BACKGROUND: Tumor Treating Fields (TTFields) are low-intensity electrical fields that target proliferating cells by hindering formation of mitotic spindle and translocation of charged organelles. TTFields have been recently approved for the treatment of both recurrent and newly diagnosed Glioblastoma (GBM). Immunotherapeutic approaches for treatment of GBM are considered promising, and multiple strategies are currently being evaluated in basic research and clinical trials. Combining TTFields and immune-based therapies is a rational approach as they possess markedly different mechanisms of action (MOA). Conversely, TTFields may potentially abrogate various cellular functions required for effective T cell responses. We performed an in-vitro evaluation on the effect of TTFields on select human T cell functions that are pivotal for an effective anti-tumoral response. The study objective was to evaluate the potential compatibility between immune-based therapies and TTFields. METHODS: Peripheral blood mononuclear cells were isolated from healthy donors. Cells were cultured under normal versus TTFields conditions using the inovitro TTFields system, either with or without Phytohemaglutenin (PHA - a super antigen). Cellular responses were monitored using an 8-color flow cytometry panel that concurrently evaluated proliferation (CFSE dilution), cytokine secretion (IFNγ), cytotoxic degranulation (CD107a surface presentation), and T cell activation/ exhaustion (PD1 expression). The effect on T cell viability was assessed in a separate assay, by comparing the live-to-dead ratio of cells cultured in normal versus TTFields settings.

RESULTS: TTFields did not alter the functionality of non-activated T cells. Viable PHA-activated T cells cultured under TTFields exhibited no change in PD1 up-regulation, IFNγ secretion and CD107a surface-expression. The T cells exhibited reduced proliferation, which is in line with the known MOA of TTFields. As the presence of polyfunctional T cells is associated with effective anti-tumoral responses, a single-cell level polyfunctionality analysis of activated T cells was performed. The analysis demonstrated that under TTFields conditions non proliferating cells retained all other combinations of immune functions. TTFields were found to have a minor effect on the viability of un-activated T cells. In activated cells, there was a moderate effect on cells that did not attempt to proliferate, but TTFields substantially reduced the viability rate of cells that had proliferated. These findings were true for both helper and cytotoxic T cells.

CONCLUSIONS: Pivotal T-cell response parameters, but not proliferation, were found to be unhindered by TTFields. Our current data suggests that the integration of TTFields with various immunotherapeutic approaches may be a rational strategy to explore for the treatment of brain tumors.

Citation Format: Gil Diamant, Ilan Volovitz, Zvi Ram. Evaluating the in-vitro effects of tumor treating fields on T cell responses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 617. doi:10.1158/1538-7445.AM2017-617