CD8A and leukoplakia: We observed significantly increased mean density (cells/mm2) of all PD-1+ T cells and PD-1+ CD8+ T cells (D, 42.3 vs. 8.8; S, 21 vs. 0; DSI, 122.8 vs. 5.4) within the dysplastic epithelium, the stroma, and at the DSI (all P < 0.01) among proliferative leukoplakia tissues compared with localized leukoplakia.