Abstract 621: Evaluating the compatibility of tumor treating electric fields with key anti-tumoral T cell functions
Authors: Diamant Gil , Simchony Hadar , Shiloach Tamar , Globerson-levin Anat , Eshhar Zelig , Grossman Rachel , Ram Zvi , Volovitz Ilan 
Published: August 2018

Background: Tumor Treating Fields (TTFields) are low-intensity electric fields that target proliferating cells by hindering mitotic spindle formation and charged organelle translocation. TTFields are FDA-approved for treatment of newly diagnosed and recurrent glioblastoma. Combining TTFields with immunotherapy is a rational approach due to their different mechanisms of action (MOA) and to TTFields' ability to induce immunogenic cell death (ICD). Conversely, TTFields may interfere with immune functions critical for effective T cell responses. Here, we evaluated the effects of TTFields on select pivotal anti-tumoral T cell functions.

Methods: T cells from healthy donors' peripheral blood or from viably dissociated fresh glioblastoma samples were cultured under normal or TTFields conditions, with or without superantigen stimulation. Multiparametric flow cytometry (8 colors) was used to assess T cell responses by monitoring select pivotal anti-tumoral functions: proliferation (CFSE dilution), IFNγ secretion (intracellular staining), cytotoxic degranulation (CD107a surface expression) and activation/exhaustion (PD1 expression). T cell viability under TTfields was assessed in a dedicated assay. Direct cytotoxicity under TTFields was evaluated using a chimeric antigen receptor (CAR) T cell-based assay.

Results: The viability of superantigen-stimulated T cells that attempted to proliferate decreased under TTFields, in line with TTFields' MOA. Small or no reductions in viability were found in activated T cells that did not attempt to proliferate and in unstimulated T cells.

The functionality of peripheral-blood T cells and tumor-infiltrating T cells (TILs) stimulated by superantigen under TTFields was unhindered: T cells exhibited comparable PD1 upregulation, IFNγ secretion and CD107a surface-expression as controls. T cell polyfunctionality was previously reported to be associated with effective anti-tumoral responses. A polyfunctionality analysis conducted on our data demonstrated that T cells that had lost the capacity to proliferate under TTFields conditions, retained all other polyfunctional combinations. PD1+ TILs, a subset containing most of the tumor antigen-specific T cells, exhibited unaltered viability and functionality when cultured under TTFields. Lastly, the cytotoxic capability of CAR T-cells (which utilize the same killing machinery as normal T cells) was unaffected by TTFields.

Conclusions: All anti-tumoral T cell functions examined, with the exception of proliferation, were unhindered by TTFields. Our findings, together with the plausible synergism of TTFields

with systemic anti-tumoral immune responses, warrant the further preclinical and clinical investigation into the combination of these therapeutic approaches.

Citation Format: Gil Diamant, Hadar Simchony, Tamar Shiloach, Anat Globerson-levin, Zelig Eshhar, Rachel Grossman, Zvi Ram, Ilan Volovitz. Evaluating the compatibility of tumor treating electric fields with key anti-tumoral T cell functions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 621.