(PDF) Gene Therapy in the Treatment

Gene Therapy
INTRODUCTION
Gene therapy is the process of new genes into cells for restoring or adding gene
expression. The main objective of doing this is to treat a person from many diseases.
In this process, generally a mutated gene is being replaced by with DNA that
encodes a functional copy. A therapeutic drug is generated by encoding DNA.
Adeno associated virus vector production – 'A': The expression cassette
containing promoter, intron, and target gene and polyadenylation sequence is
flanked with adeno associated virus (AAV) inverted terminal repeats (ITRs).
'B': AAV rep and cap sequences without ITRs are provided Trans
'C': The helper virus can be adenovirus, herpes simplex virus (HSV) or
baculovirus depending upon the production system utilized.
If these three components are introduced to host cells for a once under
proper conditions then AAV vectors will be developed.
Hemophilia is an X linked disorder that is characterized by continuous bleeding in
joints and muscles and increase in risk for intracranial hernorrhage. The main cause
of this disease is deficiency of the functional plasma clotting factor VIII. This results
from mutations in the FVIII gene. The Adeno associated viruses of parvovirus
family are small viruses that have a genome of single stranded DNA. Such kind of
virus is used for inserting genetic material at a particular site on chromosome with a
certainty of hundred percent. On the other hand there are few disadvantages of use of
adeno-associated virus is that it includes small amount of DNA it is capable to carry
and produce.
Virus Gene Therapy of Haemophilia Disease
Gene therapy is defined as the insertion of a gene into cells for correcting a
dysfunction in cells or for providing a new cellular function. Some diseases like
combined immunodeficiency syndromes, cystic fibrosis, haemophilia, cancers,
muscular dystrophy are some examples of results of defective genes. The gene
therapy is used for correcting replacing defective genes. The gene therapy is useful
in treatment of combined immunodeficiency syndromes that reflects remarkable
therapeutic benefit.
Philadelphia is a fully integrated commercial gene therapy that is dedicate for
challenging the inevitability of genetic diseases. The gene therapy begins with
scientists in creation if new, working copy of a missing or non-working gene. In this
gene therapy, a vector carries a new working copy of a gene through the body and
into the nucleus of a cell. When the gene is in nucleus, the vector is broken down
into the body.

Virus Gene Therapy of Haemophilia Disease
Haemophilia is a rare disease in which blood does not clot properly and majorly it
affects men. Proteins are responsible for clotting and work with platelets to stop
bleeding. Individuals who are suffering from haemophilia produce a low amount of
factor VII and factor IX. This results in bleeding more than a normal person. These
individuals are more susceptible to internal bleeding. Sometimes, bleeding causes
fatal because if it occurs in brain, then it is hazardous. In this disease, blood does not
clot as it should clot. Haemophilia is an inherited disorder and the individual is born
with this disease. This is caused because of a defect in clotting factor genes on the X
chromosome. Hemophilia is generally found in men and these are passed from
mother to son. There is no X chromosome present in male and that is why they are
not able to make up for defective gene. As females have XX chromosome and males
have XY chromosome, females are the carriers of this disease. Females carry the
disease hemophilia but they do not have this disorder. Defective genes cause
hemophilia and in females, if a girl is suffering from hemophilia then there must be
presence of abnormal gene on both of the chromosomes. This is a very rare
condition and this is not found in girls. Another reason by which hemophilia is
caused is spontaneous genetic mutation. This disorder can be developed if the body
of an individual generates antibodies that creates clotting element in blood. This
stops clotting element from functioning and bleeding does not stops.
Current and Emerging Gene Therapies
Various studies state that haemophilia can be treated permanently by gene therapy. In
a case adeno, associated virus was used to deliver a codon-optimized version of
human factor VIII gene. The vector was administered into three different cohorts of
patients such as low, high and medium dosage groups. This therapy was managed and
it has no adverse reactions because of the treatment. Bleeding decreases after the
gene therapy and this allows cessation of prophylactic FVIII treatments. The on
demand factor VII therapy is used for self-diagnosing bleeding after gene therapy.
Gene therapy can be useful for treatment of haemophilia. The people who are
suffering from haemophilia are relaxed by knowing the breakthrough in modern era
gene therapy that is founded to prevent haemophilia. In the gene therapy, a wild type
FIX in Adeno associated virus’s vector that contains liver specific promoter that
enables peripheral administration. Most of the patients of haemophilia who are given
high dosage experiences an increase in alanine aminotransferase with a drop of FIX
expression in presence of capsid related T-cell reactivity. These patients reacted to
short courses of steroids. Another gene therapy for Haemophilia was discovered in
which Adeno associated viruses, which contains FIX gene with Padua mutation,
achieved a FIX level of 33%.
CONCLUSION
From the above analysis, it has been concluded that gene therapy for hemophilia is a
safe treatment so far. The safety and efficacy of individual lasts for at least 6 years.
The vectors of Adeno associated viruses are episomal, they do not integrate, and that
is why there can be loss of efficacy. This is because of the turnover of transduced
hepatocytes. These vectors are non-integrating in nature.
References
Chandrakasan, S. and Malik, P., 2014. Gene therapy for hemoglobinopathies: the
state of the field and the future. Hematology/Oncology Clinics. 28(2).
pp.199-216.
Kaliberov, S. A. and Buchsbaum, D. J., 2012. Cancer treatment with gene therapy
and radiation therapy. In Advances in cancer, research (Vol. 115, pp. 221-
263). Academic Press.