Interestingly, data from HNSCC patients treated with neoadjuvant immunotherapy (nivolumab as monotherapy or in combination with ipilimumab) demonstrated that ICI-fostered early intra-tumoral responses are primarily mediated by pre-existing T cell populations with a TRM gene program, which is characterized by tissue residency, cytotoxicity, effector functions and inhibitory receptors including PD-1 [46]. This evidence concerns the gene PDCD1 and head and neck squamous cell carcinoma.