PDCD1 and head and neck squamous cell carcinoma: This is well exemplified by Gemcitabine treatment, which selectively eliminated CD11b+ Gr-1+ cells and efficiently enhanced the efficacy of a combination of resiquimod immunomodulatory and PD-L1 blockade against a murine HNSCC tumor highly infiltrated by TANs [57], or by c-MET (tyrosine-protein kinase Met) inhibitors, which enhanced anti-PD-1 treatment efficacy via blockade of neutrophil recruitment [27].