It’s often upregulated in exhausted T cells and associated with resistance to PD-1 blockade, making it a promising target for combination therapies.62 For example, a study found that co-expression of PD-1 and TIM-3 on TILs in head and neck squamous cell carcinoma (HNSCC) correlates with an exhausted immune phenotype and resistance to PD-1 inhibition. Here, PDCD1 is linked to head and neck squamous cell carcinoma.