StemCell Therapy

Gene therapy has been headline news in recent years, in part due to the rapid development of biotechnology that enables doctors to administer such treatments. Broadly, gene therapies are techniques used to treat or prevent disease by tweaking the content or expression of cells' DNA, often by replacing faulty genes with functional ones.

The term "gene therapy" sometimes appears alongside misinformation about mRNA vaccines, which include the Pfizer and Moderna COVID-19 vaccines. These vaccines contain mRNA, a genetic cousin of DNA, that prompts cells to make the coronavirus "spike protein." The vaccines don't alter cells' DNA, and after making the spike, cells break down most of the mRNA. Other COVID-19 shots include the viral vector vaccines made by AstraZeneca and Johnson & Johnson, which deliver DNA into cells to make them build spike proteins. The cells that make spike proteins, using instructions from either mRNA or viral vector vaccines, serve as target practice for the immune system, so they don't stick around long. That's very, very different from gene therapy, which aims to change cells' function for the long-term.

Let's take a dive into what gene therapy actually is, addressing some common questions along the way.

DNA is a molecule that stores genetic information, and genes are pieces of genetic information that cells use to make a particular product, such as a protein. DNA is located inside the nucleus of a cell, where it's packaged into chromosomes, and also inside mitochondria, the "power plant" organelles located outside the nucleus.

Although there are mitochondrial diseases that could someday be cured with gene therapy, currently, the term gene therapy refers to treatments that target nuclear genes the genes on the 23 pairs of chromosomes inside the nucleus.

Classically, gene therapy has referred to the process of either "knocking out" a dysfunctional gene or adding a copy of a working gene to the nucleus in order to improve cell function. Gene therapy is currently directed at diseases stemming from a problem with just one gene, or at most a few genes, rather than those that involve many genes.

However, the field of gene therapy is now expanding to include strategies that don't all fall into the classic categories of knocking out bad genes or adding good genes. For example, researchers at Sangamo Therapeutics are developing genetic techniques for treating Parkinson, Alzheimer and Huntington diseases that work by ramping up or suppressing the activity of specific genes.

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While the treatments may add genes to body cells, knock out genes or act in some way to change the function of genes, each gene therapy is directed to the cells of particular body tissues. Thus, when scientists and doctors talk about what gene therapy does to DNA, they are not talking about all of the DNA in the body, but only some of it.

Gene therapy can be either ex vivo or in vivo.

Ex vivo gene therapy means that cells are removed from the body, treated and then returned to the body. This is the approach used to treat genetic diseases of blood cells, because bone marrow can be harvested from the patient, stem cells from that bone marrow can be treated with gene therapy for instance, to supply a gene that is missing or not working correctly and the transformed cells can be infused back into the patient.

In vivo gene therapy means that the gene therapy itself is injected or infused into the person. This can be through injection directly to the anatomic site where the gene therapy is needed (a common example being the retina of the eye), or it can mean injection or infusion of a genetic payload that must travel to the body tissues where it is needed.

In both ex vivo and in vivo gene therapy, the genetic payload is packaged within a container, called a vector, before being delivered into cells or the body. One such vector is adeno-associated virus (AAV). This is a group of viruses that exist in nature but have had their regular genes removed and replaced with a genetic payload, turning them into gene therapy vectors.

AAV has been used to deliver gene therapy for many years, because it has a good safety record. It is much less likely to cause a dangerous immune response than other viruses that were used as vectors several decades ago, when gene therapy was just getting started. Additionally, packaging genetic payloads within AAV carriers allows for injected or infused gene therapy to travel to particular body tissues where it is needed. This is because there are many types of AAV, and certain types are attracted to certain tissues or organs. So, if a genetic payload needs to reach liver cells, for example, it can be packaged into a type of AAV that likes to go to the liver.

In the early days of gene therapy, which began in 1989, researchers used retroviruses as vectors. These viruses delivered a genetic payload directly into the nuclear chromosomes of the patient. However, there was concern that such integration of new DNA into chromosomes might cause changes leading to cancer, so the strategy was initially abandoned. (More recently, scientist have successfully used retroviruses in experimental gene therapies without causing cancer; for example, a retrovirus-based therapy was used to treat infants with "bubble boy disease.")

After moving away from retroviruses, researchers turned to adenoviruses, which offered the advantage of delivering the genetic payload as an episome a piece of DNA that functions as a gene inside the nucleus but remains a separate entity from the chromosomes. The risk for cancer was extremely low with this innovation, but adenovirus vectors turned out to stimulate the immune system in very powerful ways. In 1999, an immune reaction from adenovirus-carrying gene therapy led to the death of 18-year-old Jesse Gelsinger, who'd volunteered for a clinical trial.

