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Abstract
Background Natural Killer (NK) cells are innate immune cells able to reject hematological malignancies and correlate with better prognosis in solid tumors. However, conventional NK (cNK) cell anti-tumor activity is limited by the immune suppressive tumor microenvironment (TME). The subset of NK cells, adaptive NK (aNK) cells have immunological memory and accumulate in cytomegalovirus (CMV) infected individuals.1 These aNK cells can resist immune suppression of the TME.2 Glioblastoma (GBM) is the most aggressive brain tumor that has a very poor dismal prognosis and immunosuppressive TME.3
Methods We develop an artificial 3D model of GBM TME, using U251 tumor cells, myeloid derived suppressor cells (MDSC), and NK cells, to analyze the tumor infiltration and killing by NK cells that have developed memory against autologous tumor antigens presented by dendritic cells (DCs), using the live imaging analyzer Incucyte.
Results Our data suggest that aNK cells recognize GBM antigens and we demonstrate that NK cells can infiltrate and kill tumor cells (figure 1), especially when previously primed by antigen loaded DCs. Furthermore, using a flow cytometry-based analysis called Metflow we have discovered that aNK cells have a different metabolic profile than cNK cells. While cNK cells were dysfunctional in the TME when inhibiting glycolysis, aNK cells were still activated relaying on alternative metabolic pathways, such as the TCA cycle (figure 2).
Conclusions Our data suggest that aNK cells have a higher metabolic plasticity and resistance to TME, making them a great target for immunotherapy against GBM tumors.
References
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Sarhan D, et al. Adaptive NK Cells with Low TIGIT Expression Are Inherently Resistant to Myeloid-Derived Suppressor Cells. Cancer Res 2016;76:5696–5706.
Grech N, Dalli T, Mizzi S, Meilak L, Calleja N, Zrinzo A. Rising Incidence of Glioblastoma Multiforme in a Well-Defined Population. Cureus. 2020 May 19;12(5):e8195. doi: 10.7759/cureus.8195. PMID: 32572354; PMCID: PMC7302718.
Ethics Approval All research involving human blood was ethical approved by the university research ethic committee.
Graphics comparing the evolution of spheroids area (left Y axis, continuous lines) and NK cell infiltration (right Y axis, discontinuous lines) over time (X axis) between the different conditions tested: spheroids with NK cells non-stimulated with U251 lysate (’Spheroids + NK’, in dark blue), spheroids with NK cells stimulated with U251 lysate (’Spheroids + NKlys’, in light blue), spheroids with MDSCs and NK cells non-stimulated with U251 lysate (’Spheroids + NK + MDSCs’, in green) and spheroids with MDSCs and NK cells stimulated with U251 lysate (’Spheroids + NKlys + MDSCs’, in red).
aNK cells in filled pattern vs. cNK cells in white. The graphs show the fold change in the activation of each cell type for different metabolic pathway, The activation of aNK cells against an antigen is dependent on
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