PDCD1 and head and neck squamous cell carcinoma: The use of TLR7 and TLR9 agonists injected into the tumour in combination with PD-1 blockade to improve the efficacy of ICIs, in experimental animal models of HNSCC was associated with an increased M1/M2 ratio and higher recruitment of tumour-specific IFNγ-producing CD8+ T cells (CTL), leading to suppression of cancer growth and prevention of metastasis in HNSCC models [100,478].