Human papillomavirus life cycle: active and latent phases

Productive infection by human papillomaviruses (HPV) is dependent upon the differentiation of the host cell. Following entry into basal epithelial cel ls, HPV genomes are established as autonomous replicating extrachromosomal elements and a low level of HPV expression occurs. Upon differentiation of infected cells, productive replication and expression of capsid genes is in duced resulting in the synthesis of progeny virions. Evidence from immunosu ppressed patients as well as individuals with recurring laryngeal papilloma tosis suggest that certain HPV types can exist in a latent state. In latent ly infected cells, HPV DNA may be present but no differentiation-dependent synthesis of virions occurs. The presence of a latent state for HPVs can be a determining factor in the effectiveness of therapeutic methods for treat ment of infections.