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Title: Molecular mechanisms governing CD4+ T cell recognition of human papilloma virus (HPV) E6 in cervical carcinoma
Author: Lehain, Stephanie
ISNI:       0000 0004 2748 9379
Awarding Body: Cardiff University
Current Institution: Cardiff University
Date of Award: 2009
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Genital human papillomavirus (HPV) infection is common and the majority of infected individuals successfully clear with this virus. But in less than 5% of the cases the infection by high-risk HPV induces cervical cancer, which is preceded by a phase of persistent HPV infection during which the host immune system fails to eliminate the virus. Effective eradication of HPV-positive tumours may require both CD8+ and CD4+ T-cell-mediated immune responses. Specific CD4 T cell responses against the protein E6 of the HPV16 have been described in healthy subjects, but appear absent in patients with cervical cancer. This suggests the importance of specific CD4+ T-cell responses against E6 protein for the clearance of the virus. The aim of this project was to investigate the molecular interactions involved in T cell recognition of the HPV16 E6127-141 (DKKQRFHNIRGRWTG) peptide, in particular, mapping the important amino acids for T cell receptor (TCR) and MHC contact. Initially, this was to be done directly by studying the biophysical interactions between soluble TCR and MHC molecules. Several constructs were made with the pBACgus expression vector in an attempt to generate soluble HLA-DR1/HPV16 E6127-141 complexes. These vectors were used to generate recombinant baculovirus to infect insect cells, but unfortunately no stable MHCipeptide complexes were expressed.. Since the biophysical approach was unsuccessful, the impact of changes in the peptide structure was assessed using functional T cell activation (IFN-gamma secretion). Two separate T-cell clones against HPV16 E6127-141 were tested against truncated versions of the peptide. The results show that the amino acids from the Cterminal end are essential for functional activation of both T-cell lines. Conversely, the amino acids from the N-terminal end do not appear to be as important. These variations in the responses induce by truncated peptides could be due to effects on TCR contact or MHC binding. However, molecular modelling of the HPV16 E6127-141 associated with the MHC complex suggests that the Cterminal end of the peptide contributes to MHC binding.. These two clones were tested against variants of HPV16 E6127-141 from different High risk HPV types (HPV31, 52, 33, 58, 67). Three types of response could be demonstrated. Indeed two peptides (HPV31, 52) have a null effect on the two T-cell clones, two others (HPV33, 58) have a partial agonist effect and one peptide (HPV67), has an antagonist effect on the T-cell clone. Based on these limited results, a model mechanism for viral immune evasion is proposed, whereby co-infection or sequential infection by different high risk HPV types could induce antagonistic effects on T cell responses. This could potentially inhibit effective clearance of a single HPV type, leading to viral persistence and disease.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available