Dependoparvovirus

Dependoparvovirus is a genus of small, non-enveloped viruses in the Parvoviridae family, subfamily Parvovirinae. The best-known members are the adeno-associated viruses (AAVs), which are studied extensively as dependoparvoviruses because they rely on a helper virus to replicate. In most cells, replication occurs only in the presence of a helper, such as adenovirus or herpesvirus; in the absence of a helper, replication is greatly restricted and the virus may persist as an episome or integrate at low frequency.

The genome of dependoparvoviruses is a linear single-stranded DNA molecule about 4.7 kilobases in length. It contains two main coding regions: rep, which encodes replication-associated proteins, and cap, which encodes the structural capsid proteins. The genome is flanked by inverted terminal repeats that act as origins of replication. Production typically requires providing Rep and Cap in trans, often via a helper virus or a helper plasmid system. AAV genomes can integrate into the host genome at a specific site (AAVS1 on human chromosome 19) or remain as latent episomes; integration is not essential for replication and occurs with low frequency.

Virions are small, about 20–26 nanometers in diameter, with a robust icosahedral capsid. Dependoparvoviruses have a broad vertebrate host range and show tissue tropism determined largely by serotype; AAVs can infect non-dividing cells, enabling long-term expression in various tissues. They are generally non-pathogenic in humans.

In research and medicine, dependoparvoviruses, especially AAVs, are widely used as gene therapy vectors. They offer low pathogenicity and the potential for durable transgene expression, though payload capacity is limited to roughly 4.7 kilobases. Vector production often employs helper-based systems to supply required Rep and Cap functions.