Stem-like, antigen-experienced PD-1+TCF-1+CD8+ T cells, or ‘stem-like T cells’, have emerged as important determinants of the immune response in chronic infections and cancer, with the size of their tumour-associated pool critical to the success of cancer immunotherapies blocking PD-1 or PD-L1 (refs. 1–3). This evidence concerns the gene PDCD1 and neoplasm.