Arshdeep Vinod Chauhan

The Types of Gene Therapy

There are two types of gene therapy:

Somatic Gene Therapy-(Body Cells):

Somatic Gene Therapy is a process in which “altered genes are inserted into the affected part of the body, or body cells are removed, treated with altered genes, and replaced”. (citation 1.8)

The Pros- Unlike germ line gene therapy in which reproductive cells are modified, somatic gene therapy modifies body cells. Those who undergo the process of somatic gene therapy do not pass the genes, which were altered, on to their offspring. This is advantageous because it does not interfere with ethical concerns regarding natural infant development. Another beneficial reason for using somatic gene therapy is that it is a much safer process, and not as life challenging like germ line therapy.

(citation 1.8)

The Cons- Although the ability of not passing down the modified genes to offspring may appear beneficial, it also has its cons. By being unable to pass down the altered genes to the offspring, future generations will not be able to have the same health benefits as their parents did because the effects will stop at the patient who has undergone somatic gene therapy. Another con is that somatic gene therapy is only temporary. Those who undergo somatic gene therapy, will often require to "receive this treatment many times for the rest of their lives"(citation 1.8) . This is because “body tissue cells, in which the genes were inserted, are lost”(citation 1.8). Also, some viruses that are used by gene therapists to insert genes into the cells can result in an accidental immune system response.

(citation 1.8)

Germ Line Therapy-(Reproductive Cells):

Germ Line is defined as “a cell lineage which consists of cells which are used to pass down genetic inheritance to the next generation” (citation 1.9).Germ cells include cells that make eggs and sperm, called gametocytes. Germ line can be used to trace back many generations. When cells divide and develop into an embryo, the germs cells nullify. Later on, these cells will produce eggs or sperm in the embryo that will eventually become an adult organism. In germ line gene therapy “changes could be made to the lineage of cells which contain genetic information that will be passed down.” (citation 1.9)

The Pros- This type of therapy actually has a future in offering patients a true cure to the disease. Another benefit is that parents can have a healthy child. This is because germ line therapy focuses on treating the reproductive cells, so that any kinds of genetic defects would not be passed down to offspring. It is more efficient and also cost saving unlike somatic gene therapy. It is a one time process, which benefits not only the patient, but the generations to come.

(citation 1.9)

The Cons- Too much extensive research needs to be done on early embryos, which thus will result in too many topics to research. Germ-line therapy is seen as holding too much “scientific uncertainty and risk” (citation 1.10). Germ-line therapy violates the way things work naturally. This means that it goes against religious reasons because man has intentionally modified an embryo so that the offspring and the other generations to come may not develop a genetic defect.

(citation 1.9) (citation 1.10)

The DNA Delivery Vehicle:

In order to replace a malfunctioning gene, scientists must replace it with a therapeutic gene by inserting it into the genome. So now how can this be done? To have successful gene delivery, there must be an efficient way to deliver DNA into the cells, and actually make it work! Scientists use vectors, which are also known as the DNA delivery vehicle, in order to deliver the DNA into the cell. A gene therapy vector must be customized in accordance to the features of the disorder that is to be treated. However, the most challenging part about gene therapy is choosing the right and most suitable vector.

(citation 1.11)

There are two types of vectors that can be used:

Viral Vectors: This type of vector uses viruses to transfer genes into cells.

Non-Viral Vector: This type of vector uses plasmids, which are circular DNA molecules. By nature, plasmids are used by bacteria to transfer genes from cell to cell.

(citation 1.11)

Click on this video to learn about how gene therapy by viruses are done! (citation 3.4)

Want to know what kinds of vectors are used? Click on the picture above to explore the Vector Toolbox!

(citation 1.11) (citation 2.8)

This chart shows all the different types of vectors used in Gene Therapy.

(citation 2.9)

Ex Vivo versus In Vivo Gene Therapy

(citation 2.10)

(citation 2.11)