Impact of PRaG Therapy on Peripheral Immune Cells of Subcutaneous Tumor Peritoneal Metastasis Model of Colon Cancer

Abstract

Immune cells in peripheral blood may be closely related to the efficacy of immune checkpoint inhibitors. T cells originally present in tumors may have limited antitumor effects, and T cells that respond to immune checkpoint inhibitors may be derived from peripheral blood. Therefore, in this study, subcutaneous tumor peritoneal metastasis model of colon cancer was constructed to reveal the changes of T cells and their subsets (CD4+T cells, CD8+T cells, CD226+T cells), MDSCs and their subsets (G-MDSCs, M-MDSCs) in peripheral blood of mice after PRaG therapy. A total of 90 male Balb/c mice aged 6-8 weeks were divided into five groups: control group, PD-1 inhibitor group, radiation group, radiation + PD-1 inhibitor group, and radiation + PD-1 inhibitor +GM-CSF (PRaG therapy) group. The subcutaneous tumor peritoneal metastasis model of colon cancer was constructed. 3×105 CT26.WT cells was inoculated subcutaneously at the right thigh root, and 5 days later, 1×105 CT26.WT cells was inoculated on the left side at the junction of the anterior superior iliac spine and the midabdominal line. The subcutaneous tumor was selected for radiotherapy of 8 Gy×3. GM-CSF (100ng, i.p.) was given on the 1st day and PD-1 inhibitor (0.25mg/kg, i.p.) was given on the 2nd day after radiotherapy with one cycle every 3 days. On day 22, the peripheral blood of mice was collected. The proportion of immune cells was detected by flow cytometry. Compared with other groups, PRaG therapy decreased the proportion of CD4+T cells and increased the proportion of CD8+T cells. Moreover, PRaG therapy increased the proportion of CD226+CD4+T cells and CD226+CD8+T cells. Finally, PRaG therapy increased the proportion of M-MDSCs and decreased the proportion of G-MDSCs. PRaG therapy can improve the immune microenvironment of peripheral blood of subcutaneous tumor peritoneal metastasis model of colon cancer in mice.