Medical Biology - Theses
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ItemManipulating the humoral immune response using epigenetic modifiers( 2020)The generation of protective antibody is one of the most important parts of the humoral immune response and is the basis for the vast majority of successful vaccination strategies. Antibody is produced by rare populations of differentiated B cells, known as plasmablasts and plasma cells. The differentiation of B cells into antibody secreting cells (ASCs) is complex and highly orchestrated by vast array of mechanisms, including epigenetic regulation. Broadly speaking, epigenetics describes all non-genetic regulation of gene expression. Hence, modifications to the chromatin, but not the underlying DNA sequence, result in altered gene expression. In recent years, epigenetic modifying compounds (EMCs) have emerged as potential therapeutic agents for the treatment of haematological malignancies and immune disorders. However, it is now clear that EMCs also modulate the immune response via both direct and indirect mechanisms. Despite the extensive studies on EMCs, the precise functional role of many of these compounds remains unknown. This thesis explores the effects of two EMCs that have previously been shown to affect the antibody response. Specifically, the Brd4 inhibitor JQ1 and GSK126, an Ezh2 inhibitor. Using quantitative analysis, I examined the effects of each EMC on different parameters that combine to control the magnitude of the antibody response. By combining functional analysis with transcriptomic and epigenomic studies, I investigated the precise molecular mechanism and gene targets of these EMCs. Thus, these studies provide the opportunity to identify novel regulators of antibody secreting response. I showed that JQ1 treatment dampens the antibody secreting response by targeting multiple parameters of B cell function, including cell proliferation and survival. The effects on B cell function were the result of global Brd4 displacement as opposed to previously suggested gene specific mechanisms. In addition, I identified the pro-apoptotic molecule Bim as the molecular target of JQ1 directly responsible for inducing apoptosis in stimulated B cells. Conversely, inhibiting Ezh2 increases B cell differentiation and antibody production of B cells. I showed that Ezh2 inhibition causes global downregulation of H3K27me3 without altering the genome accessibility. Genome-wide studies identified a number of novel regulators of Ezh2 inhibition induced ASC differentiation, including the Blimp-1 target Atoh8. Results from this thesis illustrate the strength of in vitro reductionist systems that combine functional analysis of cell biology with genomics to isolate epigenetic mechanisms that regulate immunity. JQ1 has a significant effect on B cells and has the potential to be used as a therapeutic agent to dampen the antibody secreting responses in autoimmunity, particularly those involving increased antibody production. In contrast, pharmacological inhibition of Ezh2 increases ASC differentiation and antibody production. Thus, it could potentially be used to boost antibody responses that could be applied to treat immunodeficiency or as a differentiation therapy in cancer models.