Protein engineering approaches for direct antigen targeting in CD8+ T cell inducing vaccines

Effective vaccine design and public vaccination programs have led to the eradication of several diseases and protected millions of people from deadly infections. However, intracellular infections remain a challenge and their eradication requires the activation of cytolytic mechanisms. CD8+ T cells promote effector mechanisms for infected cell killing subsequent to their priming by antigen-presenting cells. Their activation occurs upon detection of intracellular antigen in a pathway that many current subunit vaccine technologies are trying to approach by cross-presentation. Advances in CD8+ T cell-inducing subunit vaccines include direct targeting of antigens to cross-presenting cells and are studied in this thesis. Antigen delivery to the appropriate cell type for cross-presentation to CD8+ T cells can occur with fusion antibodies. Our laboratory has previously demonstrated that antigens bearing an erythrocyte-binding antibody domain (TER119) target the liver. We used this technology to fuse TER119 and ovalbumin (OVA) antigen with the BBOX domain of the high mobility group box 1 (HMGB1) danger signal and co-administer it with CpG-B adjuvant in a hepatic vaccine context. In liver vaccines, activation of local cytotoxic responses represents an important challenge. Erythrocyte-mediated OVA delivery with adjuvants resulted in cytotoxic CD8+ T lymphocyte (CTL) activation with memory formation in the liver and protection was provided after infection with Listeria monocytogenes. Another method for antigen targeting is through a cross-presenting dendritic cell (DC) subset, called CD8+ DCs. Recent studies in mice showed successful vaccination against OVA fused to XCL1 ligand, which binds CD8+ DCs. To attract CD8+ DCs to the site of injection for increased antigen uptake, we co-injected XCL1-OVA with a fusion protein consisting of XCL1 and the extracellular matrix (ECM) binding domain of placenta growth factor-2 (PlGF-2123-144), called XCL1-PlGF. XCL1-PlGF binds extracellular matrix at the injection site and attracts CD8+ DCs locally. In the context of prophylactic and therapeutic vaccination, the combination of two fusion proteins (XCL1-OVA and XCL1-PlGF) enhanced cytotoxicity and prolonged survival against B16-OVA melanoma. Finally, antigen transport via biomaterial delivery platforms was evaluated as an alternative method to deliver antigens to immunologically relevant sites. Our laboratory and others have shown that nanoscale carriers promote CTL responses in vaccination. Here we present a cationic micelle vaccination platform in which OVA and adjuvant (CpG-B and/or MPLA) loading is mediated by non-covalent molecular encapsulation and adsorption. Following a prime and double boost vaccination, CTL responses were raised in the spleen and lymph nodes of vaccinated mice, along with antigen-specific antibody production. These findings highlight the advantages of the micelle carrier platform in vaccine applications. Overall, this thesis presents novel techniques to target antigens to the appropriate cell compartments, facilitating CTL activation in vaccination either by direct targeting of antigen fused to antibodies and chemokines, or antigen delivery with polymeric vehicles. These platforms for optimized delivery seek to improve current approaches and impact the design of new strategies in CD8+ T cell inductive vaccination.


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