Different Methods of Identifying New Antigenic Epitopes of Human Papillomavirus Type 16 E6 and E7 Proteins

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Abstract
Human papillomavirus (HPV) infection is the most common cause of sexually transmitted viral infection and is the main cause of cervical cancer. Identification of HPV T-cell epitopes would be instrumental not only in our understanding of the protective immune response but also in the development of vaccines and immunotherapies. In contrast to viruses which cause systemic infection, identification of HPV epitopes is technically challenging because HPV causes a localized mucosal infection and the frequency of pathogen-specific T lymphocytes in peripheral blood is expected to be low. Here we describe three new antigenic epitopes (E7 7-15 [TLHEYMLDL], E6 52-61 [FAFRDLCIVY], and E7 79-87 [LEDLLMGTL]) of HPV 16 E6 and E7 proteins which have oncogenic activities. E7 7-15 was identified among peptides previously shown to bind to human leukocyte antigen (HLA)-A2.1 molecule, but it was found likely to be restricted by the HLA-B48 molecule. E6 52-61 (likely to be restricted by HLA-B57) and E7 79-87 (likely to be restricted by HLA-B60) were detected, based on the magnitude of the T-cell immune responses, in another individual. In particular, T-cell clones specific for the E6 52-61 epitope were isolated effectively by magnetically selecting them based on gamma interferon secretion. This is an efficient method of identifying new epitopes of antigens for which the number of specific T lymphocytes in the circulation is expected to be small, and it should be widely applicable in identifying new T-cell epitopes.

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