The invisible enemy - how human papillomaviruses avoid recognition and clearance by the host immune system.

Human papillomavirus (HPV) needs to persist in squamous epithelia for a certain amount of time to complete its reproductive cycle. Therefore, the virus has evolved multiple immune evasion strategies. The interplay of these immune evasion mechanisms with the host immune system decides whether a HPV infection is cleared or becomes persistent. Clearance of HPV-induced lesions is mediated by a cellular immune response, consisting of both cytotoxic T lymphocyte and T helper cell responses. Persistent HPV infection, on the other hand, is the single most important risk factor for the development of HPV-associated premalignant lesions and HPV-driven cancers. This article reviews the immune evasion mechanisms employed by high-risk HPVs to escape host immune recognition and attack.