Melanoma induces immunosuppression by up-regulating FOXP3+ regulatory T cells

Background. The immune response to melanoma is rarely curative, suggesting the emergence of immunosuppression. FOXP3-expressing regulatory T cells (T-reg cells) function to suppress immune responses. The objective of this study was to determine if melanoma evades immune surveillance, in part, by inducing T-reg cells. Material and methods. Peripheral blood mononuclear cells (PBMCs) were isolated and exposed to melanoma-conditioned media (MCM) or control media for 1 week. The induction of T-reg 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. Results. Normal PBMCs exposed to MCM revealed higher proportions of T-reg cells than those exposed to control media after 6 days (3.4% versus 1.3%, respectively, P < 0.02). The expression of FOXP3 in T-reg 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-beta in supernatants after 6 days growth was higher in MCM than control media, but this did not reach statistical significance. Conclusion. Exposure of PBMCs to melanoma results in induction of FOXP3(+) T-reg cells. (C) 2007 Elsevier Inc. All rights reserved.