Spontaneous T cell responses to Epstein‐Barr virus‐encoded BARF1 protein and derived peptides in patients with nasopharyngeal carcinoma: Bases for improved immunotherapy

Abstract

Immunotherapy approaches targeting Epstein‐Barr virus (EBV)‐encoded antigens induce objective clinical responses only in a fraction of patients with undifferentiated nasopharyngeal carcinoma (UNPC). In the present study, we have characterized the immunogenicity of the EBV‐encoded BARF1 oncogene with the aim to assess whether this protein could constitute a new target antigen for immunotherapy in this setting. Spontaneous CD4+ and CD8+ T cell responses specific for the recombinant p29 BARF1 protein were detected by IFNγ‐ELISPOT in both EBV‐seropositive donors and UNPC patients, but not in EBV‐seronegative individuals. Using immunoinformatic prediction tools, we have selected 5 different candidate BARF1 T cell epitopes presented by HLA‐A*0201. Although only one of these peptides was able to bind HLA‐A2 with low affinity in the T2 stabilization assay, all 5 BARF1 nonamers readily elicited specific CD8+ T cell responses in EBV‐seropositive HLA‐A*0201+ donors and UNPC patients. Notably, the magnitude of CD8+ T cell responses to the whole BARF1 protein and derived A*0201 peptides was significantly higher in UNPC patients than in healthy donors. Moreover, cytotoxic T lymphocytes specific for the p2–10, p23–31, or p49–57 BARF1 peptides were easily obtained from HLA‐A*0201+ donors. These cultures were not only able to lyse autologous targets loaded with the antigenic peptide, but also recognized tumor cells endogenously expressing BARF1 in an antigen‐specific and HLA‐A2‐restricted manner. These findings, indicate that BARF1 is a particularly attractive antigen with immunogenic properties in most UNPC patients and provide valuable information to develop new strategies to improve the efficacy of EBV‐targeting immunotherapy of UNPC patients.