Background: Tumor treating fields (TTFields) are low-intensity, intermediate frequency electric fields that affect proliferating cells. 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 the ability of TTFields to induce immunogenic cell death. Conversely, TTFields may interfere with immune functions critical for effective T-cell responses.
Objectives: To evaluate the effects of TTFields on pivotal antitumoral T-cell functions.
Methods: T-cells from healthy donor peripheral blood (PB) or from viably dissociated human glioblastoma samples were cultured under normal or TTFields conditions, with or without superantigen stimulation. Multiparametric flow cytometry (8-color) was used to assess T-cell responses by monitoring select pivotal functions: proliferation (CFSE), IFNγ secretion, cytotoxic degranulation (CD107a), and activation/exhaustion (PD-1). Cellular viability was assessed in a dedicated assay. A chimeric antigen receptor (CAR) T-cell-based assay directly evaluated cellular cytotoxicity.
Results: Activated PB T-cells and tumor-infiltrating T-cells (TILs) preserved all monitored anti- tumoral functions under TTFields, apart from proliferation. This finding also applied specifically to PD-1 + TILs, comprised predominantly of tumor antigen-specific cells. Activated T-cells that attempted to proliferate under TTFields demonstrated decreased viability, in line with TTField MOA. Small or no reduction in viability was found in T-cells that did not attempt to proliferate, whether activated or resting.
Conclusions: All monitored anti-tumoral T cell functions, except for proliferation, were unhindered by TTFields. Our results support further investigation into combinations of TTFields with T-cell based immunotherapeutic approaches.