Objective:To study the effect of splenic lymphocytes isolated from mouse models of colorectal carcinoma with liver metastases induced by oncolytic herpes simplex virus type Ⅱ(oHSV2) on the growth of pulmonary metastases of colorectal carcinoma.Methods:A total of 18 6-week-old BALB/c female mice were selected, colorectal carcinoma cell line CT26 of mice in logarithmic phase was inoculated at the right back (2×10 5 per mouse) and spleen (1×10 5 per mouse) of mice, and tumor cells had hematogenous metastasis to liver through splenic vein. CT26 colorectal carcinoma with liver metastases model was constructed. All mice were respectively divided into oHSV2 group and phosphatic buffered saline (PBS) group, 9 mice in each group according to the random number table method. Mice in oHSV2 group were treated with subcutaneous intratumoral multi-point injection of 100 μl oHSV2 (the multiplicity of infection was 1) for 6 cycles, while mice in PBS group were treated with subcutaneous intratumoral multi-point injection of 100 μl PBS for 6 cycles in total, once injection every other day; the survival of mice was analyzed by using Kaplan-Meier method and tumor growth was observed. The mice of both groups in mouse models of colorectal carcinoma with liver metastases were killed on day 20 and their splenic lymphocytes were isolated. After investigation of the most suitable inoculation number and the optimal observation time of colorectal carcinoma with pulmonary metastases CT26 cell lines, 9 6-week-old BALB/c female mice were divided into the experimental group, the negative control group and the blank control group according to the random number table method, with 3 mice in each group. Mice in the experimental group were injected with splenic lymphocytes (4×10 7 per mouse) and CT26 cells (2×10 5 per mouse) isolated from mouse models induced by oHSV2 via the tail vein, mice in the negative control group were injected with splenic lymphocytes (4×10 7 per mouse) and CT26 cells (2×10 5 per mouse) isolated from normal mice with same weeks old via the tail vein, and mice in the blank control group were injected with only CT26 cells (2×10 5 per mouse) via the tail vein. The above 3 groups were executed on day 10 after inoculation, and tumor growth, histopathological changes of mice were also observed; the survival of mice was analyzed by using Kaplan-Meier method. Results:In models of colorectal carcinoma with liver metastases, liver metastases lesions were not detected in 7 mice and 2 mice had 1-2 liver metastases lesions with long diameter less than 2 mm of oHSV2 group; in PBS group, 9 mice all had multiple liver metastases lesions with tumor long diameter ranging from 1 to 10 mm. And mice in oHSV2 group survived much longer than that of mice in PBS group ( P < 0.001). In models of pulmonary metastases, the optimal number of CT26 cells in mouse tail vein was 2×10 5 per mouse; the best observation time point was day 10 after tail vein injection. On day 24 after inoculation, all mice in the negative control group and the blank control group died, while mice in the experimental group all survived on day 60, and the difference of the overall survival in the above 3 groups was statistically significant ( P = 0.007). HE staining results showed that the lung tissues of the experimental group did not show clear tumor cells, whereas the lung tissues of the negative control group and the blank control group showed extensive diffuse tumor cells. Conclusions:Splenic lymphocytes produced by oHSV2 induction in mouse models of colorectal carcinoma with liver metastases can effectively inhibit the development of pulmonary metastases in colorectal carcinoma CT26 cell of mice.