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Viruses Jun 2020The adeno-associated virus (AAV) is a small, nonpathogenic parvovirus, which depends on helper factors to replicate. Those helper factors can be provided by coinfecting... (Review)
Review
The adeno-associated virus (AAV) is a small, nonpathogenic parvovirus, which depends on helper factors to replicate. Those helper factors can be provided by coinfecting helper viruses such as adenoviruses, herpesviruses, or papillomaviruses. We review the basic biology of AAV and its most-studied helper viruses, adenovirus type 5 (AdV5) and herpes simplex virus type 1 (HSV-1). We further outline the direct and indirect interactions of AAV with those and additional helper viruses.
Topics: Adenoviridae; Coinfection; Dependovirus; Helper Viruses; Herpesvirus 1, Human; Humans; Parvoviridae Infections; Viral Proteins; Virus Replication
PubMed: 32575422
DOI: 10.3390/v12060662 -
Viruses Jun 2021Hepatitis delta virus (HDV) is a defective human virus that lacks the ability to produce its own envelope proteins and is thus dependent on the presence of a helper... (Review)
Review
Hepatitis delta virus (HDV) is a defective human virus that lacks the ability to produce its own envelope proteins and is thus dependent on the presence of a helper virus, which provides its surface proteins to produce infectious particles. Hepatitis B virus (HBV) was so far thought to be the only helper virus described to be associated with HDV. However, recent studies showed that divergent HDV-like viruses could be detected in fishes, birds, amphibians, and invertebrates, without evidence of any HBV-like agent supporting infection. Another recent study demonstrated that HDV can be transmitted and propagated in experimental infections ex vivo and in vivo by different enveloped viruses unrelated to HBV, including hepatitis C virus (HCV) and flaviviruses such as Dengue and West Nile virus. All this new evidence, in addition to the identification of novel virus species within a large range of hosts in absence of HBV, suggests that deltaviruses may take advantage of a large spectrum of helper viruses and raises questions about HDV origins and evolution.
Topics: Animals; Evolution, Molecular; Genome, Viral; Helper Viruses; Hepatitis D; Hepatitis Delta Virus; Host Specificity; Humans; Phylogeny; Viral Proteins; Virus Replication
PubMed: 34201626
DOI: 10.3390/v13071207 -
Proceedings of the National Academy of... Sep 1993The generation of high-titer, helper-free retroviruses by transient transfection has been achieved by using the highly transfectable 293T cell line into which are stably...
The generation of high-titer, helper-free retroviruses by transient transfection has been achieved by using the highly transfectable 293T cell line into which are stably introduced constructs that express retroviral packaging functions. The resulting ecotropic virus packaging cell line BOSC 23 produces infectious retrovirus at > 10(6) infectious units/ml of supernatant within 72 hr after CaPO4-mediated transfection. A stringent assay for replication-competent virus showed that no helper virus was present. The system can produce high titers of retroviral vectors expressing genes that are extremely difficult to propagate at high titer in stable producer lines. This method should facilitate and extend the use of helper-free retroviral gene transfer, as well as be useful for gene therapy.
Topics: 3T3 Cells; Animals; Bone Marrow Transplantation; Cell Line; Cell Transformation, Neoplastic; Chloroquine; Female; Genes, abl; Helper Viruses; Humans; Male; Mice; Mice, Inbred C57BL; Plasminogen Activators; RNA-Directed DNA Polymerase; Repetitive Sequences, Nucleic Acid; Retroviridae; Transfection; Virus Replication; beta-Galactosidase
PubMed: 7690960
DOI: 10.1073/pnas.90.18.8392 -
Journal of Virology Mar 1998Recently, efficient and long-term in vivo gene transfer by recombinant adeno-associated virus type 2 (rAAV) vectors has been demonstrated in a variety of tissues....
Recently, efficient and long-term in vivo gene transfer by recombinant adeno-associated virus type 2 (rAAV) vectors has been demonstrated in a variety of tissues. Further improvement in vector titer and purity will expedite this in vivo exploration and provide preclinical information required for use in human gene therapy. In an effort to obtain higher titers, we constructed a novel AAV helper plasmid which utilizes translational control of AAV Rep genes (J. Li et al., J. Virol. 71:5236-5243, 1997). To address the issue of purity, in this study we report the first rAAV production method which is completely free of adenovirus (Ad) helper virus. The new production system uses a plasmid construct which contains a mini-Ad genome capable of propagating rAAV in the presence of AAV Rep and Cap genes. This construct is missing some of the early and most of the late Ad genes and is incapable of producing infectious Ad. Transfection of 293 cells with the new mini-Ad helper and AAV packaging plasmids results in high-titer rAAV vectors with yields greater than 1,000 transducing units, or 10(5) viral particles per cell. When rAAV vectors were produced by using this production scheme and compared to traditional heat-inactivated rAAV preparations in vitro and in vivo, we observed transduction equivalent to or better than normal levels. The complete removal of infectious Ad from AAV production should facilitate a better understanding of immune response to AAV vectors in vivo, eliminate the need for developing replication-competent Ad assays, and provide a more defined reagent for clinical use.
