Adeno-Associated Viruses (1-5)

From Stewart McNulty at Veterinary Sciences,
Queen's University, Belfast.

Are these viruses good for you?  Maybe, but don't "dependo" on it!


    The five serotypes of the human "adeno-associated viruses" (AAV), belong to the genus Dependovirus.  They earned the name "Dependovirus" because they were believed to "depend" on coinfection with an unrelated helper virus, such as adenovirus or herpesvirus, in order to replicate.  Although it has been demonstrated that these viruses are not exclusively dependent on a helper virus and are capable of autonomously replicating in the cell, they are still often referred to as Dependoviruses.


    Adeno-associated virus infection is very common throughout the world.  More than 90% of adults are seropositive. Most human transmission of AAV appears to be horizontal.


     There is no evidence that associates AAV with disease in any of its hosts, and it has no known tumor inducing function.  In the absence of a helper, a tandemly repeated double stranded form of the AAV genome becomes integrated into the cellular genome of its host.  The virus persists in this latent form indefinitely until a subsequent adenovirus infection reactivates AAV replication.  The question of the consequences to the host of latent AAV infection remains unanswered, but the possibility that AAV infection may actually be beneficial has been considered in terms of its possible ability to inhibit oncogenesis of Adenovirus and Herpesvirus.

Virus Properties and Vector Potential

    The genetic map of AAV is similar to that of autonomous parvoviruses. Although long regarded as being unable to replicate without a helper virus, it is now apparent that autonomous replication of AAV is possible when cells containing AAV are treated with any of several chemical agents that either synchronize cell division or otherwise produce favorable growth conditions for the virus. Due to a number of genetic properties, AAV has been given a significant amount of attention as a possible vector for gene therapy.  These properties include the ability to integrate and establish a latent state with high frequency, the lack of any associated known disease, and the fact that vectors can be created with the use of few viral genes that will express protein products on the surface of the transformed cell.   In fact, such vectors have been made and have shown promising results.

Inhibition of Oncogeneity

    Could AAV infection be beneficial to its host?  This question addresses a fundamental dogma of virology, that basically claims that no viral infection can be beneficial.  Certain reports have shown that AAV reduces the frequency of tumors and lengthens the induction times of occurring tumors, in newborn hamsters.  It has also been reported to inhibit oncogenicity of HSV-II transformed cells after infection, which brings up the question of whether AAV coinfection can benefit humans as well. In a retrospective epidemiological study on patients with cervical carcinoma, the patients were significantly deficient in antibodies to AAV compared to a group of matched control. So who knows, maybe AAV infection is good for the host!

see reference #14 and #15

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