PDCD1 and head and neck squamous cell carcinoma: Among them there are lymphocyte-activation gene 3 (LAG3) [41], which is targeted by relatlimab [42, 43] and eftilagimod [44]; ITIM domain (TIGIT) [45], that is inhibited by tiragolumab, a drug under investigation in combination with anti-PD-L1 atezolizumab as first-line treatment for PD-L1 positive R/M HNSCC [46]; TNFR-related gene (GITR) [47], whose agonist is under investigation in a phase Ib trial of multivalent autophagosome vaccine with anti-PD-1 immunotherapy [48].