Gelsinger's death shocked the gene therapy community, stalling the field for several years, but the current gene therapies that have emerged over the years based on AAV are not dangerous. However, they tend to be expensive and the success rate varies, so they typically are used as a last resort for a growing number of genetic diseases.

Gene therapy can treat certain blood diseases, such as hemophilia A, hemophilia B, sickle cell disease, and as of 2022, beta thalassemia. What these diseases have in common is that the problem comes down to just one gene. This made beta thalassemia and sickle cell disease low-hanging fruits for ex vivo gene therapies that involve removing and modifying bone marrow stem cells, whereas hemophilia A and hemophilia B are treated with in vivo gene therapies that target liver cells. That said, other treatments exist for these blood diseases, so gene therapy is more of a last resort.

Numerous enzyme deficiency disorders also come down to one bad gene that needs to be replaced. Cerebral adrenoleukodystrophy, which causes fatty acids to accumulate in the brain, is one such disorder that can be treated with gene therapy, according to Boston Children's Hospital. CAR T-cell therapy, which is approved for certain cancers, involves removing and modifying a patient's immune cells and is known as a "cell-based gene therapy."

Gene therapy has also been useful in treating hereditary retinal diseases, for which other treatments have not been useful.

Another group of targets for gene therapy are diseases of the nervous system.

"We are at a remarkable time in the neurosciences, where treatments for genetic forms of neurological disorders are being developed," Dr. Merit Cudkowicz, the chief of neurologyat Massachusetts General Hospital and a professor at Harvard Medical School, told Live Science.

For example, gene therapies are being developed to treat a pair of genetic diseases called Tay-Sachs disease and Sandhoff disease. Both conditions result from organelles called lysosomes filling up with fat-like molecules called gangliosides. The effects of these diseases include delay in reaching developmental milestones, loss of previously acquired skills, stiffness, blindness, weakness and lack of coordination with eventual paralysis. Children born with Tay-Sachs disease and Sandhoff disease generally dont make it past 2 to 5 years of age.

"There has been no routine antenatal or neonatal test for Tay-Sachs and Sandhoff, because there has been no available treatment whatsoever," said Dr. Jagdeep Walia, a clinical geneticist and head of the Division of Medical Genetics within the Department of Pediatrics and the Kingston Health Sciences Centre and Queen's University in Ontario, Canada. Walia is developing a gene therapy aimed at replacing the gene for Hex A, the enzyme that is deficient in these children. So far, the treatment has shown good efficacy and safety in animal models, but it still needs to be tested in human patients.

The future looks hopeful when it comes to gene therapy overall, on account of new technological developments, including CRISPR gene editing. This is an extremely powerful technique for cutting out parts of DNA molecules and even pasting new parts in analogous to what you do with text in word processing applications. CRISPR is not the first method that scientists have used to edit DNA, but it is far more versatile that other techniques. It is not yet quite ready for in vivo chromosomal manipulation, but it is advancing exponentially.

Perhaps even closer to the horizon is the prospect of delivering larger genetic payloads into cells. One big drawback of the AAV vector is that each virus particle can carry just a small amount of DNA, but recent research has revealed that a different type of virus, called cytomegalovirus, can be adapted to carry gene therapies with a much bigger payload than AAV. Not only might this some day expand gene therapy to more diseases requiring larger genes than AAV can carry, but it also could enable more than one gene to be delivered in a single therapy.

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Gene therapy: What is it and how does it work? | Live Science

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How Does Gene Therapy Work? Types, Uses, Safety – Healthline

September 21st, 2024 2:40 am

Genes are small segments of DNA that instruct your cells to make certain proteins when specific conditions are met.

Mutated genes, on the other hand, may cause your cells to make too much or too little of the necessary protein. Even small changes can have a domino effect across your body just as tiny changes in computer code can affect an entire program.

Viral vectors

Scientists dont have tweezers small enough to edit your DNA by hand. Instead, they recruit a surprising ally to work on their behalf: viruses.

Typically, a virus would enter your cells and alter your DNA to create more copies of itself. But scientists can switch out this programming with their own, hijacking the virus to heal instead of harm. These vectors, as theyre called, dont have the parts they need to cause disease, so they cant make you sick the way a regular virus could.

There are two types of gene therapy:

Gene therapy is different from genetic engineering, which means changing otherwise healthy DNA for the purpose of enhancing specific traits. Hypothetically, genetic engineering could potentially reduce a childs risk of certain diseases or change the color of their eyes. But the practice remains highly controversial since it hovers very close to eugenics.

