We have investigated the association of immunoescape mechanisms in nasopharyngeal carcinoma (NPC) lesions with Epstein-Barr virus (EBV) infection and clinical course of the disease. Tumor biopsy specimens obtained from 36 Japanese NPC patients were examined for antigen processing machinery component and HLA class I antigen expression, CD8+ T cell infiltration, and Fas, Fas ligand (FasL) and IL-10 expression using immunohistochemical staining. The results were correlated with the histopathological characteristics of the lesions, the clinical course of the disease and EBV infection. LMP2, TAP1, tapasin and HLA class I antigens were downregulated in more than 65% of the lesions tested, while FasL, Fas and IL-10 were expressed in at least 60% of the lesions. Statistical analysis showed that (i) HLA class I antigen expression was significantly correlated with LMP2 and tapasin expression (r = 0.39 and 0.45, respectively); (ii) CD8+ T cell infiltration into tumor lesions was significantly correlated with HLA class I antigen, LMP2 and Fas expression (r = 0.34, 0.49 and 0.44, respectively); (iii) LMP2 and FasL expression was significantly correlated with IL-10 expression (r = 0.49 and 0.52, respectively); (iv) IL-10 expression was significantly associated with EBERs and EBV oncoprotein LMP1 expression (p = 0.00078 and 0.015, respectively) and (v) FasL overexpression was significantly associated with reduced patients' survival (p = 0.033). Multivariate analysis identified FasL overexpression as an independent unfavorable prognostic marker. These results suggest that NPC cells may utilize multiple immunoescape mechanisms, including dysfunction of HLA class I antigens and Fas/FasL apoptosis pathways. Furthermore, FasL expression appears to be associated with IL-10 upregulation in EBV positive NPC cells. © 2007 Wiley-Liss, Inc.