Using single-cell RNA sequencing (scRNA-seq) and mass cytometry analysis of peripheral blood from patients with advanced lung cancer treated with PD-1 blockade, we identified a unique T-bet–positive Th1-like cluster that differs from Th1 in the epigenome, T-cell receptor (TCR) clonotype, and gene expression pattern (14). The gene discussed is PDCD1; the disease is lung carcinoma.