PDCD1 and neoplasm: Moreover, corroborating our ex vivo data, we found significantly increased activation of T cells from clusters relative to T cell singlets, as judged by upregulation of CD137, PD-1, CD39 and increased PD-L1 expression by tumour cells (indicative of IFNγ secretion by active neighbouring T cells) (Fig. 4e,f and Extended Data Fig. 8a–c).