CXCL12, which is involved in CXCR4-mediated recruitment of CD8+ T cell recruitment to the tumor microenvironment [24], was upregulated by ionizing radiation in MOC2 cells but not in LY2, SCC83, and CAL27 HNSCC cells (Figure 2A–D). This evidence concerns the gene CD8A and head and neck squamous cell carcinoma.