Background Pulsed Electric Field (PEF) ablation kills cells via non-thermal processes, offering improved safety and distinct immunomodulatory effects versus Radiofrequency (RFA) thermal ablation. A proprietary PEF system with an optimized immunostimulatory waveform was modified for murine treatments and previously shown to induce local and systemic anti-tumor immunity in conjunction with aPD-1.1–3 This study compares the immune responses stimulated by this PEF versus RFA, particularly regarding innate and adaptive immune cell populations.
Methods PEF or RFA treatments with equivalent ablation volumes were delivered to 4T1 orthotopic mammary murine tumors, followed by tumor resection seven days later (figure 1). Sham mice did not receive energy but underwent resection at the same timepoint. Immune cell populations in the resected tumors, including dendritic cells (DCs), Natural Killer cells, monocytic-derived immune suppressor cells (mMDSCs), neutrophils, M1 macrophages, and M2 macrophages, were assessed using flow cytometry. Flow cytometry was also used to quantify circulating regulatory T-cells and to measure tumor-specific CD8+ T-cell activation using gp70 tetramers in blood samples taken 21 days after treatment. Survival from metastatic burden was monitored.
Results PEF-treated mice significantly suppressed tumor growth and increased survival compared to RFA-treated mice despite matched partial ablation volumes (figure 2). Relative to sham controls, PEF ablation induced significant increases in 7-day intratumoral DCs (p=0.009), NK cells (p=0.006), neutrophils (p=0.01), and M1 Macrophages, while decreasing the immunosuppressive mMDSCs (p=0.001) and M2 macrophages (p=0.05) (figure 3). Conversely, RFA did not influence any of these cell populations relative to sham. At 21-days post-treatment, circulating T-cells increased in the PEF group relative to sham and RFA groups (figure 4A). Further, gp70 tetramer assay showed a significant increase in Tet+CD8+ T cells in PEF versus sham and RFA mice (figure 4B). Finally, PEF did not significantly affect regulatory T-cells, while RFA substantially increased this immunosuppressive cell population (figure 4C). Examination of the lungs in mice euthanized for burden confirmed lung metastases, while those surviving to the terminal endpoint confirmed the absence of metastasis, indicating systemic immune anti-cancer protection (figure 5).
Conclusions PEF with a proprietary immunostimulatory waveform significantly increased innate and adaptive anti-cancer immune cell populations in both short- and long-term timeframes. In contrast, RFA thermal ablation had minimal impact and even increased certain immunosuppressive cell populations. As a result, PEF treatment enhanced tumor response and improved survival compared to RFA treatment. These findings indicate that the PEF employed in this study may induce a beneficial immunostimulatory profile and better outcomes in cancer patients versus thermal ablation.
C Pastori, M Wagh, E Nafie, F Murad, R Neal. Pulsed Electric Field (PEF) Ablation Invokes Different Immune Cytokine Profile and Tumor Response than Radiofrequency Thermal Ablation for Matched Ablation Volumes in the EMT6 Mouse Model. SIR 2023, Phoenix, AZ.
E Nafie, C Pastori, M Wagh, F Murad, M Trikha, R Neal. Pulsed electrical fields in combination with anti-PD1 and survival of mice with TNBC (EMT6) murine breast tumor. Journal of Clinical Oncology 2023;41(16_suppl):540–540
E Nafie, C Pastori, M Wagh, M Trikha, R Neal. Pulsed electric fields combined with anti-PD1 prolongs survival and triggers an adaptive immune response in an IO-non-responsive orthotopic mouse model. Cancer Research 2023;83(7_Supplement):6638.
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