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Herpesviruses are virus helpers for adeno-associated virus (AAV)

Discussion in 'Other Health News and Research' started by pattismith, Nov 13, 2017.

  1. pattismith

    pattismith Senior Member

    I was reading Dr Lerner's paper about abortive infection in Herpesviruses (suggested by @Hip , thank you), and another idea hit me on the road...

    2017 Jan 31 Copyright © 2017 American Society for Microbiology.
    High Prevalence of Infectious Adeno-associated Virus (AAV) in Human Peripheral Blood Mononuclear Cells Indicative of T Lymphocytes as Sites of AAV Persistence.

    Seroepidemiology shows that infections with adeno-associated virus (AAV) are widespread, but diverse AAV serotypes isolated from humans or nonhuman primates have so far not been proven to be causes of human disease. In view of the increasing success of AAV-derived vectors in human gene therapy, definition of the in vivo sites of wild-type AAV persistence and the clinical consequences of its reactivation is becoming increasingly urgent. Here, we identify the presumed cell type for AAV persistence in the human host by highly sensitive AAV PCRs developed for the full spectrum of human AAV serotypes.
    In genomic-DNA samples from leukocytes of 243 healthy blood donors, 34% were found to be AAV positive, predominantly AAV type 2 (AAV2) (77%), AAV5 (19%), and additional serotypes.
    Roughly 11% of the blood donors had mixed AAV infections.
    AAV prevalence was dramatically increased in immunosuppressed patients, 76% of whom were AAV positive. Of these, at least 45% displayed mixed infections.
    Follow-up of single blood donors over 2 years allowed repeated detection of the initial and/or additional AAV serotypes, suggestive of fluctuating, persistent infection.
    Leukocyte separation revealed that AAV resided in CD3+ T lymphocytes, perceived as the putative in vivo site of AAV persistence.
    Moreover, infectious AAVs of various serotypes could be rescued and propagated from numerous samples. The high prevalence and broad spectrum of human AAVs in leukocytes closely follow AAV seroepidemiology. Immunosuppression obviously enhances AAV replication in parallel with activation of human cytomegalovirus (HCMV) and human herpesvirus 6 (HHV-6), reminiscent of herpesvirus-induced AAV activation.

    Adeno-associated virus is viewed as apathogenic and replication defective, requiring coinfection with adenovirus or herpesvirus for productive infection. In vivo persistence of a defective virus requires latency in specialized cell types to escape the host immune response until viral spread becomes possible. Reactivation from latency can be induced by diverse stimuli, including infections, typically induced upon host immunosuppression. We show for the first time that infectious AAV is highly prevalent in human leukocytes, specifically T lymphocytes, and that AAV is strongly amplified upon immunosuppression, along with reactivation of latent human herpesviruses. In the absence of an animal model to study the AAV life cycle, our findings in the human host will advance the understanding of AAV latency, reactivation, and in vivo pathogenesis.

    In his 2012 paper,
    Dr Lerner explains that:

    A small group of six patients in the group-A EBV subset of CFS, additionally, had repetitive elevated-serum titers of antibody to the early lytic replication-encoded proteins, EBV dUTPase, and EBV DNA polymerase. The presence of these serum antibodies to EBV dUTPase and EBV DNA polymerase indicated EBV abortive lytic replication in these 6 CFS patients.

    My question would be:
    Would it be possible that these antibodies may sign co-infection between the herpesvirus and AAV?

    This other publication about Herpesviruses and virus-helper activities suggested me that a link may exist:

    Definition of herpes simplex virus type 1 helper activities for adeno-associated virus early replication events.
    "We demonstrated that the HSV-1 DNA polymerase complex (UL30/UL42) was critical to enhance AAV DNA replication to a significant level in transfected cells and that its catalytic activity was involved in this process."

    Last edited: Nov 13, 2017
    Omar88 and anni66 like this.
  2. pattismith

    pattismith Senior Member

    According to wiki, these virus are non pathogen, and are used in gene therapy. Here an extract:

    Serotypes, receptors and native tropism
    Until the 1990s, virtually all AAV biology was studied using AAV serotype 2. However, AAV is highly prevalent in humans and other primates and several serotypes have been isolated from various tissue samples.
    Serotypes 2, 3, 5, and 6 were discovered in human cells,
    AAV serotypes 1, 4, and 7–11 in nonhuman primate samples.[46]
    As of 2006 there have been 11 AAV serotypes described, the 11th in 2004.[47] AAV capsid proteins contain 12 hypervariable surface regions, with most variability occurring in the threefold proximal peaks, but the parvovirus genome in general presents highly conserved replication and structural genes across serotypes.[46]
    All of the known serotypes can infect cells from multiple diverse tissue types. Tissue specificity is determined by the capsid serotype and pseudotyping of AAV vectors to alter their tropism range will likely be important to their use in therapy.

