INFα-2b inhibitory effects on CD4+CD25 +FOXP3+ regulatory T cells in the tumor microenvironment of C57BL/6 J mice with melanoma xenografts

Background: Regulatory T cells (Treg(s)), particularly the CD4(+)CD25(+)Foxp3(+) Treg(s), down regulate immunity and promote tumor cell growth by directly suppressing CD8(+) and CD4(+) T cells. Alternatively they can promote tumor growth by generating interleukin-10 (IL-10) and transforming growth factor beta (TGF beta) in situ, which help tumor cells to evade the immune system. Methods: In vivo tumor models were prepared via subcutaneous injection with a suspension of B16 melanoma cells into the left upper flank of C57BL/6 J mice. The mice were randomized into five groups: radiotherapy (RT), chemotherapy (CT), radiochemotherapy (RCT), Inteferon a (INF alpha) groups, and a control group. Flow cytometry was used to determine the Tregs levels in the spleen and peripheral blood, and immunohistochemistry was performed to determine the expression levels of TGF beta and IL-10 in the tumor microenvironment. Results: Tumor weight was significantly reduced in the CT or RCT groups (40.91 % and 41.83 %, respectively), while the reduction in tumor weight was relatively lower for the RT and IFN alpha groups (15.10 % and 13.15 %, respectively). The flow cytometry results showed that the ratios of CD4(+)CD25(+)Foxp3(+) Treg(s) to lymphocytes and CD4(+) cells in the spleen and in peripheral blood were significantly decreased after treatment with IFN alpha (P < 0.05). Expression of TGF beta and IL-10 in the tumor microenvironment in the CT and RT groups was higher compared with the control group (P < 0.01), while the expression of TGF beta and IL-10 in the INF alpha group was not significantly different (P > 0.05). Conclusions: The results show that INF alpha-2b inhibits cancer cell immune evasion by decreasing the levels of CD4(+)CD25(+)Foxp3(+) Treg(s) and suppressing the expression of TGF beta and IL-10 in the tumor microenvironment.