Cervical cancer is the second most common cancer in women worldwide. It is clear that persistent infection of high-risk human papillomaviruses (HR-HPVs) is the main cause for this disease. Among the several HPV types associated with carcinoma, HPV-16 is the most prevalent type and present in about 50% of tumor specimens. The major capsid protein (L1) of HPV can self-assemble into virus-like particles (VLPs) with immunogenicity similar to infectious virions. Neutralizing epitopes are the structural basis of the current prophylactic HPV vaccines. The efficacy of HPV vaccines is critically dependent upon the integrity of type-specific neutralizing epitopes. Recently, considerable headway has been made in studying the epitopes of HPV16 based on neutralizing antibodies. Notably, more and more HPV16 variants have appeared along with increasing immune pressure. To study the phenotypic variations in HPV16 L1 protein, 1 204 naturally occurring sequences were analyzed and a phylogenetic tree was then constructed including four clades. Moreover, after compared the aforementioned sequences with the 114K reference sequence, eight "hot mutation sites" , six "specialized mutation sites" and 20 "epitope-related mutation sites" were found. Generally, sera raised against VLPs can neutralize the corresponding HPV types, but not other types. However, it is not known whether intragenotypic variants of human papillomavirus type 16 (HPV-16) can be neutralized by sera vaccinated with a single variant VLPs. It is, therefore, imperative to understand the neutralizing epitopes and intragenotypic variants of HPV-16 for the production of prophylactic vaccines with high potency and broad coverage.

Human papillomavirus; Major capsid protein; Amino acid substitution; Neutralizing epitope; Variant