pathogen. Dendritic cells are unique innate immune cells that can phagocytose the pathogen and generate pathogen-associated antigenic peptides for presentation to T cells in order to initiate the acquired immune response. Dendritic cells also express cytokines which facilitate pathogen control and development of acquired immune responses, thus acting as a bridge between innate and acquired immune responses. CD8+ T cells are important cells of the adaptive immune system that play a key role in mediating clearance and protection against intracellular pathogens. Upon engagement by antigen-presenting cells, CD8+ T cells undergo massive expansion followed by a swift, extensive contraction to restore homeostasis. The mechanisms behind the expansion and contraction of CD8+ T cells are yet to be completely elucidated. FoxO3a is a transcription factor that is involved in the regulation of various vital cellular processes ranging from cell proliferation and cell metabolism to stress resistance and cell death. I have, therefore, investigated the role of FoxO3a signaling in the activation of dendritic cells and CD8+ T cells. My initial experiments indicated that FoxO3a regulates the homeostasis of various immune cells including CD8+ T cells and dendritic cells. CD8+ T cells lacking FoxO3a displayed enhanced proliferation, as evaluated by cell imaging, CFSE dilution and Ki67 staining, upon polyclonal stimulation in vitro. The modulation of cell proliferation by FoxO3a seemed to be p27kip-independent, as evaluated by western blotting. At later stages of stimulation, FoxO3a-deficient CD8+ T cells underwent reduced cell death, as assessed by cell counting and 7-AAD staining, and this seemed to be independent of Bim, Caspase 8 or Caspase 3 activation. In addition, FoxO3a regulated cytokine expression by CD8+ T cells while displaying similar NFκB activation in comparison to WT CD8+ T cells. Similar results were observed in dendritic cells upon LPS stimulation in vitro, wherein cytokine expression was higher in the FoxO3a-deficient dendritic cells and they also displayed enhanced antigen presentation to CD8+ T cells, as evaluated by CFSE dilution. Taken together, these results indicate that FoxO3a acts as a negative regulator of CD8+ T cell and dendritic cell activation.

The Inhibitor of Apoptosis (IAP) proteins are a highly conserved group of anti-apoptotic proteins that regulate various pathways, particularly those that affect proliferation and cell death. Smac mimetics compounds (SMCs) are IAP antagonists that induce the degradation of two IAPs, cellular IAP 1 (cIAP1) and cellular IAP 2 (cIAP2). cIAP1 and cIAP2 are negative regulators of the alternative NF-κB pathway, which is critical to the regulation, activation, proliferation, and survival of immune cells. Consequently, SMCs can affect immunological responses by providing co-stimulatory signals for antigen-presenting cells or promoting proliferation and activation of T cells. Due to their potent immunomodulatory properties, SMCs are an ideal candidate for new vaccine adjuvants. I sought to demonstrate the potential of SMCs as a vaccine adjuvant by evaluating SMCs effects on dendritic cells (DCs). I demonstrated that SMC treatment of bone marrow derived dendritic cells (BMDCs) induces degradation of both cIAP1 and cIAP2 and leads to activation of the alternative NF-κB signalling pathway. Furthermore, SMC treatment led to upregulation of proteins associated with DC maturation, as well as secretion of pro-inflammatory cytokines. Despite the activating effects elicited by SMCs in vitro, the use of SMCs as an adjuvant for peptide vaccination failed to prevent tumour growth. Further work to determine the best use of SMCs as adjuvants in vivo needs to be done to explore the potential of this class of drugs. Thus, these findings will guide the use of SMCs in adjuvant vaccine therapies for robust protective immunity.

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