Optimized magnitude of cryosurgery facilitating anti-tumor immunoreaction in a mouse model of Lewis lung cancer

Cryosurgery has reemerged as a less invasive local treatment with possible immune-regulatory effects. However, the optimal magnitude of cryosurgery for achieving immune-regulatory responses at abscopal tumor sites remains unclear. We aimed to investigate appropriate magnitude of cryosurgery for this goal using a mouse model. C57BL/6J mice were inoculated with Lewis lung carcinoma cells or B16 melanoma cells in bilateral flanks. The left-sided tumor was cryoablated with repeated freeze/thaw cycles either once, twice, or thrice. The peritumoral injections of LPS were performed. Abscopal tumor volumes were measured, immunohistochemistry was performed for CD4, CD8, Foxp3, and Ki-67, and proinflammatory cytokines were measured in lavage fluid of cryoablated tumor. The growth rate of the abscopal tumor was slowest in the Cryosurgery x2 group among the five experimental groups. The proportions of CD4(+) T cells and CD8(+) T cells in the abscopal tumor were also significantly higher in the Cryosurgery x2 group. The levels of IL-1 beta, IL-2, IL-6, IL-12 beta, IFN-gamma, and TNF-alpha in the peritumoral lavage fluid in Cryosurgery x2 + LPS group were significantly increased compared with the other groups. This study suggested that achievement of approximately 73 % damaged area in the cryoablated tumor by two cycles of cryosurgery generates the most favorable immune-regulatory response for abscopal tumors via activation of anti-tumor immune cells as well as increased secretion of proinflammatory cytokines.