CD8A and head and neck cancer: By additionally taking into consideration the complex interaction of cytotoxic T cells with other components of the immunological TME, e.g. the interaction of cytotoxic T cells with FoxP3+ regulatory T cells as represented by the CD8/FoxP3 ratio (43), one can even enhance the robustness and validity of CD8+ T cells as biomarker for beneficial clinical outcome in head and neck cancer (43, 45, 46).