Written for and originally published on AGT
Big Picture
Gene therapy, stem cell therapy, CAR-T, cell therapy and gene editing are all forms of genomic medicine1 – an approach to cure and treat human diseases that uses human biology rather than chemical compounds made in the lab. All of these tools are unlocking techniques and therapies with the power to cure formerly incurable diseases. Their use is ushering in a new era of healthcare.
What Is Gene Therapy?
Gene therapy is one of the tools being used by scientists as a result of the mapping of the human genome and the advances made in biotechnology. Gene therapy uses genetic material to halt the progression of a disease or cure a genetic defect. But inserting a gene is not as simple as swallowing a pill or receiving an injection. In contrast with previous generations of medicine, gene therapy takes the genetic material required to treat a disorder and introduces it into the body for uptake into the appropriate cells through what is best described as a viral update. Here’s how it’s done.
How Does It Work?
Genes are the part of an individual’s genetic material that decides an organism’s features, how it behaves in its environment and how it survives. They hold the information to build and maintain an organism’s cells and pass genetic traits to the next generation. Genes consist of a long combination of four different nucleotide bases that are known as adenine (A), cytosine (C), guanine (G), and thymine (T). The most important thing about genes is that all living things depend upon this code working correctly.2
In a monogenic disease, there is an error in one gene which generates too much, too little or incorrect protein. Most of these errors are present when we are born and populate every cell in our body. These errors can cause serious disease; however, if the error were to be corrected, it would make all the difference. So, suppose you have a gene with a mutation that tells a cell to make too much of a specific protein. In this case, the gene will continually overproduce which in some cases may not matter. However If the product of that gene and protein is toxic in large quantities, it can cause a problem.
With underexpression of a gene, it raises a similar problem and we need to bring in outside help to solve it. There are several ways to increase the product of a gene with another. The simplest way to increase expression would be to add a new copy of that gene which expresses independently normalizing the product of the gene. That’s where viral vectors come into play.
Viral Vectors — DoorDash for Genes
In gene therapy, a viral vector can be a delivery mechanism for genetic material.3 In the case of a monogenic disease, the vector will deliver the material required to fix the damaged gene. It’s not possible to just walk up, knock on the door, and hand over the new gene. It is necessary for the gene to travel through your blood or intracellular space and find the right cells which need genetic improvement. Luckily viruses have been doing this for millions of years. So scientists have modified viruses to deliver genes to the appropriate “doors”.
There are many types of viral vectors like adeno associated virus (AAV), Lentivirus, etc, but the basic theory applied is always the same. Identify a virus,, remove all the pathogenic parts, especially the ability to replicate, and add the gene you want to deliver. Then allow the viral vector to do what viruses do in nature; deliver the carried DNA sequence. If we deliberately invade a cell with the new gene, that gene will enter the nucleus of the healthy cell and replace the function of the previously missing or broken gene. The net result? Improvement if not a functional cure!
Is it “Fixed” for the Next Generation?
Can a genetic cure carry on to our children? Today, that is not possible because gene therapy uses somatic cells – cells that are not part of the egg and sperm, also known as the germline cells. It is the germline cells that pass the gene to the next generation. Gene therapy now being used to provide a “fix” that impacts only the individual receiving the inserted gene. As you’ll read in the article on gene editing, it may be possible in the future to “fix” not only the defective gene in the target patient, but also in any future offspring as well.
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