What is Gene Therapy technique and how it treat genetic disease?

The clinical outcomes of attempts to treat genetic disease have only been partially successful. More developmental work is required before the therapies can be said to be effective.

Gene therapy is a technique in which DNA is introduced into a patient to treat a genetic disease. The new DNA usually contains a functioning gene to correct the effects of a disease-causing mutation.

In other words, it is a medical strategy that addresses the underlying genetic issue in order to treat or prevent disease. Instead of utilizing drugs or surgery, gene therapy procedures allow doctors to treat a problem by changing a person’s genetic composition.

Introduction:

• Gene therapy uses segments of DNA (usually the genes) to treat or prevent disease.
• The DNA is carefully selected to correct the effect of a mutated gene that is causing disease.
• This technique was first developed in 1972, but so far got limited success in treating human diseases.
• Therefore, Gene therapy may be a promising treatment option for some genetic diseases, including muscular dystrophy and cystic fibrosis. There are two different types of gene therapy depending on which types of cells are treated:

Somatic gene therapy: 

In somatic gene therapy technique, there is a transfer of a section of DNA to any cell of the body that doesn’t produce sperm or eggs, and the effects of gene therapy will not be passed onto the offspring.

Germline gene therapy:

In germline gene therapy there is a transfer of a section of DNA to cells that produce eggs or sperm and the effects of gene therapy will be passed onto the patient’s offspring and subsequent generations.

Gene Therapy Techniques:

There are several techniques for carrying out gene therapy. These include:

Gene augmentation therapy:

• Gene therapy is used to treat diseases caused by a mutation that stops a gene from producing a functional product, such as a protein. This therapy adds DNA containing a functional version of the lost gene back into the cell.
• This new gene produces a functioning product at sufficient levels to replace the protein that was originally missing.
• Gene therapy is only successful if the effects of the disease are reversible or have not resulted in lasting damage to the body.
• For example, this can be used to treat loss of function disorders such as cystic fibrosis by introducing a functional copy of the gene to correct the disease (as mentioned in figure);

Gene inhibition therapy

• This gene therapy technique is suitable for the treatment of infectious diseases, cancer, and inherited diseases caused by inappropriate gene activity.
• The aim of this was to introduce a gene whose product either inhibits the expression of another gene or interferes with the activity of the product of another gene.
• The aim of this therapy is to eliminate the activity of a gene that encourages the growth of disease-related cells.
• For example, sometimes cancer is the result of the overactivation of an oncogene (a gene that stimulates cell growth). So, by eliminating the activity of that oncogene through gene inhibition therapy, it is possible to prevent further cell growth and stop the cancer in its tracks.

The killing of specific cells:

• It is suitable for diseases such as cancer that can be treated by destroying certain groups of cells.
• The aim is to insert DNA into a diseased cell that causes that cell to die.
• This can also be achieved in one of two ways:
  1. The inserted DNA contains a “suicide gene” that produces a highly toxic product that kills the diseased cell. The inserted DNA causes the expression of a protein that marks the cells so that the diseased cells are attacked by the body’s natural immune system.
  2. It is essential with this method that the inserted DNA is targeted appropriately to avoid the death of cells that are functioning normally.

How is DNA Transfer done?

• A section of DNA/gene containing instructions for making a useful protein is packaged within a vector, usually a virus, bacterium or plasmid.
• The vector acts as a vehicle to carry the new DNA into the cells of a patient with a genetic disease.
• Once inside the cells of the patient, the DNA/gene is expressed by the cell’s normal machinery, leading to production of the therapeutic protein and treatment of the patient’s disease.

Challenges of Gene Therapy:

Delivering the gene to the right place and switching it on:

It is crucial that the new gene reach the right cell; delivering a gene to the wrong cell would be inefficient and could also cause health problems for the patient. Even once the right cell has been targeted, the gene still has to be turned on, and cells sometimes obstruct this process by shutting down genes that are showing unusual activity.

Avoiding the immune response:

The role of the immune system is to fight off intruders. Sometimes, new genes introduced by gene therapy are considered potentially harmful intruders. This can spark an immune response in the patient that could be harmful to them. Scientists, therefore, have the challenge of finding a way to deliver genes without the immune system ‘noticing’. This is usually done by using vectors that are less likely to trigger an immune response.

Making sure the new gene doesn’t disrupt the function of other genes:

In ideal cases, when a new gene is introduced by gene therapy, it will integrate itself into the genome of the patient and continue working for the rest of their lives. There is a risk that the new gene will insert itself into the path of another gene, disrupting its activity. This could lead to lethal health effects; for example, if it clashes with an important gene involved in the regulation of cell division, it could result in cancer.

The cost of gene therapy:

Most of the genetic disorders that can be targeted with gene therapy technique are extremely rare. Gene therapy often requires an individual or case-by-case approach. This is an effective procedure, but it is also expansive.

The clinical outcomes of attempts to treat genetic disease have only been partially successful. More developmental work is required before the therapies can be said to be effective, especially in the prevention of brain damage.

This article is jointly written by Ibrahim Salam Baig1, Hafiza Mehak Yousaf2 from Department of Biological Sciences1, Department of Microbiology2, College of Veterinary & Animal Sciences, Jhang.