PDCD1 and T-cell non-Hodgkin lymphoma: In lymphoproliferative disorders, PD-1 is frequently expressed on tumor cells themselves as in tumor-infiltrating lymphocytes (TILs), while its ligands may be upregulated by tumor cells (some B-cell or T-cell lymphomas) but also TME cells such as TAMs, mast cells and mesenchymal cells [7,8,9].