CD4 and head and neck squamous cell carcinoma: Our analysis indicates that primary HNSCC tumors are both immunologically active, evidenced by immune cell infiltration, increased PD-1 expression on CD4+ & CD8+ infiltrating T cells, and the killing capacity ex vivo-and immunosuppressed, as shown by substantial PD-L1 positivity (~20% of tumor cells) and a considerable infiltration of myeloid cells with high PD-L1 expression.