PDCD1 and Kaposi's sarcoma: In NK cells, expression of PD-1 was reported in various tumor (renal cell carcinoma, multiple myeloma, ovarian carcinoma, Kaposi sarcoma or EBV-associated post-transplant lymphoproliferative disorder) and chronic infection (M. tuberculosis, Human cytomegalovirus (HCMV), Human Immunodeficiency Virus (HIV), or hepatitis C virus (HCV) infection) settings [30,60,61,62,63,64,65,66].