HPV biology
HPV are a group of small, double-stranded DNA viruses that infect the
epithelial cells of the skin and mucous membranes in humans and animals.
They are named after the warts (papillomas) that can form as a result of
infection. HPV infections are extremely common, with over 200 different
types of HPV identified to date.12,39
HPV has a non-enveloped icosahedral capsid composed of proteins called
capsomeres. The viral genome is a circular, double-stranded DNA
molecule.12,39,40 The viral life cycle begins when the
virus enters the host cell through a microtrauma or breach in the
epithelial barrier. The virus attaches to the host cell surface
receptors and enters the cell by endocytosis. Once inside, the viral
genome is released into the host cell’s
nucleus.10,12,40
HPV replicate their DNA in synchrony with the host cell’s DNA
replication. The viral genome is replicated by the host cell machinery,
using viral proteins. Viral DNA replication is tightly regulated to
ensure that viral gene expression occurs at specific stages of the host
cell cycle.7,12,39,40 HPV has a limited coding
capacity and relies on the host cell’s machinery for gene expression.
They produce two types of genes: early genes and late genes. Early genes
are expressed during the initial phase of infection and are involved in
regulating viral replication and modulating host cell functions. Late
genes are expressed later in the infection cycle and encode structural
proteins that form the viral capsid.39,40
Most HPV infections are cleared by the immune system without causing any
symptoms. However, certain high-risk HPV types can establish persistent
infections, which can lead to the development of various types of
cancer, including cervical, anal, penile, vaginal, and oropharyngeal
cancers. The expression of viral oncoproteins, such as E6 and E7, plays
a crucial role in the transformation of infected cells and the
development of cancer.7,12,39,40