Topics: Adenoviridae; Cell Line, Transformed; Cell Transformation, Viral; Dependovirus; Genetic Vectors; Helper Viruses; Humans; Plasmids; Recombination, Genetic
PubMed: 9499080
DOI: 10.1128/JVI.72.3.2224-2232.1998 -
Virology Dec 2012Molecular piracy is a biological phenomenon in which one replicon (the pirate) uses the structural proteins encoded by another replicon (the helper) to package its own... (Review)
Review
Molecular piracy is a biological phenomenon in which one replicon (the pirate) uses the structural proteins encoded by another replicon (the helper) to package its own genome and thus allow its propagation and spread. Such piracy is dependent on a complex web of interactions between the helper and the pirate that occur at several levels, from transcriptional control to macromolecular assembly. The best characterized examples of molecular piracy are from the E. coli P2/P4 system and the S. aureus SaPI pathogenicity island/helper system. In both of these cases, the pirate element is mobilized and packaged into phage-like transducing particles assembled from proteins supplied by a helper phage that belongs to the Caudovirales order of viruses (tailed, dsDNA bacteriophages). In this review we will summarize and compare the processes that are involved in molecular piracy in these two systems.
Topics: Caudovirales; Escherichia coli; Helper Viruses; Staphylococcus aureus; Virus Assembly; Virus Replication
PubMed: 23131350
DOI: 10.1016/j.virol.2012.10.028 -
BMB Reports Nov 2020Gene therapy is emerging as a treatment option for inherited genetic diseases. The success of this treatment approach greatly depends upon gene delivery vectors.... (Review)
Review
Gene therapy is emerging as a treatment option for inherited genetic diseases. The success of this treatment approach greatly depends upon gene delivery vectors. Researchers have attempted to harness the potential of viral vectors for gene therapy applications over many decades. Among the viral vectors available, gutless adenovirus (GLAd) has been recognized as one of the most promising vectors for in vivo gene delivery. GLAd is constructed by deleting all the viral genes from an adenovirus. Owing to this structural feature, the production of GLAd requires a helper that supplies viral proteins in trans. Conventionally, the helper is an adenovirus. Although the helper adenovirus efficiently provides helper functions, it remains as an unavoidable contaminant and also generates replicationcompetent adenovirus (RCA) during the production of GLAd. These two undesirable contaminants have raised safety concerns and hindered the clinical applications of GLAd. Recently, we developed helper virus-free gutless adenovirus (HF-GLAd), a new version of GLAd, which is produced by a helper plasmid instead of a helper adenovirus. Utilization of this helper plasmid eliminated the helper adenovirus and RCA contamination in the production of GLAd. HF-GLAd, devoid of helper adenovirus and RCA contaminants, will facilitate its clinical applications. In this review, we discuss the characteristics of adenoviruses, the evolution and production of adenoviral vectors, and the unique features of HF-GLAd as a new platform for gene therapy. Furthermore, we highlight the potential applications of HF-GLAd as a gene delivery vector for the treatment of various inherited genetic diseases. [BMB Reports 2020; 53(11): 565-575].
Topics: Adenoviridae; Cell Line; Gene Transfer Techniques; Genetic Therapy; Genetic Vectors; Helper Viruses; Humans; Integrases; Plasmids; Viral Proteins
PubMed: 32958121
DOI: 10.5483/BMBRep.2020.53.11.185 -
Nature May 2023As of August 2022, clusters of acute severe hepatitis of unknown aetiology in children have been reported from 35 countries, including the USA. Previous studies have...
As of August 2022, clusters of acute severe hepatitis of unknown aetiology in children have been reported from 35 countries, including the USA. Previous studies have found human adenoviruses (HAdVs) in the blood from patients in Europe and the USA, although it is unclear whether this virus is causative. Here we used PCR testing, viral enrichment-based sequencing and agnostic metagenomic sequencing to analyse samples from 16 HAdV-positive cases from 1 October 2021 to 22 May 2022, in parallel with 113 controls. In blood from 14 cases, adeno-associated virus type 2 (AAV2) sequences were detected in 93% (13 of 14), compared to 4 (3.5%) of 113 controls (P < 0.001) and to 0 of 30 patients with hepatitis of defined aetiology (P < 0.001). In controls, HAdV type 41 was detected in blood from 9 (39.1%) of the 23 patients with acute gastroenteritis (without hepatitis), including 8 of 9 patients with positive stool HAdV testing, but co-infection with AAV2 was observed in only 3 (13.0%) of these 23 patients versus 93% of cases (P < 0.001). Co-infections by Epstein-Barr virus, human herpesvirus 6 and/or enterovirus A71 were also detected in 12 (85.7%) of 14 cases, with higher herpesvirus detection in cases versus controls (P < 0.001). Our findings suggest that the severity of the disease is related to co-infections involving AAV2 and one or more helper viruses.
