Investigation of HIFU-induced anti-tumor immunity in a murine tumor model

To determine whether HIFU treatment can elicit a systemic, anti-tumor immune response in vivo, MC-38 solid tumors grown subcutaneously at the right hindlimbs of C57BL/6 mice were treated in an experimental HIFU system. Three different treatment strategies that produce thermal, mechanical, or thermal combined with mechanical damage to the tumor tissue were evaluated. To detect anti-tumor immune response, a tumor challenge was performed on the left hindlimbs of the mice one day following the HIFU treatment, and subsequently, cytotoxic T lymphocyte (CTL) response was evaluated on day 14. All three HIFU treatment strategies were found to cause significant regression of the primary tumor, with the best suppressive effect produced by the thermal HIFU. In contrast, the most significant regression of the challenged tumor with concomitantly elevated CTL response were detected in mice treated by the mechanical HIFU, followed by the thermal combined with mechanical HIFU, but not in mice treated by the thermal HIFU alone. These findings suggest that alternative treatment strategies that promote mechanical lysis of the tumor cells (in contrast to purely thermal ablation) may enhance HIFU-induced anti-tumor immune response.