Packaging capacity and stability of human adenovirus type 5 vectors

Abstract

Adenovirus vectors are extensively used for high-level expression of proteins in mammalian cells and are receiving increasing attention for their potential use as live recombinant vaccines and as transducing viruses for use in gene therapy. Although it is commonly argued that one of the chief advantages of adenovirus vectors is their relative stability, this has not been thoroughly investigated. To examine the genetic stability of adenovirus type 5 vectors and in particular to examine the relationship between genetic stability and genome size, * Corresponding author.

Adenoviruses as vaccine vectors

“…Which deletion is most suitable for an adenoviral vaccine carrier will most likely depend on a number of variables such as type and size of the insert and potentially the serotype of adenovirus that is being vectored as well as growth characteristics of individual constructs [52].…”

“…Now that adenoviral vaccine carriers are progressing toward clinical trials, a more thorough analysis of the effects of various deletions on growth properties, genome stability, and capsid stability seems warranted. Although packaging allows for some latitude in the size of the adenoviral genome, it has been shown for AdHu5 virus that overly long inserts cause genetic instability of vectors [52]. It remains to be assessed more carefully for AdHu5 as well as other less well characterized serotypes of adenovirus to what degree genome size affects genetic stability, growth characteristics [53], and thermostability [54] of the constructs.…”

Viral Vectors

“…This equated to approximately 1.8 kb of exogenous DNA (transgene) that could be inserted into a wild-type Ad genome ( Ghosh-Choudhury et al, 1987 ;Graham et al, 1977 ). However, increasing the genome length beyond 105% of the wild-type genome length can result in genetic instability and loss of the transgene ( Bett et al, 1993 ). Researchers quickly discovered that more genome space could be created for larger transgenes by specific deletions of the Ad genome.…”

Xenogenic Adenoviral Vectors

“…A huge amount of work carried out over some 30 years on HAdV2 and -5 has defined viral promoters, transcripts and their splice sites and genes that could be deleted or that would function in trans (reviewed in [2,65]). The packaging capacity of the viral capsid was also shown to be ^^105% of the viral genome [127]. The strategic design of bovine, canine, porcine, simian, and murine adenovirus vectors, although based on new genetic information, has drawn extensively on historic precedents.…”

“…For the vectors where an insertion strategy was pursued, it was particularly important to check the genome integrity because the packaging capacity of the new vectors was undefined. Mastadenoviruses can package 105 to ^107% of the wild-type genome [43,120,127], OAdV7 has a capacity of 114%, presumably because of its smaller genome and similar capsid volume [75], while the capacity of aviadenoviruses is undefined. Despite the increased packaging capacity of OAdV7, some viral genomes in which expression cassettes (ranging from 1.8 to 3.1 kb) were inserted into site I of the genome proved to be unstable upon passaging.…”