Interestingly, we found that the localization of IDO-positive cells is strongly paralleled with the localization of the lymphocytic infiltrate, with exception of FoxP3-positive regulatory T cells, which were also recruited into the tumor mass, but not localized in areas of high IDO-expression as exemplarily presented in Supplementary Figure 2 in cutaneous melanoma metastases. Here, IDO1 is linked to cutaneous melanoma.