Plasma Elicits Immunogenic Death In Melanoma Cells

Development of non-thermal plasma for cancer immunotherapeutic applications has received growing attention, namely for induction of immunogenic cancer cell death (ICD). Cancer cells undergoing ICD emit signals known as damage-associated molecular patterns (DAMPs), that can attract and stimulate local immune cells [1]. Of these, membrane-bound calreticulin is a key DAMP signal that facilitates engulfment of cancer cells by dendritic cells, a critical process for the development of a specific, anti-tumor immune response [2]. Several studies have shown that plasma treatment of cancer cell lines increased the exposure of CRT on the cell surface [3, 4]. However, the mechanism by which plasma elicits ICD is not fully elucidated. We therefore studied the interaction of plasma with melanoma cells, at ICD-inducing regimes.

The B16-F10 murine melanoma cell line and the A375 human melanoma cell line were treated with a microsecond-pulsed dielectric barrier discharge system over a range of energies and evaluated for CRT emission. We also studied changes to liquid chemistry following plasma treatment, as cells were not treated under dry conditions. Using electron paramagnetic resonance spectroscopy and colorimetric assays, we identified the reactive oxygen and nitrogen species (RONS) present in the liquid after treatment with plasma. By comparing the trends between the exposure of CRT on the cell membrane and the concentration of RONS in the liquid following increasing plasma treatment energies, we can gain insight into which species are most crucial for plasma-induction of ICD. Knowing this will facilitate the optimization of plasma systems for immunotherapy of cancers. Ongoing work includes evaluation of ICD induction of melanoma cells in an in vivo mouse model.