CD8A and head and neck squamous cell carcinoma: In our early studies of TEX, to establish a correlation of TEX with progression in HNSCC, we linked TEX functional activity (i.e., their ability to induce apoptosis of activated CD8+ T cells) with well-known markers of tumor progression, such as disease activity, lymph node involvement, and tumor stage (Kim et al., 2005b; Bergmann et al., 2009).