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Gene Therapy
By: Chris Smith and Darran Prewitt
What is gene therapy? Why is it
used?
• Gene therapy = Introduction of
normal genes into cells that
contain defective genes to
reconstitute a missing protein
product
• GT is used to correct a deficient
phenotype so that sufficient
amounts of a normal gene
product are synthesized  to
improve a genetic disorder
How is Gene Therapy Carried Out?
• Modification of somatic cells by
transferring desired gene
sequences into the genome.
• Somatic cells necessary to
ensure that inserted genes are
not carried over to the next
generation.
Forms Of Viral Transfers
• Retroviruses - A class
of viruses that can
create double-stranded
DNA copies of their
RNA genomes. These
copies of its genome
can be integrated into
the chromosomes of
host cells.
• Herpes simplex viruses
- A class of doublestranded DNA viruses
that infect a particular
cell type, neurons.
Forms Of Viral
Transfers(Cont.)
• Adenoviruses - A class
of viruses with doublestranded DNA genomes
that cause respiratory,
intestinal, and eye
infections in humans.
• Adeno-associated
viruses - A class of
small, single-stranded
DNA viruses that can
insert their genetic
material at a specific
site on chromosome
19.
Future Applications
• Researchers are also experimenting with
introducing a 47th artificial chromosome.
This chromosome would exist alongside
the standard 46, not affecting their work or
causing any mutations. It would be
capable of carrying substantial amounts of
genetic code, and scientists anticipate
that, because of its construction and
autonomy, the body's immune systems
would not attack it. A problem with this
method is the difficulty in delivering such a
large molecule to the nucleus of a target
cell.
Different Delivery Systems That are
Available
• In vivo versus ex vivo
• In vivo = delivery of genes takes
place in the body
• Ex vivo = delivery takes place out
of the body, and then cells are
placed back into the body
• Problem: Replication defective
viruses adversely affect the virus’
normal ability to spread genes in
the body
• Reliant on diffusion and spread
• Hampered by small intercellular
spaces for transport
• Restricted by viral-binding ligands on
cell surface  therefore cannot
advance far.
• More than 5000 patients have
been treated in last ~12 years
worldwide
References
• http://www.ornl.gov/sci/techreso
urces/Human_Genome/medicine/
genetherapy.shtml