HLA Class I Binding Promiscuity of the CD8 T-Cell Epitopes of Human Papillomavirus Type 16 E6 Protein

Abstract

One of the critical steps in the progression to cervical cancer appears to be the establishment of persistent human papillomavirus (HPV) infection. We have demonstrated that the lack of cytotoxic T-lymphocyte response to HPV type 16 (HPV 16) E6 protein was associated with persistence and that the potential presence of dominant CD8 T-cell epitopes was most frequently found (n ‫؍‬ 4 of 23) in the E6 16-40 region by examining the pattern of CD8 T-cell epitopes within the E6 protein in women who had cleared their HPV 16 infections. The goal of this study was to define the minimal/optimal amino acid sequences and the HLA restricting molecules of these dominant CD8 T-cell epitopes as well as those of subdominant ones if present. Three dominant epitopes, E6 29-38 (TIHDIILECV; restricted by the HLA-A0201 molecule), E6 29-37 (TIHDIILEC; restricted by B48), and E6 31-38 (HDIILECV; restricted by B4002), and one subdominant epitope, E6 52-61 (FAFRDLCIVY; restricted by B35) were characterized. Taken together with a previously described dominant epitope, E6 52-61 (FAFRDLCIVY; restricted by B57), the CD8 T-cell epitopes demonstrated striking HLA class I binding promiscuity. All of these epitopes were endogenously processed, but the presence of only two of the five epitopes could have been predicted based on the known binding motifs. The HLA class I promiscuity which has been described for human immunodeficiency virus may be more common than previously recognized.Cervical cancer is the second most common cancer among women worldwide (CANCERMondial [http://www-dep.iarc .fr/], 2005). The association between human papillomavirus (HPV) infections, most commonly HPV type 16 (HPV 16), and the development of cervical cancer has been well described (46). However, the exact mechanisms leading from HPV infection to malignancy are not well understood. One of the critical steps in the progression to cervical cancer appears to be the establishment of persistent infection. Epidemiologic evidence suggests that over 90% of women are able to clear their HPV infections, including the oncogenic HPV 16 type. The remaining women whose HPV infections persist are at risk for the development of invasive cancer. The E6 and E7 proteins of high-risk HPV types are expressed early after infection and are known to mediate cell transformation by interacting with products of cellular human tumor suppressor genes. The E6 protein can bind and promote degradation of cell-encoded p53, while the E7 protein interacts with the retinoblastoma susceptibility gene product (7,18,32,36,37,41). In a longitudinal study using multiple chromium release assays, we found that detectable responses to HPV 16 E6 were more common in those women who cleared their HPV 16 infections than in women who had viral persistence. Interestingly, no association was found for E7 (29). Furthermore, we examined the pattern of HPV 16 E6 CD8 T-cell epitopes recognized by women who had evidence of HPV 16 clearance (27). Among 23 women with evidence of HPV 16 clearance, we found evidence of potentia...

Prediction of Promiscuous Epitopes in the E6 Protein of Three High Risk Human Papilloma Viruses: A Computational Approach

“…As an experimental support to our prediction, Nakagawa et al 2004;Nakagawa et al 2007 reported a region from 52 to 61 (FAFKDLCIVY) of HPV 16 E6 protein and Rudolf et al (2001) reported KLPDLCTEL of HPV 18 E6 to be an endogenously processed T-cell epitope. As an extension, we were high risk HPV types.…”

A novel CD4 T-cell epitope described from one of the cervical cancer patients vaccinated with HPV 16 or 18 E7-pulsed dendritic cells

“…Using a method previously developed by our group for characterizing HPV-specific CD8 Tcell epitopes, antigen-specific T-cell clones were isolated and characterized [14,15]. Sufficient cells from the T-cell lines were remaining only for subjects 15-03 and 15-04 to perform this part of the analysis.…”

“…An ELISPOT assay was used to screen for epitope-specific T-cell clones as previously described [15]. Two 15-mer peptide pools (10 µM each peptide) covering the HPV 16 E7 46-70 region and covering the HPV 16 E7 61-85 region, respectively, were used.…”

“…Briefly, the T-cell lines were stimulated with positive peptide pools (10 µM each), and were positively selected with the use of the IFN-γ Secretion Assay Cell Enrichment and Detection Kit (Miltenyi Biontec Inc., Auburn, CA, USA) following manufacturer's instructions. Antigen-specific T-cell clones were isolated using a limiting dilution method as described previously [15].…”

Current Insight into Anti-HPV Immune Responses and Lessons for Prophylactic and Therapeutic Vaccines

“…In addition, E7 7-15 is also able to bind HLA-A2 and -B8 to be recognized by CTL (Oerke et al, 2005;Ressing et al, 1995). From the latter results, two hot spots of CD8+ T-cell epitopes in protein E6 may be located in the regions E6 29-38 and 52-61 and another one in protein E7 (E7 7-15) (Nakagawa et al, 2007). Nevertheless, a poor immunogenicity of E7 protein was observed in many studies during both HPV 16 infection and after peptidic vaccination using long peptides spanning both E6 and E7 Welters et al, 2008) such as those used in our study.…”