PDCD1 and mature T-cell and NK-cell non-Hodgkin lymphoma: PD-1/PD-L1 expression has also been observed on the surface of tumor ME immune cells in these PTCL subtypes, however PD-L1 expression has rarely been observed in tumor cells from these TFH subtypes, with no PD-L1+ tumors from 4 cases reported in one study [56] and 1/21 elsewhere [85].