There is a precursor subset of intratumoral exhausted CD8+ T cells (CD8+ Tpex) with less differentiation and coexpression of the inhibitory receptor PD-1 and the transcription factor TCF1 (encoded by Tcf7) that sustain the immune response in chronic infection, and tumor progression presents a link between T cell memory and exhaustion. The gene discussed is PDCD1; the disease is neoplasm.