Although the addition of types is being tested (see nine-valent vaccines), a pan-HPV selleck chemical vaccine that could be easily and cheaply produced (one antigen instead of nine or more) would limit the need for further cervical cancer screening interventions. Indeed, these have to remain in place with the current vaccine strategy as a significant fraction (approximately 30%) is caused by high-risk HPV types, which are not covered in the current formulation [64]. This double-barrel strategy becomes a heavy burden on public health spending and is difficult to implement in low-income countries. Human papillomaviruses are

small non-enveloped DNA viruses of which the capsid contains mainly the L1 protein but also smaller amounts of L2. The L1 is abundantly GPCR Compound Library present in a multivalent format in which the epitopes are present as a dense, highly repetitive array, which inhibitors strongly stimulates B cells [18]. In contrast, in the natural infection the L2 protein is barely visible for the immune system. However, the L2 protein becomes more exposed after the virus binds to the basement membrane due to conformational changes. This short and transient exposure however fails to elicit any anti-L2 neutralizing antibody response. This could partly explain the conservation of the L2 epitope. Indeed, a small proportion of the L2 protein, especially between amino acid 20 and 38, is highly

preserved between various high-risk HPV types [64]. In addition, different antibodies against

this region show neutralizing activity against a wide range of papillomaviruses. from The main problem up to now with L2-based vaccines is poor immunogenicity, as the titers of neutralizing antibodies are much lower [64]. Recently, more success has been obtained in mice by the use of bacteriophage VLPs [65] and orally administered Lactobacillus casei expressing L2 on their surface [66]. The latter induced a significant vaginal mucosal immunity with production of broadly protective IgA, which could be effective in early phases of the viral infection, suggesting that this type of oral immunisation may be a promising strategy for prophylactic vaccination of humans. In addition to the use of bacteriophages, combinations of (cocktails of) adjuvantia, multimerisation and epitope display techniques have been tested leading to antibody responses which were only slightly lower than the responses elicited by L1. Potentially due to the physiological role of L2 in the viral entry and intracellular trafficking it has been shown that L2 vaccination can be therapeutic against papillomas, even without eliciting a neutralizing antibody response [67]. In the latter case, a heavy T cell infiltrate mounted a cellular response, killing infected cells and inducing rapid clearance of virus and lesion. The L2 vaccines are therefore promising for the future but further clinical testing in human patients needs to be done before further conclusions can be drawn.