    Serotype 2
    Serotype 2 (AAV2) has been the most extensively examined so far.[48][49][50][51][52][53]
    AAV2 presents natural tropism towards skeletal muscles,[54] neurons,[48] vascular smooth muscle cells[55] and hepatocytes.[56]


    Serotype 2 and cancer
    Studies have shown that serotype 2 of the virus (AAV-2) apparently kills cancer cells without harming healthy ones.
    "Our results suggest that adeno-associated virus type 2, which infects the majority of the population but has no known ill effects, kills multiple types of cancer cells yet has no effect on healthy cells," said Craig Meyers,[62] a professor of immunology and microbiology at the Penn State College of Medicine in Pennsylvania in 2005.[63] This could lead to a new anti-cancer agent.

    Other serotypes
    Although AAV2 is the most popular serotype in various AAV-based research, it has been shown that other serotypes can be more effective as gene delivery vectors.
    For instance AAV6 appears much better in infecting airway epithelial cells,[64][65]
    AAV7 presents very high transduction rate of murine skeletal muscle cells (similarly to AAV1 and AAV5),
    AAV8 is superb in transducing hepatocytes[66][67][68]
    and AAV1 and 5 were shown to be very efficient in gene delivery to vascular endothelial cells.[69]
    In the brain, most AAV serotypes show neuronal tropism, while AAV5 also transduces astrocytes.[70]
    AAV6, a hybrid of AAV1 and AAV2,[68] also shows lower immunogenicity than AAV2.[67]

    Serotypes can differ with the respect to the receptors they are bound to. For example, AAV4 and AAV5 transduction can be inhibited by soluble sialic acids (of different form for each of these serotypes),[71] and AAV5 was shown to enter cells via the platelet-derived growth factor receptor.[72]

    AAV is of particular interest to gene therapists due to its apparent limited capacity to induce immune responses in humans, a factor which should positively influence vector transduction efficiency while reducing the risk of any immune-associated pathology.

    AAV is not considered to have any known role in disease.[73][74]

    The innate immune response to the AAV vectors has been characterised in animal models. Intravenous administration in mice causes transient production of pro-inflammatory cytokines and some infiltration of neutrophils and other leukocytes into the liver, which seems to sequester a large percentage of the injected viral particles. Both soluble factor levels and cell infiltration appear to return to baseline within six hours. By contrast, more aggressive viruses produce innate responses lasting 24 hours or longer.[75]

    The virus is known to instigate robust humoral immunity in animal models and in the human population, where up to 80% of individuals are thought to be seropositive for AAV2. Antibodies are known to be neutralising, and for gene therapy applications these do impact on vector transduction efficiency via some routes of administration. As well as persistent AAV specific antibody levels, it appears from both prime-boost studies in animals and from clinical trials that the B-cell memory is also strong.[76] In seropositive humans, circulating IgG antibodies for AAV2 appear to be primarily composed of the IgG1 and IgG2 subclasses, with little or no IgG3 or IgG4 present.[77]

    The cell-mediated response to the virus and to vectors is poorly characterised, and has been largely ignored in the literature as recently as 2005.[76] Clinical trials using an AAV2-based vector to treat haemophilia B seem to indicate that targeted destruction of transduced cells may be occurring.[78] Combined with data that shows that CD8+ T-cells can recognise elements of the AAV capsid in vitro,[79] it appears that there may be a cytotoxic T lymphocyte response to AAV vectors. Cytotoxic responses would imply the involvement of CD4+ T helper cells in the response to AAV and in vitro data from human studies suggests that the virus may indeed induce such responses, including both Th1 and Th2 memory responses.[77] A number of candidate T cell stimulating epitopes have been identified within the AAV capsid protein VP1, which may be attractive targets for modification of the capsid if the virus is to be used as a vector for gene therapy.[77][78]

    Infection cycle
    (see in wiki for details)

    The characteristic feature of the adeno-associated virus is a deficiency in replication and thus its inability to multiply in unaffected cells.
    The first factor that was described as providing successful generation of new AAV particles, was the adenovirus, from which the AAV name originated. It was then shown that AAV replication can be facilitated by selected proteins derived from the adenovirus genome,[81][82] by other viruses such as HSV,[83] or by genotoxic agents, such as UV irradiation or hydroxyurea.[84][85][86]

    ...... In the absence of helper virus or genotoxic factors, AAV DNA can either integrate into the host genome or persist in episomal form. In the former case integration is mediated by Rep78 and Rep68 proteins and requires the presence of ITRs flanking the region being integrated. In mice, the AAV genome has been observed persisting for long periods of time in quiescent tissues, such as skeletal muscles, in episomal form (a circular head-to-tail conformation)
  3. pattismith

    pattismith Senior Member

    My first question would be:

    as herpesviruses seems more prevalent and subject to reactivation in long term CFS patients, we would expect more replication of the AAV in our tissues.

    Are ME patients protected against some cancer if compared to control?

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