PDCD1 and head and neck squamous cell carcinoma: The results showed that the expression of CTLA-4, GAL9, HAVCR1, IDO-1, IDO-2, LAG-3, PD-1 and TIGHT in the IRMS low-risk group was significantly higher than that in the high-risk HNSCC group (P<0.05), indicating that the activation of efficiency immune infiltration might be triggered by up-regulation of the immune checkpoints (Figure 7D).