Quantitative real-time RT-PCR (qRT-PCR) using two independent primer sets revealed PD-1 gene (Pdcd1) expression in wild-type (WT) B16-F10 and YUMM cells, PD-1-overexpressing (OE) B16-F10 melanoma variants, unactivated and CD3/CD28-activated WT positive, but not PD-1 knockout (KO) negative, control B16-F10 or C57BL/6 T-cells. This evidence concerns the gene CD28 and melanoma.