Gene therapy is an experimental way to treat some diseases without traditional drugs or surgery.
On the surface, the concept is simple. It replaces a gene that doesn’t work with one that does.
Sometimes, a person gets a disease because they were born with a gene that doesn’t make protein the body needs. Gene therapy lets scientists put a working gene into a person’s DNA. In theory, once the body has the protein it needs, the disease will be fixed.
How Does It Work?
This is where a simple idea quickly gets complicated. But you really only need to know the big picture.
Gene therapy typically uses custom-made viruses to put the working gene into you. Viruses work by infecting cells and slipping their own genetics into your DNA. This tricks the cell into becoming a virus factory.
In the case of gene therapy, scientists put their gene of choice into the virus’s genetic material, and then “infect” a person’s cells -- but don’t worry. This “infection” is a good thing.
Which Diseases Does It Treat?
The FDA has approved several gene therapy treatments. One of the first is called CAR T-cell therapy, and it’s only for children and young adults with a type of cancer called B-cell acute lymphoblastic leukemia (ALL) who have already tried other treatments. It has also been approved for the treatment of multiple myeloma after other therapies have been tried.
Many other clinical trials are underway, often for rare conditions.
In Europe, a treatment for something called lipoprotein lipase deficiency -- a disorder in which a person can’t break down fat molecules -- became the first approved gene therapy in 2012. Another one that treats severe combined immune deficiency (you may know it as the “bubble boy” disease) is available in Europe.
Gene therapy for spinal muscular atrophy (SMA), called onasemnogene abeparvovec-xioi (Zolgensma), has also been approved.
Promising results in experiments have also been reported for other conditions, including:
- Some causes of blindness
- Immune deficiencies
- Muscular dystrophy
Is It Safe?
Safety is one of the top priorities in clinical trials. In the case of gene therapy, these studies clearly helped.
Concerns about safety caused the gene-therapy field to almost completely collapse in 1999. A teenage volunteer for a clinical trial died during an experiment.
Scientists found that their immune system reacted fiercely to the virus used in the treatment.
A year later, some people in a French trial got leukemia.
The tough lessons from those early events led to stricter safety requirements. Since then, researchers have found a way to use viruses -- safely -- to smuggle the genetic fix into your body without bothering your immune system. They’ve also developed careful guidelines that closely monitor study volunteers for side effects.
How Successful Has It Been?
It depends on the condition.
For muscular dystrophy, a 2016 review highlighted quite a few promising findings.
A form of leukemia was cured in a handful of people in a matter of days, researchers reported in 2013.
Studies for retinitis pigmentosa, which is a cause of blindness, and hemophilia have been encouraging. But in some cases, a person’s immune system starts reacting to the virus, and its effects stop.
Other trials have not gone as hoped.
The FDA approved the voretigene neparvovec-rzyl treatment in December 2017. An adeno-associated virus vector-based gene therapy, it is for treating patients with confirmed biallelic RPE65 mutation-associated retinal dystrophy.
What Is the Future?
Scientists are hopeful, but cautious, especially given the field’s turbulent history. Even once approved, some therapies will carry a hefty price tag. How high? The drug approved in Europe is said to cost about $650,000 per treatment. That's not the most expensive drug on the market.