PDCD1 and neoplasm: Though tumor-infiltrating DNT cells expressed PD-1, they were the least frequent PD-1+ T cell subset and showed the most variability in PD-1 expression compared to CD4+ and CD8+ T cells (CD4: 65.8 ± 7.1%, CD8: 67.2 ± 7.2%, DNT: 55.5 ± 11.7%, Fig. 3b).