Papillomavirus virus like particle-based therapeutic vaccine against human papillomavirus infection related diseases: immunological problems and future directions

Chronic infection with certain types of human papillomaviruses (HPV), especially HPV-16 and HPV-18, leads to the development of cervical cancer. Prophylactic HPV vaccines based on HPV virus like particles (VLPs) have now been developed. The commercial vaccines, Gardasil and Cervarix are clinically effective in preventing HPV infection but do not have a therapeutic effect against existing chronic HPV infections. However, papillomavirus (PV) VLPs elicit strong cytotoxic T cell (CTL) responses and PV VLPs without any adjuvant have therapeutic effects in animal PV infection model. Alum in Gardasil, Alum and 3-O-deacylated-4′-monophosphoryl lipid A (ASO4) in Cervarix may stimulate IL10 production and inhibit the Th1, CTL immune response of immunized individuals. PV VLPs also stimulate the production of IL10 by CD4⁺ T cells, which prevent their CTL generation effect as a therapeutic vaccine. Neutralizing IL10 at the time of PV VLPs immunization increases cytotoxic T cell responses. PV VLPs incorporating PV early protein E2, 6 and 7, together with immune stimulator that promote strong type 1 responses, and at the same time blocking the effect of IL10 may have therapeutic effect against HPV infection related diseases and are worth further basic and clinical investigation.