PDCD1 and melanoma: Despite multiple independent studies demonstrating PD-1 functional expression by live B16-F10 cells5,7,12,15,16, multiple additional tumor, and non-T immune cell types10,11, one report34 claims that “B16-F10 melanoma cells do not express PD-1” and that “PD-1 expression by non-T-cells is unlikely to be the case”.