PDCD1 and neoplasm: Interestingly, HPV+ve HNSCCs increased the expression of both PD-1 ligands (PD-L1 and PD-L2) in the stromal microenvironment, i.e., in both tumour cells (fibroblasts and macrophages) and stroma in situ in treatment-naïve primary HSNCC cell lines; however, no increase was observed for HPV−ve cells.