PDCD1 and neoplasm: To answer this, we analysed two independent unbiased single-cell RNA-sequencing datasets of human melanomas41,42, and found that around 1.5% of tumour-infiltrating CD8+ T cells expressed RAMP1. The melanoma-infiltrating RAMP1+ CD8+ T cells of the patients overexpressed the immune checkpoint receptors PD-1 (also known as PDCD1), TIM3 (HAVCR2), LAG3, CTLA4 and CD27 (Fig. 5e and Extended Data Fig. 11m).