Gene therapy may be used to treat a variety of genetic conditions, including:

Inherited vision loss

When the RPE65 gene in your retinas doesnt work, your eyeballs cant convert light to electrical signals.

The gene therapy Luxturna, approved by the Food and Drug Administration (FDA) in 2017, can deliver a functional replacement of the RPE64 gene to your retinal cells.

Blood disorders

The FDA-approved Hemgenix can treat the bleeding disorder hemophilia B. The viral vector instructs your liver cells to create more of the factor IX protein, which helps your blood clot.

Meanwhile, the gene therapy Zynteglo, approved by the FDA in 2022, treats beta-thalassemia by giving your bone marrow stem cells correct instructions for creating hemoglobin.

This blood disorder can lower the oxygen in your body because it decreases your bodys hemoglobin production.

Spinal muscular atrophy (SMA)

In infantile-onset SMA, an infants body cant make enough of the survival of motor neuron (SMN) proteins necessary to build and repair motor neurons. Without these neurons, infants gradually lose their ability to move and breathe.

The gene therapy Zolgensma, approved by the FDA in 2019, replaces faulty SMN1 genes in an infants motor cells with genes that can create enough SMN proteins.

Cerebral adrenoleukodystrophy (CALD)

Your ABCD1 gene produces an enzyme that breaks down fatty acids in your brain. If you have cerebral adrenoleukodystrophy, this gene is either broken or missing.

Skysona, FDA approved as of 2022, delivers a functional ABCD1 gene so that fatty acids dont build up and cause brain damage.

Cancers

Most cancer gene therapies work indirectly by inserting new genes into a powerful antibody called a T cell. Your changed T cells can then latch on to cancerous cells and eliminate them, similar to how they attack viruses.

Some people considering gene therapy may feel uneasy about putting viruses in their body.

Keep in mind, though, that gene therapies undergo extensive testing before approval. The viruses in gene therapies are also fixed so they cant replicate similar to many vaccines.

That said, gene therapies may pose other risks:

Despite these issues, experts generally believe gene therapy offers more benefits than risks.

Most of the conditions treated with gene therapy are life threatening. The dangers of leaving them untreated often outweigh the risks of potential side effects.

Gene therapy does come with a few drawbacks that keep it from becoming a widespread treatment.

Limited targets

Gene therapy can only target certain mutations. This means it may not work for everyone with a specific condition.

For example, two people may have inherited vision loss. Currently, gene therapy can only treat vision loss caused by the RPE64 mutation.

Time to approval

Because gene therapy research is so new, experts do extensive safety testing before introducing their treatments to the public. It can take years to get FDA approval for each new therapy.

Expense

As you might imagine, gene therapies are expensive to manufacture and administer. This not only affects funding for clinical trials but also the price of the drug.

For example, the gene therapy Zolgensma is the most expensive drug in the United States at $2.1 million per dose. Even with insurance, that kind of price tag remains out of reach for the average American.

Scientists are trying to find ways to make the development process safer, cheaper, and more efficient so more people can access gene therapy.

Gene therapy works to treat several different genetic diseases by editing the mutations that cause them. As researchers further refine and expand this technology, they may find even more conditions that could be treated with it.

Experts are also continuing to explore options to make gene therapy more affordable so people who need these treatments have an easier time getting them.

Emily Swaim is a freelance health writer and editor who specializes in psychology. She has a BA in English from Kenyon College and an MFA in writing from California College of the Arts. In 2021, she received her Board of Editors in Life Sciences (BELS) certification. You can find more of her work on GoodTherapy, Verywell, Investopedia, Vox, and Insider. Find her on Twitter and LinkedIn.

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How Does Gene Therapy Work? Types, Uses, Safety - Healthline

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In race to make gene therapy for age-related blindness, 4D Molecular announces positive results – STAT

September 21st, 2024 2:40 am

In race to make gene therapy for age-related blindness, 4D Molecular announces positive results STAT

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In race to make gene therapy for age-related blindness, 4D Molecular announces positive results - STAT

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Penn gene therapy pioneer Jim Wilson explains why he’s leaving – The Business Journals

September 21st, 2024 2:40 am

Penn gene therapy pioneer Jim Wilson explains why he's leaving The Business Journals

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Penn gene therapy pioneer Jim Wilson explains why he's leaving - The Business Journals

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StemCell Therapy

Annual Health Observances | NIAMS – National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)

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