Proliferating CD8+ T-cells were positive for the activation marker HLA-DR and for IDO and had variable expression of checkpoint molecules such as PD-1, PD-L1 and CTLA-4.These findings are in line with previous data in NSCLC and melanoma, where anti-PD-1 was reported to revitalize an already existing T-cell response consisting of primed (tumor-specific) CD8+ T-cells that had become exhausted due to chronic antigen stimulation [46,47,48]. Here, PDCD1 is linked to melanoma.