Distinct immunoreactions after a primary tumor microwave ablation using different heating parameters in a VX2 tumor model

Background: Thermal ablation of solid tumors in situ can activate the immune system and produce a specific immune response against the tumor. Microwave ablation (MWA) with different parameters can ablate tumors with similar sizes and cause different local inflammatory effects. Our aim was to determine the immunological effects induced by different energy modes of MWA for a primary tumor. Methods: Seventy rabbits with VX2 tumors that were implanted subcutaneously underneath the right second nipple were treated with high-power MWA (40 W for 1 min), low-power MWA (20 W for 2 min), or surgical resection or were left without treatment (control). Survival time was evaluated by log-rank test. On day 14 after ablation, immunohistochemistry and flow cytometry were used to evaluate the T-cell immune responses. In addition, the cytokine patterns were identified by enzyme-linked immunosorbent assay. Results: Tumor eradication was achieved completely in the MWA groups, as proven by nicotinamide adenine dinucleotide diaphorase staining. Compared with the three treatment groups, the control group had a significantly higher number of pulmonary metastases and worse survival; however, no significant difference was observed among the three treatment groups. More intra-tumoral and systemic CD4+ and CD8+ T-cells were induced in the MWA groups than in the control group. Compared with operation, MWA induced more systemic CD4+ T-cells. More intra-tumoral CD4+ and CD8+ T-cells and systemic CD4+ T-cells were induced by high-power MWA than by low-power MWA. Moreover, MWA increased the interleukin 2 (IL2) and IL12 levels and decreased the IL4, IL6, and IL10 levels. Importantly, the serum IL12 level was significantly higher after high-power MWA than after low-power MWA. Conclusion: High-power MWA enhanced the type 1 T helper immune response and may be selected for the treatment of solid tumors. Future studies are needed to confirm our results.