Towards optimising the combination of non-thermal plasma therapy with immune checkpoint inhibition in melanoma

Abstract Non-thermal plasma (NTP) is a promising cancer therapy that induces immunogenic cell death and may complement immune checkpoint inhibition (ICI). We evaluated NTP as monotherapy and in combination with different ICIs in a syngeneic murine melanoma model. Immune checkpoint-associated ligand and receptor expression was assessed in vitro and in vivo following clinically relevant treatment conditions. NTP largely preserved baseline checkpoint expression, with only limited, treatment-dependent modulations, while maintaining overall immune cell presence within the tumour microenvironment. NTP monotherapy significantly inhibited tumour growth, with the strongest effect observed at 120 s, and was associated with a modest survival benefit in the initial treatment-duration experiment. However, combining NTP with single-agent ICI did not improve tumour control or survival compared to monotherapies, while dual PD-1/CTLA-4 inhibition extended survival independently of NTP. These findings demonstrate that NTP is immunologically compatible with ICI and represents an alternative local therapy for melanoma, although further optimisation is required to unlock its full combinatorial potential.