PDCD1 and head and neck squamous cell carcinoma: Multi-parameter flow cytometry (CD8, CD4, CD45RA, FOXP3, Neuropilin-1, CD39, PD-1, Tim-3, LAG-3, CTLA-4, TIGIT, CD69, pAKT, Ki67, Bcl2) was performed on PBL from HNSCC patients (n = 50).