Melanoma Induces Immunosuppression by Up-Regulating FOXP3+ Regulatory T Cells

BackgroundThe immune response to melanoma is rarely curative, suggesting the emergence of immunosuppression. FOXP3-expressing regulatory T cells (Treg cells) function to suppress immune responses. The objective of this study was to determine if melanoma evades immune surveillance, in part, by inducing Treg cells.Material and methodsPeripheral blood mononuclear cells (PBMCs) were isolated and exposed to melanoma-conditioned media (MCM) or control media for 1 week. The induction of Treg cells in these PBMCs was determined by measuring the proportion of CD25+FOXP3+ T cells in all CD4+ T cells by flow cytometry. FOXP3 expression was determined by mean fluorescence intensity (MFI) and Western blot. Supernatant cytokines were determined by ELISA.ResultsNormal PBMCs exposed to MCM revealed higher proportions of Treg cells than those exposed to control media after 6 days (3.4% versus 1.3%, respectively, P < 0.02). The expression of FOXP3 in Treg cells from PBMCs exposed to MCM increased over time by MFI and Western blot but was not significantly different than those exposed to control media. The level of IL-10 and TGF-β in supernatants after 6 days growth was higher in MCM than control media, but this did not reach statistical significance.ConclusionExposure of PBMCs to melanoma results in induction of FOXP3+ Treg cells.