Tumor growth and cytotoxic activity after HIFU treatment. HIFU treatments inhibited the growth of (A) primary and (B) challenged tumors, and induced tumor-specific CTL response (C), and IFN-γ-secreting cells (D) in the spleens of treated mice. C57BL/6 mice were inoculated s.c. on right hind leg with 5 × 105 MC38 tumor cells and treated with different HIFU on day 9 of tumor inoculation. Mice were challenged with 1 × 106 MC38 tumor cells by s.c. inoculation on the left hind leg one day after HIFU treatment. Both primary and challenged tumor growth were monitored daily. Splenocytes obtained from control and treated mice 10 days after HIFU treatment were re-stimulated with mytomicin-pretreated MC-38 or EL4 tumor cells and CTL and ELISPOTS assays were performed. Results were expressed as mean value ± SD for each group (n = 8). *P < 0.05; **P < 0.001 versus non-treatment control. This experiment is representative of three experiments with consistent results.