Immunostimulatory effects of nanosecond pulsed electric fields

Abstract Intense pulsed electric fields (PEF) are increasingly employed for tumor ablation, including inoperable tumors, bleeding metastases, and tumors unresponsive to alternative treatments. PEF disrupt the membrane barrier of tumor cells leading to irreversible changes in homeostasis and cell death. Using different tumor models, we found that treatment with nanosecond duration pulsed electric fields (nsPEF) enhance the host antitumor immune response. The strongest effect was measured in mice bearing CT26 colon carcinoma tumors where the local treatment with nsPEF protected 78% of the animals from a second tumor cell challenge. We hypothesize that nsPEF-treated tumors act as an in-situ cancer vaccine by initiating innate immunity while molding and sustaining adaptive immunity. Indeed, we provide evidence that the damage created by these short electrical stimuli is sensed by the innate immune platform known as inflammasome. Upon assembly, the inflammasome induces proinflammatory cytokine processing and a form of cell death known as pyroptosis. We found that nsPEF triggered pyroptosis in macrophages accompanied by caspase-1 activation and release of IL-1β. Concurrently, to sustain adaptive immunity, nsPEF in tumor cells activate persistent ER-stress accompanied by phosphorylation of translation initiation factor 2α (eIF2α): a biomarker of immunogenic cell death. Tumor antigen-release from nsPEF-treated tumor cells comes with the release of damage-associated molecular patterns such as ATP, HMGB1 and calreticulin. Understanding and manipulating the cross talk between innate and adaptive immunity after nsPEF is expected to improve the immunotherapeutic response triggered by these treatments. Pulse Biosciences, Inc.