Thioredoxin induces Tregs to generate an immunotolerant tumor microenvironment in metastatic melanoma

Metastatic melanoma is a highly aggressive cancer that is very difficult to treat. Additionally, the antitumor immune reaction of melanoma is still unclear. Here we demonstrate an association between the expression and secretion of the antioxidant protein thioredoxin (TRX) and increasing tumor stage and metastasis in melanoma. To elucidate the role of TRX in melanoma, we assessed the correlation of TRX expression with different disease parameters in melanoma. We also examined the in vitro and in vivo effects of modulating TRX levels in melanoma cells using various methods of TRX depletion and augmentation. We further explored the effects of TRX on the cytokine milieu and the ability of TRX to regulate the proportion and specific activities of T-cell populations. We demonstrate that TRX expression correlates with Treg representation in clinical samples and, that modulation of TRX influences the induction of Tregs and the generation of an immunotolerant cytokine profile in mouse serum. Using a murine metastatic melanoma model, we identified a tumor immunoevasion mechanism whereby melanoma cell-secreted TRX enhances Treg infiltration. TRX displays chemotactic effects in recruiting Tregs, stimulates the conversion of conventional T cells to Tregs, and confers survival advantage to Tregs in the tumor microenvironment. In turn, this increase of Tregs generates immunotolerance in tissues and therefore decreases antitumor immune reactions. These results elucidate a mechanism by which TRX promotes metastatic melanoma in part through Treg recruitment to inhibit T-cell antitumor effects and suggest that TRX antibody may be useful in the clinic as a therapy against melanoma.