IDO1 and head and neck squamous cell carcinoma: We found that the expression of CTLA4, IDO1, TIM3, LAG3, PD1, SIGLEC10, LILRB1 and NKG2A were increased in low CDI subgroup of HPV negative HNSCC patients (Figure 4C), but not in HPV positive HNSCC patients (Figure S5D).