Cervical cancer affects nearly half a million women each year, and nearly half of them die of the disease. The greatest problem is in the developing world, though even in the UK around 3000 women develop cervical cancer each year.Infection with certain types of sexually transmitted human papillomavirus (HPV), in particular HPV 16 and HPV 18, is the main cause of cervical cancer. It has been shown that 99.7% of cervical cancers contain HPV DNA.
1HPVs are members of a large family of viruses: the so-called low-risk types (chiefly 6 and 11) are responsible for genital warts, while the high-risk types (mainly 16, 18, 31, 33, 35, 45, 52 and 56) are implicated in cervical cancer. Of these, types 16 and 18 together account for approximately 70-80% of cervical cancers.2 Infection with HPV appears to be extremely common in young people, but is usually transient.3 It appears that the presence of HPV is more meaningful in older women (over 30 years old), who have persistent infection.Screening tests detect cellular abnormalities early, but the ultimate solution to a viral disease is obviously a vaccine. In contrast to most viral vaccines, which are based on an attenuated form of the virus (for example polio vaccine), the development of an attenuated HPV vaccine has been difficult because there is no effective culture system to propagate the virus. An attenuated vaccine could also potentially cause disease in vaccinated subjects, particularly if they were immunocompromised. The solution has therefore been to manufacture virus-like particles (VLPs) using the L1 and/or L2 virus coat proteins. VLPs have the outward appearance of the actual virus and generate a powerful immune response, but as they contain no DNA they are harmless. Another problem is the number of cervical cancer HPV types which need to be included (potentially 15). However, two prophylactic vaccines against types 6, 11, 16 and 18 are showing great promise in clinical trials. 4,5 One of these contains all four HPV types and would thus protect against genital warts (types 6 and 11), as well as the most common cervical cancer HPV types (16 and 18). The other contains types 16 and 18 and thus targets cervical cancer alone. Both vaccines are currently in large, multicentre, worldwide Phase III clinical trials and have shown excellent tolerability, safety and efficacy. So far, the bivalent vaccine appears to be 90-100% effective in preventing both incident and persistent HPV 16 and 18 infection, 4 and similar results have been reported for the quadrivalent vaccine.5 A feature of HPV infection is that the virus is very successful at avoiding the host immune system, and therefore causing natural immunity. Both vaccines, however, probably due to the addition of an adjuvant, result in antibody titres that are enormously (60-100 times) higher and longer lasting (10-16 times higher at 18 months) than those generated by natural infection.4,5 HPV infection and persistence rates are endpoints which are obviously not as robust as cervical cancer rates, but given that there ...