Doherty Institute - Theses

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    Investigating the interactions between dendritic cells, T cells and B cells mediated by targeting Clec9A
    Kato, Yu ( 2016)
    Dendritic cells (DC) are endowed with an array of receptors that can be exploited for immunotherapy. Targeted delivery of antigen to CD8α+ DCs via Clec9A in vivo induces versatile immune responses, most notably potent thymus-dependent humoral responses even in the absence of adjuvant. However, the basis of the immunogenicity of Clec9A-targeted antigen remains incompletely understood. This thesis describes the complex interactions between CD8α+ DCs and T and B cells mediated by Clec9A to promote and/or regulate immunity. Characterization of CD4+ T cells responding to Clec9A-targeted antigens revealed that they had the phenotype, localization pattern and effector functions consistent with T follicular helper cells (TFH) that provide B cell help. Furthermore, targeting Clec9A primed long-lived memory CD4+ T cells capable of robust secondary TFH responses, even in the absence of adjuvant. Thus, in the steady-state Clec9A-targeted CD8α+ dendritic cells are capable of stimulating CD4+ T cells to promote the development of fully polarized TFH cells. Strikingly, Clec9A was also found to mediate direct interactions between CD8α+ DCs and B cells. B cells were rapidly activated through recognition of native antigen presented on the surface of CD8α+ DCs upon Clec9A-targeted immunization. Direct activation of B cells by CD8α+ DCs was critical for optimal Clec9A-mediated antibody responses as it enabled B cells to effectively acquire help from cognate CD4+ T cells at the T/B borders within the spleen and lymph nodes. Thus, the effective triad of interactions mediated by Clec9A drives potent antibody responses in the steady-state. Unlike TFH and B cells that were potently activated in the steady-state, cross-priming of cytotoxic lymphocytes (CTLs) by Clec9A-targeted antigen required co-administration of adjuvant. In contrast to B cells, Clec9A-mediated primary CTL responses were impaired by the presence of CD4+ T cells. Clec9A-mediated MHC II-restricted presentation favoured the expansion of pre-existing Foxp3+ regulatory T cells (Tregs) in the steady-state, which presumably impaired non-Tregs capacity to activate CD8α+ DCs. Collectively, the data presented in this thesis reveal the versatile capacity of CD8α+ DCs to interact with various cell types to promote immunity/tolerance and reinforces the notion that targeting Clec9A in vivo is a promising strategy to exploit for immunotherapy.
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    Recombinant HIV vaccines and mucosal immunity
    Tan, Hyon Xhi ( 2016)
    More than 36 million people were infected with the human immunodeficiency virus (HIV)-1 in 2015, and 17 million of this population were females. Female HIV infection has wider implications on mother-to-child transmission of HIV and the survival of children in the event of their mother’s death from AIDS. This highlights a critical need for vaccines that prevent female acquisition of HIV infection. In female sexual transmission of HIV, infection of target CD4 T-cells is highly localised in the sub-mucosal cervico-vaginal tissues for several days before systemic dissemination, and displays little or no viral diversity. Cytotoxic CD8 T-lymphocyte (CTL) responses have been correlated with effective control of acute viraemia in HIV-1 infection of humans or simian immunodeficiency virus (SIV) infection in non-human primate model. Elimination of HIV infection by CTL responses is hypothesised to be most effective during this early phase of contained infection in the cervico-vaginal tissue. In this Ph.D. thesis, vaccination strategies for the induction of tissue-resident HIV-specific CTLs in the female reproductive mucosal tissues were investigated. This thesis demonstrated that influenza virus could be genetically engineered to induce intracellular expression of whole HIV-1 p24 capsid protein. The influenza vectors developed were immunogenic for HIV-specific CD8 T-cell responses when used in prime-boost regimens. We exploited the capacity of these recombinant influenza viruses to infect mucosal tissues in order to establish HIV-specific CTL responses in the vagina mucosa. The mucosal vaccination strategies proposed here provide novel approaches for the establishment of frontline vaginal-resident HIV- specific CTLs and may induce heightened local surveillance for protection against vaginal HIV-1 exposure.