Abstract: Objective  To observe the role of CD8+ T cells in the tumor growth delay induced by Toxoplasma gondii excreted-secreted antigens （TgESA） in B16F10 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 2×105 B16F10 cells. Mice in group C were intraperitoneally injected with TgESA （100 μl per mouse） at 7 d after B16F10 cells injection. Mice of group A were only injected with PBS. On the 13th day after melanoma cell injection, the mice were sacrified 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 2×105 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.

Key words: Toxoplasma gondii, Excreted-secreted antigens, CD8+ T cell, Melanoma