Human papillomavirus vaccines

A wealth of epidemiological and molecular evidence has led to the conclusion that virtually all cases of cervical cancer and its precursor intra-epithelial lesions are a result of infection with one or other of a subset of genital human papillomaviruses (HPVs) suggesting that prevention of infection by prophylactic vaccination would be an effective anti-cancer strategy. The papillomaviruses cannot be grown in large amounts in culture in vitro, but the ability to generate HPV virus like particles (VLPs) by the synthesis and self-assembly in vitro of the major virus capsid protein L1 provides for a potentially effective sub unit vaccine. HPV L1 VLP vaccines are immunogenic and have a good safety profile. Published data from proof of principle trials and preliminary reports from large Phase III efficacy trials suggest strongly that they will protect against persistent HPV infection and cervical intra epithelial neoplasia. However, the duration of protection provided by these vaccines is not known, the antibody responses induced are probably HPV type specific and immunisation should occur pre-exposure to the virus. Second generation vaccines could include an early antigen for protection post-exposure and alternative delivery systems may be needed for the developing world.