Distinct Tumor Immune Responses to NanoPulse Stimulation (NPS) Determine Immunity

NanoPulse Stimulation (NPS) is a pulsed-power technology that stores and delivers high-powered, non-thermal nanosecond electric pulses, inducing in situ vaccination (ISV) after ablation of orthotopic rat N1-S1 liver tumors and mouse 4T1-luc breast tumors. However, NPS does not induce ISV in the ectopic mouse pancreatic cancer Pan02 and melanoma B16F10 models. The studies described here aimed to determine the immune mechanisms behind NPS responses in cancer models that either readily induced immunity with ISV or did not. In N1-S1 liver cancer, NPS triggered both adaptive (T cells) and innate immune responses (natural killer (NK) cells and NK-T cells), while reducing immunosuppressive T regulatory cells (Tregs), thereby creating a favorable environment for ISV. In 4T1-luc breast cancer, NPS selectively induced apoptosis in activated Tregs and tumor-associated macrophages (TAMs) and reduced myeloid-derived suppressor cell (MDSC) levels, relieving local and systemic immunosuppression. The decrease in Treg suppression capacity coincided with reductions in activation markers (4-1BB and TGFβ) and a shift in Treg phenotype from predominantly activated to naïve, resulting in a significant increase in the ratio of resident memory T cells to Tregs. NPS effectively reprogrammed the tumor microenvironment (TME) and secondary lymphatic systems from immuno-suppressive to immunoactive, enabling cytotoxic T-cell, NK, and NK-T-cell function and immune memory formation, eliminating cancer cells and contributing to NPS’s ISV effect. Conversely, ectopic Pan02 and B16f10 failed to reduce immunosuppression or activate cytotoxic T cells in the TME and related tissues, suggesting limited potential to induce immunity in mouse pancreatic and melanoma models, most notably due to persistent immunosuppression.