Adeno-Associated Virus Gene Expression Vector (ssAAV)

Overview

The adeno-associated virus (AAV) vector system is a popular and versatile tool for in vitro and in vivo gene delivery. AAV is effective in transducing many mammalian cell types, and, unlike adenovirus, has very low immunogenicity, being almost entirely nonpathogenic in vivo. This makes AAV the ideal viral vector system for many animal studies.

An AAV vector is first constructed as a plasmid in E. coli. It is then transfected into packaging cells along with helper plasmids, where the region of the vector between the two inverted terminal repeats (ITRs) is packaged into live virus. Any gene(s) placed in-between the two ITRs are introduced into target cells along with the rest of viral genome. 

When AAV virus is added to target cells, the single-stranded linear DNA genome is delivered into cells, where it is converted by the host cell DNA polymerase machinery into double-stranded DNA. AAV vector DNA forms episomal concatemers in the host cell nucleus. In non-dividing cells, these concatemers can remain for the life of the host cells. In dividing cells, AAV DNA is lost through the dilution effect of cell division, because the episomal DNA does not replicate alongside host cell DNA. Random integration of AAV DNA into the host genome can occur but is extremely rare. This is desirable in many gene therapy settings where the potential oncogenic effect of vector integration can pose a significant concern.

A major practical advantage of AAV is that in most cases AAV can be handled in biosafety level 1 (BSL1) facilities. This is due to AAV being inherently replication-deficient, producing little or no inflammation, and causing no known human disease.

Many strains of AAV have been identified in nature. They are divided into different serotypes based on different antigenicity of the capsid protein on the viral surface. Different serotypes can render the virus with different tissue tropism (i.e. tissue specificity of infection). When our AAV vectors are packaged into virus, different serotypes can be conferred to the virus by using different capsid proteins for the packaging. During cloning, ITRs from AAV2 are used, as this is common practice in the field and does not impact specificity. Packaging helper plasmids include a Rep/Cap plasmid, containing the replication genes from AAV2 and the capsid proteins for a chosen serotype to determine tropism. The table below lists different AAV serotypes and their tissue tropism.

List by Serotype
List by Tissue Type

Serotype Tissue tropism
AAV1 Smooth muscle, skeletal muscle, CNS, brain, lung, retina, inner ear, pancreas, heart, liver
AAV2 Smooth muscle, CNS, brain, liver, pancreas, kidney, retina, inner ear, testes
AAV3 Smooth muscle, liver, lung
AAV4 CNS, retina, lung, kidney, heart
AAV5 Smooth muscle, CNS, brain, lung, retina, heart
AAV6 Smooth muscle, heart, lung, pancreas, adipose, liver
AAV6.2 Lung, liver, inner ear
AAV7 Smooth muscle, retina, CNS, brain, liver
AAV8 Smooth muscle, CNS, brain, retina, inner ear, liver, pancreas, heart, kidney, adipose
AAV9 Smooth muscle, skeletal muscle, lung, liver, heart, pancreas, CNS, retina, inner ear, testes, kidney, adipose
AAVrh10 Smooth muscle, lung, liver, heart, pancreas, CNS, retina, kidney
AAV-DJ Liver, heart, kidney, spleen
AAV-DJ/8 Liver, brain, spleen, kidney
AAV-PHP.eB CNS
AAV-PHP.S PNS
AAV2-retro Spinal nerves
AAV2-QuadYF Endothelial cell, retina
AAV2.7m8 Retina, inner ear

Tissue type Recommended AAV serotypes
Smooth muscle AAV1, AAV2, AAV3, AAV5, AAV6, AAV7, AAV8, AAV9, AAVrh10
Skeletal muscle AAV1, AAV9
CNS AAV1, AAV2, AAV4, AAV5, AAV7, AAV8, AAV9, AAVrh10, AAV-PHP.eB
PNS AAV-PHP.S
Brain AAV1, AAV2, AAV5, AAV7, AAV8, AAV-DJ/8
Retina AAV1, AAV2, AAV4, AAV5, AAV7, AAV8, AAV9, AAVrh10, AAV2-QuadYF, AAV2.7m8
Inner ear AAV1, AAV2, AAV6.2, AAV8, AAV9, AAV2.7m8
Lung AAV1, AAV3, AAV4, AAV5, AAV6, AAV6.2, AAV9, AAVrh10
Liver AAV1, AAV2, AAV3, AAV6, AAV6.2, AAV7, AAV8, AAV9, AAVrh10, AAV-DJ, AAV-DJ/8
Pancreas AAV1, AAV2, AAV6, AAV8, AAV9, AAVrh10
Heart AAV1, AAV4, AAV5, AAV6, AAV8, AAV9, AAVrh10, AAV-DJ
Kidney AAV2, AAV4, AAV8, AAV9, AAVrh10, AAV-DJ, AAV-DJ/8
Adipose AAV6, AAV8, AAV9
Testes AAV2, AAV9
Spleen AAV-DJ, AAV-DJ/8
Spinal nerves AAV2-retro
Endothelial cells AAV2-QuadYF

Click to view user testimonials about our AAV vectors

For further information about this vector system, please refer to the papers below.

