PDCD1 and neoplasm: The anti-tumour clinical response to PD-1 blockade in patients with malignancies18,19 was recently shown to rely on precursor exhausted T-cells (Tpex), a subpopulation of CD8+ T-cells that exhibit features of exhaustion, such as PD-1 expression, but also display memory T-cell characteristics,20, 21, 22, 23 including expression of the transcription factor T-cell factor 1 (TCF-1).