Abstract: Expansion of cytotoxic T lymphocytes (CTLs) is a crucial step in almost all cancer immunotherapeutic methods. Current techniques for expansion of tumor-reactive CTLs present major limitations. The present invention comprises a novel method to effectively produce and expand tumor-activated CTLs using high-voltage pulsed electric fields. Tumor cells were subjected to high-frequency irreversible electroporation (HFIRE) with various electric field magnitudes and pulse widths, or irreversible electroporation (IRE). The treated tumor cells were subsequently cocultured with CD8+ cytotoxic T cells along with antigen-presenting cells. Tumor-activated CTLs can be produced and expanded when exposed to treated tumor cells. The activated CTLs produced with the present invention could be used for clinical applications with the goal of targeting and eliminating tumors.