By focusing on a unique target within the shell that surrounds the human papillomavirus (HPV), scientists may be able to develop an affordable vaccine that targets additional strains of this cancer-causing virus. Doug Lowy of the US National Cancer Institute recently discussed the potential benefits of this approach in March at an HPV vaccine symposium in New York.

The two HPV vaccines currently marketed by Merck and GlaxoSmithKline are composed of virus-like particles. When injected into the body, these particles induce the formation of antibodies that target a protein known as L1 that encases the papillomavirus. Although these vaccines effectively neutralize two HPV strains that can cause cervical cancer, these strains only account for approximately 70% of cervical cancers (Br. J. Cancer 95, 1459–1466; 2006; Lancet 367, 1757–1765, 2008). As a result, even vaccinated women must still be screened for signs of cervical cancer.

In an effort to develop vaccines that target a broader range of HPV strains, researchers are looking at targeting another protein known as L2. Although it also helps to form the protein shell surrounding the papillomavirus, L2 is more highly conserved across HPV strains than the L1 protein.

Studies in mice conducted by Richard Roden of Johns Hopkins University and his colleagues have shown that vaccinations containing human HPV L2 proteins protect against more HPV strains than those based on the L1 virus-like particle (Proc. Natl. Acad. Sci. USA 105, 5850–5855; 2008). Because bacteria can be engineered to produce L2 proteins in culture, L2 proteins might also be cheaper to produce than the L1 virus-like particles. However, vaccines based on L2 proteins might perhaps provide shorter protection against HPV compared with those containing L1 virus-like particles. Currently, Roden's team is tweaking and modifying L2 proteins in an attempt to broaden the range of HPV strains they neutralize.