Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2016:1382:21-39.
doi: 10.1007/978-1-4939-3271-9_2.

Delivering Transgenic DNA Exceeding the Carrying Capacity of AAV Vectors

Affiliations

Delivering Transgenic DNA Exceeding the Carrying Capacity of AAV Vectors

Matthew L Hirsch et al. Methods Mol Biol. 2016.

Abstract

Gene delivery using recombinant adeno-associated virus (rAAV) has emerged to the forefront demonstrating safe and effective phenotypic correction of diverse diseases including hemophilia B and Leber's congenital amaurosis. In addition to rAAV's high efficiency of transduction and the capacity for long-term transgene expression, the safety profile of rAAV remains unsoiled in humans with no deleterious vector-related consequences observed thus far. Despite these favorable attributes, rAAV vectors have a major disadvantage preventing widespread therapeutic applications; as the AAV capsid is the smallest described to date, it cannot package "large" genomes. Currently, the packaging capacity of rAAV has yet to be definitively defined but is approximately 5 kb, which has served as a limitation for large gene transfer. There are two main approaches that have been developed to overcome this limitation, split AAV vectors, and fragment AAV (fAAV) genome reassembly (Hirsch et al., Mol Ther 18(1):6-8, 2010). Split rAAV vector applications were developed based upon the finding that rAAV genomes naturally concatemerize in the cell post-transduction and are substrates for enhanced homologous recombination (HR) (Hirsch et al., Mol Ther 18(1):6-8, 2010; Duan et al., J Virol 73(1):161-169, 1999; Duan et al., J Virol 72(11):8568-8577, 1998; Duan et al., Mol Ther 4(4):383-391, 2001; Halbert et al., Nat Biotechnol 20(7):697-701, 2002). This method involves "splitting" the large transgene into two separate vectors and upon co-transduction, intracellular large gene reconstruction via vector genome concatemerization occurs via HR or nonhomologous end joining (NHEJ). Within the split rAAV approaches there currently exist three strategies: overlapping, trans-splicing, and hybrid trans-splicing (Duan et al., Mol Ther 4(4):383-391, 2001; Halbert et al., Nat Biotechnol 20(7):697-701, 2002; Ghosh et al., Mol Ther 16(1):124-130, 2008; Ghosh et al., Mol Ther 15(4):750-755, 2007). The other major strategy for AAV-mediated large gene delivery is the use of fragment AAV (fAAV) (Dong et al., Mol Ther 18(1):87-92, 2010; Hirsch et al., Mol Ther 21(12):2205-2216, 2013; Lai et al., Mol Ther 18(1):75-79, 2010; Wu et al., Mol Ther 18(1):80-86, 2010). This strategy developed following the observation that the attempted encapsidation of transgenic cassettes exceeding the packaging capacity of the AAV capsid results in the packaging of heterogeneous single-strand genome fragments (<5 kb) of both polarities (Dong et al., Mol Ther 18(1):87-92, 2010; Hirsch et al., Mol Ther 21(12):2205-2216, 2013; Lai et al., Mol Ther 18(1):75-79, 2010; Wu et al., Mol Ther 18(1):80-86, 2010). After transduction by multiple fAAV particles, the genome fragments can undergo opposite strand annealing, followed by host-mediated DNA synthesis to reconstruct the intended oversized genome within the cell. Although, there appears to be growing debate as to the most efficient method of rAAV-mediated large gene delivery, it remains possible that additional factors including the target tissue and the transgenomic sequence factor into the selection of a particular approach for a specific application (Duan et al., Mol Ther 4(4):383-391, 2001; Ghosh et al., Mol Ther 16(1):124-130, 2008; Hirsch et al., Mol Ther 21(12):2205-2216, 2013; Trapani et al., EMBO Mol Med 6(2):194-211, 2014; Ghosh et al., Hum Gene Ther 22(1):77-83, 2011). Herein we discuss the design, production, and verification of the leading rAAV large gene delivery strategies.

Keywords: Adeno-associated virus; Concatemer; Fragment; Hybrid; Large gene delivery; Overlapping; Split AAV method; Trans-splicing; Vector capacity.

PubMed Disclaimer

Figures

Fig. 1
Fig. 1
Overlapping AAV genome design and transduction. (a) The transgenic cassette, containing the depicted elements, is split into two separate vectors such that there is a homologous sequence overlap (gray). The total size of the transgenic DNA must be less than 4.7 kb. (b) Following co-transduction of vector genomes A and B, homologous recombination at the overlapping sequence occurs to reconstruct the depicted large transgenic DNA cassette of approximately 9 kb. Black box AAV inverted terminal repeat
Fig. 2
Fig. 2
Trans-splicingAAV vector design and transduction. (a) The genetic elements of the two required AAV plasmids are depicted. Plasmid A contains a promoter, a partial open reading frame terminated at a splice donor site, followed by a recombinogenic sequence (hybrid vectors only, AK). The vector B plasmid contains a recombinogenic sequence (hybrid vectors only, AK), a splice acceptor site, the remaining ORF followed by a poly A sequence. The transgenic DNA in each plasmid is less than 4 kb. (b) Following co-transduction vector genomes A and B can undergo end joining (left) or homologous recombination at the AK sequence (right) to reconstruct a large transgenic cassette containing the depicted intron. Black box AAV inverted terminal repeat
Fig. 3
Fig. 3
Fragment AAV vector design and transduction. (a) A single plasmid with an intact transgenic cassette is depicted. (b) During AAV vector production different sized genome fragments of the over-sized transgenic cassette are packaged. Fragments of both polarities are packaged (gray and black lines) starting at the 3′ end. Opposite polarity fragments containing regions of complementarity can anneal followed by strand synthesis to generate a large transgenic cassette. Contaminating fragment genome species below half of the intended transgenic cassette do not contain strand complementarity and are non-productive for transduction. Black box AAV inverted terminal repeat

Similar articles

Cited by

References

    1. Hirsch ML, Agbandje-McKenna M, Samulski RJ. Little vector, big gene transduction: fragmented genome reassembly of adeno-associated virus. Mol Ther. 2010;18(1):6–8. - PMC - PubMed
    1. Duan D, et al. Formation of adeno-associated virus circular genomes is differentially regulated by adenovirus E4 ORF6 and E2a gene expression. J Virol. 1999;73(1):161–169. - PMC - PubMed
    1. Duan D, et al. Circular intermediates of recombinant adeno-associated virus have defined structural characteristics responsible for long-term episomal persistence in muscle tissue. J Virol. 1998;72(11):8568–8577. - PMC - PubMed
    1. Duan D, Yue Y, Engelhardt JF. Expanding AAV packaging capacity with trans-splicing or overlapping vectors: a quantitative comparison. Mol Ther. 2001;4(4):383–391. - PubMed
    1. Halbert CL, Allen JM, Miller AD. Efficient mouse airway transduction following recombination between AAV vectors carrying parts of a larger gene. Nat Biotechnol. 2002;20(7):697–701. - PubMed