PDCD1 and melanoma: Co-staining with both ab clones revealed dual 29F.1A12/RMP1-30 positivity by nearly all PD-1 ab-reactive WT (90.8 ± 9.2%, mean ± s.e.m., n = 3) and PD-1 OE B16-F10 live (FVD−) melanoma cells (96.7 ± 0.7%, n = 3), as determined by flow cytometric analyses (Fig. 5a).