Objective   To study the effect of high intensity focused ultrasound (HIFU) in combination with HSV-tk/GCV on tumor immunological toleranc

e and specific anti-tumor immune of rabbits with XX2 tumor.    Methods   Forty experimental rabbits were randomly divided into control group

tumor-bearing group

HIFU treatment group and combined treatment group

10 in each group. Rabbits in HIFU treatment group were treated with HIFU alone and those in combined treatment group were treated with HIFU plus HSV-tk/GCV. Thirteen days after treatment

prevalence of CD4

+

CD25

+

Treg cells (Treg) in peripheral blood of each rabbit was detected by flow cytometry

levels of IL-10 and TGF-β in plasma were measured with ELISA

and in vitro killing activity of splenic lymphocytes on VX2 tumor cells was detected by MTT assay.    Results   The prevalence of Treg cells in peripheral blood and the levels of IL-10  and TGF-β were significantly higher in tumor-bearing group than in control group [(8.30±0.69)%

67.82±4.52 pg/ml and 6.55±0.45 μg/ml vs (530±045)%

54.58±3.53 pg/ml and 5.51±0.27 μg/ml

P0.01

]

and significantly lower in HIFU treatment group than in tumor-bearing group [(7.00±0.56)%

60.32±4.70 pg/ml and 6.22±0.19 μg/ml vs (8.30±0.69)%

67.82±4.52 pg/ml and 6.55±0.45 μg/ml

P0.01

]

. The prevalence of  Treg cells in peripheral blood and the level of TGF-β were lower in combined treatment group than in HIFU treatment group [(6.40±0.72)% and 5.86±0.31 μg/ml) with no significant difference observed in the level of IL-10 between the two groups (P0.05) . Killing test showed that the killing activities of HIFU treatment and combined treatment on VX2 tumor cells were (31.62±3.09)% and (29.48±2.68)%

respectively

which were significantly higher than those in control group and tumor-bearing group [(13.94±2.45)% and (12.00±2.96)%

]

with no significant difference observed between combined and HIFU treatment groups.    Conclusion   HIFU in combination with HSV-tk/GCV can improve the tumor immunological tolerance and specific anti-tumor immune of hosts. 