Rosenberg’s research revealed that the tumour antigen specificities and T-cell receptor repertoires of circulating and tumour-infiltrating CD8+ PD-1+, but not CD8+ PD-1−, cells appeared similar, implying that the circulating CD8+ PD-1+ lymphocytes might provide a view into the tumour-resident antitumour lymphocytes41. Here, PDCD1 is linked to neoplasm.