à Using a viral or some non-viral
vector system enhances the efficiency, yet the immune response activates, and
clearance of foreign particle is confirmed.
à Alternatively, the DNA which
contains the targeted transgene is may be injected and manipulated along with the
liposomes into the patients. Plasmid DNA can also be targeted using different mechanical
means e.g. gene gun. (Klink D et.al
The antibody against viral particles does not permit
the second injection of the viral vector. To reduce the amount of neutralizing
antibody generated against vectors, is the current and basic area of research for
improving the vector delivery. In all gene delivery protocols, the requirement
of transgene is to cross the cell membrane and to enter in the nucleus. The
biggest hurdle is the delivery of transgene into the intracellular compartment
effectively (G FERRARI et.al. 1991).
Many different modifications are suggested for the viral vectors and for the non-viral
vectors for targeting the gene into the tissue. For example, VP22, which is a
protein of herpes simplex virus, contains a property of spreading from one cell
to another cell, and this attribute has been implemented in designing many
(Figure 2 General ways of in vivo gene therapy)
Classification of vectors for in vivo approach:
Viral vectors can be categorized into two main divisions,
integrating and non-integrating vectors which are based on their specific
recombination capability to the chromosome of host cell. Adeno associated
viruses are those, which are known for targeting the genetic material(DNA) to
chromosome number 19 of human genome. The genes are incorporated into the
chromosome which lead to a stable expression of targeted desired protein.
Another type is known as TEMPORARY in which the proteins are expressed for a
short time period only and in this case, the gene is not well integrated or
manipulated with the chromosome.
A flowsheet is
presented following to know about the classes of different vectors which are
associated with in vivo somatic cell gene transfer. The sheet is a better
explanation of theory.
Cystic Fibrosis Treatment with in
vivo somatic cell gene therapy:
Gene therapy has been developed as a unique treatment
for the patients suffering from cystic fibrosis (CF), which is a condition that
has been widely-researched till now and yet for which no specific kind of
treatment exists that could halt the progression and development of lung
diseases. One way to treat CF is by using gene therapy (somatic cell gene
transfer in vivo) which involves the transfer of corrected copies of a
regulator named, cystic fibrosis transmembrane conductance regulator (CFTR)
gene into the epithelial cells right into the air passage (Burney et.al. 2012).
CFTR gene was cloned in 1989 that led to
proof-of-principle studies and researches of CFTR gene transfer in vivo and in
different animal models. Earliest and basic clinical trials of many CF patients
were performed in 1993 which use both viral and non-viral gene transferring
agents in both nasal passage and in other bronchial epithelial epithelium.
Disadvantages/Demerits of In vivo
somatic cell gene therapy:
Along with all the potential uses of in vivo gene
therapy, there are also exist some potential disadvantages of in vivo therapy
which are as follows:
à the target cell infection is usually
à Many different types of cells have
the chances to be infected during the injecting of in vivo vectors in central
nervous systems e.g. in glia, neurons etc.
à the technique may be proving toxic
and cause toxicity of cells.
à Some vectors can be proving toxic
for host cells and reduce their immune response effectively.