CD8A and head and neck squamous cell carcinoma: In contrast, the infiltration of CD4+ T cells (particularly Tregs) plays an immunosuppressive role, which led to decreased CD8+/Treg ratios within tumors in spite of the high CD8+ T-cell infiltrates, and is correlated with poor prognosis of patients with HNSCC (Russell et al., 2013; Mandal et al., 2016).