PDCD1 and melanoma: Flow cytometric analyses revealed RMP1-30 reactivity with both live (1.4 ± 0.5%, mean ± s.e.m., n = 6) and dead (3.6 ± 1.1%) WT B16-F10 melanoma cells, markedly enhanced binding to PD-1 OE (73.0 ± 4.1% vs. 10.7 ± 3.9%, n = 4, respectively, Fig. 3a), and no reactivity with PD-1 KO B16-F10 variants (0.0 ± 0.0% vs. 0.0 ± 0.0%, n = 3, respectively, Fig. 3a).