The interplay between immunosuppressive actors has also been demonstrated in the peripheral blood of melanoma patients, where IDO was linked with increased PD‐L1 + cytotoxic T‐cells which are in turn associated with increased CTLA‐4 expression by Tregs and monocytic myeloid‐derived suppressor cell (mMDSC) levels.25 Here, IDO1 is linked to melanoma.