Download Lecture 3 - Lectures For UG-5

Gene therapy and viral vector
Lecture 3
Viral Vectors
retrovirus
 adenovirus
 adeno-associated virus
 herpes virus
 pox virus
 human foamy virus (HFV)
 lentivirus
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Adenovirus
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Medium-sized (90-100nm)
Nonenveloped (without an outer lipid bilayer)
Double stranded DNA
Derived from Human Adenoids (tonsils) in 1953
They have a broad range of vertebrate hosts; in humans, 100
distinct adenoviral serotypes have been found to cause a wide
range of illnesses, from mild respiratory infections in young
children (known as the common cold) to life-threatening multiorgan disease in people with a weakened immune system.
Serotype or serovar are distinct variations within a species of bacteria
or viruses or among immune cells of different individuals.
Different types/serotypes are associated with different conditions:
respiratory disease (mainly species HAdV-B and C)
conjunctivitis (HAdV-B and D)
gastroenteritis (HAdV-F types 40, 41, HAdV-G type 52)
obesity or adipogenesis (HAdV-A type 31, HAdV-C type 5, HAdV-D types 9, 36,
37)
How Adenovirus enters the host cell?
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Entry of adenoviruses into the host cell involves two sets of
interactions between the virus and the host cell.
Entry into the host cell is initiated by the knob domain of the fiber
protein binding to the cell receptor. The two currently established
receptors are: CD46 for the group B human adenovirus serotypes
and the coxsackievirus adenovirus receptor (CAR) for all other
serotypes.
This is followed by a secondary interaction with an integrin molecule.
It is the co-receptor interaction that stimulates entry of the
adenovirus.
Binding to integrin results in endocytosis of the virus particle
via clathrin-coated pits.
Attachment to integrin stimulates cell signaling and thus
induces actin polymerization resulting in entry of the virion into the
host cell within an endosome.
Entry in the nucleus
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Once the virus has successfully gained entry into the
host cell, the endosome acidifies, which alters virus
topology.
These changes, as well as the toxic nature of the
pentons, destroy the endosome, resulting in the
movement of the virion into the cytoplasm.
With the help of cellular microtubules the virus is
transported to the nuclear pore complex, whereby
the adenovirus particle disassembles.
Viral DNA is subsequently released, which can enter
the nucleus via the nuclear pore.
After this the DNA associateswith histone molecules.
Thus, viral gene expression can occur and new virus
particles can be generated.
Benefits
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Their basic biology has been studied extensively,
The viral genome can accommodate large
heterologous transgene insertions,
They readily infect quiescent and dividing cells,
They can be amplified to high titers and they have
previously been shown to be relatively safe for
use in humans.
The family Adenoviridae consists of five genera,
including genus Mastadenovirus and genus
Aviadenovirus, which infect mammals and birds
respectively.
The adenovirus vector most commonly used for
clinical trials and experimental gene therapy
applications is species C adenovirus, HAdV-C5.
Drawbacks
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Adenovirus delivered genes can be lost due
to genetic instability therefore repeated
doses are necessary to maintain the
expression of transgene.
They would not integrate into the host
genome, their gene expression is too short
term.
Immunologic responses against adenoviruses
have made their clinical application limited to
a few tissues, such as liver, lung (especially
for CF(Cystic Fibrosis) treatment), or
localized cancer gene therapy.
Drawbacks
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Although the risk of serious disease
following natural adenovirus infection is
rare and the viral genome would not
integrate into the host genome, gene
therapy by adenoviral vectors has caused
serious bad side effects and even death of
some patients.
Adeno-associated vectors
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Adeno-associated vectors (AAV) are like adenoviral
vectors in their features but because of having some
deficiency in their replication and pathogenicity, are
safer than adenoviral vectors.
In human, AAVs are not associated with any disease.
Another special character of AAV is their ability to
integrate into a specific site on chromosome 19 with no
noticeable effects cause long-term expression in vivo.
AAVs have been used in the treatment of some
diseases, such as CF, hemophilia B, Leber
congenital amaurosis, and AAT (Alpha-1
antitrypsine) deficiency.
The use of antisense oligodeoxynucleotides targeted to the reninangiotensin system [hormone system that regulates blood pressure and
water (fluid) system] and adeno-associated virus vector delivery of
antisense DNA offers a new approach to prolonged hypertension
therapy with a single administration.
Drawbacks
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The major disadvantages of these vectors
are complicated process of vector
production and the limited transgene
capacity of the particles (up to 4.8 kb).
Comparison
Lecture prepared from
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http://www.ncbi.nlm.nih.gov/pmc/articles/
PMC3507026/#!po=5.42169