Understanding investigational gene therapy
The science behind the ongoing clinical research
Gene therapy is in clinical trials to understand the risks and whether it may have a positive effect on people with certain genetic conditions. Those trials may be limited to certain people, like adults, or to certain forms of the condition. To understand the science behind it, let’s start at the beginning.
Understanding investigational gene therapy
The science behind the ongoing clinical research
Gene therapy is in clinical trials to understand the risks and whether it may have a positive effect on people with certain genetic conditions. Those trials may be limited to certain people, like adults, or to certain forms of the condition. To understand the science behind it, let’s start at the beginning.
What is a gene?
You’ve probably heard about genes and how you got your hair color from this parent and your eye color from that parent. But, how much do you really know about genetics and how genes work?
GENES ARE STEP-BY-STEP INSTRUCTIONS FOR THE HUMAN BODY
The key role of genes is to provide the instructions for making proteins. Proteins are the building blocks of the body and serve important functions like tissue repair and helping blood to clot.
As humans, we all have similar instructions. In fact, less than 0.1 percent of our genetic makeup is different. But small differences in our genes are what give us our unique individual traits on the outside (in terms of hair color, eye color, and height) and on the inside (for bodily functions such as tissue repair and fighting infection).
GENES ARE SEGMENTS OF DNA
Think of DNA as the language used in your genetic instructions. DNA is made up of components called nucleotide bases that are like the letters of a word. You must have the correct nucleotide bases and they must appear in the correct order for the gene to be readable so it can fulfill its intended purpose—producing proteins.
DNA stands for deoxyribonucleic acid. The 4 nucleotide bases responsible for gene construction are adenine (A), guanine (G), cytosine (C), and thymine (T). These nucleotides pair up with each other, A with T and C with G.
BUT WHERE ARE OUR GENES?
They can be found in our chromosomes, which contain hundreds to thousands of genes. Your chromosomes lie deep within a structure called the nucleus, which acts as the command center of the cells that make up your body.
Human cells typically contain 23 pairs of chromosomes. In males and females, 22 of those pairs look the same. The 23rd pair, also called the sex chromosomes, differs between males and females. Females have two copies of the X chromosome while males have one X and one Y chromosome.
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What causes genetic conditions?
Did you know there are approximately 20,000 genes in the human body? Unfortunately, a mutation, or variation, in just one gene can lead to a genetic condition. Knowing what causes a genetic condition is the first step in understanding how, potentially through ongoing research in gene therapy, physicians might be able to treat these conditions differently.
GENETIC CONDITIONS ARE THE RESULT OF MUTATIONS
Genetic conditions are the result of mutations, or changes, in the structure of a gene. These mutations are most often passed down from parents but can sometimes happen spontaneously. Cystic fibrosis and hemophilia are examples of genetic conditions.
In regard to hemophilia, the gene responsible for producing factor VIII is located in the X chromosome. Because females have two X chromosomes, both chromosomes would need to have the mutation for them to be severely affected by the disease. However, they can carry the mutated gene and pass it on to their children.
MUTATIONS CAN AFFECT YOUR GENETIC INSTRUCTIONS
A mutation can affect the genetic instructions in your body. The instructions can be missing or incorrect, changing the way proteins are produced. This can result in the production of a protein that does not work properly or, in some cases, the protein is not produced at all.
Mutations can take the form of changed base pairs, extra DNA where it doesn’t belong, missing DNA, or repeated DNA. In people with hemophilia A or B, the genetic mutation affects the body’s ability to produce a protein called factor VIII or factor IX, respectively. These proteins are critical for blood to clot.
THERE ARE 3 TYPES OF GENETIC CONDITIONS
The 3 types of genetic conditions are single-gene conditions, multi-gene conditions, and chromosomal conditions. Hemophilia is an example of a single-gene (or monogenic) condition.
- Monogenic conditions are caused by a mutation in a single gene. Other examples include cystic fibrosis and Huntington disease
- Multifactorial inheritance conditions, or multi-gene conditions, develop from multiple small genetic mutations and can lead to some of the more common diseases we’re familiar with, such as heart disease and diabetes
- Chromosome disorders are caused by changes to the number or structure of chromosomes. Down syndrome is the most common disorder related to a numerical abnormality
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What is gene therapy?
A genetic condition could potentially have a genetic solution, right? This logical thinking gave birth to the first research in gene therapy over 50 years ago. Now being evaluated in multiple clinical trials for a range of genetic conditions to determine the possible benefits and risks, gene therapy has the potential to bring an entirely new option to people with specific genetic conditions and those who support and care for them.
GENE THERAPY SEEKS TO ADDRESS GENETIC MUTATIONS
Simply put, gene therapy is being researched in clinical studies as a novel method that attempts to use genes to treat or prevent disease.
METHODS OF GENE THERAPY BEING STUDIED
A few different approaches to gene therapy are being explored. Gene therapy may involve attempting to repair or replace a mutated gene, disabling a mutated gene that is causing trouble, or introducing a functional copy of the gene into the body to help the problematic mutated gene.
