[Role of CD8+ T cells in the tumor growth delay induced by Toxoplasma gondii excreted-secreted antigen in B16F10 mouse melanoma model].

Objective: To observe the role of CD8+ T cells in the tumor growth delay induced by Toxoplasma gondii excreted-secreted antigens (TgESA) in B16FI0 mouse melanoma model in the early stage.

Methods: TgESA were prepared by incubating T. gondii tachyzoites for 12 h in vitro. 15 C57BL/6 mice were randomly assigned to group A, B, and C (5 mice per group). Each mouse in group B and C was subcutaneously injected in right flank with 2 x 10(5) B16F10 cells. Mice in group C were intraperitoneally injected with TgESA (100 microl per mouse) at 7d after B16F10 cells injection. Mice of group A were only injected with PBS. On the 13th day after melanoma cell injection, the mice were sacrificed and spleen was removed. The percentage of CD8+ T cells in the spleen was analyzed by flow cytometry. CD8+ T cells were isolated from spleen cells by using immunomagnetic beads. The activity of CD8+ T cells against B16F10 melanoma cells was determined by LDH release assay at different effect-to-target cell ratios (2.5:1, 5:1, and 10:1). Other 30 C57BL/6 mice were randomly divided into group E, F, and G. Each mice were injected with 2 x 10(5) B16F10 cells. At the same time, mice in group F and G were simultaneously injected via the tail vein with CD8+ T cells isolated from mice in group B and C. Tumor growth, mortality and survival time of mice were observed and recorded during 35-d observation period.

Results: The percentage of CD3+CD8+T cells in the spleen cells of group C [(15.74 +/- 0.28)%] was significantly higher than that of group B [(14.18 +/- 0.27)%] and A [(13.86 +/- 0.13)%] (P < 0.05). At different effect-to-target cell ratios, the activity of CD8+ T cells against B16F10 cells in group C was significantly higher than that of group B (P < 0.05). The average time of tumor formation in group G [(14.9 +/- 1.2) d] was longer than that in group F [(11.9 +/- 0.7) d] and E [(9.4 +/- 1.2) d] (P < 0.05). The tumor size in these groups increased, but there was no obvious difference in the tumor growth rate among the three groups. The tumor size of group G was significantly smaller than the other two groups (P < 0.05). In group E, F and G, mice began to die on the 26th day, the 29th day and the 30th day after tumor inoculation, and the number of survival mice was 3, 5 and 7, respectively, at the 35th day after injection.

Conclusions: TgESA may up-regulate the quantity and function of CD8+ T cell in B16F10 melanoma mouse model, which plays a role of delaying tumor growth in early stage.