Topics: Child; Humans; Acute Disease; Adenovirus Infections, Human; Coinfection; Dependovirus; Epstein-Barr Virus Infections; Hepatitis; Herpesvirus 4, Human; Herpesvirus 6, Human; Enterovirus A, Human; Helper Viruses
PubMed: 36996871
DOI: 10.1038/s41586-023-05949-1 -
ACS Synthetic Biology Oct 2022Recombinant adeno-associated viruses (rAAV) are important gene delivery vehicles for gene therapy applications. Their production relies on plasmid transfection or virus...
Recombinant adeno-associated viruses (rAAV) are important gene delivery vehicles for gene therapy applications. Their production relies on plasmid transfection or virus infection of producer cells, which pose a challenge in process scale-up. Here, we describe a template for a transfection-free, helper virus-free rAAV producer cell line using a synthetic biology approach. Three modules were integrated into HEK293 cells including an rAAV genome and multiple inducible promoters controlling the expression of AAV Rep, Cap, and helper coding sequences. The synthetic cell line generated infectious rAAV vectors upon induction. Independent control over replication and packaging activities allowed for manipulation of the fraction of capsid particles containing viral genomes, affirming the feasibility of tuning gene expression profiles in a synthetic cell line for enhancing the quality of the viral vector produced. The synthetic biology approach for rAAV production presented in this study can be exploited for scalable biomanufacturing.
Topics: Humans; Dependovirus; Synthetic Biology; HEK293 Cells; Genetic Vectors; Helper Viruses
PubMed: 36219557
DOI: 10.1021/acssynbio.2c00207 -
Human Gene Therapy Nov 1998Retroviral vectors based on human foamy virus (HFV) have been developed and show promise as gene therapy vehicles. Here we describe a method for the production of HFV...
Retroviral vectors based on human foamy virus (HFV) have been developed and show promise as gene therapy vehicles. Here we describe a method for the production of HFV vector stocks free of detectable helper virus. The helper and vector plasmid constructs used both lack the HFV bel genes, so recombination between these constructs cannot create a wild-type virus. A fusion promoter that combines portions of the cytomegalovirus (CMV) immediate-early and HFV long terminal repeat (LTR) promoters was used to drive expression of both the helper and vector constructs. The CMV-LTR fusion promoter allows for HFV vector production in the absence of the Bel-1 trans-activator protein, which would otherwise be necessary for efficient transcription from the HFV LTR. Vector stocks containing either neomycin phosphotransferase or alkaline phosphatase reporter genes were produced by transient transfection at titers greater than 10(5) transducing units/ml. G418-resistant BHK-21 cells obtained by transduction with neo vectors contained randomly integrated HFV vector proviruses without detectable deletions or rearrangements. The vector stocks generated were free of replication-competent retrovirus (RCR), as determined by assays for LTR trans-activation and a marker rescue assay developed here for the detection of Bel-independent RCR.
Topics: Base Sequence; DNA Primers; Genetic Vectors; Helper Viruses; Humans; Spumavirus; Virus Replication
PubMed: 9853518
DOI: 10.1089/hum.1998.9.17-2517 -
Molecular Therapy : the Journal of the... Jun 2003We present a simple and safe strategy for producing high-titer adeno-associated virus (AAV) vectors derived from six different AAV serotypes (AAV-1 to AAV-6). The...
We present a simple and safe strategy for producing high-titer adeno-associated virus (AAV) vectors derived from six different AAV serotypes (AAV-1 to AAV-6). The method, referred to as "HOT," is helper virus free, optically controllable, and based on transfection of only two plasmids, i.e., an AAV vector construct and one of six novel AAV helper plasmids. The latter were engineered to carry AAV serotype rep and cap genes together with adenoviral helper functions, as well as unique fluorescent protein expression cassettes, allowing confirmation of successful transfection and identification of the transfected plasmid. Cross-packaging of vector DNA derived from AAV-2, -3, or -6 was up to 10-fold more efficient using our novel plasmids, compared to a conservative adenovirus-dependent method. We also identified a variety of useful antibodies, allowing detection of Rep or VP proteins, or assembled capsids, of all six AAV serotypes. Finally, we describe unique cell tropisms and kinetics of transgene expression for AAV serotype vectors in primary or transformed cells from four different species. In sum, the HOT strategy and the antibodies presented here, together with the reported findings, should facilitate and support the further development of AAV serotype vectors as powerful new tools for human gene therapy.
Topics: Cell Line; DNA Replication; DNA-Binding Proteins; Dependovirus; Genetic Vectors; Helper Viruses; Humans; Plasmids; Serotyping; Viral Proteins; Virus Assembly; Virus Replication
PubMed: 12788658
DOI: 10.1016/s1525-0016(03)00095-9