Earliest human history indicates that people, through trial and error, searched for and found out which of the easily accessible chemicals and plants had therapeutic effects.
Centuries later, we still are attempting to find novel and effective drugs to treat existing and newly emerging diseases.
Medicine at the moment is highly dependent on these drugs, whose development in the modern era is facilitated by the use of highly efficient biochemical, molecular and imaging techniques to understand the mechanistic pathways of various diseases.
These drugs bring their effect by binding to high affinity receptors and micromolecules found under pathologic or non-pathologic conditions.
Simply put, receptors are macromolecules that bring about a biochemical or physiological change upon binding other molecules (ligands), such as hormones. Some receptors are found on the surface of a cell while others are found inside the cell.
In addition, the near completion of the human genome project has helped us to define the genetic bases of various diseases leading to an improved etiology and pathophysiology.
But these and other scientific discoveries have indicated the limitations of conventional drug treatment.
It is now clear that regenerative and reparative treatments have to take different avenues than drug administration.
Hence, the scientific world is giving a lot of attention to developing novel techniques to treat a number of degenerative diseases such as Parkinson’s and Alzheimer’s diseases.
One of the techniques that promises a feasible way for treatment of various diseases is the delivery of exogenous genetic material through the use of viral vectors, or gene therapy.
A gene, simplistically, is a sequence of DNA that encodes for a specific protein. Proteins are macromolecules that have structural, catalytic and regulatory function in all organisms.
The theme of gene therapy is to change defective genes that are associated with the cause and/or progression of a disease.
This may be achieved through a number of mechanisms. One method is through the insertion of a normal gene into a nonspecific location of a genome in order to replace a non-functional gene.
The second method is to change an abnormal gene with a normal gene.
Another method that is also employed is the selective reverse mutation of an abnormal gene, which changes an abnormal gene to a normal gene. It is also possible to turn off an abnormal gene through the delivery of other specific genes.
The idea of gene therapy seems simple. But in reality, actual trials must overcome a number of hurdles.
First and foremost, the delivery vehicle for the gene must be safe to the organism.
Second, it must have a high percentage of efficiency in delivering the gene to the target cells.
Last, but not least, the vector system must be highly specific in targeting certain cell types and have a mechanism to regulate the levels of expression of the gene delivered in the target tissue.
To anyone’s surprise, viruses, the agents that cause many types of diseases, fulfill the above criteria for the most part, making them ideal vectors in gene therapy.
Different viruses have their own advantages and shortcomings in their application for gene therapy. Some viruses that are being used for such purposes are Herpes simplex Viruses, Human Immunodeficiency viruses (HIV), adenoviruses (causative agents of common cold) and adeno-associated viruses (which don’t cause any type of human diseases).
The ability of viruses to encase and deliver viral and non-viral genes to the host cells under pathologic conditions is being utilized by genetically altering viruses to lose their virulence (lose their ability to cause diseases) and carry normal human DNA.
Some diseases such as Severe Combined Immunodeficiency (SCID) have been treated through this method (though have showed some serious complications) while for others such as Parkinson’s disease have just started clinical trials.
University of Bridgeport
Saturday, July 5, 2025