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Gene
Therapy
 One
of the most amazing genetic applications in medicine is
gene therapy. Also known as somatic gene therapy and therapeutic
gene therapy, this procedure involves inserting (or sometimes
deleting) portions of the genes in diseased patients so
that they can be cured and live healthier lives.
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Two
methods exist for inserting genetic material into
human chromosomes. The first, called the ex vivo technique,
involves surgically removing cells from the affected
tissue area, injecting or splicing the new DNA (the
DNA that will correct the disease) into the cells
and letting them divide in cultures. The new tissues
are placed back into the affected area of the patient.
Often, doctors need only culture the patient’s bone
marrow because it produces the blood that will eventually
travel throughout the body. This type of surgery,
however, is especially painful, and patients usually
have to undergo it twice--once to extract the marrow
and then again to replace it--because the culturing
time takes many hours to complete.The second method
is called the in vivo technique and requires no surgery
or even anesthesia. In this process, the therapeutic
DNA is injected directly into the body cells, usually
via one of two types of viruses. The most frequently
used type is the very simple retrovirus. Dr. Richard
Mulligan of MIT has synthetically created the perfect
retrovirus: it has no reproduction sequence and exists
solely to deliver therapeutic DNA during gene therapy.
It has no viral DNA (DNA that would make the cell--and
you-- sick) whatsoever and only carries the new DNA
that has been spliced into it. After injecting the
diseased cell with the new therapeutic DNA, it then
dies. Using retroviruses is very safe and provides
long-lasting effects. Unfortunately, the new DNA it
injects will only help the new daughter cells and
not those that already exist. The second type of virus
used for the in vivo technique is called an adenovirus,
the equivalent of the common cold virus. Although
this virus will also die after injecting its spliced
therapeutic DNA, it will be attacked by the immune
system and the patient will suffer from a temporary
sore throat and runny nose. The adenovirus works the
same way the retrovirus does, but its effects are
much more immediate--within 48 hours. Unlike the retrovirus,
though, the new DNA’s effects wear off within weeks.
Scientists like the fact that only a few millimeters
of altered adenovirus solution is needed to cure the
patient, whereas several liters of retrovirus are
needed to obtain a much slower result. |
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There
are other gene therapy techniques, although they aren’t
as frequently used. One method involves inserting
therapeutic DNA into cultured endothelium tissue (endothelium
is the membrane that lines all of the blood vessels)
and then grafting it into the patient. Another technique
requires the patient to receive an electric shock
while submerged in a bath of a therapeutic DNA solution.
The shock opens the skin pores, allowing the DNA to
enter. Still other options include skin grafts, connective
tissue grafts, and injecting the liver with the therapeutic
DNA. |
   
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