The research described in this thesis focuses on strategies to enhance NBL immunogenicity to improve outcome of children suffering from HR-NBL. The main objective was to find pharmacological and cell-based strategies to induce one of the most important prerequisites for cytotoxic T-cell engagement: cell surface display of MHC-I. The ultimate goal is to effectively engage T-cells, thereby enhancing anti-tumor cytotoxicity and creating immunological memory to prevent future relapse.
To improve the current therapy regimen, we need to understand why the current strategy fails. The pilot data of the functional, longitudinal immune monitoring strategy we developed shows clues for therapy improvement and emphasizes the potential of such a monitoring strategy to study therapy responses in patients. However, we can show the potential, but we do need collaborative approaches within the European association involved with neuroblastoma research (SIOPEN) to gain enough power to be able to draw firm conclusions in such a rare disease treated with many different treatment arms.
We identified HDAC inhibition as a promising approach to induce surface display of MHC-I expression on NBL cells, thereby causing in vitro susceptibility to NBL-specific T-cell cytotoxicity. The HDACi Entinostat induces a general increase in factors important in both innate and adaptive immunogenicity, which, to our surprise, was accompanied by a switch towards a more undifferentiated, MES NBL cell lineage. This implies that chemo-resistant NBL cells are more sensitive to immunotherapy, and vice versa. These new insights in cell lineage plasticity in response to chemo- and immunotherapy stresses the importance of considering therapy timing to reach maximum therapy efficacy.
Immune monitoring during therapy revealed that, besides the low immunogenicity of NBL cells in general, immune cells themselves may be dysfunctional, which further complicates the generation of NBL-specific immune responses. Adoptive cell therapy strategies may therefore be required complementary to immunogenicity-enhancing strategies to maximize anti-tumor responses. This thesis hints to the potential of cell therapy strategies which combine natural NK-cell cytotoxicity with TCR-mediated cytotoxicity of T-cells in one cell to overcome MHC-I plasticity-related immune evasion.
Altogether, understanding of the impact of (timing of) individual components of the HR-NBL treatment regimen on tumor destruction, tumor phenotype, immunogenicity, and immune cell function is key to further improve efficacy of the treatment regimen. This thesis identifies and shows the potential of strategies to increase NBL immunogenicity to, among others, T-cells, to induce an NBL-specific immune response and generate immunological memory to prevent future relapse. This is a start, but translating our findings to a fully immunocompetent setting, together with investigation of other immunogenicity-restricting processes, is needed to bring mastering of this game of hide and seek to the next level.