Early Immunologic Response of Irreversible Electroporation versus Cryoablation in a Rodent Model of Pancreatic Cancer

Purpose: To investigate the differences in immune responses between cryoablation and irreversible electroporation (IRE) in a preclinical mouse model. Material and Methods: A mouse pancreatic cancer cell line (PANC-2) was implanted in the bilateral flanks of mice, and tumor-bearing mice were divided into 6 groups. One of the tumors was ablated either with contact cryoablation using an argon-cooled cryoablation probe for 1 minute at 5% power or by IRE for a total of 64 100-μs-duration, 1250-V/cm ² pulses with 100-ms spacing. The contralateral tumors in the same animal served as controls. At immediate, 6, 12, and 24 hours after ablation, the tumors were processed for immunostaining with F480 (macrophages), CD3 (T cells), and CD-56 (natural killer cells) antibodies. Results: CD3 staining demonstrated significantly more T cells in the IRE group than in the cryoablation group at 6 hours (45 vs 16; P =.027), 12 hours (67 vs 33; P =.020), and 24 hours (161 vs 94; p =.003), with almost a 2-fold increase at every time point. Although the mean number of natural killer cells in the treated tumors was higher, no significant differences were observed between the 2 groups at any of the time points. A significant difference was observed in F480 positivity between the cryoablation group and the IRE group at 12 hours (210 vs 356; P =.0004) and 24 hours (220 vs 328; P =.04), respectively. Conclusions: In a mouse model of pancreatic cancer, IRE evokes a more robust infiltration of macrophages and T cells than cryoablation within 24 hours.