Nanosecond electroporation causes SP2/0 cell tumor ablation and anti-tumor immune responses in BALB/c mice

Abstract

Calcium electroporation is a new modality of electrochemotherapy. It utilizes short pulsed electric fields (PEF) pulses to permeabilize cell membranes and expose them to supraphysiological doses of calcium, which leads to acute cancer cell death. We have investigated the influence of nanosecond electroporation on tumors growth and formation of anti-tumor immune response. Luciferase expressing SP2/0 myeloma cells were used to induce tumors in BALB/c mice. The tumors were treated with 12 kV/cm nanosecond range PEF with and without CaCl2. Electroporation resulted in partial or complete tumor regression and significant prolongation of lifespan. However, CaCl2 did not show a synergistic effect. PEF induced development of anti-tumor immune response. The number of CD4 and CD8 T cells in spleens were increased in PEF treated mice compared to tumor-bearing and tumor free mice. The tumor growth caused increased suppressor cells (myeloid suppressor, CD4+CD25+ and Tr1 suppressor T cells) as well as CD8+Dx5+ cells in the spleens. The percentage of that cells decreased after PEF treatment. PEF treatment caused increased CD4+ Tcm (CD44+CD62L+) cells in spleens and lymph nodes, decreased CD4+CD28- cells in spleens, lymph nodes and in tumor infiltrated CD4 cells. Cytotoxic T lymphocytes obtained from mice with complete tumor remission showed better results in CTL assay compared to cells obtained from tumor free o tumor-bearing mice. PEF treatment induced formation of tumor cell specific antibodies in the blood. Our results show that tumor treatment with PEF induces anti-tumor immune response and prolongs lifespan of mice.