Search

The Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) is generally expressed in all EBV-associated tumours and is therefore an interesting target for immunotherapy. However, evidence for the recognition and elimination of EBV-transformed and Burkitt's lymphoma (BL) cells by cytotoxic T lymphocytes (CTLs) specific for endogenously presented EBNA1-derived epitopes remains elusive. We confirm here that CTLs specific for the HLA-B35/B53-presented EBNA1-derived HPVGEADYFEY (HPV) epitope are detectable in the majority of HLA-B35 individuals, and recognize EBV-transformed B lymphocytes, thereby demonstrating that the GAr domain does not fully inhibit the class I presentation of the HPV epitope. In contrast, BL cells are not recognized by HPV-specific CTLs, suggesting that other mechanisms contribute to providing a full protection from EBNA1-specific CTL-mediated lysis. One of the major differences between BL cells and lymphoplastoid cell lines (LCLs) is the proteasome; indeed, proteasomes from BL cells demonstrate far lower chymotryptic and tryptic-like activities compared with proteasomes from LCLs. Hence, inefficient proteasomal processing is likely to be the main reason for the poor presentation of this epitope in BL cells. Interestingly, we show that treatments with proteasome inhibitors partially restore the capacity of BL cells to present the HPV epitope. This indicates that proteasomes from BL cells, although less efficient in degrading reference substrates than proteasomes from LCLs, are able to destroy the HPV epitope, which can, however, be generated and presented after partial inhibition of the proteasome. These findings suggest the use of proteasome inhibitors, alone or in combination with other drugs, as a strategy for the treatment of EBNA1-carrying tumours., (© 2011 The Authors. Immunology © 2011 Blackwell Publishing Ltd.)

The Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) is regularly expressed in all proliferating virus-infected cells and is therefore an interesting target for immunotherapy. Alleles of the human leucocyte antigen (HLA) -A2 family are dominantly expressed in Caucasians so we sought to identify EBNA1-specific cytotoxic T-lymphocyte (CTL) responses restricted through this allele. We report on the characterization of the LQTHIFAEV (LQT) epitope. LQT-specific memory CTL responses were reactivated in three of 14 healthy EBV seropositive donors (21%) whereas responses to HLA-A2-restricted epitopes, two derived from LMP2 and one from EBNA3A, were detected in 93%, 71% and 42% of the donors, respectively. The LQT-specific CTL clones did not lyse EBV-carrying lymphoblastoid cell lines and Burkitt's lymphoma cell lines nor EBNA1-transfected Burkitt's lymphoma cells but specifically released interferon-gamma upon stimulation with HLA-matched EBNA1-expressing cells and this response was enhanced by deletion of the Gly-Ala repeat domain that inhibits proteasomal degradation. The poor presentation of the endogenously expressed LQT epitope was not affected by inhibition of peptidases that trim antigenic peptides in the cytosol but full presentation was achieved in cells expressing a trojan antigen construct that releases the epitope directly into the endoplasmic reticulum. Hence, inefficient proteasomal processing appears to be mainly responsible for the poor presentation of this epitope.