Adenoviruses & Viral Gene Therapy Vectors

Question 1

General structure of the adenovirus virion

Answer 1

• Adenovirus is a non-enveloped icosahdral linear dsDNA virus.
• It is heat stabile and lacks lipids which confers a r_esistance to lipid solvents_, including bile salts.
• Its structure permits survival in the lower GI tract, feces, and throat.
• Has a fiber protein for attachment.

Question 2

Types of dz caused by adenovirus

Answer 2

• Pharyngoconjunctival fever, conjunctivitis (via dissemination in swimming pools), epidemic keratoconjunctivitis
• Diarrhea in children (via fecal-oral mode of transmission)
• Respiratory illness
• Ocular infections
• CNS infection
• Genitourinary tract infections
• Obesity
• HIV-infected patients
• Disseminated or subclinical infections

Question 3

Types of respiratory illnesses caused by adenovirus

Answer 3

• Acute, pneumonia
• Middle upper respiratory tract infection
• Sporadic/epidemic severe respiratory disease
• Acute respiratory disease
• Fatal nonbacterial pneumonia in infants
• Recent severe pneumonia outbreaks
• fatal pneumonia in military recruits (rare)

Question 4

Tyeps of genitourinary tract infections caused by adenovirus

Answer 4

• Epidemic infantile gastroenteritis
• Acute hemorrhagic cystitis

Question 5

Types of DNA Virus gene therapy vectors

Answer 5

• Retroviruses
• Adenoviruses
• Adeno-associated virus (AAV)

Question 6

Retrovirus vectors: advantages & disadvantages

Answer 6

• Adv.
  
  • 8 kb of foreign DNA can be used
  • Stable expression of the transduced gene because of proviral integration in host DNA
• Disadv.
  
  • Relatively small amounts of virus obtained during growth
  • Virions are not very stable
  • Low efficiency of transduction of certain non-mitotic cells

Question 7

Adenovirus vectors: advantages

Answer 7

• Very high titers can be obtained
• Virions are stable
• The viral chromosome does not normally integrate
• Non-mitotic cells are efficiently transduced
• 8-36 kb of foreign DNA can be inserted
• Can be made to selectively replicate in, and kill, tumor cells
• Inflammatory response is potential advantage when targeting tumor cells or when used as a vaccine agent

Question 8

Adenovirus vectors: disadvantages

Answer 8

• Elicit a strong inflammatory response
  
  • almost all people have Ab titer against the adenoviruses most used as vectors ==> repeated use of this virus problematic
  • most adenovirus genes are conserved in the vector leading to inflammatory vector response
• Expression of the transduced gene will be transient in mitotic cells
• Death of patient in gene therapy trial

Question 9

Adeno-associated virus vectors: advantages & disadvantages

Answer 9

• Adv.
  
  • High titers can be obtained
  • The virions are very stable
  • Approximately 5 kb of foreign DNA can be introduced
  • Hasn’t been shown to cause clinical sx
• Disadv.
  
  • viral chromosome integrates into host DNA ==> potentially mutagenic event
  • Second strand DNA synthesis, gene expression, and integration are typically very slow in the absence of helper virus
  • The small size of the genome means that large genes cannot be introduced