Significant differences in the CD4+/CD39+ T-cell population were detected in tumor tissue (28.8 ± 17.1% of T cells) compared to PBMC HNSCC (8.9 ± 10.2%, p < 0.0001), but not compared to non-cancerous mucosa (19.7 ± 18.4%). Here, CD4 is linked to head and neck squamous cell carcinoma.