References Topic
Methods in Enzy. 507:229-54 (2012) Review of AAV virology and uses
Curr Opin Pharmacol. 24:59-67 (2015) AAV use in gene therapy, and serotype differences

Highlights

Our AAV vector system is optimized for high copy number replication in E. coli, high-titer packaging of live virus, efficient transduction of host cells, and high-level transgene expression. This viral vector can be packaged into virus using all known capsid serotypes, is capable of very high transduction efficiency, and presents low safety risk.

Advantages

Safety: AAV is the safest viral vector system available. AAV is inherently replication-deficient, and is not known to cause any human diseases.

Low risk of host genome disruption: Upon transduction into host cells, AAV vectors remain as episomal DNA in the nucleus. The lack of integration into the host genome can be a desirable feature for in vivo human applications, as it reduces the risk of host genome disruption that might lead to cancer.

High viral titer: Our AAV vector can be packaged into high titer virus. When AAV virus is obtained through our virus packaging service, titer can reach >1013 genome copy per ml (GC/ml).

Broad tropism: A wide range of cell and tissue types from commonly used mammalian species such as human, mouse and rat can be readily transduced with our AAV vector when it is packaged into the appropriate serotype. But some cell types may be difficult to transduce, depending on the serotype used (see disadvantages below).

Effectiveness in vitro and in vivo: Our vector is often used to transduce cells in live animals, but it can also be used effectively in vitro.

Disadvantages

Small cargo space: AAV has the smallest cargo capacity of any of our viral vector systems. AAV can accommodate a maximum of 4.7 kb of sequence between the ITRs, which leaves ~4.2 kb cargo space for user's DNA of interest.

Difficulty transducing certain cell types: Our AAV vector system can transduce many different cell types including non-dividing cells when packaged into the appropriate serotype. However, different AAV serotypes have tropism for different cell types, and certain cell types may be hard to transduce by any serotype.

Technical complexity: The use of viral vectors requires the production of live virus in packaging cells followed by the measurement of viral titer. These procedures are technical demanding and time consuming relative to conventional plasmid transfection. These demands can be alleviated by choosing our virus packaging services when ordering your vector.

Key components

5' ITR: 5' inverted terminal repeat. In wild type virus, 5' ITR and 3' ITR are essentially identical in sequence. They reside on two ends of the viral genome pointing in opposite directions, where they serve as the origin of viral genome replication.

Promoter: The promoter that drives your gene of interest is placed here.

Kozak: Kozak consensus sequence. It is placed in front of the start codon of the ORF of interest to facilitate translation initiation in eukaryotes.

ORF: The open reading frame of your gene of interest is placed here.

Regulatory element: Allows the user to add the Woodchuck hepatitis virus posttranscriptional regulatory element (WPRE). WPRE enhances virus stability in packaging cells, leading to higher titer of packaged virus; enhances higher expression of transgenes.

BGH pA: Bovine growth hormone polyadenylation. It facilitates transcriptional termination of the upstream ORF.

3' ITR: 3' inverted terminal repeat. See description for 5’ ITR.

Ampicillin: Ampicillin resistance gene. It allows the plasmid to be maintained by ampicillin selection in E. coli.

pUC ori: pUC origin of replication. Plasmids carrying this origin exist in high copy numbers in E. coli.

Representative vector design

VB ID Vector name Descriptions
VB010000-9394npt pAAV[Exp]-CMV>EGFP:WPRE A single-stranded AAV (ssAAV) mammalian gene expression vector encoding CMV-driven EGFP with a WPRE regulatory element.
VB231214-1622uat pAAV[Exp]-CAG>hSMN1[NM_000344.4]:WPRE A single-stranded AAV (ssAAV) vector expressing a human survival motor neuron gene SMN1, which is associated with SMA, driven by a CAG promoter with the regulatory element WPRE.
Design My Vector  Request Design Support