Gene therapy is
the treatment of disease by rebuilding defective genetic material (Ermak G, 2015). The whole process involves identifying abnormal gene, synthesizing and
delivering identical healthy gene into a cell, tissue, or whole organ, with the
goal of curing a disease or at least improving the clinical status of a
patient.
How to identify an affected gene?
In order to understand
the genetic mechanisms behind a genetic disease, clinical signs such as family
history are of great importance. The occurrence of a condition among family
members can be learnt from family history and serves as an evidence of a
certain disease caused by a specific abnormal gene.
Besides, some genetic tests are used in current clinical trials, including cytogenetic testing, biochemical testing and molecular testing. Cytogenetics focus on the relationship between chromosomes and cell behavior, involving the examination of whole chromosomes for abnormalities. Clinical testing for a biochemical disease utilizes techniques that examine the protein instead of the gene. If the function of the protein is unknown, a better choice may be a molecular testing which involves effective testing of DNA. However, molecular testing can be intricate in some clinical cases since many different mutations can occur in the same gene (Chi-Yan T et al., 2007).
How to synthesize a gene?
The first step
of gene synthesis is gene sequencing. According to the sequence, DNA that
contains gene of interest must be extracted from living organisms and purified.
Then, the gene can be isolated from DNA through specific enzymes or synthesized
by polymerase chain reaction (PCR), a method widely used in molecular biology
to rapidly make millions to billions of copies of a specific DNA sample.
How to deliver the gene?
It’s not easy
to transfer the gene into cells since all cells are covered with membranes that
protect them from environment. Thus, a carrier called a vector is needed to
help the gene pass through the cell membranes. Due to their ability of
infecting cells, specific viral vectors are frequently adopted to transfer the exogenous
gene. Some types of
virus, such as retroviruses, integrate their genetic material (include the new
gene) into a chromosome in the human cell. Other viruses, such as adenoviruses,
introduce their DNA into the nucleus of the cell, but the DNA is not integrated
into a chromosome.
Vectors used in gene therapy clinical trials(Samantha G et al., 2018)
The
applications of those viruses are limited by some biosafety issues. For
example, they must be modified before injected into human body so that they won’t
lead to any disease. As a
result, non-viral methods in clinical trials has rapidly increased in recent
years. Some physical methods, including sonoporation and electroporation,
involve modifying the permeability of the cell plasma
membranes. Others use special way to speed up the delivery. For instance,
magnetofection technique uses magnetic fields to concentrate particles
containing nucleic acid into the target cells resulting in rapid and highly
efficient nucleic acid delivery. Chemical methods like oligonucleotides and lipoplexes
have also been developed to improve the delivery of the new DNA into the cell.
Hopefully, the delivered gene will make a functioning protein which can treat or
prevent a disease.
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