Figure 2.

Human papillomavirus (HPV) use a unique strategy for propagation, limited to stratified flattened epithelial tissue of mucosa and skin. Initially, HPV must infect stem cells or basal cells of the tissue where a phase of latent infection is established in which viral DNA replicate without making virions. In the upper layer, as cells differentiate, vegetative replication of viral DNA coordinates with expression of capsid proteins to make virions that are then freed to search for new host cells. Expression levels of E6 and E7 in basal cells are considered to be quite low. However, as such infections can continue for years and even for decades, cells may acquire high‐level expression of E6 and E7 through mutations and integration of the viral genome. Such cells could become immortal and tumorigenic with further genetic and epigenetic events.