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The advantages of genetic immunization over conventional
technologies in generating antibodies are manifold:
1. Rapid antibody development
2. Antibodies recognise the native protein
3. High affinity antibodies
4. Tailor-made antibodies
5. No incidence of protein contamination
1. Rapid antibody
development. Conventional technologies usually either
generate antibodies against purified proteins, or against
synthetic peptides based on amino acid sequences derived from
DNA sequence data. Genetic immunization involves introducing
the gene in the form of a cDNA directly into an animal which
translates this cDNA into protein thus stimulating an immune
response against the foreign protein. Following conventional
methods, proteins are either extracted directly from tissues
or in a recombinant form after expression of the cDNA in bacteria,
yeast or eukaryotic cells. In all of these cases, the methods
are both time-consuming and costly. Protein purification is
not necessary for the genetic immunization approach, which
can save between four to six months in time over recombinant
protein generation for developing monoclonal antibodies.
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2. Antibodies
recognise the native protein. Although the synthetic
peptide approach is comparable in speed, the quality of antibodies
generated by genetic immunization is far superior. This is
because the protein is made by the immunized animal, utilzing
complex cellular mechanisms that allow it to gain a native
conformation. Antibodies are then generated against a native
protein, such as is found in the blood or tissues of its host
species. The class of proteins that are most interesting as
targets for diagnostics and therapy are generally either membrane-bound
or secreted molecules. They create problems for conventional
antibody technology because in their native form, they are
often modified by glycosylation, or in some cases exist as
multiple membrane-spanning proteins that are not soluble following
isolation or synthesis in recombinant systems. All of these
problems are avoided if the immunized animal makes the protein
itself.
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3. High affinity
antibodies. Antibodies generated by genetic immunization
at GENOVAC have been shown to have binding affinities to the
protein in the sub-nanomolar range, which are approximately
100x higher than conventionally developed antibodies and much
higher than single chain antibodies. GENOVAC´s results confirm
published data for much higher avidity of sera generated by
genetic immunization as compared with that gained by immunization
with a corresponding recombinant protein. This stronger binding
is again an important characteristic of the type of antibody
needed for diagnosis or therapy, especially where the proteins
to be detected are only present at low concentrations. Therefore,
antibodies generated by genetic immunization are ideally suited
for diagnostic and therapeutic applications.
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4. Tailor-made
antibodies. DNA constructs are easy to manipulate,
thus it is possible to focus on individual protein domain-encoding
regions. For example, antibodies can be focused against functional
domains e.g., to activate or inhibit target receptor proteins.
Alternatively, specific exons may be chosen for immunization
if antibodies are needed to differentiate specific protein
isoforms. Mutations can also be introduced into DNA sequences,
so that allelic variants or viral strain variants can be differentiated.
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5. No incidence
of protein contamination. Protein purification used
for conventional immunization often leads to contamination
problems, which can induce antibodies with the wrong specificity.
This problem does not exist for genetic immunization because
protein contamination is easily removed from DNA and only
the gene of interest is expressed in the animal.
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