PDCD1 and cancer: To further reveal T cells gradual dysfunctionality in oral precancer and cancer, we performed multiple immunofluorescences for Pan-CK, CD3, CD8 and PD-1 in tissue sections of 7 OLK, 8 preca-OLK and 7 OSCC and found that the proportion of CD3+CD8+PD-1+cells (exhausted CD8+T cells) in total cells in preca-OLK and OSCC were significantly higher than that in OLK (Figure 3F-G).