INDUCTION OF ANTI-TUMOR IMMUNITY BY TUMOR TREATING FIELDS (TTFIELDS) IN GLIOBLASTOMA

Abstract INTRODUCTION The novel approved GBM treatment TTFields employs alternating, intermediate-frequency (200kHz) electric fields to disrupt mitotic macromolecules leading to chromosome mis-segregation and apoptosis. Emerging evidence indicates that TTFields may also induce inflammation; however, the mechanism and whether this can be harnessed as cancer immunotherapy remain unclear. METHODS Multiple GBM cell lines were treated with TTFields using Inovitro, an in vitro TTFields system and integrity of the nuclear envelope and content and activation of key DNA sensor inflammatory pathways analyzed by immunostaining, expression profiling, and protein assays. In a syngeneic orthotopic murine model, TTFields-treated GBM cells were used to provide an in-situ vaccination platform. For validation, we performed bulk and single-cell RNAseq of PBMCs from 12 newly diagnosed GBM patients treated with TTFields. RESULTS TTFields induce focal disruption of the nuclear envelope, leading to cytosolic release of large micronuclei clusters that recruit and intensely activate the 2 major DNA sensors – cGAS and AIM2, and their cognate inflammasomes, thereby releasing pro-inflammatory cytokines and type-1 interferons (T1IFNs) that promote development and maturation of DCs and cytotoxic T cells. In murine model, TTFields-treated GBM cells induce anti-tumor memory immunity both intratumorally and systemically, producing a cure rate of 40% and partial immunity in an additional 25% in a STING- and AIM2-dependent manner. In patients with newly diagnosed GBM patients, we sequenced a total of 193,760 PBMCs and detected robust post-TTFields activation of adaptive immunity via the T1IFN trajectory anchored by plasmacytoid DCs, which was strongly correlated with the TCRαβ clonal expansion index observed in 11 of 12 patients (Spearman coefficient r=-0.8, P=0.014). Importantly, we also defined a T cell-based gene signature predictive of TTFields effects on T cell activation and TCRαβ clonal expansion. CONCLUSION Collectively, these studies define a novel strategy using TTFields to improve immunotherapy in GBM and potentially other solid tumors.