title: Vector and helper genome rearrangements occur during production of helper-dependent adenoviral vectors.
abstract: Helper-dependent adenoviral vectors (HD Ad) hold extreme promise for gene therapy of human diseases. All viral genes are deleted in HD Ad vectors, and therefore, the presence of a helper virus is required for their production. Current methods to minimize helper contamination in large-scale preparations rely on the use of the Cre/loxP system. The inclusion of loxP sites flanking the packaging signal results in its excision in the presence of Cre recombinase, preventing helper genome encapsidation. It is well established that the level of Cre recombinase activity is important in determining the degree of helper contamination. However, there is little information on other mechanisms that could also play an important role. We have generated several HD Ad vectors containing a rapalog-inducible system to regulate transgene expression, or LacZ under the control of the elongation factor 1 α promoter. Large-scale production of these vectors resulted in abundant helper contamination. Viral DNA analysis revealed the presence of rearrangements between vector and helper genomes. The rearrangements involved a helper DNA molecule with a fragment of the left arm of the HD Ad vector, including its ITR, packaging signal, and some stuffer sequence. Overall, our data suggest that helper DNA molecules that accumulate after Cre recombinase activity are prone to rearrangements, resulting in helper genomes that have incorporated a packaging signal from the vector. Helper particles with rearranged genomes have a growth advantage. This study identifies a novel mechanism leading to helper contamination during helper-dependent adenoviral vector production.
authors.affiliation: Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, IN 46202, USA.
authors.forename: Miwon
authors.initials: M
authors.lastname: Ahn
authors.forename: Aisha
authors.initials: A
authors.lastname: Gamble
authors.forename: Scott R
authors.initials: SR
authors.lastname: Witting
authors.forename: Jack
authors.initials: J
authors.lastname: Magrisso
authors.forename: Sneha
authors.initials: S
authors.lastname: Surendran
authors.forename: Silvana
authors.initials: S
authors.lastname: Obici
authors.forename: Núria
authors.initials: N
authors.lastname: Morral
mesh_terms: D000256:Adenoviridae / Q000235:genetics*; D015153:Blotting, Western; D004279:DNA, Viral / Q000235:genetics / Q000302:isolation & purification*; D005786:Gene Expression Regulation; D015321:Gene Rearrangement; D015316:Genetic Therapy; D005822:Genetic Vectors; D057809:HEK293 Cells; D006378:Helper Viruses / Q000235:genetics*; D006801:Humans; D019426:Integrases / Q000032:analysis / Q000378:metabolism; D007763:Lac Operon; D016133:Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D019076:Transgenes; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D004279:DNA, Viral; D014764:Viral Proteins; C045073:Cre recombinase; D019426:Integrases