Abstract
In this thesis I have explored the process of MHC-1-mediated antigen presentation in two distinctive cell types: dendritic cells and neuroblastoma tumor cells. Dendritic cells (DCs) are pivotal players that bridge innate and adaptive immunity. DCs are able to engulf tumor-derived material and cross-present tumor-derived antigen fragments to CD8+ T-cells.
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In Chapter 2, I give an overview of recent literature about cross-presenting tumor cell material by dendritic cells. Tipping the scale towards antigen preservation causes a complete stop of antigenic peptide production and subsequent loss of antigen cross-presentation, as described in Chapter 3. Here, cowpox virus-derived protein CPXV012 delivered into the endosomal pathway of dendritic cells as a soluble protein. In this endosomal environment, soluble CPXV012 colocalizes with endocytosed antigen. By blocking endosomal acidification, it prevents the degradation of antigen, a process that is required to liberate antigenic peptide to be cross-presented by MHC-1. Peptides that are produced by endosomal processing of antigen do not only reach MHC-1 for presentation, but also MHC 2. MHC 2 presents antigen to helper CD4+ T-cells that aid in the priming of CD8+ T-cells. The benefit of reaching both CD4+ and CD8+ T-cells when initiating an immune response is investigated in Chapter 4. Given the pivotal role of dendritic cells in eliciting cellular immunity, they may be useful for therapeutic purposes. In Chapter 5, I explore this option using a vector derived from Rift Valley Fever virus (bunyaviridae) that targets dendritic cells in vitro and in vivo. In prophylactic and therapeutic settings of vaccination this viral vector was able to confer protection against a lymphoma tumor challenge. Neuroblastoma is the most deadly pediatric solid tumor and currently lacks a cellular immunotherapeutic treatment strategy. Tumor-specific CD8+ T-cells may be effective to destroy neuroblastoma tumor cells. However, neuroblastoma tumors were shown not to be immunogenic due to low MHC-1 expression levels and lack of broadly- expressed antigens. How to increase neuroblastoma immunogenicity is discussed in Chapter 6. I show that the preferred antigen in melanoma (PRAME) is expressed in >90% of high-risk neuroblastoma tumors and PRAME-specific T-cells are able to recognize neuroblastoma cells, but only when MHC-1 levels are upregulated e.g. by previous NK cell attack. The regulation of MHC-1 expression in neuroblastoma is further investigated in Chapter 7. MHC-1 expression, and thus T-cell recognition of neuroblastoma, appears to depend on the activation of the transcription factor NFκB. Through systematic gene deletions, I have identified factors that suppress NFκB activity in neuroblastoma cells. Tumor expression of these NFκB supressors are correlated with worse survival of neuroblastoma patients, suggesting they could be relevant targets for the development of future (immuno)therapies against neuroblastoma. Finally, the role of NFκB suppression in neuroblastoma development, immunogenicity and immunotherapy is reviewed and discussed in Chapter 8.
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