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 β (TGFβ) 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 α (INFα) groups, and a control group. Flow cytometry was used to determine the Treg(s) levels in the spleen and peripheral blood, and immunohistochemistry was performed to determine the expression levels of TGFβ 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 IFNα 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 IFNα (P < 0.05). Expression of TGFβ 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 TGFβ and IL-10 in the INFα group was not significantly different (P > 0.05). CONCLUSIONS: The results show that INFα-2b inhibits cancer cell immune evasion by decreasing the levels of CD4(+)CD25(+)Foxp3(+) Treg(s) and suppressing the expression of TGFβ and IL-10 in the tumor microenvironment.