Identification of an HLA‐A24‐restricted cytotoxic T lymphocyte epitope from human papillomavirus type‐16 E6: The combined effects of bortezomib and interferon‐γ on the presentation of a cryptic epitope

<jats:title>Abstract</jats:title><jats:p>About 50% of cervical cancers are associated with human papillomavirus type 16 (HPV‐16), and since the HPV‐16 E6 and E7 oncoproteins are constitutively expressed in the tumor cells, they are attractive targets for cytotoxic T lymphocyte (CTL)‐mediated immunotherapy. Nevertheless, only a limited number of HPV‐16 E6 epitopes have been identified to date. Using reverse immunological methods, we have generated a CTL clone against the HPV‐16 E6<jats:sub>49–57</jats:sub> epitope restricted by HLA‐A*2402, which is the most common allele in Japan and relatively frequent worldwide, capable of lysing 293T cells transduced with HLA‐A*2402 and HPV‐16 E6. Although it was unable to recognize the SiHa cervical cancer cell line positive for HPV‐16 and HLA‐A*2402, the cells became susceptible to lysis when transduced with E6‐E7 genes, which was unexpectedly offset by pretreatment with interferon (IFN)‐γ alone. Interestingly, however, combined pretreatment with a proteasome inhibitor, bortezomib and IFN‐γ fully restored CTL‐mediated lysis of the original SiHa cells. Furthermore, such intervention of 2 of 4 other cervical cancer cell lines expressing HPV‐16 E6 and HLA‐A*2402 was found to induce IFN‐γ production by specific CTLs. Tetramer analysis further revealed that induction of E6<jats:sub>49–57</jats:sub>‐specific T cells was possible in 5 of 7 patients with HPV‐16‐positive high grade cervical intraepithelial neoplasia or cervical cancer by <jats:italic>in vitro</jats:italic> stimulation with E6<jats:sub>49–57</jats:sub> peptide. Thus, these findings together indicate that E6<jats:sub>49–57</jats:sub> is a candidate epitope for immunotherapy and immunological monitoring of such patients. © 2006 Wiley‐Liss, Inc.</jats:p>