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Step 1
Use the growth medium, which includes PCR primers,
to make billions of copies of a single gene.
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Genetic vaccines, sometimes called naked-DNA
vaccines, are currently being developed to fight
diseases such as AIDS. The goal of these vaccines is
to use a gene from a pathogen to generate an immune
response. A gene contains the instructions to create
a protein. With a genetic vaccine, small loops of
DNA in the vaccine invade body cells and incorporate
themselves into the cells' nuclei. Once there, the
cells read the instructions and produce the gene's
protein.
Using a technique called PCR, which stands for
polymerase chain reaction, you'll make many copies
of a specific gene. The work of finding the gene and
copying sequences of its DNA is done by
"primers."
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Step 2
Combine the virus genes with vectors.
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To make your genetic vaccine, you'll use vectors.
Vectors are agents that are able to enter and
instruct cells to create proteins based on the
vector's DNA code. In this case, the vectors are
loops of double-stranded DNA. You can exploit the
vector's ability to create proteins by splicing a
gene from the virus into a vector. The cell that the
vector later invades will then produce proteins
created by the virus.
The vectors and copied genes have been treated with
restriction enzymes, which are agents that cut DNA
sequences at known locations. The enzymes have cut
open the round vectors and trimmed the ends of the
copied genes.
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Step 3
Add bacteria to the vectors to allow the altered
vectors to replicate.
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The ends of the vectors have again come together,
but now with a gene spliced into the loop. You'll
need many copies of the vector/gene loop for your
genetic vaccine. These copies can be produced with
the help of bacteria.
Vectors are capable of self-replicating when within
a bacterial host, as long as that host is in an
environment conducive to growing. After you combine
the vectors and bacteria, the vectors will be
shocked into the bacteria.
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Step 4
Use the purifier to separate the altered vectors
from the bacteria.
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The final vaccine should include only the vectors,
so you'll need to separate them from the bacteria
after enough copies have been produced. This can be
done with a detergent, which ruptures the cell walls
of the bacteria and frees the DNA within.
The relatively large bacterial DNA can then be
separated from the smaller DNA loop that makes up
the vector.
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Step 5
Fill the syringe with the altered vectors.
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Upon inoculation, billions of copies of the altered
vector will enter the body. Of these, only 1 percent
will work their way into the nuclei of body cells.
But that's enough.
The body's immune system responds to these proteins
once they leave the cell. But more importantly, it
also reacts to proteins that are incorporated into
the cells' walls. So in addition to mounting an
attack against the free-floating proteins, the
immune system attacks and eliminates cells that have
been colonized by a pathogen. The vaccine, then,
works like a live vaccine, but without the risk.
(With a live vaccine, the pathogen can continue to
replicate and destroy cells as it does so.)
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Done
The naked-DNA vaccine is complete.
Select another pathogen.
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Congratulations. You have just produced a naked-DNA
HIV vaccine.
Trials for a genetic vaccine that may protect
against AIDS began in 1995. These vaccines, which
contained HIV genes, were given to patients who
already were infected with HIV. A year later, the
trials were expanded to test people without HIV.
These trials are still being conducted and have not
yet produced conclusive results.
Human trials for genetic vaccines against herpes,
influenza, malaria, and hepatitis B are also
underway.
Note: Although the genetic material of HIV is RNA,
the procedure for making the vaccine is similar.
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