Changes in peripheral blood level of regulatory T cells in patients with malignant melanoma during treatment with dendritic cell vaccination and low-dose IL-2

In this study, changes in peripheral blood regulatory T cell (Treg) levels were evaluated in 46 progressive patients with melanoma treated with a dendritic cell-based vaccine and concomitant low-dose IFN-α and IL-2. The regulatory subset of CD4 T cells, characterized by CD25(high) , was prospectively analysed in fresh blood, and treatment-associated quantitative and qualitative changes were analysed. By the 4th vaccine, patients showed a marked increase in CD4+ CD25(high) T cell subset from 6% to 22% (P<0.001). At the 6th vaccine, a general decline was observed and a significantly (P=0.01) lower level of CD4+ CD25(high) Treg cells was reached in the group of patients who attained disease stabilization (9.5%) compared to patients with continued progressive disease (14.5%). However, when FoxP3 was employed for retrospective analysis of Tregs on frozen blood, this difference did not reach significance (P=0.09). The vast majority of the Treg produced IL-10 and, to a varying extent, TGF-β. In addition, sorted CD4+ CD25(high) CD127⁻ Tregs were able to suppress proliferation of peripheral blood mononuclear cells in a dose-dependent manner, thus suggesting a regulatory functionality. These findings emphasize the need for strategies to effectively eliminate Treg cells to optimize the clinical effectiveness of cancer immunotherapy.