Applications of Gene Therapy - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 271

Nucleus

Gene to be
transferred

Target cell DNA

Vector

Intracellular
effect

Extracellular effect

Figure 6.1 Simplified schematic diagram on the basis of gene therapy. First, the foreign
genetic material to be delivered has to be packaged in a suitable vector. (A) Introduction of
the vector containing therapeutic genetic material into the cell cytoplasm. (B) Transfer of
therapeutic genetic material into the nucleus of the recipient cell, followed by integration to
cellular DNA. (C) Expression of the foreign therapeutic gene, resulting in synthesis of the
desired protein product.

gene can potentially cure the disease, which would be a significant improvement
over lifelong protein replacement therapy or no therapy at all. For acquired diseases
like cancer, gene therapy allows local production or cancer-cell targeted expression
of a therapeutic gene product. Basically, there are four protocols or strategies that are
used to achieve the goals of gene therapy.

1. In vitro approach
2. Ex vivo approach
3. In situ approach
4. In vivo approach

The in vitro approach utilizes reporter genes like pEGFP , -gal in the cultured cells
to evaluate the transfection efficiencies of a gene carrier system [4] . The ex vivo
approach involves initial removal of the target cells from the body, which are then
cultured in vitro and incubated with vector containing the gene to be delivered. The
genetically altered cells are then reintroduced into the patient's body. This approach
is most frequently used for easily accessible body cells and tissues like epithelial
cells, blood cells, muscle cells, stem cells, and so forth [5] . The in situ protocols uti-
lize the direct injection of the DNA-vector system in close proximity of target cells
in the body, for example, in aerosol administration of the cystic fibrosis (CF) gene-
containing vector to the respiratory tract or direct injection of vectors in tumor mass.