Gene therapy is one of the newest approaches to the treatment of diseases. It’s well suited for illnesses that can be pinpointed down to the specific gene sequence causing them.
Suppose you have a gene for reading my articles on LinkedIn. But in your case, the gene is damaged or missing from your DNA. Then you will suffer by being unable to read my articles, no matter how badly you want to read them.
But, if the gene is somehow made available to your cellular system, and you receive a full functioning gene, then you can start reading my articles religiously again. It’s not like I have that many writings here, but this may not be the best example, so let’s try another approach.
Imagine you took your car to the mechanic because of a flat tire. Upon inspection, the mechanic finds a nail, pierced your tire, and causing its current state manifested as a flat tire.
Everything else works fine, but the car cannot move because of the flat tire.
So, the mechanic removes the nail, puts a patch on the tire, fills it with air, and now you can resume your day. Similarly, gene therapy relies on identifying the “nail on your tire,” but instead of a nail, it’s a damaged DNA/gene sequence.
There are two main methods to supply genes to a patient with an underlying damaged DNA/gene sequence to restore proper body function:
Ex-vivo gene therapy is when the patient’s cells are removed from their body, treated in the laboratory under the highest sterile regulations, and then returned to the patient’s body.
Examples include some Chimeric Antigen Receptor-T cell therapies (CAR-T). The cells, when removed from the body, are injected with genetic material that they lacked, and in turn, they now possess a complete DNA/gene sequence that can produce the proteins needed for normal functioning of the body.
Being that cells are so small, scientists rely on vectors (biological syringe) such as viruses to transfer these genetic materials to the inside of cells.
I know that with COVID-19, people are scared of viruses, but viruses train their whole lives for – infecting cells with genetic sequences.
In biotechnology, we leverage these viral vectors to deliver functional versions of DNA/gene sequences to those found damaged in the patient.
Marvelously, once the cells receive the functional DNA sequences, they know what to do with this new genetic information. They read it, translate it, and use it to restore the proper functioning of the body when returned into the patient’s body.
Because of the need to extract cells from the patient’s body first, Ex-Vivo gene therapy works best for the treatment of blood disorders because of obvious reasons, serum-based cells are more easily removed from the patient and easily returned into the patient.
In-Vivo gene therapy is the approach for diseases where it’s not feasible to use Ex-Vivo methods. For this method, a vector carrying the gene of interest is delivered into the patient’s body systemically or locally intravenously (IV) or via injection method by a medical professional.
Where and how the viral vector gets delivered into the patient depends on the type of disease. For instance, if its spinal cord injury, the vector would be injected into the spinal cord, if its an eye injury, the injection would be in the eye. If it’s a muscle-related disease, then an IV would be most appropriate because muscles can be found everywhere in the body.
To sum it up, the main driver for gene therapy success is the vector.
A vector is any vehicle that can shuttle genetic information to the interior of a cell (aka nucleus), then once inside the nucleus, they release that information so that a cell’s internal mechanism can interpret this information and transcribe it into functional proteins that drive our bodily functions and allow us to have “normal” operation.
For gene therapy, one of the most successful vectors has been a small virus called Adeno-Associated Virus (AAV). AAV-based gene therapy approaches have received approvals for sale as medication or cures for deadly diseases, such as Spinal Muscular Atrophy (SMA), a condition that significantly limits patients who are born with the gene disorders to live only up to their 2nd birthdays.
Using AAV gene therapy, patients are living beyond their second birthdays, and a limited lifespan is becoming a thing of the past for some families.
Many more AAV-based treatments are being investigated for their potential to cure disease. Still, due to its tiny size of 25nm diameter, the powerful curative features of AAV gene therapy are unavailable for other genetic-based conditions whose DNA sequence is beyond the packaging capacity of AAV vectors.
In future Layman Terms’ article, I will review some of the AAV features that make it great for gene therapy and maybe some of its inherent limitations, such as its size, that still needs to be overcome for AAV gene therapy to make an even greater impact as a medical treatment.