PDCD1 and mature T-cell and NK-cell non-Hodgkin lymphoma: High levels of PD-1 expression measured on T-reg cells in PTCL were thus identified to be associated with poorer prognosis in a group of patients (115) and recently, PD-L1 expression alongside V-domain immunoglobulin suppressor of T cell activation (VISTA) in NKTCL has been found to act as synergistic negative predictors of prognosis, further establishing the role of T cell suppression in oncologic immune evasion (116, 117).