- With the method of gene therapy called gene transfer, a functional gene is inserted into a cell with the hope it will work in place of the mutated gene. Viral, chemical, and physical methods are being explored for transferring genes. With in vivo gene transfer, the transfer of the new gene occurs inside the body after systemic delivery, often using an IV infusion
- In ex vivo gene therapy, a type of cell-based therapy being researched, the process happens outside the body. First, affected cells are removed from the body via a biopsy. Functional genetic material is introduced into the cells. The cells undergo a change in this process, and then are delivered back into the patient’s body
- In gene editing, the idea is to make changes to the original DNA. This technique makes it possible to repair the original DNA or add new DNA in a specific location or remove the original DNA. Zinc finger nucleases and CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) are methods of gene editing being researched
OVER 50 YEARS OF RESEARCH
Gene therapy has been explored as a potential treatment approach for well over 50 years. In the past decade, the FDA and EMA (European Medicines Agency) have approved gene therapies for genetic conditions. Gene therapy is currently being researched in many clinical trials for various genetic disorders, including hemophilia A and B.
To explore future, current, and past research in gene therapy, visit ClinicalTrials.gov.
- Gene therapy timeline
- 1972 — Concept of gene therapy considered as a form of treatment in the journal Science
- 1984 — Dr. Gordan Vahar publishes a paper reporting successful factor VIII cloning
- 1990 — First gene therapy trial in humans
- 1999 — Lessons learned regarding risks related to potential for severe immune response in early gene therapy trial with non-AAV vector
- 2003 — The Human Genome Project is completed
- 2003 — China approves the first gene therapy for the treatment of head and neck cancers
- 2005 — First gene therapy trial in hemophilia B using AAV vector technology
- 2015 — First gene therapy trial in hemophilia A using AAV vector technology
- 2017 — The first gene therapy, for a genetic disease that causes blindness, is approved in the United States
- Future — Additional gene therapies are being researched
ONGOING RESEARCH
Gene therapy is in ongoing clinical trial research to determine the potential risks and benefits of treatment.
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How is gene therapy designed to work?
It's not magic—it's science in progress and, if the trials are successful, it has the potential to offer a remarkably different approach to the way we've historically managed genetic disease. Let's look at an example…
GENE TRANSFER
Currently undergoing clinical trials in many different conditions, including hemophilia A and B—this method of gene therapy aims to introduce a functioning gene that is intended to allow the body to produce what it lacks.
CREATING A FUNCTIONING GENE
The gene transfer process begins when a functional copy of a mutated gene is created in a laboratory. The functional gene is developed to contain the instructions for making a needed protein.
BUILDING A TRANSPORT VEHICLE
The functional gene now has to be delivered into the body. To protect the gene and allow it to move around the body, a transport vehicle is created from a neutralized virus.
The transport vehicle created from a virus is called a viral vector. When a viral vector is created, the inner viral material is removed in a lab, leaving behind the outer protein shell. Viruses used in gene transfer include adenoviruses, adeno-associated viruses (AAV), and lentiviruses. Ongoing studies are evaluating the body's immune response to gene therapy.
DELIVERING THE FUNCTIONAL GENE
A functional gene is placed inside the transport vehicle and large numbers are administered via an intravenous infusion. The transport vehicle is designed to target the functional gene toward a preferred tissue. In hemophilia A and B, the liver is the target because it can make the proteins required for blood to clot. In other diseases, such as Huntington disease, the brain is the target.
The type of AAV used to make the transport vehicle helps determine which parts of the body are targeted. Different viruses target certain bodily tissues more than others. While certain tissues are targeted, the AAV can travel throughout the body. When the functional gene is placed inside the AAV, additional DNA is included that is intended to allow it to work and promote production of the protein only within the targeted cells. Research is ongoing to understand to what extent the AAV may deliver the functional gene to the body’s other tissues.
MAKING PROTEINS
Once introduced to the body, the new gene is designed to work in place of the gene that isn’t functioning properly. If successful, the goal for this new gene is to provide instructions for the body to make the protein it needs. In the case of hemophilia, the liver is targeted to make the proteins.
- The new, functional gene enters the nucleus of the targeted cells. There, it is generally expected to reside as an episome, or circular piece of DNA, outside the chromosomes. The original genetic material found in the chromosomes is intended to be left unchanged. This means the mutated gene would still be there and can be passed on to a person’s offspring. In some cases, the gene integrates directly into the existing DNA. Research is ongoing to better understand the rate and impact of integration.
- Ongoing clinical trials are being conducted to understand how gene therapy will affect the human body. Please be sure to read through the section "WHAT ARE THE RISKS OF GENE THERAPY?"
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What are the goals of gene therapy in clinical trials?
We typically take medicine to help us feel better, whether physically or mentally. In the case of gene therapy, clinical trials are underway to determine the risk and whether the need for further treatment and the burdens of chronic disease could be reduced or eliminated for some people. It’s important to remember that the long-term effects of gene therapy are also being studied and have not yet been determined.
SO, WHAT DO WE HOPE FOR FROM GENE THERAPY RESEARCH?
Gene therapy aims to address specific mutations in an individual's genetic instructions, allowing the body to produce the proteins it needs.
INTRODUCING WORKING GENES
One goal of gene therapy is to introduce functioning genes into the body to try to target the mutations that are responsible for genetic conditions.
PRODUCING PROTEIN
Also being researched is a way for the new, functional gene to help the body produce the protein it needs to function properly. For example, in hemophilia A or B, the goal is to allow the body to produce factor VIII or factor IX, respectively, on its own.
POTENTIALLY REDUCING THE NEED FOR TREATMENT
Research is ongoing to determine if gene therapy can help the body produce the proteins it needs. This may lead to less reliance on currently available medication.
POTENTIALLY ELIMINATING OR REDUCING SYMPTOMS
Clinical trials are evaluating whether gene therapy could eliminate or reduce symptoms, possibly lessening both the physical and emotional burden of a disease. However, gene therapy may not be able to address preexisting damage. All of these goals as well as the risks are currently being evaluated in clinical trials in humans.
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