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Kortlynn Johnson
What is Gene Therapy?
 A technique for correcting defective genes responsible
for disease development1
Correcting Faulty Genes
Doctors may use 1 of these approaches1:
1.
A normal gene may be inserted into a nonspecific
location within the genome to replace a
nonfunctional gene.

*Most common*
2. An abnormal gene could be swapped for a normal
gene through homologous recombination.
3. The abnormal gene could be repaired through
selective reverse mutation, which returns the gene to
its normal function.
4. The regulation (the degree to which a gene is turned
on or off) of a particular gene could be altered.
How Does Gene Therapy Work?1
 In most gene therapy studies, a "normal" gene is
inserted into the genome to replace an "abnormal,"
disease-causing gene.
 Carrier molecule  Vector
 Most common carrier  Virus
A Vector in ACTION!!!2
Types of Vectors1
 Retroviruses
 Create double-stranded DNA copies of their RNA
genomes
 These copies of its genome can be integrated into the
chromosomes of host cells
 Adenoviruses
 Have double-stranded DNA genomes that cause
respiratory, intestinal, and eye infections in humans.
Types of Vectors1
 Adeno-associated viruses
 Small, single-stranded DNA viruses that can insert their
genetic material at a specific site on chromosome 19
 Herpes simplex viruses
 Double-stranded DNA viruses that infect a particular
cell type – neurons
Non-Viral Approaches1
 Direct introduction of therapeutic DNA into target
cells
 Simplest method
 This approach is limited in its application because it can
be used only with certain tissues and requires large
amounts of DNA.
Non-Viral Approaches1
 Another nonviral approach involves the creation of an
artificial lipid sphere with an aqueous core.
 This liposome, which carries the therapeutic DNA, is
capable of passing the DNA through the target cell's
membrane.
Non-Viral Approach
(Liposome Method)3
Applications of Gene Therapy1
 Current
 Researchers also are experimenting with introducing a
47th (artificial human) chromosome into target cells.
 This chromosome would exist autonomously alongside
the standard 46 --not affecting their workings or causing
any mutations.
Applications of Gene Therapy1
 It would be a large vector 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 potential method is the difficulty in
delivering such a large molecule to the nucleus of a
target cell.**
Gene Therapy: Going Global1
 The School of Pharmacy in London is testing a
treatment in mice, which delivers genes wrapped in
nanoparticles to cancer cells to target and destroy
hard-to-reach cancer cells. (March 2009)
 UK researchers from the UCL Institute of
Ophthalmology and Moorfields Eye Hospital NIHR
Biomedical Research Centre announced results from
the world’s first clinical trial to test a revolutionary
gene therapy treatment for a type of inherited
blindness. The results show that the experimental
treatment is safe and can improve sight. (April 2008)
Gene Therapy: Going Global1
 In France, gene therapy performed on children
suffering from Severe Combined Immunodeficiency
was halted because one of the patients developed
leukemia as a direct consequence of the treatment.
(October 2002)4
Gene Therapy: Going Global1
 China’s first gene therapy was just recently approved in
2003.
 China's medicines authority approved the cancer
therapy after it achieved promising results in a clinical
trial.
Setbacks for Advancement…1
 The Food and Drug Administration (FDA) has not yet
approved any human gene therapy product for sale.
Setbacks for Advancement…1
 In 1999, gene therapy suffered a major setback with the
death of 18-year-old Jesse Gelsinger. Jesse was
participating in a gene therapy trial for ornithine
transcarboxylase deficiency (OTCD).
 He died from multiple organ failures 4 days after
starting the treatment. His death is believed to have
been triggered by a severe immune response to the
adenovirus carrier.
Some Ethical Questions to Consider
about Gene Therapy1
 What is normal and what is a disability or disorder,
and who decides?
 Are disabilities diseases? Do they need to be cured or
prevented?
 Does searching for a cure demean the lives of
individuals presently affected by disabilities?
 Preliminary attempts at gene therapy are exorbitantly
expensive. Who will have access to these therapies?
Who will pay for their use?
Pros and Cons of Gene Therapy5
Pros
 Wipe out genetic disease
before it can begin and
eliminate suffering for future
applications
 Good technique for diseases
not researched yet
 People carry defected genes
and may be unaware
 Gene therapy can eliminate
the consequences of carrying
these genes
Cons
Putting human fate into our
own hands
Creating a “superior race”
“Playing God”
References
1.
2.
3.
4.
5.
http://www.ornl.gov/sci/techresources/Human_Gen
ome/medicine/genetherapy.shtml#whatis
http://www.unitedspinal.org/publications/action/w
p-content/gene-therapy.jpg
http://www.nature.com/gt/journal/v13/n18/images/3
302838f1.jpg
http://www.newscientist.com/article/dn2878miracle-gene-therapy-trial-halted.html
http://www.ndsu.edu/pubweb/~mcclean/plsc431/stu
dents/eric.htm